Scientist says interstellar travel might be possible without spaceships

Forget about spaceships: aliens could be "cosmic hitchhikers" traveling on free-floating planets, by nicole karlis, published june 5, 2022 10:00am (edt), updated june 6, 2022 3:42am (edt).

While a warp drive almost certainly isn't a thing that will ever exist, there's no law of physics that says interstellar travel isn't possible. Perhaps that is one reason why the sci-fi idea isn't out of the realm of possibility, and why some scientists aren't afraid to seriously contemplate how such a thing might work.

Enter a new research article in the International Journal of Astrobiology,  in which author Irina Romanovskaya, a professor of Physics and Astronomy at Houston Community College, proposes extraterrestrial civilizations could already be doing this in a peculiar way. Indeed, Romanovskaya says that interstellar travel would likely create technosignatures — such as radio waves , industrial pollution , light pollution, or anything that would suggest advanced technology is being used — when aliens engage in such travel.

Astronomers and astrophysicists have generally searched for extraterrestrial life by looking for biosignatures — such as water, oxygen or chlorophyll — on other planets . But interestingly, Romanovskaya proposes that interstellar travel might be happening via free-floating planets, not spaceships, like we see in the movies.

"Modern telescopes can search for various technosignatures that extraterrestrials, including migrating civilizations on free-floating planets, can produce," Romanovskaya wrote in an email to Salon. "For example, James Webb Space Telescope can search for signs of extraterrestrial life on planets in planetary systems, as well as technosignatures produced by extraterrestrial technologies on free-floating planets, which I propose in my research paper." 

RELATED: Are we looking for aliens all wrong?

Indeed, in the paper, Romanovskaya suggested the free-floating planet scheme as a means of "migrating" to another planetary system, like a vast transport. Such a proposal is certainly a means for a civilization to flee a dying star that would engulf them otherwise; indeed, Earth's own sun will render the planet uninhabitable in less than a billion years, unless our orbit shifts. 

"Some extraterrestrial civilizations may migrate from their home planetary systems to other planetary systems," Romanovskaya writes in the research paper. "They would most likely encounter serious or insurmountable technical problems when using spacecraft to transport large populations over interstellar distances."

"With little starlight reaching free-floating planets, extraterrestrials could use controlled nuclear fusion as the source of energy, and they could inhabit subsurface habitats and oceans of the free-floating planets to be protected from space radiation."

Essentially, Romanovskaya thinks that aliens could be "cosmic hitchhikers" by taking advantage of various flyby events via free-floating planets. Unlike Earth, free-floating planets are not gravitationally bound to their stars like Earth, hence making them more mobile. A study published in the journal Nature Astronomy  found at least 70 nomad exoplanets in our galaxy, suggesting that  they're not as rare as scientists previously thought . It's possible that these planets have liquid oceans under thick layers and some could even host simple life forms.

Want more health and science stories in your inbox? Subscribe to Salon's weekly newsletter The Vulgar Scientist .

"Some advanced civilizations may send their populations or technologies to other stars during flyby events, some advanced civilizations may build stellar engines and some advanced civilizations may use free-floating planets as interstellar transportation to relocate their populations to other planetary systems," Romanovskaya wrote. "Various methods of interstellar migration and interstellar colonization may contribute to propagation of advanced extraterrestrial civilizations in the Galaxy, and each method of interstellar migration can produce a set of observable technosignatures."

OK, but how exactly would alien civilizations use these planets to travel through the galaxy?

"With little starlight reaching free-floating planets, extraterrestrials could use controlled nuclear fusion as the source of energy, and they could inhabit subsurface habitats and oceans of the free-floating planets to be protected from space radiation," Romanovskaya said . "That would also prepare them for colonization of oceans in planetary systems."

Not everyone in the astrophysics world agrees that hitching a ride on lost planets is a viable method of interstellar transit. Avi Loeb , the former chair of the astronomy department at Harvard University, told Salon that he saw "no obvious benefit to using a free floating planet instead of a spacecraft." Loeb has previously argued that a rare interstellar object, called ' Oumuamua , bore almost all of the traits one might expect of an interstellar alien probe when it whizzed through our solar system in 2017. 

"The only reason Earth is comfortable for 'life as we know it' is because it is warmed by the Sun," Loeb said. "But a free floating planet is not attached to a star, and its surface would naturally be frozen."

Moreover, Loeb said a free-floating planet's large mass would make it more difficult to navigate to a desired destination.

"It is much easier to design a small spacecraft that offers the ideal habitat, engine and navigation system," Loeb said. "It is far better to own a car than to hitchhike."

Romanovskaya responded to Loeb's criticism of the concept in an email to Salon, noting that manufactured interstellar spacecraft would be exceedingly difficult to manufacture for large populations. "As a means of interstellar migrations of large populations, free-floating planets offer obvious benefit of offering 'natural' gravity and huge resources for migrating civilizations," Romanovskaya noted, adding that scientific studies have suggested that it is "very unlikely that advanced civilizations can build world ships for large populations."

Romanovskaya noted that 'Oumuamua, were it some kind of interstellar craft, would certainly not be a transport.

"Oumuamua-type objects are too small (e.g., Oumuamua is less than 800 meters long) to carry tens of thousands or millions of intelligent beings," she noted. 

Editor's note: This story was updated on June 6, 2022 to add additional comments from Dr. Romanovskaya. 

More stories on astronomy:

  • Astronomers plan to double-down on the search for extraterrestrial life
  • The Hubble Space Telescope's weird computer glitch, explained
  • The once-sedate astronomy world is quarreling over whether 'Oumuamua was an alien craf

Nicole Karlis is a senior writer at Salon, specializing in health and science. Tweet her @nicolekarlis .

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Comment and Space

Why space is the impossible frontier.

By Theunis Piersma

10 November 2010

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Encouraging words, but could our bodies handle it?

(Image: NASA)

Dreams of long-haul space travel or even colonisation ignore basic biological constraints that anchor us firmly to the Earth, argues Theunis Piersma

AT A news conference before his first experience of weightlessness in 2007, theoretical physicist Stephen Hawking said that he hoped his zero-gravity flight would encourage public interest in space exploration. He argued that with an ever-increasing risk of wiping ourselves out on Earth, humans would need to colonise space.

Hawking has since argued that we must do this within two centuries or else face extinction . He was no doubt encouraged by US President Barack Obama’s announcement in April this year of a new initiative to send people to Mars by 2030 .

Hawking, Obama and other proponents of long-term space travel are making a grave error. Humans cannot leave Earth for the several years that it takes to travel to Mars and back, for the simple reason that our biology is intimately connected to Earth.

To function properly, we need gravity. Without it, the environment is less demanding on the human body in several ways, and this shows upon the return to Earth. Remember the sight of weakened astronauts emerging after the Apollo missions? That is as nothing compared with what would happen to astronauts returning from Mars.

One of the first things to be affected is the heart, which shrinks by as much as a quarter after just one week in orbit ( The New England Journal of Medicine , vol 358, p 1370 ). Heart atrophy leads to decreases in blood pressure and the amount of blood pushed out by the heart. In this way heart atrophy leads to reduced exercise capacity. Astronauts returning to Earth after several months in the International Space Station experience dizziness and blackouts because blood does not reach their brains in sufficient quantities.

Six weeks in bed leads to about as much atrophy of the heart as one week in space, suggesting that the atrophy is caused by both weightlessness and the concomitant reduction in exercise.

Other muscle tissue suffers too. The effects of weightlessness on the muscles of the limbs are easy to verify experimentally. Because they bear the body’s weight, the “anti-gravity” muscles of the thighs and calves degenerate significantly when they are made redundant during space flight.

Despite the best attempts to give replacement exercise to crew members on the International Space Station, after six months they had still lost 13 per cent of their calf muscle volume and 32 per cent of the maximum power that their leg muscles could deliver ( Journal of Applied Physiology , vol 106, p 1159 ).

Various metabolic changes also occur, including a decreased capacity for fat oxidation, which can lead to the build-up of fat in atrophied muscle. Space travellers also suffer deterioration of immune function both during and after their missions ( Aviation, Space, and Environmental Medicine , vol 79, p 835 ).

Arguably the most fearsome effect on bodies is bone loss ( The Lancet , vol 355, p 1569 ). Although the hardness and strength of bone, and the relative ease with which it fossilises, give it an appearance of permanence, bone is actually a living and remarkably flexible tissue. In the late 19th century, the German anatomist Julius Wolff discovered that bones adjust to the loads that they are placed under. A decrease in load leads to the loss of bone material, while an increase leads to thicker bone.

It is no surprise, then, that in the microgravity of space bones demineralise, especially those which normally bear the greatest load. Cosmonauts who spent half a year in space lost up to a quarter of the material in their shin bones, despite intensive exercise ( The Lancet , vol 355, p 1607 ). Although experiments on chicken embryos on the International Space Station have established that bone formation does continue in microgravity, formation rates are overtaken by bone loss.

What is of greatest concern here is that, unlike muscle loss which levels off with time, bone loss seems to continue at a steady rate of 1 to 2 per cent for every month of weightlessness. During a three-year mission to Mars, space travellers could lose around 50 per cent of their bone material, which would make it extremely difficult to return to Earth and its gravitational forces. Bone loss during space travel certainly brings home the maxim “use it or lose it”.

“Losing 50 per cent of bone material would make it extremely difficult to return to Earth’s gravity”

Bone loss is not permanent. Within six months of their return to Earth, those cosmonauts who spent half a year in space did show partial recovery of bone mass. However, even after a year of recovery, men who had been experimentally exposed to three months of total bed rest had not fully regained all the lost bone, though their calf muscles had recovered much earlier ( Bone , vol 44, p 214 ).

