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Is Time Travel Possible?

We all travel in time! We travel one year in time between birthdays, for example. And we are all traveling in time at approximately the same speed: 1 second per second.

We typically experience time at one second per second. Credit: NASA/JPL-Caltech

NASA's space telescopes also give us a way to look back in time. Telescopes help us see stars and galaxies that are very far away . It takes a long time for the light from faraway galaxies to reach us. So, when we look into the sky with a telescope, we are seeing what those stars and galaxies looked like a very long time ago.

However, when we think of the phrase "time travel," we are usually thinking of traveling faster than 1 second per second. That kind of time travel sounds like something you'd only see in movies or science fiction books. Could it be real? Science says yes!

Image of galaxies, taken by the Hubble Space Telescope.

This image from the Hubble Space Telescope shows galaxies that are very far away as they existed a very long time ago. Credit: NASA, ESA and R. Thompson (Univ. Arizona)

How do we know that time travel is possible?

More than 100 years ago, a famous scientist named Albert Einstein came up with an idea about how time works. He called it relativity. This theory says that time and space are linked together. Einstein also said our universe has a speed limit: nothing can travel faster than the speed of light (186,000 miles per second).

Einstein's theory of relativity says that space and time are linked together. Credit: NASA/JPL-Caltech

What does this mean for time travel? Well, according to this theory, the faster you travel, the slower you experience time. Scientists have done some experiments to show that this is true.

For example, there was an experiment that used two clocks set to the exact same time. One clock stayed on Earth, while the other flew in an airplane (going in the same direction Earth rotates).

After the airplane flew around the world, scientists compared the two clocks. The clock on the fast-moving airplane was slightly behind the clock on the ground. So, the clock on the airplane was traveling slightly slower in time than 1 second per second.

Credit: NASA/JPL-Caltech

Can we use time travel in everyday life?

We can't use a time machine to travel hundreds of years into the past or future. That kind of time travel only happens in books and movies. But the math of time travel does affect the things we use every day.

For example, we use GPS satellites to help us figure out how to get to new places. (Check out our video about how GPS satellites work .) NASA scientists also use a high-accuracy version of GPS to keep track of where satellites are in space. But did you know that GPS relies on time-travel calculations to help you get around town?

GPS satellites orbit around Earth very quickly at about 8,700 miles (14,000 kilometers) per hour. This slows down GPS satellite clocks by a small fraction of a second (similar to the airplane example above).

Illustration of GPS satellites orbiting around Earth

GPS satellites orbit around Earth at about 8,700 miles (14,000 kilometers) per hour. Credit: GPS.gov

However, the satellites are also orbiting Earth about 12,550 miles (20,200 km) above the surface. This actually speeds up GPS satellite clocks by a slighter larger fraction of a second.

Here's how: Einstein's theory also says that gravity curves space and time, causing the passage of time to slow down. High up where the satellites orbit, Earth's gravity is much weaker. This causes the clocks on GPS satellites to run faster than clocks on the ground.

The combined result is that the clocks on GPS satellites experience time at a rate slightly faster than 1 second per second. Luckily, scientists can use math to correct these differences in time.

Illustration of a hand holding a phone with a maps application active.

If scientists didn't correct the GPS clocks, there would be big problems. GPS satellites wouldn't be able to correctly calculate their position or yours. The errors would add up to a few miles each day, which is a big deal. GPS maps might think your home is nowhere near where it actually is!

In Summary:

Yes, time travel is indeed a real thing. But it's not quite what you've probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second. And there are important reasons why we need to understand this real-world form of time travel.

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Time travel is possible, but it’s a one-way ticket

Chenoa van den Boogaard , Physics and Astronomy editor

The ability to travel through time, whether it is to fix a mistake in the past or gain insight into the future, has long been embraced by science fiction and debated by theoretical physicists. While the debate continues over whether travelling into the past is possible, physicists have determined that travelling to the future most certainly is. And you don’t need a wormhole or a DeLorean to do it.

Real-life time travel occurs through time dilation, a property of Einstein’s special relativity . Einstein was the first to realize that time is not constant, as previously believed, but instead slows down as you move faster through space.

As part of his theory, Einstein re-envisioned space itself. He coined the phrase “spacetime,” fusing the three dimensions of space and one dimension of time into a single term. Instead of treating space as a flat and rigid place that holds all the objects in the universe, Einstein thought of it as curved and malleable, able to form gravitational dips around masses that pull other objects in, just as a bowling ball placed in the centre of a trampoline would cause any smaller object placed on the trampoline to slide towards the centre.

Courtesy and © of NASA

A computer-generated representation of Einstein’s curved spacetime. The Earth creates a gravitational dip in the fabric of spacetime which is deepest at its core. Courtesy and © of NASA

The closer an object gets to the centre of the dip, the faster it accelerates. The centre of the Earth’s gravitational dip is located at the Earth’s core, where gravitational acceleration is strongest. According to Einstein’s theory, because time moves more slowly as you move faster through space, the closer an object is to the centre of the Earth, the slower time moves for that object.

This effect can be seen in GPS satellites, which orbit 20,200 kilometres above the Earth’s surface. These satellites have highly precise clocks onboard that gain an average of 38 microseconds per day due to time dilation. While this time gain seems insignificant, GPS satellites rely on their onboard clocks to maintain precise global positioning. Running 38 microseconds fast would result in a positioning error of nearly 10 kilometres, an error that would increase daily if the time difference were not constantly corrected.

A more dramatic example of time dilation can be seen in the movie Interstellar when Matthew McConaughey and his crew land on a planet with an extreme gravitational field caused by a nearby black hole. Because of the black hole’s intense gravitational influence, time slows dramatically for the crew on the planet, making one hour on the surface equal to seven years on Earth. This is why, when the crew returns to Earth, Matthew McConaughey’s daughter is an old woman while he appears to be the same age as when he left.

So why hasn’t humanity succeeded in making such drastic leaps forward in time? The answer to this question comes down to velocity. In order for humanity to send a traveller years into the future, we would either have to take advantage of the intense gravitational acceleration caused by black holes or send the traveller rocketing into space at close to the speed of light (about 1 billion km/h). With our current technology , jumping a few microseconds into the future is all humans can manage.

But if technology one day allows us to send a human into the future by travelling close to the speed of light, would there be any way for the traveller to use time dilation to return to the past and report her findings? “Interstellar travel reaching close to the speed of light might be possible,” says Dr. Jaymie Matthews , professor of astrophysics at the University of British Columbia, “[but] this voyage is one way into the future, not back to the past.”

If we can’t use time dilation to return to the past, does this mean that the past is forever inaccessible? Perhaps not. Einstein proposed that time travel into the past could be achieved through an Einstein-Rosen bridge, a type of wormhole. Wormholes are theoretical areas of spacetime that are warped in a way that connects two distant points in space.

Image by Panzi, CC-BY 3.0

A visualization of a wormhole: The fabric of spacetime curves back upon itself, forming a bridge between two distant locations. Image by Panzi , CC-BY 3.0

Einstein’s equations suggested that this bridge in space could hypothetically connect two points in time instead if it were stable enough. “At the moment, even an Einstein-Rosen bridge cannot [be used to] go back in the past because it doesn’t live long enough – it is not stable,” Matthews explains.

“Even if it was stable, it [requires] other physics, which we don’t have. Hypothetical particles and states of matter that have “exotic” physical properties that would violate known laws of physics, such as a particle having a negative mass. That is why “wormholes” are only science fiction.”

While it would be fascinating to travel back in time to see the dinosaurs or to meet Albert Einstein and show him the reality of time travel, perhaps it is best if the past remains untouched. Travelling to the past invites the possibility of making an alteration that could destroy the future. For example, in Back to the Future , Marty McFly travels to the past and inadvertently prevents his parents from meeting each other, nearly preventing his own existence. But if he had undone his own existence, how could he have travelled back in time in the first place?

Marty’s adventures are a variation of the grandfather paradox: what happens if you go back in time and kill your grandfather before your father is conceived? If you are successful, how is it possible that you’re alive to kill your grandfather in the first place?

A recent study at the University of Queensland may have the answer to this baffling paradox. In this study, the researchers prove mathematically that paradox-free time travel is possible, showing that the universe will self-correct to avoid inconsistencies. If this is true, then even if we could travel back in time, we would never be able to alter events to create a different future.

While these new findings are enlightening, there appears to be more evidence that, although time dilation can allow us to glimpse the future, we will never be able to visit the past. As the late Stephen Hawking said in his book Black Holes and Baby Universes , “The best evidence we have that time travel [into the past] is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”

Banner image by Alex Lehner, CC BY 2.0

240 thoughts on “ Time travel is possible, but it’s a one-way ticket ”

How do I go about time travel? what do I need how do I get those required things?

Very large ring magnets and some mathematics and will to see it in reality.

How about a sphere magnet ship…

hoe about 3d time and hemi synch or portals augmented reality,power of suggestion..drugs pcp binural tones frequency amplitude .virtual computing ie.

I’m a time traveling tourist, Stephen Hawking was wrong.

Time is simply a measurement of space under the amount given its mass and the amount of light and dark in which governs its mass in a 4dimensional reality step outside of the force in which permenates its flow one would reside there would be no past present or future there be a fixed permance of a constant here and now and so ok then what is to come.

Very well explained article !!

But I think if physics says time travel can be possible then it’s definitely possible. Considering not to go back to your childhood and fix things but rather can go to the past but as invisible person to them. So that,

No actions by you would impact your future.

Regards, Kirankumar DR

Tell me more

Yes.. I wish I can do this too 🙂

We will understand it better, by and by…

I have a theory for warp speed, but nasa would have to put it to the test…check my Facebook

I am reading for this drive , i am ready , without think my life safe or not

@Ravi chandila English translation please?

Please someone help me I just want to send a message to myself in my past.,to get the love of my life, he never revealed to me his feelings now my life is ruined by the decision of my elders Please help me, it’s question of my life and death. Nazneen

Is time travel machine is their, if the time travel machine is true can it move to the past . To bring back my lost life

That’s the problem you know.. it is not there that’s why we aren’t able to travel time..and yes it it will be built then you will be able to do so…..

damn my life is also lost and broken but still no one can give a time machine for free

DO NOT change the future. That’s why people like you couldn’t go. One wrong person to ruin it for the rest of us

On the point of time reversal, it is evidently impossible. The Uncertainty Principle prohibits spacetime reversal. The Universe is unable to remember its past (as a consequence of the Uncertainty Principle), therefore the Universe cannot reorganise itself.

Can I have to go on my past with another time travel it is a possible when just tell me about one thing that can I have to go in my past one year

we dont need magnets.we need a strong gravitational force to warp spacetime allowing us to travel through with speed of sound or speed of light or faster.we need to learn how to control such force carefully or it could be lethal.gravity slows down time.but it can theoratically work both ways.if we can reverse the gravity’s natural reaction we could speed up a spacecraft faster than light(its all relative(and theoratical))

I WAS ACTUALLY JUST THINKING THE SAME THINFG BEFORE READING YOUR PIECE. VERY WELL EXPLAINED, AND IT DOES MAKE ALOT OF SENSE. WELL DONE.

oh and I forgot to add it can be the key to look into the universe and also travelling time(theoratical).speed and gravity are the key to the universe(theory not proved)

All you really need is a crystal diode with 16 sides, a large pain of glass, and a frequency transmitter near a bathtub full of ice cold water….if you reach the right frequency you can travel through time forward and reverse…

Magnetized metal(VCR Reading Head), to read time out of the Magnetosphere all around earth. The Magnetosphere kills 2 birds with one stone- it protects earth and it records human time:

Mystery solved and I will explain, I was in a coma 3 months and I experienced things, I traveled time forward and backward, it is not a one way ticket. Movies and songs are recorded on magnetic tape in a VCR tape Cartridge or Cassette tape,   Magnetic tape recording works by converting electrical signals into magnetic energy, which imprints a record of the signal onto a moving tape covered in magnetic particles.   3D life on earth(a movie), and the Magnetosphere all around earth coming from the core of earth(MAGNETIC ACTIVITY) without Atom Made Tape, is like a movie on magnetic Atom made tape in a VCR tape cartridge. Revolution and Rotation is the motor(VCR).

This is why people have those freaky Deji’vu feelings like they have lived this before, BECAUSE YOU HAVE, and how people can be psychic, and how there is Prophecy in the Bible. When a person dies, their Spirit- MIND(Thoughts, Feelings, Urges(Physical and mental personality)) breaks out of human body- a stopped heart is what releases the spirit from the human body. Then the Soul(Life) with the memory of your existence in it breaks out of spirit and goes back to your birthday with a erased memory, meanwhile your spirit goes back in time to when you were a teenager starting the mental puberty, maturity from that adult spirit you died with in last life.In that old movie Star Wars or maybe it was the Empire Strikes Back, there is a scene where Princess Laya plays like a 3D movie, that is EXACTLY how its of life on earth.

Mr Snow, I believe you as I have seen it too. As humans we have deep knowledge of things we cannot rationally explain but you have done a great job here.

I thought that Analogy would be a better and easier way to explain, or in a picture of the earth from far out in space with the atmosphere around it looks like a DVD disk and the earth being the center sticker but is in 3D.

Actually you are on to several things here. I have also had the infusion of knowledge that also had to do with comparing life to recorded movies and music. I know you were using it to explain your theory, but I do think there is something there, I always have. When you watch a movie you are seeing the past. Why can’t you somehow use a recording as a base to go back into? I agree with everything you said here, and it’s worth looking into.

Jeffrey, very interesting idea!! Could be something to that. As far as your coma experiences, I think there are things we just do not understand and are nearly impossible to explain. Perhaps time IS like a video tape, or a DVD? Magnetism is one of the forces of nature. I too have had some odd experiences that suggest that we are able to perceive things beyond our five known senses.

I think if you have had a near death experience, such as being in a coma, then you have experienced the powerful hallucinations provided by the chemical substance DMT which your body creates naturally in times of extreme trauma, but also found in most plants and used recreationally by some who are brave enough and into that kind of thing. Your theory is interesting, but completely unproven and as far as I know untested. If things were so simple, I’m sure many scientists would have already thought of such an idea and tested it.

How do I travel through time

Be alive and live life to the fullest is the best way to travel through time ! OR Befriend grey aliens../ They may hold the key to the sum of all knowledge in the universe..

Sounds good will it work

Really log vaps mil sakte hau h kya

Can you plz explain I didn’t get it

You dont first all you are not experienced in the field of the space time continum and you could you upset the already fragile and multitude of alternate realitys that have looping due irresponsible ones who somehow gotten the technology causing another altered time frame there are a disarray multiple reality which are looping in earths 4dimensonal time frame time traveling is not for a vacation or just to get a joy ride its a serious and complex reality not be joked about it is a real thing and certain individual have are upset the balance of earths original time zone note now the gaurdians of this region of milky way the galatic order of the light keepers Angelic gaurdians of the (names with held)are working over time ooh nice pun (over TIME) ha wow to restore Earth back to a original time continum

Who said I want a joy ride, my life is devastated even my kids are suffering, I want to commit suicide but can’t leave my kids back, Being captive for most of my life, if my life is changed nothing will be disturbed, only thing happens is 3 life’s will be saved. And more so over I don’t want to travel I just want to send a message to myself in my past plz on the date of 30th May 1996. My life is ruined plz help me, it was my dad,brother, sister who pushed me into the dungeon and my husband and his family took over the charge of torturing me. Nazneen

I want to go back in time and tell my 5 year old self to burn the creepy dolls that my mom bought cause there is demons in it at the same time I will kidnap and torture my dad right now go back in time and show the younger version of my dad show him what will happen to his future self if he don’t get rid of those possessed objects and keeps letting my mom buy those antiques I’m 18 now I’m single no girlfriend no friend alone nothing very depressed too and I try to remember the positive things that happened in my life which there aren’t many tho but the demons keep squeezing my memory brain and my mom keeps on making so much loud noise including her damn mouth I have attempted to burn the demonic dolls but I only burned them for a minute or two with gas cause I was worried I might accidentally set my whole neighborhood on fire but then my mom threw it all in the recycle instead of the trash so the demons just keep bothering me its driving me nuts he he.

Access to a Quantum Computer Network on the web would be a good start. A series of ChatBots and webhook sites strategically placed in not only space, but in time. A series of algorithms and I think information can be transferred backwards to ones self…

How do we know that there are no horde of tourists among ourselves?

How do we know we’re all not tourists?

We’re all time travelers. We all travel into the future daily. 1 second at a time. Lol…

Agreed! I had the same thought!

Excellent question

If is possible, I would like to go back to: January the 1st 1975 & relive the 70’s as I prefer that decade to the awful one I am facing now, Back then We had more police our streets & left our front doors open, Those days were far much more better .

https://3netra.co.in/61-2/

Please do comment on my blog post regarding time travel

how about you ask the flash to help you

I need the time travel so I’m fails so many times i love time travel i have to go fast and future so i have no idea im travel is a my dream so my dream solution plz say me i have time travel so please help me someone please…..

I think you are over reacting

When we look at the stars now it is what they looked like years ago so what if we go to the stars and look down?

You cant go to the stars. It will just take billions and billions of years to go even to the next nearest star than our Sun- proxima centuri. Sorry to say, but do you think that you will be alive all those years??

You can do that without going to the stars… our planet reflects light as well thus making it visible from other parts of the universe…. has the word “reflection” crossed your mind ? 😉

Contact me on my hangout I will help you [email protected]

bro just time travel its not that hard

Please help me to time travel, can I see myself when I go back in time like Harmaini sees herself in Harry potter?? Or can I send messages to myself I know the particular date when to send. It’s not the mistake I had done in my past but it was done by my father and brother who are safe, happy enjoying their lives,my life is totally ruined Please help me. Nazneen

I want to go back in time to save my wife .it was a bad mastake she died .that could be changed i need to go back and save her. Please help me.yours gordon sutcliffe

Would love to hear more how it’s possible, as I am really so desperate to go back in time. I lost my wife 6mons back because of COVID and I will do the impossible things to make it happen.

DMT Experience

what is that?

Dmt experience. Time travel, out of body and sometimes superhuman capabilities.

Jump into a black hole

We have to lose something(the past) to gain something(the future) in time travel.Time cannot be played with.Am I correct.

you need to have d e t e r m i n a t i o n

Time machine is possible

speeder than light LOL

speeder than light cuz if the light break it limits it will move backward in time

Don’t Just don’t disturb the past

I want to go back in time and see my dad. I miss him.

mee too raina I lost my father the day before you posted the comment 18th may, crap it hurts me so much. I would rather die to bring those moments back….

Everything is connected . Time isn’t real .

It is universe we travel to and not a time line in one universe

Ask trump….Mandela effect…. dmt 5th dimension

u need an X-WING starfighter and a lightsaber to fight the knights at past and a R2-B2 to track

The fact that no one has time travelled to the past is the proof that time travelling will NEVER exist.

Others have. Portals open most of the time. Example: Miami Fl. Magnetic Material gets bombarded by the sun. Which fractures and formed portals within that area. Ley lines can lead to the portals of travel within miami for just to start. One can laugh or wonder if. In my experience jumping for the better the word of it (Movie Jumper) can be done. You can either Teleport or Time Travel. Our sun open these portals everyday. The best time when Sun spots start to emerge. All that electrons traveling at light speed is enough to rupture our magnetic fields on Earth. You will return of course. Like water on a lake or an ocean time will corrects itself. Your inner clock is your ticket back home. With a little math,fourth dimensional thinking,a magnetic meter, the right location,history research and luck. You may get to expirence it. First clue….cold spots…it may not be a ghost.

Plz can you help me please help me you can save my life

I wish I could help you, I can sense your sufferings.

You need a bag of hyperlink modules to start, then nuclear beepbeep gatangas, when you have that come back here and I will tell you what you need next.

You need high voltage beepbeep gatangas and a large broonasic magnet of about 450 Gauss, come back here when you have these and I will tell you the rest.

you need an old fashioned police box

If you rotate the center of the earth in the opposite direction, then the whole earth can be moved back in time, on the other hand, if you move the center of the earth and change its position by separating it from the part of the earth, then you will be able to time correctly. Let’s reach the other side.

How I could time travel any time travel machines inverted

give audition in the flash series..

I think that to go back in time you’d to travel faster than the speed of light since time stops at the speed of light but if you wanted to go back to say mlk’s assassination you would need to go at least 10 times the speed of light

You don’t want to, the moment you wrote that message is a historical point in time.

When time travel is possible, you should d̵͔̮͉̣̯̳͌i̩͒̍̆͟ͅs͎̲̖͙̺ͬ̽̊͆͢r̖̹͆͂̚͘ê̛̫̪̱͇̘̩ͬg̖͉̤͚ͭͣ̊̌͜a̯̗͚̬͍̱̦͑͂͒͡ṟ̝ͦ͗͘d͋҉̪̖̥͔̟̟͚̻ ͎̬ͧ̔́i̧͚̫̻̇ͮͫ̆t̩̻͉̩̘̰̠̫̓̂̕ ̦̻̳̦̉͆̊̇̀i̴̗͍̞͙͇ͣ̈́mͦ̑ͦ̚͏͚̜̬̹̘̟̭m̱͕̻͇̮̠̰̼ͫ̌͆͡e̢͈̜̱ͩd̵̦͙͔̭̹̃̿̈̚ͅi̛̖̬͓͚̩̝̗ͯa̦͎̭̣̭̘͔͙̅̏́ṯ̴̟ͥ̀͗e̵͎̭͓̟͗ͨ̂͒l̼͕͕ͦͦ͜y̸͙̯̺̘͉ͣ,͈̻͙̭̺̘̞̑ͫ͜ ͔̗̣͒͜d̶͇͚͉̦̞̗͛̍o̞̮̻̲̜̠̒ͩ̈́̀ͅ ̲̙̦̮̺̉́͂̏̀ṋ̞͖̌͠o̬͕̯̩͓̮̫̝͛ͩ̐͛͜t̼̙̿͊͆̕ ̲͚̲̬̦̗̐̀m̢̹̜̭̠̬͗̆ͣą̲̺̻͈̹͎̈́̇̉͛ǩ̜̪̱̀e̜̳͔͉̣͓̓͗͘ ̉҉̲̞̘͈ͅc̴̦̣̝͇͈̙̋ͥ́o̫͇͇̘̻̠̹͎ͯ̀n̺̹̣̦̔̇̾͢t͚̹͚̙̞̪̗̺̄͂͜a̞̗̖̻̩͉̋͛̆͘c͙̙̎͘t̻̠̣͉̹̠̣̲̐ͧͩ̈́̕ ̶͕̗̬̿w͓̞͍̹̰͖͉ͦ͐͡i͎̞̾ͦ̃̈́̕t̜̺̖̭̍ͦ͞h͙̰̬̖͎̰͛̇ͮͫ͡ ͣͯ͏͕̻͚̹̺ā̱̙̝̦̤̼̥͡n̶͔̜ͥ͆̌̋y̷͓̻̺̺͉͇̻ͨọ̱͙̜̈́̉ͣ̔͟ņ̦̟͔̜̫̗̒ͬe̡͕̮̓͂̚ ̡͓̘͚̭̹͔̉͐͋̽t̖͍͚̝̬͈̝͌͋͘ͅẖ̗̖͚̼͔͕͆̓̾͜a͈̣͍͕͍̋ͦͩͭ͢t̖̪̤̳͎̱̏͡ ̛̻̠̼̬̓ͫl̶̞̤̣͔̗͔̂ͅö̹̞̦̖͚̫̜̱́ͯ͠o̧̯̱̪̓ͮ̋k͉͎̝̻̓ͧ̕s̤͈̪̍͟ ̤̞̳͔̝̪̟̹̔̂ͨ͜h̛̝̲̰̻͗̅̏̃u̜̙͐̇̈͝m̧̞̮̟̦̳̟̊a̸͓̺̲̼̜͊͛̐n̶̳̮̒.͇̻͚͓̳̺̜̱͋ͬ͗ͩ͢

It’s Close I can feel it

Yes it becomes a history but my life also in the past changes and the present also with it. The way I’m suffering from the pain and want to end my life I’m 100% sure at least sure no one around me is or was as hopeless and horrible as my hubby I’m devastated I really want to send a message to my past it may not start but it will definitely change. I was forced, not given any option, my father and brother gave me wrong information and had no concerns for me. It was just survival for me. I repent for not killing myself when I had time, but now if I have a chance why not. Now when I’m out of my marriage I come to know a guy then had feelings for me, was madly in love and wanted to ask for my hand, now I want to inform my self and change everything plz help me.

I too would like to go back in time. I just wish he lived a happy eternal life. I would just like to repeat to come back in 2020.

I heard from a guy in Idaho that time travel is possible. You’ll need to go online and purchase a pogo stick looking device and make sure not to forget the crystals.

I think u need a black-hole-proof spaceship, go to the centre, escape the black hole and viola! You are now in the past. If you can’t escape, then you’d travel to a time where that black hole didn’t exist.

Believe me you time travel! If not physically then you do mentally,like you through dreams.

Though they sale it online, it would not take the chance. It is as simple as beating the speed of light and having some system to send you to the time you want. Time however is not real, and were just traving universes. It will all be in the open in 2028 according to other travelers.

All you need base on how to travel to time is very simple but had to find firstly find a way to get to space through a space rocket secondly find a very perfect consifigration for traveling to tiTme then find a very fast rocket that could create a form of force reaction in space in order yo enable fast speed in space for the break through of non gravity in space and make sure that while doing all you activities is not far away from planet and not also to close to planet earth and make sure that you are with wristwatchs whose time is set disame then you can to the future

Man you can get all you need for too build a time machine in your local store man, man I sure wished I’d kept mine but it frightened the heck off me man, sometimes when I fart I find a grape in my pants

time travel is a fake, baseless and delusional idea. If you believe in that crap then tell us if we are living in the future or in the past. To travel backward the entire system has to return all along with nature and events, it won’t be for you alone except time travel only happens in the mind.

you would need to get about 1,000,000 pounds of silicon and then somehow conduct enough energy to make 500 cars run without an engine and then go to a nuqular power plant and somehow make a portal. but the whole world could go out of orbit if you do that so I wouldent sugest it.

Time machine is good and bad because,with the time machine you will know about your future which is not good.

Is time travel actually a real thing because if it is then I need it because I am trying to go back in time to fix all of my mistakes

So what if time travel is the reason that we now believe there are other realities in our own world.this could be that a Time traveler we could only go back and couldn’t come back, and on doing so if you do something to change the past in stead make a new reality.making other things are deferent and ours realty stays the same . sometimes reality gets mixed up make the mandela effect that we see today

Time in the future it is faster then now. The past is slower so you can travel . It is up to you. One way is to meditate. You can travel and see any body you want right now. You can fly faster then light. That is one way. You go to the future. To go to the past you sleep for a long time. Some time you go to the future or the past. Your heart well stop and your body gets cold. Sometimes you can control it sometimes you can’t.

but how do we know that is really true ? i mean i want to figure this out, i want to time travel, but how is it that simple ? so many people have been trying to figure this out for many years and its that simple ?

Yeah what if you get stuck in there what do you do than

You cant go there in the first place. Dont worry. With current technology, we will only end up messing some few microseconds. Highly doubtful, if we can end up getting the news of travelling hundreds of years in our lifetime.

wait what would happen if someone saw you while you where in past/future i’m curious

Time is an illusion based on perceived reality and is only relative to our limitations. Time isn’t what it seems and all things can’t be figured out

Im on a school computer looking this up and i found this article and scrolling trough it and ive not heard one statement here as good as yours bro

This is blowing my mind people, then I see the school boy on the post. Great stuff, whoever reads this is already capable of travelling through time. Think about all people who have posted on this thread, now think about who will read mine. Now think of those €opposite trolls $ who never ever bother posting on you tube thread etc. But ONE comment from one of the time travellers who wrote on this thread. So that opposite troll is me,I don’t normally post.however because of previous comments I’m posting here. And I love the DMT shit I loved that and lived that one out in real life,,,,another day.

So my point is ifOne or two threads have made me write this….then what will my post make others write , think…..then I could travel back and not write this…. then what. Love the conception of time how can u travel something that doesn’t YOU perceive to be time, like a train can only run on its train tracks, a car can only drive on a road etc It’s posibble I know it is. Sometimes when u have fun times moves swift but locked in jail it goes snail pace. U c me. I write letters to myself from past from future. Remember everything that happens in present becomes part the past. But the future is what you hold in your hands. Question is, now you know….what the f are u gonna do about it?.. 01/04 ==== 21

Hahahah only realised school boy is named BIG dick pissing myself laughing I gotta go pee. Respect certified

so not halal mode

True so were not traveling in time. It is just different universe (on what we call) different time, day, tears, etc.

You would be scared for life

you will desepear

Maybe it has happened before and we just don’t know that they’re from the future. If people in the future time traveled, the would know that it’s dangerous to mess with the past and would pretend to be part of the past.

I believe time travel is already possible, however we cannot fix past mistakes without altering future predicaments. Say we stop JFK’s assasination, that would completely change the future from that point forward to one none of us can know/guess or conclude the effects? Other time travel purposes go to the future I think that from now our world will die off before 2096 basdd on overpopulation, global warming & polution as such creating islands of plastic waste in our oceans. The best thing my opinion go back to the garden of Eden, kill that Serpent Satan before he tricks Eve into the forbidden fruit. Then let God raise, enlighten & teach us how to be humanly sustainable on his planet & I guarantee technology & smart phones? Ain’t no part of it!!

Time travel possible but one n only theory of Stephen hawking

How it is possible to jump in time …??

Many ways. The most used is creating a black hole which can be done in a few ways. 1) traveling forwards or backwords faster than the speed of light 2) been known during heavy lightning strikes. Each way is a fast movement that opens the black hole. It has been done by the Government since the 1980s though they claimed they never beet the speed of light until 2002. However, Time is a illusion and their for we are actually traveling different universe that are differnt than ours even if the difference is by 1 thing. Each universe may have (what we call) different time, days and years. And each time we change that time line we created a new one. It is belief as CERN has said they destroy 5 universe, that they can travel to them. Since 2012 it has seem we been shifting and is now belief they have possibly came together. The event is known as The Mandela Effect.

No one has the right theory in my thinking. Only a few things are wrong. It is universes with (what we call) different time, days and years we are traveling to and not time itself as it is a illusion. Their is no stop to how much we can do, or where we can go. No limit as such say.

There is no God. No magical serpent or Garden of Eden ever existed. Basing a scientific theory on archaic stories does no one any good.

You choose a hopeless eternity. I choose hope through the promise of salvation through Christ for those who believe. You see, I have child in heaven. Thankfully, have a hopeful reality that I can embrace. There is a God. Our known universe is only 14 or so billion years old… is it mathematically possible that random molecules out of the Big Bang mixed in just the right way from to form a complex cellular organism… with DNA… and result in humans and such diversity of life forms? It’s naive to accept this as a result of chance. Think about it. How is that remotely possible without a creator?

Hahaha. You make it seem as tho the big bang happened, and we just popped into existence? Naw it’s called evolution baby, we started out as microscopic organisms, seriously, when did you drop out of school? But that’s like saying a some guy writes a book to explain away natural phenomenons that they were to stupid (un-evolved) to grasp and the concept good and bad and the eternal damnation, And thus, the Bible, and boom, everyone now was made by God, hahaha. When you can prove he/she exists, and that the Bible was a autobiography, and not just some twisted piece of Fiction, that has no real basis in reality, and cannot be proved to be more that a work of Fiction. Rather than being used as the16th Century control tact, ‘be good or you’ll go to hell’. But I guess that’s what they mean when they say ignorance is bliss, (maybe if I was as ignorant as y’all believers I’d believe to). But I can’t see how a ‘GOD’ would ever ask one of its creations to kill another.. Genocide, Crusades, all the ethnic cleansing.. All In the name of God Almighty! Hahahahahhaaa. Aliens are more believable than this shit, and theirs no proof they exist either. Hahahahaha. Fug’n Bible thumpers. ‘Step out side your faith and see the world for what it really is, a complex organism, mad of gravity and dust, quite a unique specimen! And we, yes Bible bangers, this includes you, are destroying it like the bubonic plague.’. ‘The end is coming and it’s our fault’

Have you taken the time to read The Old Testament and the prophecies therein that came to be ?.

How do you explain that ?.

My last post should read GS not G

You have not had an encounter yet with God. Don’t be so certain on yuour theory of evolution. He came and shook my reality to it’s core. Made thing possibly that no one could ever explain.

What are you talking about? Ur so wrong and funny in every way.

BlissfullyInformed just told me his comment was all an April fools prank. He believes in Jesus and was just fooling.

Time travel is very much possible just as you decided to come existence in this century meaning one can decide to be in another time zone . life is all about numbers, you just have to work on numbers

I’m pretty sure ppl don’t decide to come into existence. If that were true I wouldn’t be replying to your comment.

Un like your other reply, I understand what you mean. Each timeline (or universe as some see it) can easily be traveled to at will. No different than traveling threw your time you want to visit.

Science has proven a few things from the Bible is true. God does exist. Christians are confused with time and what it says. For a example. God created the world, as science even belives it was God who created the big bang, yet the bang has happen itself creating the moon, planets and stars. Christians also fail to understand chapter 1 and 2 of gen. spoke of two different creations which can be why we see dinosaurs before humans as chapter 1 spoke of animals first and humans 2nd. Their also was different time than, as without the moon a full day is 6 hours. It would take 4 days back than to equal are 1 day. Time is lost and Christians are just confuse on that time. That does not proof their is no God. As they have already found the robes of Jesus and remains of Noah’s ark, it proves much did happen. The bible only has less than 50% of what was written.

Changing the past is impossible, because if we went back into the past, that means we were already there during the time you experienced it.

We all know how to get into time travel but how do we get out……..

You don’t need time travel – all you need is life. And what is life? Life is the evolution of the impossible into the inevitable over an infinite amount of time.

if it is shown that if something, such as a solution to a particular class of equations, were possible, then two mutually contradictory things would be true, such as a number being both even and odd. The contradiction implies that the original premise is impossible.

This is called proof by impossibility. Thus if some traveled back in time far enough to kill his grandfather, we have the contradiction and therefore it is impossible.

You could argue that he would be able to time travel, but not kill his grandfather. However almost anything a person does going back in time would cause the same contradiction, thererfore it is the traveling back in time that is impossible.

Actually, it probably is possible to travel back in time, however to do so, you would also have to travel so far in space that you cannot see anything that happened before your current time due to the speed of light, because this to could affect the future.

The reason I am here is that, i really want to go back the day when our matriculation exam was just finished. Everything around me is peaceful and happy. Currently, I am living in dire situation. People are dying outside on the streets. Smokes everywhere. Everything is in doom. Ah, yeah. I really miss my past. If you are reading this, you can judge me in anyways. I just want to live peacefully and happily.

You must live in Portland

I entirely know what you say and how you feel, Robin. I am totally convinced that future is no promise to offer a better place to live. World is becoming unnecessarily more complex and more horrible and more insecure. Therefore, travelling back in time to a point where things were still far away from such ordeals is what I aspire. But I think if it is possible to travel back in time without the possibility of carrying our lived experiences with us, it will be useless as we will be repeating the same mistakes over and over again. Now, this begs the questions “in what type of physique could we imagine ourselves back there if such time travel becomes possible? That is, becoming younger again in a physical regression (as I said this would be a torture without having learned from all these later years)? Or appearing at our desired times in our present physique and age? I believe the most ideal one would be if we appeared at our desired point in time at the same age that we were at that point of time with a good feeling of our later lived experiences.

Mam all u need to do is just run faster as much as u can or visit the black hole because in both condition time just slow it down ….

Time travel is simple. If you do happen to travel to the past you create a new time line not affecting the time line you left. In essence you going to the past is now your future. Even if you were able to return you may never know if you remained in your time-line or created a new one. So even if you changed something in your travels it would happen in the future not the past.

Sorry time traveling is not possible, there is no way you can go into the past or the future ‍♂️. You can only be in the time you are already in.

Incorrect. General relativity allows time travel into the future. You need a space ship that can travel extremely fast though, approaching the speed of light, or you need to get close to a supermassive black hole.

It is travel into the past that there is no known practical way to do, and is probably impossible.

So what happens when we Die? Where do we go? I want to go back in time so I can meet my childhood friends…

Simple question from a simple mind:

At what point, when a person says they are from the future, do we stop throwing them in the funny farm and actually start listening??

When they show actual proof. Not just some random prediction of the future.