Space agencies will have to become very creative in addressing the issue of bone loss during flights to Mars. There are concepts in development for spacecraft with artificial gravity, but nobody even knows what gravitational force is needed to avoid the problems. So far, boneless creatures such as jellyfish are much more likely than people to be able to return safely to Earth after multi-year space trips. For humans, gravity is a Mars bar.

The impossibility of an escape to space is just one of many examples of how our bodies, and those of our fellow organisms, are inseparable from the environments in which we live. In our futuristic ambitions we should not forget that our minds and bodies are connected to Earth as by an umbilical cord.

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Visits to and From Extraterrestrials: Why They Never Occurred, and Probably Never Will

by Morton Tavel

W e have recently been flooded with much excitement about the possibility of aliens traveling in UFOs (now labeled UAPs, Unidentified Aerial Phenomena), that may be visiting us from distant worlds. Much of skeptical attention, however, has focused on how we form beliefs and evaluate possible conspiracies rather than on considering the basic physical and biological requirements that may prevent us from believing such events are even possible. There are good reasons why alien visits from distant worlds are not — and likely never will be — a real possibility. Such myths seem more designed to titillate us for mundane, rather than celestial, reasons.

The public has long been, largely since religious visitations have seemed less believable, enamored by outer space as exemplified by the popularity of science fiction programs such as Star Trek , Star Wars , E.T. , and the like. The recent unmanned excursions to Earth’s Moon and nearby planets have further whetted the public’s appetite. That may also explain the recent increased interest in the possibility of aliens from distant worlds traveling in UAPs. Much of our attention, however, has focused on our chasing “weird” aerial phenomena rather than exploring the basic physical and biological limitations that prevent either aliens or us from meeting each other or reaching distant planets far from home. Although we have sought diligently over most of the past century to identify aerial phenomena and link them to distant worlds, all these attempts have resulted in abject failure. Such alleged “discoveries” can be explained by earth-bound phenomena 1 , 2 such as mylar balloons, drones, foreign aircraft, space trash, distorted photos of flying insects and other objects, e.g., artillery shells. Although some of these phenomena remain unexplained, no substantive evidence of alien life or extraterrestrial vehicles has been uncovered. Because of facts to be noted, I contend that they never will. Why? Let’s explore this issue from a purely scientific, biological perspective and begin by posing two questions:

  • Given our current or probable future technology, what is the possibility that we could reach (either with manned or unmanned spacecraft) planets in this or other galaxies?
  • What possible circumstances would allow those from other planets to reach us?

A product of over three billion years of evolution, we have reached a level of intelligence that enabled us to build machines that can reach beyond our atmosphere, and into space. However, distance is a major barrier, and according to present information, the distance to Proxima Centauri b, the closest exoplanet to Earth, is 40,208,000,000,000 kilometers, or 4.2 light-years from our Sun. The maximum speed of our spacecraft (currently approximately 6.5 percent of the speed of light) is a related limitation. Although we cannot predict the maximum velocity of future spacecraft, according to Einstein’s theory, the speed of light is a cosmic speed limit that cannot be surpassed, and radio waves are similarly limited. So, practically speaking, we should accept that faster-than-light travel is impossible, especially for any object with mass, such as a spacecraft.

If we assume there are no intelligent occupants on planets in our solar system, i.e., we need to search for intelligent life elsewhere, and given our present rocket technology, NASA estimates it would take approximately 73,000 years for a present spacecraft to reach Proxima Centauri b. We could postulate higher velocities, but thus far, humans haven’t figured out how to even approach such rates, further raising the question of whether we, or any other advanced culture, could accomplish this task. Can we hope to overcome these limitations in the future? Possibly, but at present, humans can conceivably only travel to any of the known planets or moons within our own solar system, and not to any destinations beyond. Just to reach Neptune (the most distant planet in the solar system) would require 12 years one-way. Manned space travel to another star system, at least with the technology we have today, is still only a dream. Given our limited lifespan, it would be virtually impossible to send a manned spacecraft to any such destination, let alone to expect a return voyage. Even with a craft that could achieve the unlikely speed of about 50 percent of the speed of light, this would require at least nine years one-way, to reach the nearest galaxy… Other potentially hospitable planets would likely be far more, and prohibitively, distant. In short, any voyage from Earth to distant, habitable planets, is clearly beyond our reach, both now and, very likely, in the foreseeable future. Sending unmanned craft would require radio waves to control or at least track them, requiring impractically large time delays.

We could conceivably take human beings only to any of the known planets or moons within our Solar System, but not to any objects beyond this gravitational sphere. If we extend our present laws of physics to their limits, travel might extend further into the universe, but even if we were to reach such unlikely huge distances, our current lifespan would preclude occupied travel. This means that distant planets outside our solar system would continue to be physically unreachable. Any attempt at long-distance human space travel would create another major problem: humans are evolutionarily adapted to gravity, which means that prolonged weightlessness is harmful in many ways, among which are atrophy of muscle (including the heart!) and bone tissue. Under the influence of gravity, fluid — which makes up about 60 percent of the human body weight — tends to accumulate in the lower part of the body. Through the course of evolution, we have developed systems balancing blood flow to the heart and the brain. In the absence of gravity, these systems cause fluid to accumulate in the upper body. This change in fluid distribution is also reflected in problems with keeping balance, as well as upper body swelling and a loss of sense of taste and smell. Such adaptations may result in dangerous consequences following return to Earth. One of them is “orthostatic intolerance,” which is the inability to stand for 10 or more minutes without fainting. To overcome such problems, bodily exercises with artificially created gravity have been proposed, but the long-term effects of this measure cannot be predicted. In short, these, and other unknown factors, render us physically unequipped for prolonged space travel.

The question of whether Earth could be reached by occupants from different galaxies is more speculative. It would require the presence of intelligent life elsewhere, combined with the need to overcome the barriers just depicted for us.

It seems likely that intelligence and advanced culture would stem from evolution on a planet able to support some form of life. Such life could be constructed from carbon atoms and possess DNA, but this may not be the case. Out of the thousands of exoplanets in other galaxies, a few possess conditions that are favorable for life as we know it, i.e., moderate temperatures, water, sunlight, etc. However, meeting such requirements is extremely daunting. 3 From our experience on Earth, the progression from the earliest life forms, such as microorganisms, to the presence of humans required approximately three to four billion years, but the component required for space travel only appeared in the last 100 years. While it is possible that this process has occurred on one or more of the many distant planets, evolution requires multiple and successive life cycles in which mutations or physical changes allow for successive adaptations, each more favorable for survival. As this dynamic process proceeds, new generations replace prior ones, with the latter dying off. Although our telescopes have identified thousands of planets around neighboring stars, some of which might be capable of supporting life, and by implication many astronomers extrapolate this to conclude that there are very likely trillions of planets in the cosmos, which means that no matter how improbable it is that any one of them could support life, the law of large numbers suggests that some will. After all, relatively intelligent beings, represented by dinosaurs, existed on Earth for about 200 million years, but none had intelligence that approached our own.

But let’s assume intelligent aliens did exist and had spacecraft that could achieve a very high velocity. If an alien entity were to attain even 30–50 percent of the speed of light, reaching the necessary distances would still require a prohibitively long time, as exemplified by our reaching a neighboring galaxy, cited above. Given our current state of knowledge, it’s likely that no living forms, however advanced, could reach even a fraction of this speed with an occupied vehicle. If superior technology were developed to allow for travel closer to light speed, travel of any kind might extend further into the universe, but any biological organism would be limited by a finite lifespan. This also means that any living alien beings are likely subject to similar laws of evolution, and this fact alone would render any such visits highly unlikely.

Could occupants of a distant planet even reach us with an unoccupied spacecraft or one carrying robots? That is a possibility, but that effort would be subject to the same limitations we would encounter in our attempt to reach distant worlds. There is little reason to believe that a distant life form would correctly identify the presence of life on this planet, and from the huge distances separating us, they would have little incentive to capitalize on this knowledge, other than merely satisfying curiosity. And even informative radio signals would require inordinate return times to provide useful data or even to direct the control of such distant vehicles or robots.

If there were highly intelligent life on distant planets, we might postulate that they might attempt to contact us through radio signals, also sometimes called “Fast Radio Bursts” (FRBs). Prior to 2020, weak signals, billions of light years away, had been observed outside our galaxy. Interestingly, on April 28, 2020, two ground-based radio telescopes detected an intense pulse of radio waves. 4 It only lasted a mere millisecond but, for astonished astronomers, it was a major discovery, representing the first time such a radio burst had ever been detected from Earth. It was believed to have originated an estimated 30,000 light-years from a planet within the Milky Way. Rather than originating from life forms, however, observational evidence suggests that the origin of such signals is very likely a magnetar, a type of young neutron star born from the embers of supernovas with a magnetic field 5,000 trillion times more powerful than Earth’s, thereby making them the universe’s most powerful magnets. By no means is this evidence of alien life!

Us and Them

Exploring the flip side, what efforts are we expending to help alien cultures detect our presence and composition? At present, we are sending out both radio signals and spacecraft into space. A strenuous effort was made in 1974, when a team of scientists, including astronomers Frank Drake and Carl Sagan, transmitted a radio message from the Arecibo Observatory in Puerto Rico toward Messier 13, a cluster of stars about 25,000 light-years away. 5 This image, sent in binary code, depicted a human stick figure, a double-helix DNA structure, a model of a carbon atom, and a diagram of a telescope. The message attempts to provide a snapshot of who we are as human beings in the language of math and science. Yet it is, quite literally, a shot in the dark. It will take around 25,000 light-years to reach Messier 13. Hypothetical aliens might still be able to detect the signal as it whizzes past — it has 10 million times the intensity of radio signals from our sun. But who around here in subsequent centuries would even be able to recognize such an achievement?