I don’t believe that “glimpses into the future” could be possible. If it were so, we could glimpse blueprints of the future that we could bring back to the present and build before they were invented. My personal.beleif is in any time frame there is only one active time which is the present. The past no longer exists and the future hasn’t occurred yet, so there is no such thing as ‘time travel’ except for the frame we are in now.

First off time is not real we make time if you travel anywhere all you are doing is beating the Earth speed try this for a mathematical equation the Earth travels a thousand miles per hour you’re not beating human time that is your own equation the Earth travels a thousand miles per hour a space shuttle travel 17,000 mph you can beat time that you made so time is not real you are only beating the Earth speed if you go in a space shuttle and go around the earth 17,000 miles per hour the Earth only travels a thousand miles per hour plus it has all types of gravitational pull from the Moon Earth’s access on the til t you figure out the mathematical equation I cannot time travel is real if you can beat the Earth speed and we can it has nothing to do with its 12:00 it’s 1:00 that’s not real time is made up as a mathematical equation you can beat the Earth speed you can go back into the Earth’s time in a space shuttle but you’re not beating anything except the Earth’s speed think about that one time is not real at all all it is is a mathematical equation think about that one real long

What I’m trying to say is this a space shuttle travel 17,000 mph the Earth travels a thousand you beat it 16 times faster that’s all you did you’re not beating any time you’re not beating 1:00 you’re not beating 3:00 all you’re doing is beating the Earth’s time you can go in reverse around the Earth 17,000 mph okay you can go forward with the Earth’s centrifugal force 17,000 miles per hour you’re not beating anything you’re beating a mathematically equation that we we created astronauts been traveling time for instance for years and haven’t told us because of the space shuttle that does travel 17,000 mph it beats the Earth speed 16 times a boggles my mind you have the Earth access the moon gravitational pull but you can get in a space shuttle and travel 17,000 miles per hour and beat the Earth’s speed 17 times think about it

If any scientist or anybody can actually answer this question how do you set up this equation with the Earth spinning a thousand miles per hour you have the moon pulling gravity the Earth’s access on until I want to know tell me then wondering for a while this equation popped into my head about 2 years ago I’m not a math whiz or anything I just thought about it weird how the mind works I’m not into space or any space stuff at all I’m Samanthas boy friend John antos wrote this

I liked your post and the knowledge you given. I also written a post on Time Travel.

how would any of that stuff be true because e’*34+Em would stop all the forss of vissecs and how would we do it if you now what i mean??? also thanks for the scuff for my project

I would love it if I had a real life time machine here with me now which could take me to anytime I want, the past, present or future. If I had a time machine here with me now, I would go to the past in September 2004 when I was born and give myself to another family that is actually rich and not this horrible family that I have now.

that not nice

Close but not quite right scientists of the idiotic variety, yes, you don’t want people to travel back in time to mess with their own pasts, of course, but you say it’s impossible, but it’s not, and I’m always ignored with my crazed crackpot theories, so what’s the harm in telling the truth as I see it, while it could be possible to travel to the past, here in lies the problem with rewriting the future, while some believe it’s possible to travel back in time, but it’s very expensive and definitely a one-way trip to the future or to the past. Basically Doc Brown got the mechanism for time travel almost right but the energy out put needs to be quadrupled instead, allowing for the ‘physical item, being or vehicle’ to transport through time without killing the time traveler in question. Wormholes are unpredictable, until warp speed for spaceships are a thing, it is not possible for the space ships to achieve time travel, unless they want to enter a black hole, which I would not recommend. as you need warp speed to survive the emptiness of the black hole, without being ripped to shreds. Say for example, Back to the future 1, the timeline doesn’t erase it continues on without the ‘said time traveler’ in existence basically the Marty from Wimpy George’s timeline did time travel to the past and messed with his parent’s meeting so to speak, but never return to the same timeline therefore Marty A went known as a Missing Child in timeline A, while it continues on without him, however Marty A became Marty B/C, in the Successful George Timeline. So that is what I’m talking about. the timeline changes only for the time traveler themselves the ones who are left behind don’t experience a thing of timeline rewritten-ism, as it would never happen in the first place. The other thing is if you want to mess with your own childhood, to make a better life for the past self, the key thing to remember it’s not really you. It’s an alternative version of you, that you interfered with. creating a parallel timeline to it’s original, yet slightly different. Yes it would be awkward to raise yourself. but as long as you are staying in the past, nothing should happen until the age you traveled back in time, unless of course you touched your past self and suddenly de-aged and merged with your past self, is an option 1, option 2 the future self explodes spreading guts all over the place and therefore the past self, of you became a murderer of your future self, I am more inclined to believe option 1 as option 2 seems a little too out there. Basically you would have two memories one of the former timeline and one of the current different timeline. Still traveling through time is truly a one way trip and if you want to travel through time, you would need some time travel mechanism, the way you scientist talk is basically a dream version, or an OBE version (OUT-OF-BODY-EXPERIENCE) which is basically a vivid/lucid dream which is not true time travel, the true time travel is based on the BTTF Trilogy not the idiotic versions you preach about. I believe I’ve said enough.

Mystery solved and I will explain, I was in a coma 3 months and I experienced things, I traveled time forward and backward, it is not a one way ticket. Movies and songs are recorded on magnetic tape in a VCR tape Cartridge or Cassette tape, Magnetic tape recording works by converting electrical signals into magnetic energy, which imprints a record of the signal onto a moving tape covered in magnetic particles. 3D life on earth(a movie), and the Magnetosphere all around earth coming from the core of earth(MAGNETIC ACTIVITY) without Atom Made Tape, is like a movie on magnetic Atom made tape in a VCR tape cartridge. Revolution and Rotation is the motor(VCR).

This is why people have those freaky Deji’vu feelings like they have lived this before, BECAUSE YOU HAVE, and how people can be psychic, and how there is Prophecy in the Bible. When a person dies, their Spirit- MIND(Thoughts, Feelings, Urges(Physical and mental personality)) breaks out of human body- a stopped heart is what releases the spirit from the human body. Then the Soul(Life) with the memory of your existence in it breaks out of spirit and goes back to your birthday with a erased memory, meanwhile your spirit goes back in time to when you were a teenager starting the mental puberty, maturity from that adult spirit you died with in last life.In that old movie Star Wars or maybe it was the Empire Strikes Back, there is a scene where Princess Laya plays like a 3D movie, that is EXACTLY how its of life on earth.

If only wish I could undo everything what I’ve done wrong in the past, I’d be more happier

And that my friend is absolutely what you do not or would not know. Everyone focuses on what they don’t or haven’t had rather than what positives they do have around them. To change the ingredients of a past life only changes the flavour you have in this life, it does not make you happier.

No, travel to the future is not possible. Like, future is unpredictable and always have been so give up on that field

Already has been, and has been proven.

Time travel is not so possible for every one , but there are already time travelers on earth #@*

Who are these time travelers?

Depends if it is the Governments (they done it since the 80s), or if it was a Accidental travel, or a simple us creating our own machine. Either way, one can easily find storys, and other evidence with a good research. I have a website that shows the effects of change cause by time travel.

They are out their (done by the government since the 80s) but the future is open with time travel (told its open since 2028) so they travel back much.

Time travel 101-

Create a closed loop circuit around a full metal structure, hermetically seal it and bring O2, Use two tesla coils to create north and south poles. (Artificial Magneto sphere.) Make sure to pain the outside in lead to prevent any cosmic rays from penetrating the materials on the inside. (Radiation = bad). Connect a ball made of w/e with wires that alternate the current from the coils to w/e panel on the outside of the structure to make it move via inductive magnetic / electric Lorentzo (Lorentzo = ExMfield = Velocity. = Antigravity) Create Antigravity by using forces from the inside reactor. (Pressurized Mercury, and Tesla Turbine.) Then Move 10-100x faster than light depending on the charged field, Friction will be added to the electric field instead of the craft allowing the G-forces not to crush you inside. The field will take the pressures of outer space, The temperature of space will allow for super conductivity of the structure.

Eventually you will arrive in the future, if you stay in one place. but account for the movement of earth in your travel log. To see outside you will need a monitor / camera system, as any leaks through a viewing area will cause death by radiation from the cosmic rays from the field you have created.

The O2 can be used as a backup generator, through air pressure and the tesla turbine.

There are many different ways to make wormholes, but the curvature of space is really hard to calculate to send a machine far out to the end and create a link with the machine that wants to travel there. And leaving one behind to get back.

If you can imagine it, it can be done. You just need the knowledge of not dying to complete it.

U.S.S. Tourist, You’re a time traveler or just insanely smart.

You don’t need to go the speed of light. Human Time is recorded in the magnetospere as a movie is record, ed on magnet VCR Tape or a song on a record. A VCR or record does not have to go light speed to retrieve the recorded info. All of life is recorded in 3D by our Magnetosphere. My Analogy is imagine a VCR tape cartridge being the earth, imagine life on earth being the movie but in 3D with out adom made tape, imagine Rotation and Revolution of Earth being the VCR putting all in to motion- playing. That is how its done, the magnetosphere kills two birds with one stone, it protects earth and records time, human time is in a magnetic bubble that is why the Bible refers our time is different from gods time and this is how God the maker(PLANET OF UNITED SUPREME BEINGS) can flip through our time to know everything. By the way long before life on earth, he built the original 7 wonders of world(Pyramids) to Pump the Seven gasses into the atmosphere of this planet found in the goldilocks zone, so Life can live on it, and that life of all types is his technological cyborgs that grow and multiply on earth also he seeded it with plant, trees, sea creature and things that fly,. Anyway that above is how time is recorded.

Until recently, I thought my neighbor was a crackpot until he actually invented a time machine. He utilized an ordinary closet, and showed me the sophisticated (to me) instrumentation he had installed. I was very skeptical at first, until he offered a small demonstration and entered the time coordinates and energized his invention. To my amazement, when I opened the door, the clock on the wall was 30 minutes later than when we stepped into the machine. OMG!!! Destroy this thing before it destroys us!!!.

So happy to have my husband back after 6 months of separation. get any kind of relationship/marriage help you want from….Robinsonbuckler11 @gmail com………………………

I find it odd that people say time travel isn’t possible yet… If time travel is possible, it has always existed. Meaning, there is not past present it future, only our perception of time. What we know as past present and future have always been occurring simultaneously, so travel was invited the moment the universe wss formed. Dinosaurs are roaming the earth right now, and forever. A version of me is typing this and has always been typing this, within this perceived moment of “time” and time travel has always happened, whether or not we exist in that reality at the right “time” to observe time travel is the only question.

I find it odd that people say time travel isn’t possible yet… If time travel is possible, it has always existed. Meaning, there is no past present or future, only our perception of time. What we know as past present and future have always been occurring simultaneously, so travel was invited the moment the universe was formed. Dinosaurs are roaming the earth right now, and forever. A version of me is typing this has always been typing this, within this perceived moment of “time” and time travel has always happened, whether or not we exist in that reality at the right “time” to observe time travel is the only question.

Their had to be one point however, when it was created and started, and for that, there was nothing but the current time. Once it was created, than we had a pass, present and future to which we can go back to millions of years to see Adam and Eve with the dinosaurs or go millions of years in the future. However, given the events that changes, each time a new time line has been created. We also have destroyed the planet and repopulated many times in the last million years. Each event changed, or something we do different (without traveling) enters a new universe where some things may be different or the same. Today are universe are shifting a lot.

To be fair, even if it is a one way trip into the past, that doesn’t stop machines going back. We could send a machine back and order it to do anything we want and then tell it to meet us at a certain time in the future. We send it back, then go straight to the meeting point we agreed and then we’ll be able to prove if it worked or not.

I’m a girl who has read a book about seeing future through a box. So is it actually possible?

Time travel has been done on purpose by the Government since the late 1980s. From research, the mostly use kids, or future Presidents. Their are some cases where people have been struck by lightning or came across some tragically event that cause them to leave their timeline either forward or behind in time. The Mandela Effect is the current cause of how things go wrong when time travel is not done right. Click on my name to see the website.

Even as traveling to a location as a future or pass date is possible as what people here mean. However, as you said, it is numbers. Time is a illusion and we do not travel threw time, just universe that are different than ours. What we call time dates and months is what changes each universe. We are all from different universes today as they came together. The mandela effect is a fine example.

thx to eleon wont we soon be able to digitize our conscious being, then accelerate that data pass the speed of light some how then download it into some android or something…..i dunno…..just a thought

I want to go to my elementary school again. Someone help me out, I know its Idiotic but stil.. I am not good at science. As far I understood, 1) we can trace through time if we travel fast than speed of light.. I think memory os the only thing that is faster than light, Yeah I can go to Paris within 1 sec in my memory but yeah its illustion, i want in real 2) Through Blackhole – I think its Bermuda triangle

if you travel back in time you will still be your age now. That is how it worked with others. No one gets younger otherwise traveling to far back would kill you. No school would let you return to school as a adult so not possible.

Plz help me I just want to send a message to myself in my past and save my self from a beast plz help Nazneen

Would love to experience many moments in life again for the first time again!

I think that time traveling should be left alone, for the sake of humanity. There are some things we’re not ready for yet.

Well stephen hawking may be wrong. I mean, the study proved that the universe self corrects itself to prevent inaccuracies. So maybe tourists from past do visit us but we don’t remember them as the universe alters our memory. If you guys have read about Butterfly Effect, a simple mistake today may grow through years to become a giant disaster in future so if you think of it, oncoming tourists from future may cause giant inaccuracies. Imagine this, You have travelled to past. You brought two cakes for yourself, so you pay the shopkeeper 20$. The shopkeeper invests the 20$ in stocks, strikes gold there and becomes a rich businessman.His daughter goes to Cambridge and marries someone else than the person she was supposed to marry according to time. Can you imagine the magnitude of inaccuracy after 100 years? Therefore, whatever the tourists from future do, is corrected by the universe and we don’t remember it. Creepy, but food for thought.It also adds a special meaning to the word ‘Fate’.

How much wacky terbacky (i.e. weed) you be smokin’ JOE JOE?

Hmmmm…. As brilliant of a mind as Stephen Hawkins was, how is he so sure that he would even recognize hordes of tourists from the future? Almost everyone is aware of the warning of the Butterfly Effect. So I’m sure any future visitors Intelligent enough for Past-Time travel would be amply attuned to this.

Most future people coming to the pass (our time) seems careless and not intelligent. Most are taking FBI lie detector test and telling us what is happening in the future. That is a bad idea, because if you tell us (example) who is the next President, and the Government does not like the person they than can change that event to let someone else in (as seen in 2020) One should never acknowledge who he or she is or why they are their. Most traveling is to get knowing of the pass or to pick up certain things. Since are pass is changing, events are changing and are timelines are messed up, someone made a mistake. The Mandela Effect is a fine example.

Wow that’s great plz help me go to my past plz,I can’t do it by my own at least help me send a msg to myself in my past Nazneen

I think it is possible, but time traveling is really just changing universe created by different time lines. Our whole solar system is in a whole different place now and Earth is much smaller in this universe from the one I grew up end. Someone has already changed the timeline.

Roads? Where we’re going, you don’t need roads!

Youre wrong about your measurement of speed for traveling, in order for time to slow down, with inside an object compared to outside. Scientists proved that time with inside an object at an excelorated speed actually appeared to have slown down during the duration of time for the test. The speed was far less then the terminal speed of a rocket for NASA at 256,000 kms p/h.

In to the volicity of space. Generating a vacuum of space, could be no different the the actual transport of matter over frequency where in fact matter can be carried by sound. It is believed that an alien civilization harnessed this energy in the form of bolisks that where believed to carry the same properities and in consideration of harmonic resinance, the simularities could be used in order to carry large weight. In accordance with a documentry on theoretical science.

However the properties, present the fact that a working property controdicts your counter intuative theory of gravitational deceloration of matter to colide within itself to absorb all things into non existance as to the transfer of matter into energy, rather then your idiolisms of transfer between dimentional space to another destination that is not linked or the transfer between time that isnt, either.

However to reproduce the fabric of time within space in a practical measurement as I have mentioned, would put an end to all the lunacy of an unmeasureable field, which people fail to identify. Like running into a glass window. Only to not know what forcefield is present.

Time travel into the past can be achieved simply going faster than the speed of light.

The closer you get to the speed of light the slower time goes

If you reach the speed of light time stops

If you go faster than the speed of light it starts to reverse

Why does no one seem to know this?

Christopher Reeves did this in Superman 3 brah.

Any time travel, pass and future, is by going faster than the speed of light. It is said by reversing that that you can go back in time. However, I assume since the Government has done this since the 80s they have better ways (maybe tying in a date) and not having to go to a unknown date.

I want to send a message to myself in the past on a particular date plz can you help me, this means a lot lot lot to me,plz help me Nazneen

Why don’t we drop the declaratory statements that it “is or isn’t possible!” Until someone actually does so. Just say “maybe”.

People have and their are records both to the pass and future. The Government has done it since the 80s as part of the “star wars project” and are much better at it today. This explains the black holes in the sky of 2019, and the CERN destroying 5 parallel universes in 2013. We also see changes because of time travel events changing time. The Mandela Effect is a find example.

I want to send a msg to myself and my family in the past ,is it possible plz help me my life will be saved one who helps me saves me and my kids from a pack of beasts,

The worst idea ever. We all want to do this and where does it stop. A lottery win does not sound bad if you knew the actual location, time and place. After a while though, would you not want to write that hit song, become the author of the Harry Potter books, stop 9/11? The idea of giving your pass self (a time time travel was not proven) information of the future could change things in a major way. This would cause one small thing to change creating many others to change. This has already happen in simple ways of the The Berenstein Bears changing to The Berenstain Bears. This is a small event but this event “The Mandela Effect” now has over 3,000 changes.

What if you decided to give your pass self information about a lottery ticket that would be a winner, bought late at night and he was hit by a car on the way to get it. Changes the whole future. However, If detailed right, done right, with no large changes, it may not effect much, but to know your being given info from yourself in a future time (when that was not known much or provrn back than) You would either assume it is a joke or you gone crazy.