We have also launched two rockets, Voyagers 1 and 2, into deep space, each carrying 12-inch (30cm) golden phonograph records that contain pictures and sounds of Earth, symbolic directions on the cover for playing the record, and data detailing the location of Earth. The record is intended as a combination time capsule and an interstellar message to any civilization, alien, or future human, that may recover either of the Voyagers. Here too, the likelihood of any recognizable response seems very slim.

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The idea that aliens could reach us — with or without occupied vehicles — is based upon several speculative assumptions, none of which are presently realistic. Given our current technology, there is no real likelihood that we could reach distant worlds outside the solar system, even with unoccupied spacecraft. If we were able to employ highly advanced robots, the time required to reach distant galaxies employing radio guidance and similar responses would be impractically excessive, given our present limited lifespan. Theoretically, a civilization lasting for tens of millions of years might have spread throughout the galaxy, but no confirmed signs of civilizations or intelligent life elsewhere have been found, either in our galaxy or in the observable universe of two trillion galaxies. 6 , 7 , 8

END

About the Author

Morton Tavel is a retired physician specializing in internal medicine and cardiovascular diseases. He was a Clinical Professor at Indiana University School of Medicine and the president of the Indiana division of the American Heart Association. He authored over 140 research publications, editorials, and a medical textbook. His previous article for Skeptic appeared in vol. 23 no. 4 .

  • https://bit.ly/3G1MYwH
  • https://bit.ly/3U12NJV
  • Tyson, N.D.G. (2021). Cosmic Queries: Star Talk’s Guide to Who We Are, How We Got Here, and Where We’re Going. National Geographic
  • Bochenek, C. D., Ravi, V., Belov, K. V., Hallinan, G., Kocz, J., Kulkarni, S. R., & McKenna, D. L. (2020). A fast radio burst associated with a Galactic magnetar. Nature, 587 (7832), 59–62.
  • https://bit.ly/3Kfe4mH
  • Tarter, J. (2006). The Cosmic Haystack Is Large. Skeptical Inquirer, 30 (3), 31.
  • Alexander, A. (2002). The Search for Extraterrestrial Intelligence: A Short History, Part 7: The Birth of the Drake Equation. The Planetary Society.
  • Conselice, C. J., Wilkinson, A., Duncan, K., & Mortlock, A. (2016). The evolution of galaxy number density at z<8 and its implications. The Astrophysical Journal, 830 (2), 83.

This article was published on June 30, 2023.

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Can we time travel? A theoretical physicist provides some answers

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Emeritus professor, Physics, Carleton University

Disclosure statement

Peter Watson received funding from NSERC. He is affiliated with Carleton University and a member of the Canadian Association of Physicists.

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Time travel makes regular appearances in popular culture, with innumerable time travel storylines in movies, television and literature. But it is a surprisingly old idea: one can argue that the Greek tragedy Oedipus Rex , written by Sophocles over 2,500 years ago, is the first time travel story .

But is time travel in fact possible? Given the popularity of the concept, this is a legitimate question. As a theoretical physicist, I find that there are several possible answers to this question, not all of which are contradictory.

The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of thermodynamics or relativity . There are also technical challenges: it might be possible but would involve vast amounts of energy.

There is also the matter of time-travel paradoxes; we can — hypothetically — resolve these if free will is an illusion, if many worlds exist or if the past can only be witnessed but not experienced. Perhaps time travel is impossible simply because time must flow in a linear manner and we have no control over it, or perhaps time is an illusion and time travel is irrelevant.

a woman stands among a crowd of people moving around her

Laws of physics

Since Albert Einstein’s theory of relativity — which describes the nature of time, space and gravity — is our most profound theory of time, we would like to think that time travel is forbidden by relativity. Unfortunately, one of his colleagues from the Institute for Advanced Study, Kurt Gödel, invented a universe in which time travel was not just possible, but the past and future were inextricably tangled.

We can actually design time machines , but most of these (in principle) successful proposals require negative energy , or negative mass, which does not seem to exist in our universe. If you drop a tennis ball of negative mass, it will fall upwards. This argument is rather unsatisfactory, since it explains why we cannot time travel in practice only by involving another idea — that of negative energy or mass — that we do not really understand.

Mathematical physicist Frank Tipler conceptualized a time machine that does not involve negative mass, but requires more energy than exists in the universe .

Time travel also violates the second law of thermodynamics , which states that entropy or randomness must always increase. Time can only move in one direction — in other words, you cannot unscramble an egg. More specifically, by travelling into the past we are going from now (a high entropy state) into the past, which must have lower entropy.

This argument originated with the English cosmologist Arthur Eddington , and is at best incomplete. Perhaps it stops you travelling into the past, but it says nothing about time travel into the future. In practice, it is just as hard for me to travel to next Thursday as it is to travel to last Thursday.

Resolving paradoxes

There is no doubt that if we could time travel freely, we run into the paradoxes. The best known is the “ grandfather paradox ”: one could hypothetically use a time machine to travel to the past and murder their grandfather before their father’s conception, thereby eliminating the possibility of their own birth. Logically, you cannot both exist and not exist.

Read more: Time travel could be possible, but only with parallel timelines

Kurt Vonnegut’s anti-war novel Slaughterhouse-Five , published in 1969, describes how to evade the grandfather paradox. If free will simply does not exist, it is not possible to kill one’s grandfather in the past, since he was not killed in the past. The novel’s protagonist, Billy Pilgrim, can only travel to other points on his world line (the timeline he exists in), but not to any other point in space-time, so he could not even contemplate killing his grandfather.

The universe in Slaughterhouse-Five is consistent with everything we know. The second law of thermodynamics works perfectly well within it and there is no conflict with relativity. But it is inconsistent with some things we believe in, like free will — you can observe the past, like watching a movie, but you cannot interfere with the actions of people in it.

Could we allow for actual modifications of the past, so that we could go back and murder our grandfather — or Hitler ? There are several multiverse theories that suppose that there are many timelines for different universes. This is also an old idea: in Charles Dickens’ A Christmas Carol , Ebeneezer Scrooge experiences two alternative timelines, one of which leads to a shameful death and the other to happiness.

Time is a river

Roman emperor Marcus Aurelius wrote that:

“ Time is like a river made up of the events which happen , and a violent stream; for as soon as a thing has been seen, it is carried away, and another comes in its place, and this will be carried away too.”

We can imagine that time does flow past every point in the universe, like a river around a rock. But it is difficult to make the idea precise. A flow is a rate of change — the flow of a river is the amount of water that passes a specific length in a given time. Hence if time is a flow, it is at the rate of one second per second, which is not a very useful insight.

Theoretical physicist Stephen Hawking suggested that a “ chronology protection conjecture ” must exist, an as-yet-unknown physical principle that forbids time travel. Hawking’s concept originates from the idea that we cannot know what goes on inside a black hole, because we cannot get information out of it. But this argument is redundant: we cannot time travel because we cannot time travel!

Researchers are investigating a more fundamental theory, where time and space “emerge” from something else. This is referred to as quantum gravity , but unfortunately it does not exist yet.

So is time travel possible? Probably not, but we don’t know for sure!

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Why We’ll Never Live in Space

Medical, financial and ethical hurdles stand in the way of the dream to settle in space

By Sarah Scoles

Illustration of a woman at a desk and her dog living in a spacecraft.

Tavis Coburn

N ASA wants astronaut boots back on the moon a few years from now, and the space agency is investing heavily in its Artemis program to make it happen. It's part of an ambitious and risky plan to establish a more permanent human presence off-world. Companies such as United Launch Alliance and Lockheed Martin are designing infrastructure for lunar habitation. Elon Musk has claimed SpaceX will colonize Mars. But are any of these plans realistic? Just how profoundly difficult would it be to live beyond Earth—especially considering that outer space seems designed to kill us?

Humans evolved for and adapted to conditions on Earth. Move us off our planet, and we start to fail—physically and psychologically. The cancer risk from cosmic rays and the problems that human bodies experience in microgravity could be deal-breakers on their own. Moreover, there may not be a viable economic case for sustaining a presence on another world. Historically, there hasn't been much public support for spending big money on it. Endeavors toward interplanetary colonization also bring up thorny ethical issues that most space optimists haven't fully grappled with.

At the 2023 Analog Astronaut Conference, none of these problems seemed unsolvable. Scientists and space enthusiasts were gathered at Biosphere 2, a miniature Earth near Tucson, Ariz., which researchers had built partly to simulate a space outpost. Amid this crowd, the conclusion seemed foregone: living in space is humans' destiny, an inevitable goal that we must reach toward.

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The conference attendees know it's a big dream. But their general outlook was summed up by Phil Hawes, chief architect for Biosphere 2, who gave the opening talk at the meeting. He recited a toast made by the first team to camp out here decades ago: "Here's to throwing your heart out in front of you and running to catch up with it."

The question remains as to whether we can—and will—ever run fast enough.

In 1991 eight people entered Biosphere 2 and lived inside for two years. This strange facility is a 3.14-acre oasis where scientists have re-created different terrestrial environments—not unlike an overgrown botanical garden. There's an ocean, mangrove wetlands, a tropical rainforest, a savanna grassland and a fog desert, all set apart from the rest of the planet they're mimicking. One goal, alongside learning about ecology and Earth itself, was to learn about how humans might someday live in space, where they would have to create a self-contained and self-sustaining place for themselves. Biosphere 2, located on Biosphere 1 (Earth), was practice. The practice, though, didn't quite work out. The encapsulated environment didn't produce enough oxygen, water or food for the inhabitants—a set of problems that, of course, future moon or Mars dwellers could also encounter. The first mission and a second one a few years later were also disrupted by interpersonal conflicts and psychological problems among the residents.

Today the people who participate in projects like Biosphere 2—simulating some aspect of long-term space travel while remaining firmly on Earth—are called analog astronauts. And although it's a niche pursuit, it's also popular: There are analog astronaut facilities in places such as Utah, Hawaii, Texas and Antarctica. People are building or planning them in Oman, Kenya and Israel. And they all share the goal of learning how to live off Earth while on Earth.

The people who are mingling on Biosphere's patio, where the desert sunset casts a pink light on the habitat's glass exterior, are part of that analog world. Some of them have participated in simulation projects or have built their own analog astronaut facilities; others are just analog-curious. They are astronomers, geologists, former military personnel, mail carriers, medical professionals, FedEx employees, musicians, artists, analysts, lawyers and the owner of the Tetris Company. On this night many have donned Star Wars costumes. As the sun goes down, they watch the rising moon, where many here would like to see humans settle.

Human bodies really can't handle space. Spaceflight damages DNA, changes the microbiome, disrupts circadian rhythms, impairs vision, increases the risk of cancer, causes muscle and bone loss, inhibits the immune system, weakens the heart, and shifts fluids toward the head, which may be pathological for the brain over the long term—among other things.

At the University of California, San Francisco, medical researcher Sonja Schrepfer has dug into two of the conditions that afflict space explorers. Her research, using mice floating within the International Space Station, has revealed that blood vessels leading to the brain get stiffer in microgravity. It's part of why today's astronauts can't simply walk out of their capsules once they return to Earth, and it would play out the same way on Mars—where there's no one to wheel them to their new habitat on arrival. Schrepfer and her colleagues did, however, uncover a molecular pathway that might prevent those cardiovascular changes. "But now the question I try to understand is, 'Do we want that?'" she says. Maybe the vessels' stiffening is a protective mechanism, Schrepfer suggests, and limbering them up might cause other problems.

She also wants to figure out how to help astronauts' faltering immune systems, which look older and have a harder time repairing tissue damage than they should after spending time in space. "The immune system is aging quite fast in microgravity," Schrepfer says. She sends biological samples from young, healthy people on Earth up to orbit on tissue chips and tracks how they degrade.

Vision and bone problems are also among the more serious side effects. When astronauts spend a month or more in space, their eyeballs flatten, one aspect of a condition called spaceflight-associated neuro-ocular syndrome, which can cause long-lasting damage to eyesight. Bones and muscles are built for life on Earth, which involves the ever present pull of gravity. The work the body does against gravity to stay upright and move around keeps muscles from atrophying and stimulates bone growth. In space, without a force to push against, astronauts can experience bone loss that outpaces bone growth, and their muscles shrink. That's why they must do hours of exercise every day, using specialized equipment that helps to simulate some of the forces their anatomy would feel on the ground—and even this training doesn't fully alleviate the loss.

Perhaps the most significant concern about bodies in space, though, is radiation, something that is manageable for today's astronauts flying in low-Earth orbit but would be a bigger deal for people traveling farther and for longer. Some of it comes from the sun, which spews naked protons that can damage DNA, particularly during solar storms. "[That] could make you very, very sick and give you acute radiation syndrome," says Dorit Donoviel, a professor at the Baylor College of Medicine and director of the Translational Research Institute for Space Health (TRISH).

Future astronauts could use water—perhaps pumped into the walls of a shelter—to shield themselves from these protons. But scientists don't always know when the sun will be spitting out lots of particles. "So if, for example, astronauts are exploring the surface of the moon, and there is a solar particle event coming, we probably have the capability of predicting it within about 20 to 30 minutes max," Donoviel says. That means we need better prediction and detection—and we'd need astronauts to stay close to their H2O shield.

If you didn't get to safety in time, the nausea would come first. "You would vomit into your spacesuit," Donoviel says, "which now becomes a life-threatening situation" because the vomit could interfere with life-support systems, or you might breathe it in. Then comes the depletion of cells such as neutrophils and red blood cells, meaning you can't battle germs or give your tissues oxygen effectively. You'll be tired, anemic, unable to fight infection, and throwing up. Maybe you'll die. See why lots of kids want to be astronauts when they grow up?

White geometric shaped buildings, identified as “The Biosphere 2 research facility” set in desert landscape.

From September 1991 to September 1993, eight people lived inside the Biosphere 2 research facility in Arizona, helping scientists learn how humans might live in outer space. Credit: Science History Images/Alamy Stock Photo

There's another type of radiation, galactic cosmic rays, that even a lot of water won't block. This radiation is made of fast-moving elements—mostly hydrogen but also every natural substance in the periodic table. The rays burst forth from celestial events such as supernovae and have a lot more energy and mass than a mere proton. "We really cannot fully shield astronauts from them," Donoviel says. And inadequately shielding explorers makes the problem worse: the rays would split when they hit a barrier, making more, smaller particles.

The radiation an astronaut en route to Mars might get from galactic cosmic rays at any one time is a small dose. But if you're on a spaceship or a planetary surface for years, the calculus changes. Imagine, Donoviel says, being in a room with a few mosquitoes. Five or 10 minutes? Fine. Days? Months? You're in for a whole lot more itching—or, in this case, cancer risk.

Because shielding astronauts isn't realistic, Donoviel's TRISH is researching how to help the body repair radiative damage and developing chemical compounds astronauts could take to help fix DNA damage in wounds as they occur. "Everybody's worried about waiting for the cancer to happen and then killing the cancer," Donoviel says. "We're really taking the preventive approach."

Even if most of the body's issues can be fixed, the brain remains a problem. A 2021 review paper in Clinical Neuropsychiatry laid out the psychological risks that astronauts face on their journey, according to existing research on spacefarers and analog astronauts: poor emotional regulation, reduced resilience, increased anxiety and depression, communication problems within the team, sleep disturbances, and decreased cognitive and motor functioning brought on by stress. To imagine why these issues arise, picture yourself in a tin can with a small crew, a deadly environment outside, a monotonous schedule, an unnatural daytime-nighttime cycle and mission controllers constantly on your case.

Physical and mental health problems—though dire—aren't even necessarily the most immediate hurdles to making a space settlement happen. The larger issue is the cost. And who's going to pay for it? Those who think a billionaire space entrepreneur is likely to fund a space colony out of a sense of adventure or altruism (or bad judgment) should think again. Commercial space companies are businesses, and businesses' goals include making money. "What is the business case?" asks Matthew Weinzierl, a professor at Harvard Business School and head of its Economics of Space research efforts.

For the past couple of years Weinzierl and his colleague Brendan Rousseau have been trying to work out what the demand is for space exploration and pursuits beyond Earth. "There's been a ton of increase in supply and cutting of costs of space activity," Weinzierl says, "but who's on the other side?" Space companies have historically been insular: specialists creating things for specialists, not marketing wares or services to the broader world. Even commercial undertakings such as SpaceX are supported mostly by government contracts. Company leaders haven't always thought through the capitalism of their ideas; they're just excited that the rockets and widgets work. "Technical feasibility does not equal a strong business case," Rousseau says.

Today private spaceflight companies target tourists for business when they're not targeting federal contracts. But those tourists aren't protected by the same safety regulations that apply to government astronauts, and an accident could stifle the space tourism industry. Stifling, too, is the fact that only so many people with money are likely to want to live on a place like Mars rather than take a short joyride above the atmosphere, so the vacation business case for permanent space outposts breaks down there as well.

Interior view of greenhouse identified as “Biosphere2.”

The Biosphere 2 research facility in Arizona houses a greenhouse. Credit: Kike Calvo/Universal Images Group via Getty Images

People tend to liken space exploration to expansion on Earth—pushing the frontier. But on the edge of terrestrial frontiers, people were seeking, say, gold or more farmable land. In space, explorers can't be sure of the value proposition at their destination. "So we have to be a little bit careful about thinking that it will just somehow pay off," Weinzierl points out.

Weinzierl and Rousseau find the idea of a sustained human presence in space inspiring, but they're not sure when or how it will work from a financial perspective. After all, inspiration doesn't pay invoices. "We'd love to see that happening," Rousseau says—he thinks lots of people would. "As long as we're not the ones footing the bill."

Many taxpayers would probably agree. As hard as it is for space fans to believe, most people don't place much value on astronaut adventures. A 2023 Pew poll asked participants to rate the importance of nine of NASA's key missions as "top priority," "important but lower priority," or "not too important/should not be done." Just 12 and 11 percent of people thought sending humans to Mars and to the moon, respectively, should be a top priority. That placed those missions at the bottom of the list in terms of support, behind more popular efforts such as monitoring Earth's climate, watching for dangerous asteroids and doing basic scientific research on space in general.

Similarly, a 2020 poll from Morning Consult found that just 7 to 8 percent of respondents thought that sending humans to the moon or Mars should be a top priority. And although history tends to remember the previous moon exploration era as a time of universal excitement for human spaceflight, polls from the time demonstrate that that wasn't the case: "Consistently throughout the 1960s, a majority of Americans did not believe Apollo was worth the cost, with the one exception to this a poll taken at the time of the Apollo 11 lunar landing in July 1969," wrote historian Roger Launius in a paper for Space Policy . "And consistently throughout the decade 45–60 percent of Americans believed that the government was spending too much on space, indicative of a lack of commitment to the spaceflight agenda."