I don’t want to win a lottery, my decision about my career and studying was right but my family and their cruelty has put me into this worst condition I just want to go back complete my studies and live a life like a human not like a animal or slave,help me plz Nazneen

Can someone take me to 2013? i can pay later to all of you in bitcoins so its a win win and you dont need to do anything, just wait

LOL but still complicating on my side

You travel in your dreams where time and space colloids ..That’s y sometimes the dream which you dreamt might be a 10 mins reel time but you felt dreaming whole time like 6 to 8hrs .. Probably even traveling to parallel universe

I agree. Dreams as we know it is not a simple sleep. The part of the brain we do not use while awake, we use at night. This is the phenomenon part of the brain that can do thing we feel a human can not do. We of course use less than 30% of our brain. By the use of 100% of the brain we would use both sides and be able to do common things such as read thoughts, move things without touching them etc. The idea of using this side of the brain, would be the theory we can leave our bodies and visit different universe, see what could of happen shall we done something different, and even see future events. This may be why we notice different memories to some things as we could of held some from another reality.

It would be very weird, however, if we were trapped in that universe, or another body and fail to return to ours. Is that how people die in their sleep?

i just fell like going to late 70’s, where i can see majority of family.. i am willing to trade life for it…..

Time travel to the pass is just as common as the future. However, as both has been done it is NOT travel threw time. Time is a illusion we created. We are actually traveling threw different universe with (what we call) different time, dates, years, etc. The Mandela Effect is a find example how traveling threw different reality’s change the time lines.

As a add on to the above, Time travel is not a theory, has been proven, and has been done by the Government since the 1980s. Their is many residue in our history to even show some time travel storys to be real.

Where can one get a reverse watch, is it really possible to go back in past with its help, is it sooo easy ,plz help me ??????? Nazneen

US20060073976A1- search this patent number,this describes the process for time travelling,I really don’t think magnetic energy will work,maybe heat focused on a specific point could expand the fabric of space and make a hole in it.even then I will the hole take you to another time.it would be one thing to time travel but selecting a point in time would be impossible.you could only travel to the time you device was built?

Is there a watch which back travels in time or reverse time watch? Is it true? How to get one? But with that how can I send a message to myself in my past, plz help Nazneen

I don’t believe such a watch exist and their are plenty of smart minds with huge funds trying to travel.right now there are only theories.

Thank you very much for your response. I just want to send a message to myself in my past. Nothing much will be changed but 3 literally dying devastating lives will be saved. We are suffering for the mistakes and egoistic arrogance of others so if possible plz help me

Traveling back in time isn’t just a when problem, it’s a *where* problem. Where was the place you’re standing right now a thousand years ago, or a thousandth of a second ago? There is no useful answer to those questions, so there’s nowhere to travel back in time to.

Traveling forward in time? You’re doing it now.

when you step through a door is time lost when you come back through? lets say you return days Later how much time did you loose. what exactly is Time,.? is dialation a safe way to return ,. a Blackhole will assist you in in travel, the question is will you arrive safe,.

Traveling back in time is impossible. 2 reasons why that are never taken into account.

A) The stuff you are made of ( subatomic material) is being used by something else. It I not like you are a facsimile of the already existing material. What you are made of is exactly the same existing material. The problem is exact stuff can not exist in 2 different places in the same point in time. You will either : Decompile or fall out of phase with the universe. Both bad outcomes for the time traveler.

B) Lets look at it from logical commonsense. You have a bar of gold . You intend to send the bar back 1 second in time. Now you have 2 bars of gold . You send those 2 bars back one second . You have 4 bars …… do that 50 times . You have over 900 trillion bars of gold. All made of the exact subatomic particles. The more the bars back the more the existing mass of the universe increase. What are the consequences of changing the mass of the universe . Hence the paradox . Information can not be destroyed., It also can not be created.

At least this is the way my brain perceives going back in time.

Time is a function of change. None of the 4 forces The strong force , The weak force , Electromagnetism and Gravity can not work without time.

I will figure out time travel one day but only for the past.

I wish I could travel back to 18th of June to save my mom.

Is time travel really a one way ticket? Theoretically, if you can go one way, you should be able to go back.

Time is not one way. It’s consequences are however irreparable given certain circumstances and is not something that should be taken lightly or thought of in a manner of disregard. I’ve only very recently decided to take to your social platforms regarding space and time.

You can try finding me on Instagram. I’m not familiar with these platforms to better direct you there. My Instagram name is johnrvh

On Twitter it seems to be @_JohnRvH

If I go forward I will have to pay extra bills and taxes. I don’t think I can afford it.

You’re the first person I’ve come across in this timeline that has a sense of humor. Thankfully, going forward is not possible if that future hasn’t been created yet.

timetraval is no joke if its created the whole universe could go out of orbit.

Cauchy problem converging to non minimal terraces as t → +∞

Stephen Hawking may he rest in peace a genius but not all knowing. As far as he knows we haven’t been flocked by tourists, in the same maybe these UFO sightings are actually time travelers from the future coming to the past to view how we really lived why things really happened the way they did, etc. To limit the imagination of possible and impossible is wrong then you create fantasy. And we have learned from history that there is truth in fantasy. I.e. the different mythos of the different ancient cultures from around the world including those of the Norse. Improbable and probable should be more appropriate. It’s possible because it can be imagined improbable die to the right math or this or that not existing or matching up. I also believe that if time travel to the past were possible that the changing of something in the past would create a new timeline running current with your timeline at which will inevitably collide and will cause the collapse of the universe at which point a new universe will be born.

so i think the speed of light is only relative to deciding a point of destination -initially- as specific gravity of destination needs to be ascertained to calculate the frequency needed to run an alcubierre-white engine to bend space correctly to cross space ‘quickly’, the point of reference may well be jupiter in our solar system for the fact of the moons that orbit it, i surmise that by using a ‘dead end ‘ equation that usually puts notable mathematicians into the outer regions by trying to solve it may actually be the key as calculations end in a loop of 4-2-1 ie 3N+1; this process of calculation creates a sine wave over time/distance relative to specific gravity of chosen destination – as time is determined by gravity therefore if the speed of light to a destination can be used to ascertain the specific gravity of a ‘body’ to visit ie a star or sun due to receivable resonant frequencies emitted by the body, then the constrictions of the speed of light do not exist other than to give a constant, by using the 3N+1 method of calculation ,once the speed of light and returning resonant frequencies of a destination are determined the calculation can be extrapolated to match the distance giving the end point -in doing this the sine wave required can be ascertained and be condensed to create a wormhole and allow the alcubierre-white engine to ‘bend or distort space enough so that the bubble you are in matches the required specific gravity of the destination – the frequency of the body nearest to the destination point should be used and resonated inside the bubble to create synchronicity of frequency and cause attraction i also believe that travelling through space require the ability to see things from different perspectives and it requires the ability to navigate through a series of what may be described as “Aims Windows” where your point of view needs to change inherently with a given position at a given point in the galaxy

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Time travel: Is it possible?

Science says time travel is possible, but probably not in the way you're thinking.

time travel graphic illustration of a tunnel with a clock face swirling through the tunnel.

Albert Einstein's theory

  • General relativity and GPS
  • Wormhole travel
  • Alternate theories

Science fiction

Is time travel possible? Short answer: Yes, and you're doing it right now — hurtling into the future at the impressive rate of one second per second. 

You're pretty much always moving through time at the same speed, whether you're watching paint dry or wishing you had more hours to visit with a friend from out of town. 

But this isn't the kind of time travel that's captivated countless science fiction writers, or spurred a genre so extensive that Wikipedia lists over 400 titles in the category "Movies about Time Travel." In franchises like " Doctor Who ," " Star Trek ," and "Back to the Future" characters climb into some wild vehicle to blast into the past or spin into the future. Once the characters have traveled through time, they grapple with what happens if you change the past or present based on information from the future (which is where time travel stories intersect with the idea of parallel universes or alternate timelines). 

Related: The best sci-fi time machines ever

Although many people are fascinated by the idea of changing the past or seeing the future before it's due, no person has ever demonstrated the kind of back-and-forth time travel seen in science fiction or proposed a method of sending a person through significant periods of time that wouldn't destroy them on the way. And, as physicist Stephen Hawking pointed out in his book " Black Holes and Baby Universes" (Bantam, 1994), "The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future."

Science does support some amount of time-bending, though. For example, physicist Albert Einstein 's theory of special relativity proposes that time is an illusion that moves relative to an observer. An observer traveling near the speed of light will experience time, with all its aftereffects (boredom, aging, etc.) much more slowly than an observer at rest. That's why astronaut Scott Kelly aged ever so slightly less over the course of a year in orbit than his twin brother who stayed here on Earth. 

Related: Controversially, physicist argues that time is real

There are other scientific theories about time travel, including some weird physics that arise around wormholes , black holes and string theory . For the most part, though, time travel remains the domain of an ever-growing array of science fiction books, movies, television shows, comics, video games and more. 

Scott and Mark Kelly sit side by side wearing a blue NASA jacket and jeans

Einstein developed his theory of special relativity in 1905. Along with his later expansion, the theory of general relativity , it has become one of the foundational tenets of modern physics. Special relativity describes the relationship between space and time for objects moving at constant speeds in a straight line. 

The short version of the theory is deceptively simple. First, all things are measured in relation to something else — that is to say, there is no "absolute" frame of reference. Second, the speed of light is constant. It stays the same no matter what, and no matter where it's measured from. And third, nothing can go faster than the speed of light.

From those simple tenets unfolds actual, real-life time travel. An observer traveling at high velocity will experience time at a slower rate than an observer who isn't speeding through space. 

While we don't accelerate humans to near-light-speed, we do send them swinging around the planet at 17,500 mph (28,160 km/h) aboard the International Space Station . Astronaut Scott Kelly was born after his twin brother, and fellow astronaut, Mark Kelly . Scott Kelly spent 520 days in orbit, while Mark logged 54 days in space. The difference in the speed at which they experienced time over the course of their lifetimes has actually widened the age gap between the two men.

"So, where[as] I used to be just 6 minutes older, now I am 6 minutes and 5 milliseconds older," Mark Kelly said in a panel discussion on July 12, 2020, Space.com previously reported . "Now I've got that over his head."

General relativity and GPS time travel

Graphic showing the path of GPS satellites around Earth at the center of the image.

The difference that low earth orbit makes in an astronaut's life span may be negligible — better suited for jokes among siblings than actual life extension or visiting the distant future — but the dilation in time between people on Earth and GPS satellites flying through space does make a difference. 

Read more: Can we stop time?

The Global Positioning System , or GPS, helps us know exactly where we are by communicating with a network of a few dozen satellites positioned in a high Earth orbit. The satellites circle the planet from 12,500 miles (20,100 kilometers) away, moving at 8,700 mph (14,000 km/h). 

According to special relativity, the faster an object moves relative to another object, the slower that first object experiences time. For GPS satellites with atomic clocks, this effect cuts 7 microseconds, or 7 millionths of a second, off each day, according to the American Physical Society publication Physics Central .  

Read more: Could Star Trek's faster-than-light warp drive actually work?

Then, according to general relativity, clocks closer to the center of a large gravitational mass like Earth tick more slowly than those farther away. So, because the GPS satellites are much farther from the center of Earth compared to clocks on the surface, Physics Central added, that adds another 45 microseconds onto the GPS satellite clocks each day. Combined with the negative 7 microseconds from the special relativity calculation, the net result is an added 38 microseconds. 

This means that in order to maintain the accuracy needed to pinpoint your car or phone — or, since the system is run by the U.S. Department of Defense, a military drone — engineers must account for an extra 38 microseconds in each satellite's day. The atomic clocks onboard don’t tick over to the next day until they have run 38 microseconds longer than comparable clocks on Earth.

Given those numbers, it would take more than seven years for the atomic clock in a GPS satellite to un-sync itself from an Earth clock by more than a blink of an eye. (We did the math: If you estimate a blink to last at least 100,000 microseconds, as the Harvard Database of Useful Biological Numbers does, it would take thousands of days for those 38 microsecond shifts to add up.) 

This kind of time travel may seem as negligible as the Kelly brothers' age gap, but given the hyper-accuracy of modern GPS technology, it actually does matter. If it can communicate with the satellites whizzing overhead, your phone can nail down your location in space and time with incredible accuracy. 

Can wormholes take us back in time?

General relativity might also provide scenarios that could allow travelers to go back in time, according to NASA . But the physical reality of those time-travel methods is no piece of cake. 

Wormholes are theoretical "tunnels" through the fabric of space-time that could connect different moments or locations in reality to others. Also known as Einstein-Rosen bridges or white holes, as opposed to black holes, speculation about wormholes abounds. But despite taking up a lot of space (or space-time) in science fiction, no wormholes of any kind have been identified in real life. 

Related: Best time travel movies

"The whole thing is very hypothetical at this point," Stephen Hsu, a professor of theoretical physics at the University of Oregon, told Space.com sister site Live Science . "No one thinks we're going to find a wormhole anytime soon."

Primordial wormholes are predicted to be just 10^-34 inches (10^-33 centimeters) at the tunnel's "mouth". Previously, they were expected to be too unstable for anything to be able to travel through them. However, a study claims that this is not the case, Live Science reported . 

The theory, which suggests that wormholes could work as viable space-time shortcuts, was described by physicist Pascal Koiran. As part of the study, Koiran used the Eddington-Finkelstein metric, as opposed to the Schwarzschild metric which has been used in the majority of previous analyses.

In the past, the path of a particle could not be traced through a hypothetical wormhole. However, using the Eddington-Finkelstein metric, the physicist was able to achieve just that.

Koiran's paper was described in October 2021, in the preprint database arXiv , before being published in the Journal of Modern Physics D.

Graphic illustration of a wormhole

Alternate time travel theories

While Einstein's theories appear to make time travel difficult, some researchers have proposed other solutions that could allow jumps back and forth in time. These alternate theories share one major flaw: As far as scientists can tell, there's no way a person could survive the kind of gravitational pulling and pushing that each solution requires.

Infinite cylinder theory

Astronomer Frank Tipler proposed a mechanism (sometimes known as a Tipler Cylinder ) where one could take matter that is 10 times the sun's mass, then roll it into a very long, but very dense cylinder. The Anderson Institute , a time travel research organization, described the cylinder as "a black hole that has passed through a spaghetti factory."

After spinning this black hole spaghetti a few billion revolutions per minute, a spaceship nearby — following a very precise spiral around the cylinder — could travel backward in time on a "closed, time-like curve," according to the Anderson Institute. 

The major problem is that in order for the Tipler Cylinder to become reality, the cylinder would need to be infinitely long or be made of some unknown kind of matter. At least for the foreseeable future, endless interstellar pasta is beyond our reach.

Time donuts

Theoretical physicist Amos Ori at the Technion-Israel Institute of Technology in Haifa, Israel, proposed a model for a time machine made out of curved space-time — a donut-shaped vacuum surrounded by a sphere of normal matter.

"The machine is space-time itself," Ori told Live Science . "If we were to create an area with a warp like this in space that would enable time lines to close on themselves, it might enable future generations to return to visit our time."

Amos Ori is a theoretical physicist at the Technion-Israel Institute of Technology in Haifa, Israel. His research interests and publications span the fields of general relativity, black holes, gravitational waves and closed time lines.

There are a few caveats to Ori's time machine. First, visitors to the past wouldn't be able to travel to times earlier than the invention and construction of the time donut. Second, and more importantly, the invention and construction of this machine would depend on our ability to manipulate gravitational fields at will — a feat that may be theoretically possible but is certainly beyond our immediate reach.

Graphic illustration of the TARDIS (Time and Relative Dimensions in Space) traveling through space, surrounded by stars.

Time travel has long occupied a significant place in fiction. Since as early as the "Mahabharata," an ancient Sanskrit epic poem compiled around 400 B.C., humans have dreamed of warping time, Lisa Yaszek, a professor of science fiction studies at the Georgia Institute of Technology in Atlanta, told Live Science .  

Every work of time-travel fiction creates its own version of space-time, glossing over one or more scientific hurdles and paradoxes to achieve its plot requirements. 

Some make a nod to research and physics, like " Interstellar ," a 2014 film directed by Christopher Nolan. In the movie, a character played by Matthew McConaughey spends a few hours on a planet orbiting a supermassive black hole, but because of time dilation, observers on Earth experience those hours as a matter of decades. 

Others take a more whimsical approach, like the "Doctor Who" television series. The series features the Doctor, an extraterrestrial "Time Lord" who travels in a spaceship resembling a blue British police box. "People assume," the Doctor explained in the show, "that time is a strict progression from cause to effect, but actually from a non-linear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbly, timey-wimey stuff." 

Long-standing franchises like the "Star Trek" movies and television series, as well as comic universes like DC and Marvel Comics, revisit the idea of time travel over and over. 

Related: Marvel movies in order: chronological & release order

Here is an incomplete (and deeply subjective) list of some influential or notable works of time travel fiction:

Books about time travel:

A sketch from the Christmas Carol shows a cloaked figure on the left and a person kneeling and clutching their head with their hands.

  • Rip Van Winkle (Cornelius S. Van Winkle, 1819) by Washington Irving
  • A Christmas Carol (Chapman & Hall, 1843) by Charles Dickens
  • The Time Machine (William Heinemann, 1895) by H. G. Wells
  • A Connecticut Yankee in King Arthur's Court (Charles L. Webster and Co., 1889) by Mark Twain
  • The Restaurant at the End of the Universe (Pan Books, 1980) by Douglas Adams
  • A Tale of Time City (Methuen, 1987) by Diana Wynn Jones
  • The Outlander series (Delacorte Press, 1991-present) by Diana Gabaldon
  • Harry Potter and the Prisoner of Azkaban (Bloomsbury/Scholastic, 1999) by J. K. Rowling
  • Thief of Time (Doubleday, 2001) by Terry Pratchett
  • The Time Traveler's Wife (MacAdam/Cage, 2003) by Audrey Niffenegger
  • All You Need is Kill (Shueisha, 2004) by Hiroshi Sakurazaka

Movies about time travel:

  • Planet of the Apes (1968)
  • Superman (1978)
  • Time Bandits (1981)
  • The Terminator (1984)
  • Back to the Future series (1985, 1989, 1990)
  • Star Trek IV: The Voyage Home (1986)
  • Bill & Ted's Excellent Adventure (1989)
  • Groundhog Day (1993)
  • Galaxy Quest (1999)
  • The Butterfly Effect (2004)
  • 13 Going on 30 (2004)
  • The Lake House (2006)
  • Meet the Robinsons (2007)
  • Hot Tub Time Machine (2010)
  • Midnight in Paris (2011)
  • Looper (2012)
  • X-Men: Days of Future Past (2014)
  • Edge of Tomorrow (2014)
  • Interstellar (2014)
  • Doctor Strange (2016)
  • A Wrinkle in Time (2018)
  • The Last Sharknado: It's About Time (2018)
  • Avengers: Endgame (2019)
  • Tenet (2020)
  • Palm Springs (2020)
  • Zach Snyder's Justice League (2021)
  • The Tomorrow War (2021)

Television about time travel:

Image of the Star Trek spaceship USS Enterprise

  • Doctor Who (1963-present)
  • The Twilight Zone (1959-1964) (multiple episodes)
  • Star Trek (multiple series, multiple episodes)
  • Samurai Jack (2001-2004)
  • Lost (2004-2010)
  • Phil of the Future (2004-2006)
  • Steins;Gate (2011)
  • Outlander (2014-2023)
  • Loki (2021-present)

Games about time travel:

  • Chrono Trigger (1995)
  • TimeSplitters (2000-2005)
  • Kingdom Hearts (2002-2019)
  • Prince of Persia: Sands of Time (2003)
  • God of War II (2007)
  • Ratchet and Clank Future: A Crack In Time (2009)
  • Sly Cooper: Thieves in Time (2013)
  • Dishonored 2 (2016)
  • Titanfall 2 (2016)
  • Outer Wilds (2019)

Additional resources

Explore physicist Peter Millington's thoughts about Stephen Hawking's time travel theories at The Conversation . Check out a kid-friendly explanation of real-world time travel from NASA's Space Place . For an overview of time travel in fiction and the collective consciousness, read " Time Travel: A History " (Pantheon, 2016) by James Gleik. 