When space agency officials discuss why people should care about human exploration, they often say it's for the benefit of humanity. Sometimes they cite spin-offs that make their way to citizens as terrestrial technology—such as how telescope-mirror innovations improved laser eye surgery. But that argument doesn't do it for Linda Billings, a consultant who works with NASA. If you were interested in furthering a technology, she suggests, you could invest directly in the private sector instead of obliquely through a space agency, where its development will inevitably take longer, cost more and not be automatically tailored toward earthly use. "I don't see that NASA is producing any evidence that [human settlement of space] will be for the benefit of humanity," she says.

Whether tax dollars should support space travel is an ethical question, at least according to Brian Patrick Green of Santa Clara University. Green became interested in science's ethical issues when he worked in the Marshall Islands as a teacher. The U.S. used to detonate nuclear weapons there, causing lasting environmental and health damage. Now the islands face the threat of sea-level rise, which is likely to inundate much of their infrastructure, erode the coasts and shrink the usable land area. "That got me very interested in the social impacts of technology and what technology does to people and societies," he says.

In space travel, "Why?" is perhaps the most important ethical question. "What's the purpose here? What are we accomplishing?" Green asks. His own answer goes something like this: "It serves the value of knowing that we can do things—if we try really hard, we can actually accomplish our goals. It brings people together." But those somewhat philosophical benefits must be weighed against much more concrete costs, such as which other projects—Earth science research, robotic missions to other planets or, you know, outfitting this planet with affordable housing—aren't happening because money is going to the moon or Mars or Alpha Centauri.

And an even simpler ethical question is, "Should we actually send people on these sorts of things?" Green says. Aside from incurring significant risks of cancer and overall body deterioration, astronauts aiming to settle another world have a sizable chance of losing their lives. Even if they do live, there are issues with what kind of an existence they might have. "It's one thing just to survive," Green says. "But it's another thing to actually enjoy your life. Is Mars going to be the equivalent of torture?"

If people make the attempt, we will also have to acknowledge the risks to celestial bodies—the ones humans want to travel to as well as this one, which they may return to if they haven't purchased a one-way ticket. The moon, Mars or Europa could become contaminated by microscopic Earth life, which NASA has never successfully eradicated from spacecraft, although it tries as part of a "planetary protection" program. And if destination worlds have undetected life, then harmful extraterrestrial microbes could also return with astronauts or equipment—a planetary-protection risk called backward contamination. What obligation do explorers have to keep places as they found them? Setting aside the question of whether we can establish ourselves beyond Earth, we also owe it to ourselves and the universe to consider whether we should.

on this question, science-fiction scholar Gary Westfahl casts doubt on space travel's inherent value. In his vast analyses of sci-fi, he has come to view the logic and drive of the enterprise as faulty. "I inevitably encountered the same argument: space travel represents humanity's destiny," he says of the impetus for writing his essay "The Case against Space." Space explorers are often portrayed as braver and better than those who remain on their home planet: they're the ones pushing civilization forward. "Philosophically, I objected to the proposition that explorers into unknown realms represented the best and brightest of humanity, that progress could be achieved only by boldly venturing into unknown territories," Westfahl says. After all, a lot of smart and productive people (not to mention a lot of happy and stable people) don't spend their lives on the lam. "Clearly, history demonstrates no correlation between travel and virtue," he writes. "The history of our species powerfully suggests that progress will come from continued stable life on Earth, and that a vast new program of travel into space will lead to a new period of human stagnation," he concludes ominously.

A close up view of the surface of Earth’s moon revealing craters, shown against a black background.

Celestial bodies, including our moon, are at risk of contamination by microscopic Earth life. Credit: NASA’s Scientific Visualization Studio

In some ways, the desire for simpler living is part of what motivates space explorers. Astronauts are stuck with just a few people they have to get along with, or else they'll be miserable—a communal way of living that's more common to villages. They must make do with the nearby supplies or create their own, like people did before Walmart and Amazon. Communication with those beyond their immediate sphere is slow and difficult. They have a strict but straightforward and prescribed work schedule. Everything is a struggle; there are no conveniences. Unlike in a modern, digitally connected environment, their attention isn't split in many directions—they are focused on the present. Or at least that's how analog astronaut Ashley Kowalski felt during the SIRIUS 21 endeavor, an eight-month-long joint U.S.-Russia "lunar mission" that took place in a sealed space in Moscow.

Kowalski's talk at the Analog Astronaut Conference at Biosphere 2 was called "Only Eight Months." The goal of those eight months was to study the medical and psychological effects of isolation. She and her teammates regularly provided blood, feces and skin samples so researchers could learn about their stress levels, metabolic function and immunological changes. Researchers also had them take psychological tests, sussing out their perception of time, changes in cognitive abilities and shifts in interpersonal interactions. Inside they had to eat like astronauts would, guzzling tubes of Sicilian pizza gel and burger gel. Kowalski would squeeze them into rehydrated soup to make meals heartier. Via their greenhouse, they got about a bowl of salad between the six of them every three weeks.

Kowalski missed freedom and food and friends, of course. But the real struggle came with her return to the real world once the isolation was over: "reentry, not to the atmosphere but to the planet," she told the conference audience. She didn't remember how to go about having friends, hobbies or a job and had trouble dealing with requests coming from lots of sources instead of just mission control. In the Q&A period after the talk, Tara Sweeney, a geologist in the audience, thanked Kowalski for talking about that part of the experience. Sweeney had just returned from a long stay in Antarctica and also didn't quite know how to reintegrate into life in a more hospitable place. They had both missed "Earth," the real world. But it was hard to come back.

Still, the Analog Astronaut Conference crowd remained optimistic. "Where do we go from here?" conference founder and actual astronaut Sian Proctor asked at one point. On cue, the audience members pointed upward and said, "To the moon!"

Analog-astronaut work can't solve space travel's hardest problems—the intractable medical troubles, the in-red money questions, the touchy ethical quandaries. But while we all wait to see whether we'll ever truly migrate off this planet, and whether we should, these grounded astronauts will continue to escape Earth, for a time at least, without leaving it.

Sarah Scoles is a Colorado-based science journalist, a contributing editor at Scientific American and Popular Science, and a senior contributor at Undark . She is author of Making Contact (2017) and They Are Already Here (2020), both published by Pegasus Books. Her newest book is Countdown: The Blinding Future of Nuclear Weapons (Bold Type Books, 2024).

Scientific American Magazine Vol 329 Issue 3

Can the EmDrive actually work for space travel?

Don't get your hopes up.

The

Paul M. Sutter  is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of Ask a Spaceman and Space Radio , and author of How to Die in Space . He contributed this article to Space.com's Expert Voices: Opinions and Insights .

The " EmDrive " claims to make the impossible possible: a method of pushing spacecraft around without the need for — well, pushing. No propulsion. No exhaust. Just plug it in, fire it up and you can cruise to the destination of your dreams. 

But the EmDrive doesn't just violate our fundamental understanding of the universe; the experiments that claim to measure an effect haven't been replicated. When it comes to the EmDrive, keep dreaming. 

Related: Superfast spacecraft propulsion concepts (images)

Microwaves of the future

It goes by various names — the EmDrive, the Q-Drive, the RF Resonant Cavity, the Impossible Drive — but all the incarnations of the device claim to do the same thing: bounce some radiation around inside a closed chamber, and presto-chango you can get propulsion.

This is a big deal, because all forms of rocketry (and indeed, all forms of motion across the entire universe) require conservation of momentum. In order to set yourself in motion, you have to push off of something. Your feet push off of the ground, airplanes push themselves off of the air, and rockets push parts of themselves (e.g., an exhaust gas) out the back end to make them go forward.

But the EmDrive doesn't. It's just a box with microwaves inside it, bouncing around. And supposedly it is able to move itself.

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Explanations for how the EmDrive could possibly work go past the boundaries of known physics. Perhaps it's somehow interacting with the quantum vacuum energy of space-time (even though the quantum vacuum energy of space-time doesn't allow anything to push off of it). Perhaps our understanding of momentum is broken (even though there are no other examples in our entire history of experiment). Perhaps it's some brand-new physics, heralded by the EmDrive experiments.

Don't play with momentum

Let's talk about the momentum part. Conservation of momentum is pretty straightforward: in a closed system, you can add up the momenta of all the objects in that system. Then they interact. Then you add up the momenta of all the objects again. The total momentum at the beginning must equal the total momentum at the end: momentum is conserved.

The idea of the conservation of momentum has been with us for centuries (it's even implied by Newton's famous second law), but in the early 1900s it gained a new status. The brilliant mathematician Emmy Noether proved that conservation of momentum (along with other conservation laws, like conservation of energy) are a reflection of the fact that our universe has certain symmetries.

For example, you can choose a suitable location to perform a physics experiment. You can then pick up your physics experiment, transport it to anywhere in the universe and repeat it. As long as you account for environmental differences (say, different air pressures or gravitational fields ), your results will be identical.

This is a symmetry of nature: physics doesn't care about where experiments take place. Noether realized that this symmetry of space directly leads to conservation of momentum. You can't have one without the other.

So, if the EmDrive demonstrates a violation of momentum conservation (which it claims to do), then this fundamental symmetry of nature must be broken.

But almost every single physical theory, from Newton's laws to quantum field theory, expresses space symmetry (and momentum conservation) in their base equations. Indeed, most modern theories of physics are simply complicated restatements of momentum conservation. To find a breaking in this symmetry wouldn't just be an extension of known physics — it would completely upend centuries of understanding of how the universe works.

The universe: Big Bang to now in 10 easy steps

The reality of experiment

That's certainly not impossible (scientific revolutions have happened before), but it's going to take a lot of convincing to make that happen.

And the experiments so far have not been all that satisfying.

Ever since the introduction of the EmDrive concept in 2001, every few years a group claims to have measured a net force coming from its device. But these researchers are measuring an incredibly tiny effect: a force so small it couldn't even budge a piece of paper. This leads to significant statistical uncertainty and measurement error. 

Indeed, of all the published results, none have produced a measurement beyond "barely qualifying for publication," let alone anything significant.

Still, other groups have developed their own EmDrives, attempting to replicate the results, like good scientists should. Those replication attempts either fail to measure anything at all, or found some confounding variable that can easily explain the measured meager results, like the interaction of the cabling in the device with the Earth's magnetic field .

So that's what we have, nearly 20 years after the initial EmDrive proposal: a bunch of experiments that haven't really delivered, and no explanation (besides "let's just go ahead and break all of physics, violating every other experiment of the past 100 years") of how they could work. 

Groundbreaking, physics-defying revolution in space travel or a pipe dream? It's pretty clear which side Nature is on.

Learn more by listening to the episode "Could the "EmDrive" really work? on the Ask A Spaceman podcast, available on  iTunes and on the Web at http://www.askaspaceman.com . Thanks to Mitchell L. for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter .

Follow us on Twitter @Spacedotcom or Facebook. 

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Paul Sutter

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.

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  • Geomartian For a drive to work it must pass one of these tests. Newtonian It has to exhaust matter or energy to produce propulsion. Since this device is closed and emits nothing it fails the Newtonian test. Gravity or Temporal Gravity is produced by a gradient in the rate of time. Time is the cause, the force that a temporal gradient produces is called gravitation. Gravity is the effect not the cause. Does this device cause the time rate of clocks to change when it is in operation? If it doesn’t affect clocks, then it is not affecting gravity. Reply
  • Wolf28 "But the EmDrive doesn't. It's just a box with microwaves inside it, bouncing around. And supposedly it is able to move itself. " While a gyroscope does not provide propulsion, it is a self-contained instrument that can "move" an object, or rather, orient it to a desired position without "pushing" off of anything. As far as I know, it uses inertia to accomplish this. I guess I'm asking, what's the difference between angular momentum and linear momentum? And why can we control one with inertia from a gyroscope and not the other with inertia from an EmDrive? Thanks, Reply
  • YetAnotherBob The results HAVE been verified. Thrust from the 'Impossible' drive have been observed in England, in the USA at several locations, in Communist China and at some other locations. The test that is most often cited against it comes from Germany. That though found they had a defective force balance. They concluded that every balance was defective. It's a very poor test and a fallacious criteria. To date, no one has tried what would be the real test, sending up a satellite with one of these attached and turning it on, then waiting. It might be a long wait. Months would be required before any real conclusion could be reached. That's based on the best estimates of the forces reported in the successful tests. Classical Physicists don't want to accept anything that looks as if it 'violates' classical Newtonian Physics. Though it really doesn't violate what Sir Isaac Newton actually said. Newton gave a simple law. "For every Action there is an equal and opposite Reaction." It means that if you expel something, you get pushed in the opposite direction. It's true and it works! It's how rockets go, and why. It's also why things that seem nonsensical to some, such as 'Solar Sails' work. But Newton never said 'Only' in that equation. He knew of other things that didn't seen to him to be included. One of those is magnetism. Since then, we've managed to account for magnetism, apparently. Magnetic forces can pull or push something without any material connection. We see that happen all the time. It's how all of our electric motors work. That though doesn't mean that the 'Impossible Drive' works or doesn't work. That must be established through experiment. So far none of the experiments have been enough to either give a definite Yes or No. A real explanation for how or why it might work will come only after showing that it actually does work. It might take years or even decades. It was that way for superconductors and radioactivity after all. The Author is correct however in his assertion that this won't provide us with a space drive. It won't even replace the tiny ion thrusters that correct some satellites orientation today. It's really a simple matter of power in and thrust out. The best any EM drive or Mach Thruster has done is essentially Kilowatts in and PicoNewtons out. Honestly the thrust from infrared Radiation is greater. And that's if all the tests which have been done and showed thrust are correct. If we continue to study it, then maybe someday we might have some sort of space drive. But not today and most likely not this century. Reply
  • petecarter Newton's Third Law is inviolate, it's another way of saying momentum (both linear and angular) is always and everywhere conserved, no exceptions. This follows from Noether's Theorem, which says that every symmetry in nature leads to a conservation Law. The symmetry that any behavior of nature is the same over any interval of time leads to conservation of energy; that it's the same in any location in space leads to conservation of linear momentum; and that it's the same however things are oriented in space leads to conservation of angular momentum. So the ONLY way, and NO exceptions, to accelerate a spaceship or any other massive object, is to push or eject or shoot or exhaust something in the other direction. It can be as simple as getting a rowboat across a pond by throwing rocks out the back end, or it can be done (very poorly) by shooting radiation out the back. That this is a very poor method can be seen by looking at the relativistic energy-momentum-mass equation, E^2 = p^2*c^2 + m^2*c^4. For radiation m = 0; taking the square root and diving by c gives p = E/c. So you can generate a HUGE amount of radiant energy and blast it out the rear, but the momentum that's transferred to the ship is all that energy divided by the speed of light, which is a REALLY BIG number. In other words, many megawatts of radiant power provide at most a teeny-weeny bit of momentum. In short, the EM drive or anything remotely like it will NOT work. Reply
  • Karl Goldman Aww...classical...remembering tripanning at it's best. Yes I have read the same thing about the impossible drive. I think that humans tend to like functions that exist and can be proven in the large world. Functional basis for things too small or too large require some form of belief. We should explore the microscopic more carefully, who knows it might get us out of the house and solve corona virus like issues. Perhaps a two rung DNA molecule could stand some scrutiny about its folds. After all its easier to believe in "Death after Life than Life after Death". Reply
  • Robert Lucien Howe Ah the simple assumptions that are so easy to make. Statement : In a closed system the balance of momentum is always preserved.. Spot the error? In a 'closed system..' However the LIGO experiment recently proved the existence of gravity waves, and they would mean that even in a completely isolated object momentum isn't a completely closed system. In effect LIGO proves that gravity engines are possible because local gravity waves would close any imbalance in momentum. A final comment though. Despite the above I am pretty sceptical about the EM drive. To manipulate space time itself which is what it would need to be doing would require a direct FTL causal interaction. A working EM drive breaks Special Relativity and demands the requirement for a new physics. That would be wonderful but it just seems far too easy an answer.. Saying this EM waves would be the way to go if you wanted to go trying to look into the FTL. Reply
  • chadow10 Although I agree that this could be disproven and may not happen, the work continues as well as funding. I do take issue with the closed mindedness that I continue to hear from the scientific community and the superior tone of these type of articles. Science continues to discover new things and prove themselves wrong. 2 new organs have been discovered in the human body in 2 years. Closest red giant proven to be closer and smaller than previously thought. But EM drive is impossible and we can accurately measure all the matter in the universe? Right. Reply
  • Ron Marshall This is a worthless article. People some of which are scientists keep forgetting the experiment is the sole reality check of the scientific method. You can claim the experiment is in error, but preexisting theory does not disprove experiment. Reply
Ron Marshall said: This is a worthless article. People some of which are scientists keep forgetting the experiment is the sole reality check of the scientific method. You can claim the experiment is in error, but preexisting theory does not disprove experiment.
Wolf28 said: "But the EmDrive doesn't. It's just a box with microwaves inside it, bouncing around. And supposedly it is able to move itself. " While a gyroscope does not provide propulsion, it is a self-contained instrument that can "move" an object, or rather, orient it to a desired position without "pushing" off of anything. As far as I know, it uses inertia to accomplish this. I guess I'm asking, what's the difference between angular momentum and linear momentum? And why can we control one with inertia from a gyroscope and not the other with inertia from an EmDrive? Thanks,
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SPACE TRAVEL IS IMPOSSIBLE, AND THAT’S A PROVABLE FACT

chelsea_bonestell_026.jpg

DOES ANYBODY REMEMBER THE SUMMER OF 2013 WHEN A DUCK was photographed by the Mars Rover? Yeah, I thought there had to be some sort of alternative explanation too. And then when these Flat Earthers  started telling me how “Mars” really exists here on Earth, in Canada of all places, on an extremely isolated section of the map called Devon Island, I quickly brushed the entire idea off. The Mars Research Station, which is no secret, made sense. I mean, why shouldn’t the boys over at NASA have a Mars simulation training ground here on Earth? That’s before I did the research for myself.

See, much like the impossibility of testing “gravity” in the lab, or observing a curve to the earth, or the bizarre belief in an arching surface of water, all necessary components to make a globe earth work; thrust and combustion , I also came to learn, are simply impossible in a vacuum of space . I have yet to see it replicated in any experiment. NASA is a fraud.

There’s a channel on YouTube which I think everyone should subscribe to. It’s called Cody’s Lab. What’s important to note about Cody is that he is not a Flat Earther. At least, not yet. Just know that his masterful debunking of NASA is not a Flat Earth agenda. I’m going to post two of his experiments in a vacuum chamber below, which just goes to show once again that the biggest “scientific assertions” implementing from a belief in the globe cannot be replicated here on the actual Earth in which we live on.

God is not a liar, but man is. The Bible is true and the Earth is flat.

https://youtu.be/jYfwlzWOYCE

https://youtu.be/HwK7staIj-Y

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The 3-body problem is real, and it’s really unsolvable

Oh god don’t make me explain math

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Rosalind Chao as Ye Wenjie standing in the middle of three overlapping circles

Everybody seems to be talking about 3 Body Problem , the new Netflix series based on Cixin Liu’s Remembrance of Earth’s Past book trilogy . Fewer people are talking about the two series’ namesake: The unsolvable physics problem of the same name.