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Vicky Stein is a science writer based in California. She has a bachelor's degree in ecology and evolutionary biology from Dartmouth College and a graduate certificate in science writing from the University of California, Santa Cruz (2018). Afterwards, she worked as a news assistant for PBS NewsHour, and now works as a freelancer covering anything from asteroids to zebras. Follow her most recent work (and most recent pictures of nudibranchs) on Twitter. 

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meaning of travel through time

Life's Little Mysteries

Where Does the Concept of Time Travel Come From?

Time; he's waiting in the wings.

Wormholes have been proposed as one possible means of traveling through time.

The dream of traveling through time is both ancient and universal. But where did humanity's fascination with time travel begin, and why is the idea so appealing?

The concept of time travel — moving through time the way we move through three-dimensional space — may in fact be hardwired into our perception of time . Linguists have recognized that we are essentially incapable of talking about temporal matters without referencing spatial ones. "In language — any language — no two domains are more intimately linked than space and time," wrote Israeli linguist Guy Deutscher in his 2005 book "The Unfolding of Language." "Even if we are not always aware of it, we invariably speak of time in terms of space, and this reflects the fact that we think of time in terms of space."

Deutscher reminds us that when we plan to meet a friend "around" lunchtime, we are using a metaphor, since lunchtime doesn't have any physical sides. He similarly points out that time can not literally be "long" or "short" like a stick, nor "pass" like a train, or even go "forward" or "backward" any more than it goes sideways, diagonal or down.

Related: Why Does Time Fly When You're Having Fun?

Perhaps because of this connection between space and time, the possibility that time can be experienced in different ways and traveled through has surprisingly early roots. One of the first known examples of time travel appears in the Mahabharata, an ancient Sanskrit epic poem compiled around 400 B.C., Lisa Yaszek, a professor of science fiction studies at the Georgia Institute of Technology in Atlanta, told Live Science 

In the Mahabharata is a story about King Kakudmi, who lived millions of years ago and sought a suitable husband for his beautiful and accomplished daughter, Revati. The two travel to the home of the creator god Brahma to ask for advice. But while in Brahma's plane of existence, they must wait as the god listens to a 20-minute song, after which Brahma explains that time moves differently in the heavens than on Earth. It turned out that "27 chatur-yugas" had passed, or more than 116 million years, according to an online summary , and so everyone Kakudmi and Revati had ever known, including family members and potential suitors, was dead. After this shock, the story closes on a somewhat happy ending in that Revati is betrothed to Balarama, twin brother of the deity Krishna. 

Time is fleeting

To Yaszek, the tale provides an example of what we now call time dilation , in which different observers measure different lengths of time based on their relative frames of reference, a part of Einstein's theory of relativity.

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Such time-slip stories are widespread throughout the world, Yaszek said, citing a Middle Eastern tale from the first century BCE about a Jewish miracle worker who sleeps beneath a newly-planted carob tree and wakes up 70 years later to find it has now matured and borne fruit (carob trees are notorious for how long they take to produce their first harvest). Another instance can be found in an eighth-century Japanese fable about a fisherman named Urashima Tarō who travels to an undersea palace and falls in love with a princess. Tarō finds that, when he returns home, 100 years have passed, according to a translation of the tale published online by the University of South Florida . 

In the early-modern era of the 1700 and 1800s, the sleep-story version of time travel grew more popular, Yaszek said. Examples include the classic tale of Rip Van Winkle, as well as books like Edward Belamy's utopian 1888 novel "Looking Backwards," in which a man wakes up in the year 2000, and the H.G. Wells 1899 novel "The Sleeper Awakes," about a man who slumbers for centuries and wakes to a completely transformed London. 

Related: Science Fiction or Fact: Is Time Travel Possible ?

In other stories from this period, people also start to be able to move backward in time. In Mark Twain’s 1889 satire "A Connecticut Yankee in King Arthur's Court," a blow to the head propels an engineer back to the reign of the legendary British monarch. Objects that can send someone through time begin to appear as well, mainly clocks, such as in Edward Page Mitchell's 1881 story "The Clock that Went Backwards" or Lewis Carrol's 1889 children's fantasy "Sylvie and Bruno," where the characters possess a watch that is a type of time machine . 

The explosion of such stories during this era might come from the fact that people were "beginning to standardize time, and orient themselves to clocks more frequently," Yaszek said. 

Time after time

Wells provided one of the most enduring time-travel plots in his 1895 novella "The Time Machine," which included the innovation of a craft that can move forward and backward through long spans of time. "This is when we’re getting steam engines and trains and the first automobiles," Yaszek said. "I think it’s no surprise that Wells suddenly thinks: 'Hey, maybe we can use a vehicle to travel through time.'"

Because it is such a rich visual icon, many beloved time-travel stories written after this have included a striking time machine, Yaszek said, referencing The Doctor's blue police box — the TARDIS — in the long-running BBC series "Doctor Who," and "Back to the Future"'s silver luxury speedster, the DeLorean . 

More recently, time travel has been used to examine our relationship with the past, Yaszek said, in particular in pieces written by women and people of color. Octavia Butler's 1979 novel "Kindred" about a modern woman who visits her pre-Civil-War ancestors is "a marvelous story that really asks us to rethink black and white relations through history," she said. And a contemporary web series called " Send Me " involves an African-American psychic who can guide people back to antebellum times and witness slavery. 

"I'm really excited about stories like that," Yaszek said. "They help us re-see history from new perspectives."

Time travel has found a home in a wide variety of genres and media, including comedies such as "Groundhog Day" and "Bill and Ted's Excellent Adventure" as well as video games like Nintendo's "The Legend of Zelda: Majora's Mask" and the indie game "Braid." 

Yaszek suggested that this malleability and ubiquity speaks to time travel tales' ability to offer an escape from our normal reality. "They let us imagine that we can break free from the grip of linear time," she said. "And somehow get a new perspective on the human experience, either our own or humanity as a whole, and I think that feels so exciting to us." 

That modern people are often drawn to time-machine stories in particular might reflect the fact that we live in a technological world, she added. Yet time travel's appeal certainly has deeper roots, interwoven into the very fabric of our language and appearing in some of our earliest imaginings. 

"I think it's a way to make sense of the otherwise intangible and inexplicable, because it's hard to grasp time," Yaszek said. "But this is one of the final frontiers, the frontier of time, of life and death. And we're all moving forward, we're all traveling through time."

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Originally published on Live Science .

Adam Mann is a freelance journalist with over a decade of experience, specializing in astronomy and physics stories. He has a bachelor's degree in astrophysics from UC Berkeley. His work has appeared in the New Yorker, New York Times, National Geographic, Wall Street Journal, Wired, Nature, Science, and many other places. He lives in Oakland, California, where he enjoys riding his bike. 

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meaning of travel through time

Is time travel possible? Why one scientist says we 'cannot ignore the possibility.'

meaning of travel through time

A common theme in science-fiction media , time travel is captivating. It’s defined by the late philosopher David Lewis in his essay “The Paradoxes of Time Travel” as “[involving] a discrepancy between time and space time. Any traveler departs and then arrives at his destination; the time elapsed from departure to arrival … is the duration of the journey.”

Time travel is usually understood by most as going back to a bygone era or jumping forward to a point far in the future . But how much of the idea is based in reality? Is it possible to travel through time? 

Is time travel possible?

According to NASA, time travel is possible , just not in the way you might expect. Albert Einstein’s theory of relativity says time and motion are relative to each other, and nothing can go faster than the speed of light , which is 186,000 miles per second. Time travel happens through what’s called “time dilation.”

Time dilation , according to Live Science, is how one’s perception of time is different to another's, depending on their motion or where they are. Hence, time being relative. 

Learn more: Best travel insurance

Dr. Ana Alonso-Serrano, a postdoctoral researcher at the Max Planck Institute for Gravitational Physics in Germany, explained the possibility of time travel and how researchers test theories. 

Space and time are not absolute values, Alonso-Serrano said. And what makes this all more complex is that you are able to carve space-time .

“In the moment that you carve the space-time, you can play with that curvature to make the time come in a circle and make a time machine,” Alonso-Serrano told USA TODAY. 

She explained how, theoretically, time travel is possible. The mathematics behind creating curvature of space-time are solid, but trying to re-create the strict physical conditions needed to prove these theories can be challenging. 

“The tricky point of that is if you can find a physical, realistic, way to do it,” she said. 

Alonso-Serrano said wormholes and warp drives are tools that are used to create this curvature. The matter needed to achieve curving space-time via a wormhole is exotic matter , which hasn’t been done successfully. Researchers don’t even know if this type of matter exists, she said.

“It's something that we work on because it's theoretically possible, and because it's a very nice way to test our theory, to look for possible paradoxes,” Alonso-Serrano added.

“I could not say that nothing is possible, but I cannot ignore the possibility,” she said. 

She also mentioned the anecdote of  Stephen Hawking’s Champagne party for time travelers . Hawking had a GPS-specific location for the party. He didn’t send out invites until the party had already happened, so only people who could travel to the past would be able to attend. No one showed up, and Hawking referred to this event as "experimental evidence" that time travel wasn't possible.

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March 18, 2024

The Great Debate: Could We Ever Travel through Time?

Our space and physics editors go head-to-head over a classic mind-bending question.

By Clara Moskowitz & Lee Billings

cemagraphics/Getty Images

Illustration of a Bohr atom model spinning around the words Science Quickly with various science and medicine related icons around the text

Clara Moskowitz: Hi, I’m Clara Moskowitz, a space editor here at Scientific American. We’re taking a break this week to look back at some of our favorite podcast episodes. I chose this one about the physics of time travel, because I’m a big sci-fi geek, so I’m fascinated by the topic. But also, it was such a fun debate to have with my colleague and friend, Lee Billings, another space editor here. We each picked a side – I was pro time travel, he was con—and dug our heels in. Check it out!

[Clip: Show theme music]

Moskowitz: We’re here today to talk about time travel. A perennial – dare I say, timeless–topic of science fiction, but is it possible? Is there any chance at all that it could actually happen?

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Lee Billings: No. No, no no no no. (laughs). Well, kinda. Not really. ARGH. I’m Lee Billings.

Moskowitz: I’m Clara Moskowitz, and this is Cosmos, Quickly , the biweekly space podcast from Scientific American . 

Moskowitz: We’re going to have a little friendly debate.

Billings: Really? I came for a throwdown.

Moskowitz: Well, a wrangle. A parley. A confab. Lee, what do you have against time travel?

Billings: So I love the idea of time travel! And in fact I do it all the time—like most everyone else I’m traveling into the future at one second per second. I’m less of a fan, though, of more speculative time travel, which is good fodder for goofy sci-fi stories, but in the real world it’s an implausible distraction.

Moskowitz: But really, we can stay within plausible physics and still see how more extreme versions of time travel are possible. See, Einstein’s special theory of relativity shows that the rate time flows at depends on how fast you’re moving. 

Billings: Einstein strikes again, what a rascal.

Moskowitz: If you’re traveling in a starship at close to the speed of light, you’ll still experience the familiar one-second-per-second ticking of a clock– but an observer back on Earth would see your clock moving glacially slow. To them, you’d be moving through time at a snail’s pace. That means that when you finally got back,  maybe only a year would have passed for you, but a century could have gone by for your friends on Earth. Ergo, you just traveled to the future! 

Billings: Right, right, no one’s disputing any of that! We can even measure this sort of “time dilation” right now on Earth, not with starships, but with subatomic particles. Some of those particles have very short lifetimes, decaying almost instantaneously. But if we drastically speed them up, like in a particle accelerator, we find they endure longer in proportion to how fast they’re going. So riddle me this, though, Clara: How can we travel into the past? That’s something so hard to do–effectively impossible, almost–that it’s scarcely worth thinking about.

[Clip: Back to the Future : “This is what makes time travel possible. The flux capacitor!”]

Moskowitz: I get it—no one has yet conceived of a way to journey to the past. But the crazy thing is it’s not impossible. Time is one of the four dimensions in the universe, along with three dimensions of space. And we move through space in all directions just fine, and according to physics, travel through time should be just as possible.

One way that people have looked into is via a wormhole—a shortcut bridge through spacetime that was predicted by general relativity. Wormholes can connect distant points in spacetime, meaning you could conceivably use one to bridge not just the gap between here and a distant galaxy, but the span between 2023 and 1923. 

[CLIP: Interstellar : “That’s the wormhole.”]

Billings : Ah yes, wormholes—the last refuge of scoundrels and desperate physicists. The trouble with wormholes Clara, is that, unlike a DeLorean, we have no evidence they actually exist—and, even if they did, it seems the only ways to make them traversable and stable involves using negative energy or negative mass  to prop them open. And, guess what, just like wormholes themselves, we have no evidence these weird forms of matter and energy actually exist, either. And let’s just beat this dead horse one more time—even if wormholes exist, as well as the means to make them traversable, to go back in time seems to require anchoring one end in a region of very warped spacetime, like around a black hole, or accelerating it to nearly lightspeed. Are you sensing a theme here, Clara?

Moskowitz: Yeah, yeah. All I can say is that just because there’s no evidence any of these things exist, there’s also no evidence they don’t or can’t exist. Wormholes are real solutions to the equations of general relativity, and even negative energy and mass are concepts that come up in the math and aren’t prohibited.

Billings: Well how about some more practical arguments, then? If time travel were possible, wouldn’t we have met some time travelers by now? Wouldn’t someone have gone back and killed Hitler—or at least prevented me from wearing that ridiculous outfit to my high school prom? You know there’s a famous story about physicist Stephen Hawking, who invited time travelers to come to a party he was holding. The trick was the the party happened in 2009, but the invitation came out in a miniseries that was broadcast in 2010—thus, only time travelers would have been able to attend. 

[CLIP: Stephen Hawking Time Travel Party: “Here is the invitation, giving the exact coordinates in time and space. I am hoping in one form or another it will survive for many thousands of years.”]

Billings: Sadly, the hors d'oeuvres went uneaten and the champagne sat unopened, because, clearly, time travel to the past is impossible! 

Moskowitz: I admit a party with Stephen Hawking should have been pretty alluring to time travelers, if they were out there. But you’re forgetting about the International Clause of Secrecy that all time travelers probably have to swear to, making sure to hide their identities and abilities from those in earlier eras.  

Billings: Hmm, yes the clause of secrecy here. Feels like we’re really veering into science fiction territory special pleading here. And don’t forget all the paradoxes that we have to worry about too. There are lots of good reasons to think time travel might introduce insurmountable paradoxes in physics. The most famous being the grandfather—or grandmother—paradox. If time travel were possible into the past, so the thinking goes, then a person could go back in time and kill their own grandparents, thus making it impossible for them to be born and impossible for them to travel back in time to ever commit the murder, and so on and so on.

Moskowitz: I wonder if it could be like a many-worlds scenario, where each change a time traveler makes to the past spawns a whole new universe that carries on from that point. So if I went back in time and killed one of my forebears, then a new branch universe would begin where that whole line of descendents, including me, never existed. I mean, it sounds crazy, but then again, physics is pretty enamored with multiverses, and they seem to pop up for lots of reasons already. Maybe it’s not impossible? 

Billings: If not impossible, then I’d say, implausible.

Moskowitz: Well, I’m forever an optimist, Lee! Thanks for listening to the Cosmos, Quickly .

Billings: Our show is produced by Jeff DelViscio, Tulika Bose and Kelso Harper.  Our music was composed by Dominic Smith.

Moskowtiz: If you like the show, please consider rating or leaving a review. You can also email feedback, questions, and tips to [email protected]

Billings: For more spacetime hijinks and all your science news, head to SciAm.com. This has been Cosmos, Quickly . I’m Lee Billings. 

Moskowitz: I’m Clara Moskowitz. 

Billings: And we’ll see you next time, in the future!

meaning of travel through time

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Time travel for travelers? It’s tricky.

Scientific theories suggest it’s possible to travel through time. But the reality isn’t so clear.

A photo illustration of Robot Restaurant in Tokyo.

Time travel has fascinated scientists and writers for at least 125 years. The concept feels especially intriguing now, when physical travel is limited. Here, a photo illustration of Tokyo’s Robot Restaurant captures the idea of speeding through time.

I’m stuck at home, you’re stuck at home, we’re all stuck at home. Jetting off to some fun-filled destination like we used to might not be in the cards for a little while yet. But what about travelling through time? And not just the boring way, where we wait for the future to arrive one second at a time. What if you could zip through time at will, travelling forward to the future or backward to the past as easily as pushing buttons on the dashboard of a souped-up DeLorean, just like in the movie Back to the Future ?

Time travel has been a fantasy for at least 125 years. H.G. Wells penned his groundbreaking novel, The Time Machine , in 1895, and it’s something that physicists and philosophers have been writing serious papers about for almost a century.

What really kick-started scientific investigations into time travel was the notion, dating to the closing years of the 19th century, that time could be envisioned as a dimension, just like space. We can move easily enough through space, so why not time?

A photo illustration of Tokyu Plaza.