This makes sense, because it’s confusing . In physics, the three-body problem attempts to find a way to predict the movements of three objects whose gravity interacts with each of the others — like three stars that are close together in space. Sounds simple enough, right? Yet I myself recently pulled up the Wikipedia article on the three-body problem and closed the tab in the same manner that a person might stagger away from a bright light. Apparently the Earth, sun, and moon are a three-body system? Are you telling me we don’t know how the moon moves ? Scientists have published multiple solutions for the three-body problem? Are you telling me Cixin Liu’s books are out of date?

All I’d wanted to know was why the problem was considered unsolvable, and now memories of my one semester of high school physics were swimming before my eyes like so many glowing doom numbers. However, despite my pains, I have readied several ways that we non-physicists can be confident that the three-body problem is, in fact, unsolvable.

Reason 1: This is a special definition of ‘unsolvable’

Jin Cheng (Jess Hong) holds up an apple in a medieval hall in 3 Body Problem.

The three-body problem is extra confusing, because scientists are seemingly constantly finding new solutions to the three-body problem! They just don’t mean a one-solution-for-all solution. Such a formula does exist for a two-body system, and apparently Isaac Newton figured it out in 1687 . But systems with more than two bodies are, according to physicists, too chaotic (i.e., not in the sense of a child’s messy bedroom, but in the sense of “chaos theory”) to be corralled by a single solution.

When physicists say they have a new solution to the three-body problem, they mean that they’ve found a specific solution for three-body systems that have certain theoretical parameters. Don’t ask me to explain those parameters, because they’re all things like “the three masses are collinear at each instant” or “a zero angular momentum solution with three equal masses moving around a figure-eight shape.” But basically: By narrowing the focus of the problem to certain arrangements of three-body systems, physicists have been able to derive formulas that predict the movements of some of them, like in our solar system. The mass of the Earth and the sun create a “ restricted three-body problem ,” where a less-big body (in this case, the moon) moves under the influence of two massive ones (the Earth and the sun).

What physicists mean when they say the three-body problem has no solution is simply that there isn’t a one-formula-fits-all solution to every way that the gravity of three objects might cause those objects to move — which is exactly what Three-Body Problem bases its whole premise on.

Reason 2: 3 Body Problem picked an unsolved three-body system on purpose

A woman floating in front of three celestial bodies (ahem) in 3 Body Problem

Henri Poincaré’s research into a general solution to the three-body problem formed the basis of what would become known as chaos theory (you might know it from its co-starring role in Jurassic Park ). And 3 Body Problem itself isn’t about any old three-body system. It’s specifically about an extremely chaotic three-body system, the exact kind of arrangement of bodies that Poincaré was focused on when he showed that the problem is “unsolvable.”

[ Ed. note: The rest of this section includes some spoilers for 3 Body Problem .]

In both Liu’s books and Netflix’s 3 Body Problem , humanity faces an invasion by aliens (called Trisolarans in the English translation of the books, and San-Ti in the TV series) whose home solar system features three suns in a chaotic three-body relationship. It is a world where, unlike ours, the heavens are fundamentally unpredictable. Periods of icy cold give way to searing heat that give way to swings in gravity that turn into temporary reprieves that can never be trusted. The unpredictable nature of the San-Ti environment is the source of every detail of their physicality, their philosophy, and their desire to claim Earth for their own.

In other words, 3 Body Problem ’s three-body problem is unsolvable because Liu wanted to write a story with an unsolvable three-body system, so he chose one of the three-body systems for which we have not discovered a solution, and might never.

Reason 3: Scientists are still working on the three-body problem

Perhaps the best reason I can give you to believe that the three-body problem is real, and is really unsolvable, is that some scientists published a whole set of new solutions for specific three-body systems very recently .

If physicists are still working on the three-body problem, we can safely assume that it has not been solved. Scientists, after all, are the real experts. And I am definitely not.

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A Total Solar Eclipse Is Coming. Here’s What You Need to Know.

These are answers to common questions about the April 8 eclipse, and we’re offering you a place to pose more of them.

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The sun flares at the edge of the moon during a total eclipse.

By Katrina Miller

On April 8, North America will experience its second total solar eclipse in seven years. The moon will glide over the surface of our sun, casting a shadow over a swath of Earth below. Along this path, the world will turn dark as night.

Skywatchers in Mexico will be the first to see the eclipse on the mainland. From there, the show will slide north, entering the United States through Texas, then proceeding northeast before concluding for most people off the coast of Canada.

Why eclipses happen is simple: the moon comes between us and the sun. But they are also complicated. So if you’ve forgotten all of your eclipse facts, tips and how-to’s since 2017, we’re here to explain it for you.

But before we dive in, there is one thing to know that is more important than anything else: It is never safe to look directly at the sun during an eclipse (except for the few moments when the moon has fully obscured its surface). At all other times, watch the event through protective eye equipment . Read on to learn about how to watch an eclipse safely.

What is a total solar eclipse?

A solar eclipse occurs when the moon orients itself between Earth and the sun, shielding the solar surface from our view.

In cosmic terms, it is unusual that this happens: the moon is about 400 times smaller than the sun, but it is about 400 times closer to us. That means that when these two celestial bodies are aligned, they appear to be the same size in the sky.

What other types of eclipses are there?

Annular solar eclipses occur when the moon is farther from Earth and appears too small to completely shield the sun’s surface. Instead, the outer part of the solar disk remains uncovered — a “ring of fire” in the sky.

Partial solar eclipses happen when Earth, the moon and the sun are imperfectly aligned. The moon only obscures a chunk of the sun. There will be two in 2025.

Earth can also get between the moon and the sun, creating a lunar eclipse. This can be observed once or twice a year .

How dark will it be during the eclipse?

In any given place along the eclipse path, the event will last around two hours or more.

The event will commence with a partial solar eclipse, as the moon takes a small bite out of the sun’s edge, then consumes more and more of its surface. According to NASA , this can last anywhere from 70 to 80 minutes.

The phase of the eclipse where the moon has completely blocked the sun’s surface is called totality. This is the only time the event can be viewed with the naked eye.

The length of totality varies by location. In April, some places will experience this phase for more than four minutes; others, for only one to two minutes.

During totality, the sky will get dark as night and the temperature will drop. Wispy white strings of light from the sun’s outer atmosphere, or corona, will suddenly be visible. Lucky viewers may even spot a thin, reddish-pink circle around the edge of the moon. That’s the chromosphere, an atmospheric layer below the sun’s corona. Its color comes from the presence of hydrogen throughout the layer.

After totality, the sun will slowly peek out from behind the moon again — another partial eclipse that will last the same amount of time as the first one. The moon will recede until the sun is back to normal brightness in our sky.

How can I watch the solar eclipse safely?

In general, avoid looking directly at the sun without special equipment to protect your eyes. Inexpensive options for watching the eclipse include paper solar viewers and glasses. If you are using equipment purchased for a past solar eclipse, make sure to inspect it. Toss anything with scratches or other signs of damage.

According to NASA , it is not safe to look at the sun through any optical device while using paper glasses or viewers. To watch the eclipse through cameras, binoculars or telescopes, buy a special solar filter.

The only time you can view a solar eclipse with the naked eye is during the moments of totality. Once the moon begins to reveal the surface of the sun again, return to watching the event through protective equipment to avoid injury.

What happens if I look at the eclipse without protection?

In general, staring directly at the sun, even for a few seconds, can cause permanent damage to your eyes . This can range from blurry or distorted vision to something even more serious, like blind spots. Because there are no pain receptors in the retina, you won’t feel it while it’s happening.

The same is true during an eclipse — except during the brief moments of totality, when the moon has hidden the face of the sun. At all other times, use protective eye equipment to view the event.

What do I do if I can’t find eclipse glasses?

If it’s too late to get glasses or viewers, there’s always a do-it-yourself option: a pinhole camera to indirectly experience the eclipse. You can create one using cardstock , a cardboard box , a kitchen strainer or even your fingers . These designs project an image of the eclipse onto the ground or some other surface that is safe to look at.

Where are the best places to watch the eclipse?

The total eclipse will sweep across large portions of Mexico, the United States and eastern Canada. For the most dramatic show, it’s best to experience the eclipse along the path of totality, which is where the moon will completely blot out the sun.

The Path of the Eclipse

On April 8, a total solar eclipse will cross North America from Mazatlán, Mexico, to the Newfoundland coast near Gander, Canada. Viewers outside the path of the total eclipse will see a partial eclipse, if the sky is clear .

space travel is impossible reddit

Percentage of

the sun obscured

during the eclipse

Indianapolis

Little Rock

San Antonio

space travel is impossible reddit

Viewers near Mazatlán, a beach town on the Pacific shoreline of Mexico, will be the first place to experience totality on North America’s mainland. Various sites in Mexico along the eclipse’s path will experience the longest duration of totality — as long as four minutes and 29 seconds.

Cities across the United States, including Dallas, Indianapolis and Cleveland, will most likely be hot spots for the upcoming eclipse. Other notable locations include Carbondale, Ill., which also saw totality during the solar eclipse in 2017; small towns west of Austin, Texas, which are projected to have some of the best weather in the country along the eclipse path; and Niagara Falls, if the skies are clear. Six provinces of Canada are in the path of totality, but many of them have a very cloudy outlook.

When does the eclipse begin and end?

The show begins at dawn, thousands of miles southwest of the Pacific shore of Mexico. The moon starts to conceal the sun near Mazatlán at 9:51 a.m. local time. Viewers near Mazatlán will experience totality at 11:07 a.m. for four minutes and 20 seconds.

Then the moon’s shadow will swoop through Mexico, crossing over the Texas border at 1:10 p.m. Eastern time. Totality in the United States will start at 2:27 p.m. and end at 3:33 p.m. Eastern time.

Canadians will experience the solar eclipse in the afternoon for nearly three hours. The eclipse concludes beyond Canada’s boundaries when the sun sets over the Atlantic Ocean.

Video player loading

How long will the eclipse last?

The duration of totality depends on how far a given location on Earth is from the moon. Places with the longest totality are closest to the moon and farther from the sun. The speed of the lunar shadow is slowest over spots with the longest totality.

In April, the longest period of totality will occur over Durango, a state in Mexico, for a total of four minutes and 29 seconds. Along the centerline, the location of shortest totality on land is on the eastern coast of Newfoundland and Labrador in Canada, for about two minutes and 54 seconds. But totality is even shorter along the edges of the total eclipse path; in some places, it lasts less than a minute.

How fast does the eclipse move?

Solar eclipses may seem to happen slowly, but the moon’s shadow is racing across the surface of Earth. Exact speeds vary by location. Eclipse calculators estimate the shadow will move between about 1,560 and 1,600 m.p.h. through Mexico, and more than 3,000 m.p.h. by the time it exits the United States. The eclipse will reach speeds exceeding 6,000 m.p.h. over the Atlantic Ocean.

When was the last total solar eclipse in the United States?

According to the American Astronomical Society , total solar eclipses happen once every year or so, but they can only be viewed along a narrow path on Earth’s surface. Many occur over water or other places that can be difficult to reach. A given location will experience totality once in about 400 years.

But some places get lucky: Carbondale, a college town in southern Illinois, saw the total solar eclipse in the United States on Aug. 21, 2017, and will experience another one this April. San Antonio experienced an annular eclipse last October, and is also in the path of totality for this year’s eclipse.

Do other planets experience solar eclipses?

Yes, any planet in our solar system with a moon can experience a solar eclipse. In February, a Martian rover captured Phobos , one of the red planet’s moons, transiting the sun.

The moons on other planets, though, appear either smaller or larger than the sun in the sky . Only Earth has a moon just the right size and at just the right distance to produce the unique effects of totality.

How will things on Earth change during the eclipse?

As the eclipse approaches its maximum phase, the air will get cooler, the sky will grow dimmer, shadows will sharpen and you might notice images of crescents — tiny projections of the eclipse — within them. Along the path of totality, the world will go dark while the moon inches toward perfect alignment with Earth and the sun.

Animals will also react to the solar eclipse. Bees stop buzzing , birds stop whistling and crickets begin chirping. Some pets may express confusion . Even plants are affected, scientists found after the solar eclipse in 2017 . They have diminished rates of photosynthesis and water loss similar to, though not as extreme as, what happens at night.

What if I can’t get to the path of totality?

Viewers in locations away from the eclipse path will see the moon partially blot out the sun, though how perceptible the effects are depends on the site’s distance from the centerline. (The closer you are, the more remarkable it will be.) Still, it won’t be quite like experiencing the eclipse during totality.

Remember that you should always wear protective eye equipment while watching a partial eclipse.

If you can’t make it to the path of totality but still want to experience it, many organizations are providing live video streams of the eclipse, including NASA and Time and Date . The Exploratorium, a museum in San Francisco, will also offer a sonification of the eclipse and a broadcast in Spanish.

What have we learned from solar eclipses?

In the 1800s, a French astronomer discovered the element helium by studying the spectrum of sunlight emitted during an eclipse. These events also allowed the first scientific observations of coronal mass ejections — violent expulsions of plasma from the sun’s corona — which can cause power outages and communication disruptions on Earth. Scientists also confirmed Einstein’s theory of general relativity, which says that massive objects bend the fabric of space-time, during a solar eclipse in 1919.

And there is more to discover. This April, NASA plans to fly instruments on planes to capture images of the solar corona, and launch rockets to study how the drop in sunlight during an eclipse affects Earth’s atmosphere. A radio telescope in California will try to use the moon as a shield to measure emissions from individual sunspots .

The public is joining the fun, too. During the eclipse, a team of ham radio operators will beam signals across the country to study how solar disturbances can affect communications. Some people along the path of totality will record sounds from wildlife . Others will use their phones to snap pictures of the eclipse to help sketch out the shape of the solar disk .

An earlier version of this article referred imprecisely to eclipse on other worlds. Some appear larger than the sun in sky, they are not all partial eclipses.

How we handle corrections

Katrina Miller is a science reporting fellow for The Times. She recently earned her Ph.D. in particle physics from the University of Chicago. More about Katrina Miller

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  1. [Discussion] Is Interstellar Travel Truly Impossible? : r/space

    If humanity survives for a long enough time and becomes sufficiently proficient at space travel, and especially if some alien threat arrives on our shores that unites humanity, yes, there's a chance (even in the sense of Dumb and Dumber) that interstellar travel is possible. Honestly, I think anyone who says otherwise is arrogant and ...

  2. Let's be honest: Is interstellar/intergallactic space travel ...

    With 2010s technology flesh-based humans can't go to Alpha Centauri and we still can't travel faster than light. The question OP is asking is: Will technology ever advance to the point where Alpha Centauri or the Sombrero Galaxy can be reached, or is intergalactic travel, like FTL travel fundamentally impossible due to physical laws.

  3. What if interstellar travelling is actually impossible? : r/space

    Even if interstellar travel is possible (albeit very difficult), you have thousands of advanced species merely hobbling from star system to star system over the course of a human lifetime. This isn't exactly a Dyson sphere civilization and we're barely finding massive planetoid bodies within our own solar system.

  4. CMV: Interstellar travel is just flat-out impossible or ...

    CMV: Interstellar travel is just flat-out impossible or thousands of years away. Not a few decades or centuries. It's just too far away, the ship mass is too limited, it's too hard to decelerate, also very hard logistics-wise and communication-wise afterwards.

  5. Why does no one who considers interstellar travel possible in ...

    A much easier solution is to develop the tech to copy the human brain to a machine, especially since that will be useful for many more than than just space travel, but will also eliminate the hostile environment problem and kind of allow for traveling at the speed of light in the form of electromagnetic data vs big old life support spaceship ...

  6. Space is impossible and we've never been close to anything ...

    Nope we have never been and are never going to 'space'. There's a firmament and the density of the area we call 'space' is not an empty vacuum. The sun isn't as far as they say They moon isn't as far and isn't a rock as they say The earth is most likely flat, Tons of evidence for this.

  7. If we can't travel faster than light... does that mean we're ...

    in simple terms: you can travel across the visible universe in 0.001 seconds if we are close enogh to the speed of light. If we traveled AT the speed of light, we would not notice any time change. at above the speed of light, time would run backwards ( i think) but at and faster than speed of light are impossible as such without using wormholes ...

  8. Interstellar travel

    Interstellar travel is the hypothetical travel of spacecraft from one star system, solitary star, or planetary system to another. Interstellar travel is expected to prove much more difficult than interplanetary spaceflight due to the vast difference in the scale of the involved distances. Whereas the distance between any two planets in the Solar System is less than 55 astronomical units (AU ...

  9. Interstellar Travel Could Be Possible Even Without Spaceships

    The author of a new research article in the International Journal of Astrobiology says that ETCs may not need starships to escape existential threats and travel to another star system. They could instead use free-floating planets, also known as rogue planets. The article is "Migrating extraterrestrial civilizations and interstellar colonization ...

  10. Is Interstellar Travel Really Possible?

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  15. Can we time travel? A theoretical physicist provides some answers

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  16. Will Light-Speed Space Travel Ever Be Possible?

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  17. Why We'll Never Live in Space

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  18. Warp drives: Physicists give chances of faster-than-light space travel

    The fastest ever spacecraft, the now-in-space Parker Solar Probe will reach a top speed of 450,000 miles (724,000 km) per hour. It would take just 20 seconds to go from Los Angeles to New York ...

  19. Can the EmDrive actually work for space travel?

    The " EmDrive " claims to make the impossible possible: a method of pushing spacecraft around without the need for — well, pushing. No propulsion. No exhaust. Just plug it in, fire it up and you ...

  20. Fact Check: Bill Nye did not suggest spaceflight is impossible in clip

    Nye has repeatedly discussed space travel, including in a video, opens new tab uploaded by the Planetary Society in 2019 about how solar sails, opens new tab could propel a spacecraft using the ...

  21. Highlights From SpaceX's Starship Test Flight

    This particular flight was not, by design, intended to make it all the way around the Earth. At 8:25 a.m. Central time, Starship — the biggest and most powerful rocket ever to fly — lifted off ...

  22. Space Travel Is Impossible, and That'S a Provable Fact

    That's before I did the research for myself. See, much like the impossibility of testing "gravity" in the lab, or observing a curve to the earth, or the bizarre belief in an arching surface of water, all necessary components to make a globe earth work; thrust and combustion, I also came to learn, are simply impossible in a vacuum of space.

  23. What is the 3-body problem, and why is it unsolvable?

    In physics, the three-body problem attempts to find a way to predict the movements of three objects whose gravity interacts with each of the others — like three stars that are close together in ...

  24. Crinacle RED vs Moondrop Space Travel vs 1More SonoFlow vs ...

    Which one is the best? I'm looking for headphones at around 50-70 dollars, these are the ones I found. What I want the most is sound quality, followed by build quality/ ability to last as long as possible, and finally the best ANC I can get at this price range (but I'd much rather have better sound quality over this, that's why I have the REDs up there.)

  25. A Total Solar Eclipse Is Coming April 8. Here's What to Know.

    In any given place along the eclipse path, the event will last around two hours or more. The event will commence with a partial solar eclipse, as the moon takes a small bite out of the sun's ...