At the end of the 19th century, scientists thought of time as a dimension like space, where travelers can go anywhere they want. This photo illustration of Tokyu Plaza in Tokyo’s Omotesando Harajuku evokes the feeling of visiting endless destinations.

“In space, you can go wherever you want, so maybe in time you can similarly go anywhere you want,” says Nikk Effingham, a philosopher at the University of Birmingham in the United Kingdom . “From there, it’s a short step to time machines.”

( Why are people obsessed with time travel? Best-selling author James Gleick has some ideas .)

Dueling theories

Wells was a novelist, not a physicist, but physics would soon catch up. In 1905, Albert Einstein published the first part of his relativity theory, known as special relativity . In it, space and time are malleable; measurements of both space and time depend on the relative speed of the person doing the measuring.

A few years later, the German mathematician Hermann Minkowski showed that, in Einstein’s theory, space and time could be thought of as two aspects of a single four-dimensional entity known as space-time . Then, in 1915, Einstein came up with the second part of his theory, known as general relativity . General relativity renders gravity in a new light: Instead of thinking of it as a force, general relativity describes gravity as a bending or warping of space-time.

But special relativity is enough to get us started in terms of moving through time. The theory “establishes that time is much more similar to space than we had previously thought,” says Clifford Johnson, a physicist at the University of Southern California. “So maybe everything we can do with space, we can do with time.”

Well, almost everything. Special relativity doesn’t give us a way of going back in time, but it does give us a way of going forward— and at a rate that you can actually control. In fact, thanks to special relativity, you can end up with two twins having different ages, the famous “twin paradox.”

Suppose you head off to the Alpha Centauri star system in your spaceship at a really high speed (something close to the speed of light), while your twin remains on Earth. When you come back home, you’ll find you’re now much younger than your twin. It’s counterintuitive, to say the least, but the physics, after more than a century, is rock solid.

“It is absolutely provable in special relativity that the astronaut who makes the journey, if they travel at very nearly the speed of light, will be much younger than their twin when they come back,” says Janna Levin, a physicist at Barnard College in New York . Interestingly, time appears to pass just as it always does for both twins; it’s only when they’re reunited that the difference reveals itself.

Maybe you were both in your 20s when the voyage began. When you come back, you look just a few years older than when you left, while your twin is perhaps now a grandparent. “My experience of the passage of time is utterly normal for me. My clocks tick at the normal rate, I age normally, movies run at the right pace,” says Levin. “I’m no further into my future than normal. But I’ve travelled into my twin’s future.”

( To study aging, scientist are looking to outer space .)

With general relativity, things really start to get interesting. In this theory, a massive object warps or distorts space and time. Perhaps you’ve seen diagrams or videos comparing this to the way a ball distorts a rubber sheet . One result is that, just as travelling at a high speed affects the rate at which time passes, simply being near a really heavy object—like a black hole —will affect one’s experience of time. (This trick was central to the plot of the 2014 film, Interstellar , in which Matthew McConaughey’s character spends time in the vicinity of a massive black hole. When he returns home, he finds that his young daughter is now elderly.)

A photo illustration created from inside Nakagin Capsule Tower.

To get around the “grandfather paradox,” some scientists theorize there could be multiple timelines. In these images of Nakagin Capsule Tower in Tokyo, Japan, time seems to pass at different rates.

But black holes are just the beginning. Physicists have also speculated about the implications of a much more exotic structure known as a wormhole . Wormholes, if they exist, could connect one location in space-time with another. An astronaut who enters a wormhole in the Andromeda Galaxy in the year 3000 might find herself emerging from the other end in our own galaxy, in the year 2000. But there’s a catch: While we have overwhelming evidence that black holes exist in nature—astronomers even photographed one last year—wormholes are far more speculative.

“You can imagine building a bridge from one region of space-time to another region of space-time,” explains Levin, “but it would require kinds of mass and energy that we don’t really know exist in reality, things like negative energy.” She says it’s “mathematically conceivable” that structures such as wormholes could exist, but they may not be part of physical reality.

There’s also the troubling question of what happens to our notions of cause and effect if backward time travel were possible. The most famous of these conundrums is the so-called “ grandfather paradox .” Suppose you travel back in time to when your grandfather was a young man. You kill him (perhaps by accident), which means your parent won’t be born, which means you won’t be born. Therefore, you won’t be able to travel through time and kill your grandfather.

Multiple timelines?

Over the years, physicists and philosophers have pondered various resolutions to the grandfather paradox. One possibility is that the paradox simply proves that no such journeys are possible; the laws of physics, somehow, must prevent backward time travel. This was the view of the late physicist Stephen Hawking , who called this rule the “ chronology protection conjecture .” (Mind you, he never specified the actual physics behind such a rule.)

But there are also other, more intriguing, solutions. Maybe backward time travel is possible, and yet time travelers can’t change the past, no matter how hard they try. Effingham, whose book Time Travel: Probability and Impossibility was published earlier this year, puts it this way: “You might shoot the wrong person, or you might change your mind. Or, you might shoot the person you think is your grandfather, but it turns out your grandmother had an affair with the milkman, and that’s who your grandfather was all along; you just didn’t know it.”

Which also means the much-discussed fantasy of killing Hitler before the outbreak of World War II is a non-starter. “It’s impossible because it didn’t happen,” says Fabio Costa, a theoretical physicist at the University of Queensland in Australia . “It’s not even a question. We know how history developed. There is no re-do.”

In fact, suggests Effingham, if you can’t change the past, then a time traveler probably can’t do anything . Your mere existence at a time in which you never existed would be a contradiction. “The universe doesn’t care whether the thing you’ve changed is that you’ve killed Hitler, or that you moved an atom from position A to position B,” Effingham says.

But all is not lost. The scenarios Effingham and Costa are imagining involve a single universe with a single “timeline.” But some physicists speculate that our universe is just one among many . If that’s the case, then perhaps time travelers who visit the past can do as they please, which would shed new light on the grandfather paradox.

( The Big Bang could have led to the creation of multiple universes, scientists say .)

“Maybe, for whatever reason, you decide to go back and commit this crime [of killing your grandfather], and so the world ‘branches off’ into two different realities,” says Levin. As a result, “even though you seem to be altering your past, you’re not really altering it; you’re creating a new history.” (This idea of multiple timelines lies at the heart of the Back to the Future movie trilogy. In contrast, in the movie 12 Monkeys , Bruce Willis’s character makes multiple journeys through time, but everything plays out along a single timeline.)

More work to be done

What everyone seems to agree on is that no one is building a time-travelling DeLorean or engineering a custom-built wormhole anytime soon. Instead, physicists are focusing on completing the work that Einstein began a century ago.

After more than 100 years, no one has figured out how to reconcile general relativity with the other great pillar of 20th century physics: quantum mechanics . Some physicists believe that a long-sought unified theory known as quantum gravity will yield new insight into the nature of time. At the very least, says Levin, it seems likely “that we need to go beyond just general relativity to understand time.”

Meanwhile, it’s no surprise that, like H.G. Wells, we continue to daydream about having the freedom to move through time just as we move through space. “Time is embedded in everything we do,” says Johnson. “It looms large in how we perceive the world. So being able to mess with time—I’m not surprised we’re obsessed with that, and fantasize about it.”

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Time Travel

There is an extensive literature on time travel in both philosophy and physics. Part of the great interest of the topic stems from the fact that reasons have been given both for thinking that time travel is physically possible—and for thinking that it is logically impossible! This entry deals primarily with philosophical issues; issues related to the physics of time travel are covered in the separate entries on time travel and modern physics and time machines . We begin with the definitional question: what is time travel? We then turn to the major objection to the possibility of backwards time travel: the Grandfather paradox. Next, issues concerning causation are discussed—and then, issues in the metaphysics of time and change. We end with a discussion of the question why, if backwards time travel will ever occur, we have not been visited by time travellers from the future.

1.1 Time Discrepancy

1.2 changing the past, 2.1 can and cannot, 2.2 improbable coincidences, 2.3 inexplicable occurrences, 3.1 backwards causation, 3.2 causal loops, 4.1 time travel and time, 4.2 time travel and change, 5. where are the time travellers, other internet resources, related entries, 1. what is time travel.

There is a number of rather different scenarios which would seem, intuitively, to count as ‘time travel’—and a number of scenarios which, while sharing certain features with some of the time travel cases, seem nevertheless not to count as genuine time travel: [ 1 ]

Time travel Doctor . Doctor Who steps into a machine in 2024. Observers outside the machine see it disappear. Inside the machine, time seems to Doctor Who to pass for ten minutes. Observers in 1984 (or 3072) see the machine appear out of nowhere. Doctor Who steps out. [ 2 ] Leap . The time traveller takes hold of a special device (or steps into a machine) and suddenly disappears; she appears at an earlier (or later) time. Unlike in Doctor , the time traveller experiences no lapse of time between her departure and arrival: from her point of view, she instantaneously appears at the destination time. [ 3 ] Putnam . Oscar Smith steps into a machine in 2024. From his point of view, things proceed much as in Doctor : time seems to Oscar Smith to pass for a while; then he steps out in 1984. For observers outside the machine, things proceed differently. Observers of Oscar’s arrival in the past see a time machine suddenly appear out of nowhere and immediately divide into two copies of itself: Oscar Smith steps out of one; and (through the window) they see inside the other something that looks just like what they would see if a film of Oscar Smith were played backwards (his hair gets shorter; food comes out of his mouth and goes back into his lunch box in a pristine, uneaten state; etc.). Observers of Oscar’s departure from the future do not simply see his time machine disappear after he gets into it: they see it collide with the apparently backwards-running machine just described, in such a way that both are simultaneously annihilated. [ 4 ] Gödel . The time traveller steps into an ordinary rocket ship (not a special time machine) and flies off on a certain course. At no point does she disappear (as in Leap ) or ‘turn back in time’ (as in Putnam )—yet thanks to the overall structure of spacetime (as conceived in the General Theory of Relativity), the traveller arrives at a point in the past (or future) of her departure. (Compare the way in which someone can travel continuously westwards, and arrive to the east of her departure point, thanks to the overall curved structure of the surface of the earth.) [ 5 ] Einstein . The time traveller steps into an ordinary rocket ship and flies off at high speed on a round trip. When he returns to Earth, thanks to certain effects predicted by the Special Theory of Relativity, only a very small amount of time has elapsed for him—he has aged only a few months—while a great deal of time has passed on Earth: it is now hundreds of years in the future of his time of departure. [ 6 ] Not time travel Sleep . One is very tired, and falls into a deep sleep. When one awakes twelve hours later, it seems from one’s own point of view that hardly any time has passed. Coma . One is in a coma for a number of years and then awakes, at which point it seems from one’s own point of view that hardly any time has passed. Cryogenics . One is cryogenically frozen for hundreds of years. Upon being woken, it seems from one’s own point of view that hardly any time has passed. Virtual . One enters a highly realistic, interactive virtual reality simulator in which some past era has been recreated down to the finest detail. Crystal . One looks into a crystal ball and sees what happened at some past time, or will happen at some future time. (Imagine that the crystal ball really works—like a closed-circuit security monitor, except that the vision genuinely comes from some past or future time. Even so, the person looking at the crystal ball is not thereby a time traveller.) Waiting . One enters one’s closet and stays there for seven hours. When one emerges, one has ‘arrived’ seven hours in the future of one’s ‘departure’. Dateline . One departs at 8pm on Monday, flies for fourteen hours, and arrives at 10pm on Monday.

A satisfactory definition of time travel would, at least, need to classify the cases in the right way. There might be some surprises—perhaps, on the best definition of ‘time travel’, Cryogenics turns out to be time travel after all—but it should certainly be the case, for example, that Gödel counts as time travel and that Sleep and Waiting do not. [ 7 ]

In fact there is no entirely satisfactory definition of ‘time travel’ in the literature. The most popular definition is the one given by Lewis (1976, 145–6):

What is time travel? Inevitably, it involves a discrepancy between time and time. Any traveller departs and then arrives at his destination; the time elapsed from departure to arrival…is the duration of the journey. But if he is a time traveller, the separation in time between departure and arrival does not equal the duration of his journey.…How can it be that the same two events, his departure and his arrival, are separated by two unequal amounts of time?…I reply by distinguishing time itself, external time as I shall also call it, from the personal time of a particular time traveller: roughly, that which is measured by his wristwatch. His journey takes an hour of his personal time, let us say…But the arrival is more than an hour after the departure in external time, if he travels toward the future; or the arrival is before the departure in external time…if he travels toward the past.

This correctly excludes Waiting —where the length of the ‘journey’ precisely matches the separation between ‘arrival’ and ‘departure’—and Crystal , where there is no journey at all—and it includes Doctor . It has trouble with Gödel , however—because when the overall structure of spacetime is as twisted as it is in the sort of case Gödel imagined, the notion of external time (“time itself”) loses its grip.

Another definition of time travel that one sometimes encounters in the literature (Arntzenius, 2006, 602) (Smeenk and Wüthrich, 2011, 5, 26) equates time travel with the existence of CTC’s: closed timelike curves. A curve in this context is a line in spacetime; it is timelike if it could represent the career of a material object; and it is closed if it returns to its starting point (i.e. in spacetime—not merely in space). This now includes Gödel —but it excludes Einstein .

The lack of an adequate definition of ‘time travel’ does not matter for our purposes here. [ 8 ] It suffices that we have clear cases of (what would count as) time travel—and that these cases give rise to all the problems that we shall wish to discuss.

Some authors (in philosophy, physics and science fiction) consider ‘time travel’ scenarios in which there are two temporal dimensions (e.g. Meiland (1974)), and others consider scenarios in which there are multiple ‘parallel’ universes—each one with its own four-dimensional spacetime (e.g. Deutsch and Lockwood (1994)). There is a question whether travelling to another version of 2001 (i.e. not the very same version one experienced in the past)—a version at a different point on the second time dimension, or in a different parallel universe—is really time travel, or whether it is more akin to Virtual . In any case, this kind of scenario does not give rise to many of the problems thrown up by the idea of travelling to the very same past one experienced in one’s younger days. It is these problems that form the primary focus of the present entry, and so we shall not have much to say about other kinds of ‘time travel’ scenario in what follows.

One objection to the possibility of time travel flows directly from attempts to define it in anything like Lewis’s way. The worry is that because time travel involves “a discrepancy between time and time”, time travel scenarios are simply incoherent. The time traveller traverses thirty years in one year; she is 51 years old 21 years after her birth; she dies at the age of 100, 200 years before her birth; and so on. The objection is that these are straightforward contradictions: the basic description of what time travel involves is inconsistent; therefore time travel is logically impossible. [ 9 ]

There must be something wrong with this objection, because it would show Einstein to be logically impossible—whereas this sort of future-directed time travel has actually been observed (albeit on a much smaller scale—but that does not affect the present point) (Hafele and Keating, 1972b,a). The most common response to the objection is that there is no contradiction because the interval of time traversed by the time traveller and the duration of her journey are measured with respect to different frames of reference: there is thus no reason why they should coincide. A similar point applies to the discrepancy between the time elapsed since the time traveller’s birth and her age upon arrival. There is no more of a contradiction here than in the fact that Melbourne is both 800 kilometres away from Sydney—along the main highway—and 1200 kilometres away—along the coast road. [ 10 ]

Before leaving the question ‘What is time travel?’ we should note the crucial distinction between changing the past and participating in (aka affecting or influencing) the past. [ 11 ] In the popular imagination, backwards time travel would allow one to change the past: to right the wrongs of history, to prevent one’s younger self doing things one later regretted, and so on. In a model with a single past, however, this idea is incoherent: the very description of the case involves a contradiction (e.g. the time traveller burns all her diaries at midnight on her fortieth birthday in 1976, and does not burn all her diaries at midnight on her fortieth birthday in 1976). It is not as if there are two versions of the past: the original one, without the time traveller present, and then a second version, with the time traveller playing a role. There is just one past—and two perspectives on it: the perspective of the younger self, and the perspective of the older time travelling self. If these perspectives are inconsistent (e.g. an event occurs in one but not the other) then the time travel scenario is incoherent.

This means that time travellers can do less than we might have hoped: they cannot right the wrongs of history; they cannot even stir a speck of dust on a certain day in the past if, on that day, the speck was in fact unmoved. But this does not mean that time travellers must be entirely powerless in the past: while they cannot do anything that did not actually happen, they can (in principle) do anything that did happen. Time travellers cannot change the past: they cannot make it different from the way it was—but they can participate in it: they can be amongst the people who did make the past the way it was. [ 12 ]

What about models involving two temporal dimensions, or parallel universes—do they allow for coherent scenarios in which the past is changed? [ 13 ] There is certainly no contradiction in saying that the time traveller burns all her diaries at midnight on her fortieth birthday in 1976 in universe 1 (or at hypertime A ), and does not burn all her diaries at midnight on her fortieth birthday in 1976 in universe 2 (or at hypertime B ). The question is whether this kind of story involves changing the past in the sense originally envisaged: righting the wrongs of history, preventing subsequently regretted actions, and so on. Goddu (2003) and van Inwagen (2010) argue that it does (in the context of particular hypertime models), while Smith (1997, 365–6; 2015) argues that it does not: that it involves avoiding the past—leaving it untouched while travelling to a different version of the past in which things proceed differently.

2. The Grandfather Paradox

The most important objection to the logical possibility of backwards time travel is the so-called Grandfather paradox. This paradox has actually convinced many people that backwards time travel is impossible:

The dead giveaway that true time-travel is flatly impossible arises from the well-known “paradoxes” it entails. The classic example is “What if you go back into the past and kill your grandfather when he was still a little boy?”…So complex and hopeless are the paradoxes…that the easiest way out of the irrational chaos that results is to suppose that true time-travel is, and forever will be, impossible. (Asimov 1995 [2003, 276–7]) travel into one’s past…would seem to give rise to all sorts of logical problems, if you were able to change history. For example, what would happen if you killed your parents before you were born. It might be that one could avoid such paradoxes by some modification of the concept of free will. But this will not be necessary if what I call the chronology protection conjecture is correct: The laws of physics prevent closed timelike curves from appearing . (Hawking, 1992, 604) [ 14 ]

The paradox comes in different forms. Here’s one version:

If time travel was logically possible then the time traveller could return to the past and in a suicidal rage destroy his time machine before it was completed and murder his younger self. But if this was so a necessary condition for the time trip to have occurred at all is removed, and we should then conclude that the time trip did not occur. Hence if the time trip did occur, then it did not occur. Hence it did not occur, and it is necessary that it did not occur. To reply, as it is standardly done, that our time traveller cannot change the past in this way, is a petitio principii . Why is it that the time traveller is constrained in this way? What mysterious force stills his sudden suicidal rage? (Smith, 1985, 58)

The idea is that backwards time travel is impossible because if it occurred, time travellers would attempt to do things such as kill their younger selves (or their grandfathers etc.). We know that doing these things—indeed, changing the past in any way—is impossible. But were there time travel, there would then be nothing left to stop these things happening. If we let things get to the stage where the time traveller is facing Grandfather with a loaded weapon, then there is nothing left to prevent the impossible from occurring. So we must draw the line earlier: it must be impossible for someone to get into this situation at all; that is, backwards time travel must be impossible.

In order to defend the possibility of time travel in the face of this argument we need to show that time travel is not a sure route to doing the impossible. So, given that a time traveller has gone to the past and is facing Grandfather, what could stop her killing Grandfather? Some science fiction authors resort to the idea of chaperones or time guardians who prevent time travellers from changing the past—or to mysterious forces of logic. But it is hard to take these ideas seriously—and more importantly, it is hard to make them work in detail when we remember that changing the past is impossible. (The chaperone is acting to ensure that the past remains as it was—but the only reason it ever was that way is because of his very actions.) [ 15 ] Fortunately there is a better response—also to be found in the science fiction literature, and brought to the attention of philosophers by Lewis (1976). What would stop the time traveller doing the impossible? She would fail “for some commonplace reason”, as Lewis (1976, 150) puts it. Her gun might jam, a noise might distract her, she might slip on a banana peel, etc. Nothing more than such ordinary occurrences is required to stop the time traveller killing Grandfather. Hence backwards time travel does not entail the occurrence of impossible events—and so the above objection is defused.

A problem remains. Suppose Tim, a time-traveller, is facing his grandfather with a loaded gun. Can Tim kill Grandfather? On the one hand, yes he can. He is an excellent shot; there is no chaperone to stop him; the laws of logic will not magically stay his hand; he hates Grandfather and will not hesitate to pull the trigger; etc. On the other hand, no he can’t. To kill Grandfather would be to change the past, and no-one can do that (not to mention the fact that if Grandfather died, then Tim would not have been born). So we have a contradiction: Tim can kill Grandfather and Tim cannot kill Grandfather. Time travel thus leads to a contradiction: so it is impossible.

Note the difference between this version of the Grandfather paradox and the version considered above. In the earlier version, the contradiction happens if Tim kills Grandfather. The solution was to say that Tim can go into the past without killing Grandfather—hence time travel does not entail a contradiction. In the new version, the contradiction happens as soon as Tim gets to the past. Of course Tim does not kill Grandfather—but we still have a contradiction anyway: for he both can do it, and cannot do it. As Lewis puts it:

Could a time traveler change the past? It seems not: the events of a past moment could no more change than numbers could. Yet it seems that he would be as able as anyone to do things that would change the past if he did them. If a time traveler visiting the past both could and couldn’t do something that would change it, then there cannot possibly be such a time traveler. (Lewis, 1976, 149)

Lewis’s own solution to this problem has been widely accepted. [ 16 ] It turns on the idea that to say that something can happen is to say that its occurrence is compossible with certain facts, where context determines (more or less) which facts are the relevant ones. Tim’s killing Grandfather in 1921 is compossible with the facts about his weapon, training, state of mind, and so on. It is not compossible with further facts, such as the fact that Grandfather did not die in 1921. Thus ‘Tim can kill Grandfather’ is true in one sense (relative to one set of facts) and false in another sense (relative to another set of facts)—but there is no single sense in which it is both true and false. So there is no contradiction here—merely an equivocation.

Another response is that of Vihvelin (1996), who argues that there is no contradiction here because ‘Tim can kill Grandfather’ is simply false (i.e. contra Lewis, there is no legitimate sense in which it is true). According to Vihvelin, for ‘Tim can kill Grandfather’ to be true, there must be at least some occasions on which ‘If Tim had tried to kill Grandfather, he would or at least might have succeeded’ is true—but, Vihvelin argues, at any world remotely like ours, the latter counterfactual is always false. [ 17 ]

Return to the original version of the Grandfather paradox and Lewis’s ‘commonplace reasons’ response to it. This response engenders a new objection—due to Horwich (1987)—not to the possibility but to the probability of backwards time travel.

Think about correlated events in general. Whenever we see two things frequently occurring together, this is because one of them causes the other, or some third thing causes both. Horwich calls this the Principle of V-Correlation:

if events of type A and B are associated with one another, then either there is always a chain of events between them…or else we find an earlier event of type C that links up with A and B by two such chains of events. What we do not see is…an inverse fork—in which A and B are connected only with a characteristic subsequent event, but no preceding one. (Horwich, 1987, 97–8)

For example, suppose that two students turn up to class wearing the same outfits. That could just be a coincidence (i.e. there is no common cause, and no direct causal link between the two events). If it happens every week for the whole semester, it is possible that it is a coincidence, but this is extremely unlikely . Normally, we see this sort of extensive correlation only if either there is a common cause (e.g. both students have product endorsement deals with the same clothing company, or both slavishly copy the same influencer) or a direct causal link (e.g. one student is copying the other).

Now consider the time traveller setting off to kill her younger self. As discussed, no contradiction need ensue—this is prevented not by chaperones or mysterious forces, but by a run of ordinary occurrences in which the trigger falls off the time traveller’s gun, a gust of wind pushes her bullet off course, she slips on a banana peel, and so on. But now consider this run of ordinary occurrences. Whenever the time traveller contemplates auto-infanticide, someone nearby will drop a banana peel ready for her to slip on, or a bird will begin to fly so that it will be in the path of the time traveller’s bullet by the time she fires, and so on. In general, there will be a correlation between auto-infanticide attempts and foiling occurrences such as the presence of banana peels—and this correlation will be of the type that does not involve a direct causal connection between the correlated events or a common cause of both. But extensive correlations of this sort are, as we saw, extremely rare—so backwards time travel will happen about as often as you will see two people wear the same outfits to class every day of semester, without there being any causal connection between what one wears and what the other wears.

We can set out Horwich’s argument this way:

  • If time travel were ever to occur, we should see extensive uncaused correlations.
  • It is extremely unlikely that we should ever see extensive uncaused correlations.
  • Therefore time travel is extremely unlikely to occur.

The conclusion is not that time travel is impossible, but that we should treat it the way we treat the possibility of, say, tossing a fair coin and getting heads one thousand times in a row. As Price (1996, 278 n.7) puts it—in the context of endorsing Horwich’s conclusion: “the hypothesis of time travel can be made to imply propositions of arbitrarily low probability. This is not a classical reductio, but it is as close as science ever gets.”

Smith (1997) attacks both premisses of Horwich’s argument. Against the first premise, he argues that backwards time travel, in itself, does not entail extensive uncaused correlations. Rather, when we look more closely, we see that time travel scenarios involving extensive uncaused correlations always build in prior coincidences which are themselves highly unlikely. Against the second premise, he argues that, from the fact that we have never seen extensive uncaused correlations, it does not follow that we never shall. This is not inductive scepticism: let us assume (contra the inductive sceptic) that in the absence of any specific reason for thinking things should be different in the future, we are entitled to assume they will continue being the same; still we cannot dismiss a specific reason for thinking the future will be a certain way simply on the basis that things have never been that way in the past. You might reassure an anxious friend that the sun will certainly rise tomorrow because it always has in the past—but you cannot similarly refute an astronomer who claims to have discovered a specific reason for thinking that the earth will stop rotating overnight.

Sider (2002, 119–20) endorses Smith’s second objection. Dowe (2003) criticises Smith’s first objection, but agrees with the second, concluding overall that time travel has not been shown to be improbable. Ismael (2003) reaches a similar conclusion. Goddu (2007) criticises Smith’s first objection to Horwich. Further contributions to the debate include Arntzenius (2006), Smeenk and Wüthrich (2011, §2.2) and Elliott (2018). For other arguments to the same conclusion as Horwich’s—that time travel is improbable—see Ney (2000) and Effingham (2020).

Return again to the original version of the Grandfather paradox and Lewis’s ‘commonplace reasons’ response to it. This response engenders a further objection. The autoinfanticidal time traveller is attempting to do something impossible (render herself permanently dead from an age younger than her age at the time of the attempts). Suppose we accept that she will not succeed and that what will stop her is a succession of commonplace occurrences. The previous objection was that such a succession is improbable . The new objection is that the exclusion of the time traveler from successfully committing auto-infanticide is mysteriously inexplicable . The worry is as follows. Each particular event that foils the time traveller is explicable in a perfectly ordinary way; but the inevitable combination of these events amounts to a ring-fencing of the forbidden zone of autoinfanticide—and this ring-fencing is mystifying. It’s like a grand conspiracy to stop the time traveler from doing what she wants to do—and yet there are no conspirators: no time lords, no magical forces of logic. This is profoundly perplexing. Riggs (1997, 52) writes: “Lewis’s account may do for a once only attempt, but is untenable as a general explanation of Tim’s continual lack of success if he keeps on trying.” Ismael (2003, 308) writes: “Considered individually, there will be nothing anomalous in the explanations…It is almost irresistible to suppose, however, that there is something anomalous in the cases considered collectively, i.e., in our unfailing lack of success.” See also Gorovitz (1964, 366–7), Horwich (1987, 119–21) and Carroll (2010, 86).

There have been two different kinds of defense of time travel against the objection that it involves mysteriously inexplicable occurrences. Baron and Colyvan (2016, 70) agree with the objectors that a purely causal explanation of failure—e.g. Tim fails to kill Grandfather because first he slips on a banana peel, then his gun jams, and so on—is insufficient. However they argue that, in addition, Lewis offers a non-causal—a logical —explanation of failure: “What explains Tim’s failure to kill his grandfather, then, is something about logic; specifically: Tim fails to kill his grandfather because the law of non-contradiction holds.” Smith (2017) argues that the appearance of inexplicability is illusory. There are no scenarios satisfying the description ‘a time traveller commits autoinfanticide’ (or changes the past in any other way) because the description is self-contradictory (e.g. it involves the time traveller permanently dying at 20 and also being alive at 40). So whatever happens it will not be ‘that’. There is literally no way for the time traveller not to fail. Hence there is no need for—or even possibility of—a substantive explanation of why failure invariably occurs, and such failure is not perplexing.

3. Causation

Backwards time travel scenarios give rise to interesting issues concerning causation. In this section we examine two such issues.

Earlier we distinguished changing the past and affecting the past, and argued that while the former is impossible, backwards time travel need involve only the latter. Affecting the past would be an example of backwards causation (i.e. causation where the effect precedes its cause)—and it has been argued that this too is impossible, or at least problematic. [ 18 ] The classic argument against backwards causation is the bilking argument . [ 19 ] Faced with the claim that some event A causes an earlier event B , the proponent of the bilking objection recommends an attempt to decorrelate A and B —that is, to bring about A in cases in which B has not occurred, and to prevent A in cases in which B has occurred. If the attempt is successful, then B often occurs despite the subsequent nonoccurrence of A , and A often occurs without B occurring, and so A cannot be the cause of B . If, on the other hand, the attempt is unsuccessful—if, that is, A cannot be prevented when B has occurred, nor brought about when B has not occurred—then, it is argued, it must be B that is the cause of A , rather than vice versa.

The bilking procedure requires repeated manipulation of event A . Thus, it cannot get under way in cases in which A is either unrepeatable or unmanipulable. Furthermore, the procedure requires us to know whether or not B has occurred, prior to manipulating A —and thus, it cannot get under way in cases in which it cannot be known whether or not B has occurred until after the occurrence or nonoccurrence of A (Dummett, 1964). These three loopholes allow room for many claims of backwards causation that cannot be touched by the bilking argument, because the bilking procedure cannot be performed at all. But what about those cases in which it can be performed? If the procedure succeeds—that is, A and B are decorrelated—then the claim that A causes B is refuted, or at least weakened (depending upon the details of the case). But if the bilking attempt fails, it does not follow that it must be B that is the cause of A , rather than vice versa. Depending upon the situation, that B causes A might become a viable alternative to the hypothesis that A causes B —but there is no reason to think that this alternative must always be the superior one. For example, suppose that I see a photo of you in a paper dated well before your birth, accompanied by a report of your arrival from the future. I now try to bilk your upcoming time trip—but I slip on a banana peel while rushing to push you away from your time machine, my time travel horror stories only inspire you further, and so on. Or again, suppose that I know that you were not in Sydney yesterday. I now try to get you to go there in your time machine—but first I am struck by lightning, then I fall down a manhole, and so on. What does all this prove? Surely not that your arrival in the past causes your departure from the future. Depending upon the details of the case, it seems that we might well be entitled to describe it as involving backwards time travel and backwards causation. At least, if we are not so entitled, this must be because of other facts about the case: it would not follow simply from the repeated coincidental failures of my bilking attempts.

Backwards time travel would apparently allow for the possibility of causal loops, in which things come from nowhere. The things in question might be objects—imagine a time traveller who steals a time machine from the local museum in order to make his time trip and then donates the time machine to the same museum at the end of the trip (i.e. in the past). In this case the machine itself is never built by anyone—it simply exists. The things in question might be information—imagine a time traveller who explains the theory behind time travel to her younger self: theory that she herself knows only because it was explained to her in her youth by her time travelling older self. The things in question might be actions. Imagine a time traveller who visits his younger self. When he encounters his younger self, he suddenly has a vivid memory of being punched on the nose by a strange visitor. He realises that this is that very encounter—and resignedly proceeds to punch his younger self. Why did he do it? Because he knew that it would happen and so felt that he had to do it—but he only knew it would happen because he in fact did it. [ 20 ]

One might think that causal loops are impossible—and hence that insofar as backwards time travel entails such loops, it too is impossible. [ 21 ] There are two issues to consider here. First, does backwards time travel entail causal loops? Lewis (1976, 148) raises the question whether there must be causal loops whenever there is backwards causation; in response to the question, he says simply “I am not sure.” Mellor (1998, 131) appears to claim a positive answer to the question. [ 22 ] Hanley (2004, 130) defends a negative answer by telling a time travel story in which there is backwards time travel and backwards causation, but no causal loops. [ 23 ] Monton (2009) criticises Hanley’s counterexample, but also defends a negative answer via different counterexamples. Effingham (2020) too argues for a negative answer.

Second, are causal loops impossible, or in some other way objectionable? One objection is that causal loops are inexplicable . There have been two main kinds of response to this objection. One is to agree but deny that this is a problem. Lewis (1976, 149) accepts that a loop (as a whole) would be inexplicable—but thinks that this inexplicability (like that of the Big Bang or the decay of a tritium atom) is merely strange, not impossible. In a similar vein, Meyer (2012, 263) argues that if someone asked for an explanation of a loop (as a whole), “the blame would fall on the person asking the question, not on our inability to answer it.” The second kind of response (Hanley, 2004, §5) is to deny that (all) causal loops are inexplicable. A second objection to causal loops, due to Mellor (1998, ch.12), is that in such loops the chances of events would fail to be related to their frequencies in accordance with the law of large numbers. Berkovitz (2001) and Dowe (2001) both argue that Mellor’s objection fails to establish the impossibility of causal loops. [ 24 ] Effingham (2020) considers—and rebuts—some additional objections to the possibility of causal loops.

4. Time and Change

Gödel (1949a [1990a])—in which Gödel presents models of Einstein’s General Theory of Relativity in which there exist CTC’s—can well be regarded as initiating the modern academic literature on time travel, in both philosophy and physics. In a companion paper, Gödel discusses the significance of his results for more general issues in the philosophy of time (Gödel 1949b [1990b]). For the succeeding half century, the time travel literature focussed predominantly on objections to the possibility (or probability) of time travel. More recently, however, there has been renewed interest in the connections between time travel and more general issues in the metaphysics of time and change. We examine some of these in the present section. [ 25 ]

The first thing that we need to do is set up the various metaphysical positions whose relationships with time travel will then be discussed. Consider two metaphysical questions:

  • Are the past, present and future equally real?
  • Is there an objective flow or passage of time, and an objective now?

We can label some views on the first question as follows. Eternalism is the view that past and future times, objects and events are just as real as the present time and present events and objects. Nowism is the view that only the present time and present events and objects exist. Now-and-then-ism is the view that the past and present exist but the future does not. We can also label some views on the second question. The A-theory answers in the affirmative: the flow of time and division of events into past (before now), present (now) and future (after now) are objective features of reality (as opposed to mere features of our experience). Furthermore, they are linked: the objective flow of time arises from the movement, through time, of the objective now (from the past towards the future). The B-theory answers in the negative: while we certainly experience now as special, and time as flowing, the B-theory denies that what is going on here is that we are detecting objective features of reality in a way that corresponds transparently to how those features are in themselves. The flow of time and the now are not objective features of reality; they are merely features of our experience. By combining answers to our first and second questions we arrive at positions on the metaphysics of time such as: [ 26 ]

  • the block universe view: eternalism + B-theory
  • the moving spotlight view: eternalism + A-theory
  • the presentist view: nowism + A-theory
  • the growing block view: now-and-then-ism + A-theory.

So much for positions on time itself. Now for some views on temporal objects: objects that exist in (and, in general, change over) time. Three-dimensionalism is the view that persons, tables and other temporal objects are three-dimensional entities. On this view, what you see in the mirror is a whole person. [ 27 ] Tomorrow, when you look again, you will see the whole person again. On this view, persons and other temporal objects are wholly present at every time at which they exist. Four-dimensionalism is the view that persons, tables and other temporal objects are four-dimensional entities, extending through three dimensions of space and one dimension of time. On this view, what you see in the mirror is not a whole person: it is just a three-dimensional temporal part of a person. Tomorrow, when you look again, you will see a different such temporal part. Say that an object persists through time if it is around at some time and still around at a later time. Three- and four-dimensionalists agree that (some) objects persist, but they differ over how objects persist. According to three-dimensionalists, objects persist by enduring : an object persists from t 1 to t 2 by being wholly present at t 1 and t 2 and every instant in between. According to four-dimensionalists, objects persist by perduring : an object persists from t 1 to t 2 by having temporal parts at t 1 and t 2 and every instant in between. Perduring can be usefully compared with being extended in space: a road extends from Melbourne to Sydney not by being wholly located at every point in between, but by having a spatial part at every point in between.

It is natural to combine three-dimensionalism with presentism and four-dimensionalism with the block universe view—but other combinations of views are certainly possible.

Gödel (1949b [1990b]) argues from the possibility of time travel (more precisely, from the existence of solutions to the field equations of General Relativity in which there exist CTC’s) to the B-theory: that is, to the conclusion that there is no objective flow or passage of time and no objective now. Gödel begins by reviewing an argument from Special Relativity to the B-theory: because the notion of simultaneity becomes a relative one in Special Relativity, there is no room for the idea of an objective succession of “nows”. He then notes that this argument is disrupted in the context of General Relativity, because in models of the latter theory to date, the presence of matter does allow recovery of an objectively distinguished series of “nows”. Gödel then proposes a new model (Gödel 1949a [1990a]) in which no such recovery is possible. (This is the model that contains CTC’s.) Finally, he addresses the issue of how one can infer anything about the nonexistence of an objective flow of time in our universe from the existence of a merely possible universe in which there is no objectively distinguished series of “nows”. His main response is that while it would not be straightforwardly contradictory to suppose that the existence of an objective flow of time depends on the particular, contingent arrangement and motion of matter in the world, this would nevertheless be unsatisfactory. Responses to Gödel have been of two main kinds. Some have objected to the claim that there is no objective flow of time in his model universe (e.g. Savitt (2005); see also Savitt (1994)). Others have objected to the attempt to transfer conclusions about that model universe to our own universe (e.g. Earman (1995, 197–200); for a partial response to Earman see Belot (2005, §3.4)). [ 28 ]

Earlier we posed two questions:

Gödel’s argument is related to the second question. Let’s turn now to the first question. Godfrey-Smith (1980, 72) writes “The metaphysical picture which underlies time travel talk is that of the block universe [i.e. eternalism, in the terminology of the present entry], in which the world is conceived as extended in time as it is in space.” In his report on the Analysis problem to which Godfrey-Smith’s paper is a response, Harrison (1980, 67) replies that he would like an argument in support of this assertion. Here is an argument: [ 29 ]

A fundamental requirement for the possibility of time travel is the existence of the destination of the journey. That is, a journey into the past or the future would have to presuppose that the past or future were somehow real. (Grey, 1999, 56)

Dowe (2000, 442–5) responds that the destination does not have to exist at the time of departure: it only has to exist at the time of arrival—and this is quite compatible with non-eternalist views. And Keller and Nelson (2001, 338) argue that time travel is compatible with presentism:

There is four-dimensional [i.e. eternalist, in the terminology of the present entry] time-travel if the appropriate sorts of events occur at the appropriate sorts of times; events like people hopping into time-machines and disappearing, people reappearing with the right sorts of memories, and so on. But the presentist can have just the same patterns of events happening at just the same times. Or at least, it can be the case on the presentist model that the right sorts of events will happen, or did happen, or are happening, at the rights sorts of times. If it suffices for four-dimensionalist time-travel that Jennifer disappears in 2054 and appears in 1985 with the right sorts of memories, then why shouldn’t it suffice for presentist time-travel that Jennifer will disappear in 2054, and that she did appear in 1985 with the right sorts of memories?

Sider (2005) responds that there is still a problem reconciling presentism with time travel conceived in Lewis’s way: that conception of time travel requires that personal time is similar to external time—but presentists have trouble allowing this. Further contributions to the debate whether presentism—and other versions of the A-theory—are compatible with time travel include Monton (2003), Daniels (2012), Hall (2014) and Wasserman (2018) on the side of compatibility, and Miller (2005), Slater (2005), Miller (2008), Hales (2010) and Markosian (2020) on the side of incompatibility.

Leibniz’s Law says that if x = y (i.e. x and y are identical—one and the same entity) then x and y have exactly the same properties. There is a superficial conflict between this principle of logic and the fact that things change. If Bill is at one time thin and at another time not so—and yet it is the very same person both times—it looks as though the very same entity (Bill) both possesses and fails to possess the property of being thin. Three-dimensionalists and four-dimensionalists respond to this problem in different ways. According to the four-dimensionalist, what is thin is not Bill (who is a four-dimensional entity) but certain temporal parts of Bill; and what is not thin are other temporal parts of Bill. So there is no single entity that both possesses and fails to possess the property of being thin. Three-dimensionalists have several options. One is to deny that there are such properties as ‘thin’ (simpliciter): there are only temporally relativised properties such as ‘thin at time t ’. In that case, while Bill at t 1 and Bill at t 2 are the very same entity—Bill is wholly present at each time—there is no single property that this one entity both possesses and fails to possess: Bill possesses the property ‘thin at t 1 ’ and lacks the property ‘thin at t 2 ’. [ 30 ]

Now consider the case of a time traveller Ben who encounters his younger self at time t . Suppose that the younger self is thin and the older self not so. The four-dimensionalist can accommodate this scenario easily. Just as before, what we have are two different three-dimensional parts of the same four-dimensional entity, one of which possesses the property ‘thin’ and the other of which does not. The three-dimensionalist, however, faces a problem. Even if we relativise properties to times, we still get the contradiction that Ben possesses the property ‘thin at t ’ and also lacks that very same property. [ 31 ] There are several possible options for the three-dimensionalist here. One is to relativise properties not to external times but to personal times (Horwich, 1975, 434–5); another is to relativise properties to spatial locations as well as to times (or simply to spacetime points). Sider (2001, 101–6) criticises both options (and others besides), concluding that time travel is incompatible with three-dimensionalism. Markosian (2004) responds to Sider’s argument; [ 32 ] Miller (2006) also responds to Sider and argues for the compatibility of time travel and endurantism; Gilmore (2007) seeks to weaken the case against endurantism by constructing analogous arguments against perdurantism. Simon (2005) finds problems with Sider’s arguments, but presents different arguments for the same conclusion; Effingham and Robson (2007) and Benovsky (2011) also offer new arguments for this conclusion. For further discussion see Wasserman (2018) and Effingham (2020). [ 33 ]

We have seen arguments to the conclusions that time travel is impossible, improbable and inexplicable. Here’s an argument to the conclusion that backwards time travel simply will not occur. If backwards time travel is ever going to occur, we would already have seen the time travellers—but we have seen none such. [ 34 ] The argument is a weak one. [ 35 ] For a start, it is perhaps conceivable that time travellers have already visited the Earth [ 36 ] —but even granting that they have not, this is still compatible with the future actuality of backwards time travel. First, it may be that time travel is very expensive, difficult or dangerous—or for some other reason quite rare—and that by the time it is available, our present period of history is insufficiently high on the list of interesting destinations. Second, it may be—and indeed existing proposals in the physics literature have this feature—that backwards time travel works by creating a CTC that lies entirely in the future: in this case, backwards time travel becomes possible after the creation of the CTC, but travel to a time earlier than the time at which the CTC is created is not possible. [ 37 ]

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Time travel could be possible, but only with parallel timelines

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Assistant Professor, Physics, Brock University

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Have you ever made a mistake that you wish you could undo? Correcting past mistakes is one of the reasons we find the concept of time travel so fascinating. As often portrayed in science fiction, with a time machine, nothing is permanent anymore — you can always go back and change it. But is time travel really possible in our universe , or is it just science fiction?

Read more: Curious Kids: is time travel possible for humans?

Our modern understanding of time and causality comes from general relativity . Theoretical physicist Albert Einstein’s theory combines space and time into a single entity — “spacetime” — and provides a remarkably intricate explanation of how they both work, at a level unmatched by any other established theory. This theory has existed for more than 100 years, and has been experimentally verified to extremely high precision, so physicists are fairly certain it provides an accurate description of the causal structure of our universe.

For decades, physicists have been trying to use general relativity to figure out if time travel is possible . It turns out that you can write down equations that describe time travel and are fully compatible and consistent with relativity. But physics is not mathematics, and equations are meaningless if they do not correspond to anything in reality.

Arguments against time travel

There are two main issues which make us think these equations may be unrealistic. The first issue is a practical one: building a time machine seems to require exotic matter , which is matter with negative energy. All the matter we see in our daily lives has positive energy — matter with negative energy is not something you can just find lying around. From quantum mechanics, we know that such matter can theoretically be created, but in too small quantities and for too short times .

However, there is no proof that it is impossible to create exotic matter in sufficient quantities. Furthermore, other equations may be discovered that allow time travel without requiring exotic matter. Therefore, this issue may just be a limitation of our current technology or understanding of quantum mechanics.

an illustration of a person standing in a barren landscape underneath a clock

The other main issue is less practical, but more significant: it is the observation that time travel seems to contradict logic, in the form of time travel paradoxes . There are several types of such paradoxes, but the most problematic are consistency paradoxes .

A popular trope in science fiction, consistency paradoxes happen whenever there is a certain event that leads to changing the past, but the change itself prevents this event from happening in the first place.

For example, consider a scenario where I enter my time machine, use it to go back in time five minutes, and destroy the machine as soon as I get to the past. Now that I destroyed the time machine, it would be impossible for me to use it five minutes later.

But if I cannot use the time machine, then I cannot go back in time and destroy it. Therefore, it is not destroyed, so I can go back in time and destroy it. In other words, the time machine is destroyed if and only if it is not destroyed. Since it cannot be both destroyed and not destroyed simultaneously, this scenario is inconsistent and paradoxical.

Eliminating the paradoxes

There’s a common misconception in science fiction that paradoxes can be “created.” Time travellers are usually warned not to make significant changes to the past and to avoid meeting their past selves for this exact reason. Examples of this may be found in many time travel movies, such as the Back to the Future trilogy.

But in physics, a paradox is not an event that can actually happen — it is a purely theoretical concept that points towards an inconsistency in the theory itself. In other words, consistency paradoxes don’t merely imply time travel is a dangerous endeavour, they imply it simply cannot be possible.

This was one of the motivations for theoretical physicist Stephen Hawking to formulate his chronology protection conjecture , which states that time travel should be impossible. However, this conjecture so far remains unproven. Furthermore, the universe would be a much more interesting place if instead of eliminating time travel due to paradoxes, we could just eliminate the paradoxes themselves.

One attempt at resolving time travel paradoxes is theoretical physicist Igor Dmitriyevich Novikov’s self-consistency conjecture , which essentially states that you can travel to the past, but you cannot change it.

According to Novikov, if I tried to destroy my time machine five minutes in the past, I would find that it is impossible to do so. The laws of physics would somehow conspire to preserve consistency.

Introducing multiple histories

But what’s the point of going back in time if you cannot change the past? My recent work, together with my students Jacob Hauser and Jared Wogan, shows that there are time travel paradoxes that Novikov’s conjecture cannot resolve. This takes us back to square one, since if even just one paradox cannot be eliminated, time travel remains logically impossible.

So, is this the final nail in the coffin of time travel? Not quite. We showed that allowing for multiple histories (or in more familiar terms, parallel timelines) can resolve the paradoxes that Novikov’s conjecture cannot. In fact, it can resolve any paradox you throw at it.

The idea is very simple. When I exit the time machine, I exit into a different timeline. In that timeline, I can do whatever I want, including destroying the time machine, without changing anything in the original timeline I came from. Since I cannot destroy the time machine in the original timeline, which is the one I actually used to travel back in time, there is no paradox.

After working on time travel paradoxes for the last three years , I have become increasingly convinced that time travel could be possible, but only if our universe can allow multiple histories to coexist. So, can it?

Quantum mechanics certainly seems to imply so, at least if you subscribe to Everett’s “many-worlds” interpretation , where one history can “split” into multiple histories, one for each possible measurement outcome – for example, whether Schrödinger’s cat is alive or dead, or whether or not I arrived in the past.

But these are just speculations. My students and I are currently working on finding a concrete theory of time travel with multiple histories that is fully compatible with general relativity. Of course, even if we manage to find such a theory, this would not be sufficient to prove that time travel is possible, but it would at least mean that time travel is not ruled out by consistency paradoxes.

Time travel and parallel timelines almost always go hand-in-hand in science fiction, but now we have proof that they must go hand-in-hand in real science as well. General relativity and quantum mechanics tell us that time travel might be possible, but if it is, then multiple histories must also be possible.

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Meaning of time travel in English

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  • around Robin Hood's barn idiom
  • baggage drop
  • communication
  • first class
  • peripatetically
  • public transportation
  • super-commuting

Examples of time travel

Translations of time travel.

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to shape something so that it can move as effectively and quickly as possible through a liquid or gas

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meaning of travel through time

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meaning of travel through time

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IMAGES

  1. PPT

    meaning of travel through time

  2. What is Time and How to Time Travel

    meaning of travel through time

  3. Where Does the Concept of Time Travel Come From?

    meaning of travel through time

  4. Why Future Time Travel Is More Likely Than Going to the Past

    meaning of travel through time

  5. Time Travel: Explained in a nutshell

    meaning of travel through time

  6. Time Travel

    meaning of travel through time

VIDEO

  1. Is Time Travel Really Possible

  2. The Epic Journey of Travel Through Time #travel #facts #world #didyouknow #history

  3. 10 Unbelievable Stories That Could Prove Time Travel

  4. What If We Could Travel Through Time?⏳

  5. Can we travel through time?

  6. Does Time Travel Really Work?

COMMENTS

  1. Is Time Travel Possible?

    What does this mean for time travel? Well, according to this theory, the faster you travel, the slower you experience time. Scientists have done some experiments to show that this is true. For example, there was an experiment that used two clocks set to the exact same time. One clock stayed on Earth, while the other flew in an airplane (going ...

  2. A beginner's guide to time travel

    Einstein found that the faster you move through space, the slower you move through time — you age more slowly, in other words. One of the key ideas in relativity is that nothing can travel ...

  3. meaning

    They're both essentially the same meaning. However, I would go with "travel through time," as it indicates more of a movement and is slightly more accurate. Note that with "he traveled in time to see his dead brother," in time also has a nuance of before it was too late.

  4. Time travel is possible, but it's a one-way ticket

    The ability to travel through time, whether it is to fix a mistake in the past or gain insight into the future, has long been embraced by science fiction and debated by theoretical physicists. ... Time travel is very much possible just as you decided to come existence in this century meaning one can decide to be in another time zone . life is ...

  5. Time travel

    An observer traveling at high velocity will experience time at a slower rate than an observer who isn't speeding through space. While we don't accelerate humans to near-light-speed, we do send ...

  6. Where Does the Concept of Time Travel Come From?

    Wells provided one of the most enduring time-travel plots in his 1895 novella "The Time Machine," which included the innovation of a craft that can move forward and backward through long spans of ...

  7. Traveling Through Time

    Angelus Silesius, a sixth-century philosopher and poet, thought the flow of time could be suspended by mental powers: Time is of your own making; its clock ticks in your head. The moment you stop ...

  8. Is Time Travel Possible?

    Time traveling to the near future is easy: you're doing it right now at a rate of one second per second, and physicists say that rate can change. According to Einstein's special theory of ...

  9. Will time travel ever be possible? Science behind curving space-time

    Time travel happens through what's called "time dilation." Time dilation , according to Live Science, is how one's perception of time is different to another's, depending on their motion ...

  10. The Great Debate: Could We Ever Travel through Time?

    And we move through space in all directions just fine, and according to physics, travel through time should be just as possible. One way that people have looked into is via a wormhole—a shortcut ...

  11. Time travel for travelers? It's tricky.

    It's tricky. Scientific theories suggest it's possible to travel through time. But the reality isn't so clear. Time travel has fascinated scientists and writers for at least 125 years. The ...

  12. What Is the Nature of Time?

    But going back to the experience of time versus a physical definition of time — the thing that introduces a wrinkle, literally, in it is that by storing information about the past and by thinking about the future, we can travel through time in ways that physical objects obeying the equations of physics really don't.

  13. Time Travel

    Time Travel. First published Thu Nov 14, 2013; substantive revision Fri Mar 22, 2024. There is an extensive literature on time travel in both philosophy and physics. Part of the great interest of the topic stems from the fact that reasons have been given both for thinking that time travel is physically possible—and for thinking that it is ...

  14. Time Travel

    Time Travel. Time travel is commonly defined with David Lewis' definition: An object time travels if and only if the difference between its departure and arrival times as measured in the surrounding world does not equal the duration of the journey undergone by the object. For example, Jane is a time traveler if she travels away from home in ...

  15. Time travel is possible

    Here we see a time loop. Green shows the short way through wormhole. Red shows the long way through normal space. Since the travel time on the green path could be very small compared to the red, a ...

  16. Time travel could be possible, but only with parallel timelines

    Time travel and parallel timelines almost always go hand-in-hand in science fiction, but now we have proof that they must go hand-in-hand in real science as well. General relativity and quantum ...

  17. Time travel

    The first page of The Time Machine published by Heinemann. Time travel is the hypothetical activity of traveling into the past or future.Time travel is a widely recognized concept in philosophy and fiction, particularly science fiction. In fiction, time travel is typically achieved through the use of a hypothetical device known as a time machine.The idea of a time machine was popularized by H ...

  18. 4 Time Travel Theories and the Physics Behind Them

    Experts have calculated the speed of light at 186,282 miles per second. This equates to 299,792 kilometres per second or an incredible 670,616,629 mph. In theory, there is nothing that travels faster than light. But if we turn to Einstein's special theory again, we know that time is not a single construct for everyone.

  19. Time travel

    Other articles where time travel is discussed: science fiction: Time travel: A complement to travel through space is travel through time. A prototype of the time travel story is Charles Dickens's A Christmas Carol (1843). The story features the Ghost of Christmas Yet to Come, who is magically able to immerse the hapless Scrooge…

  20. TIME TRAVEL Definition & Meaning

    Time travel definition: hypothetical transport through time into the past or the future.. See examples of TIME TRAVEL used in a sentence.

  21. TIME TRAVEL

    TIME TRAVEL meaning: 1. the idea of travelling into the past or the future 2. the idea of traveling into the past or the…. Learn more.

  22. Travel through

    Definition of travel through in the Idioms Dictionary. travel through phrase. What does travel through expression mean? Definitions by the largest Idiom Dictionary. ... It is my plan for a machine to travel through time. View in context. Sophia having directed her guide to travel through bye-roads, across the country, ...

  23. Authenticate an official document for use outside the U.S

    If the country where you want to use your document is on the 1961 Hague Convention member list, you will need an apostille. Documents such as vital records issued by a U.S. state will need an apostille from that state's secretary of state. Federal documents will need an apostille from the U.S. Department of State.