Setting: Modern Earth; technology no more advanced that what's reasonable within the next thirty years.

Premise: A prehistoric (and broken) alien device is discovered on Earth, and researchers determine that it was built to allow either time travel or teleportation (or both).

Scientists reverse engineer the device to create a crude (and functional) version. They send objects through, and are able to retrieve them.

Technicals: The human-built version of the device actually sends objects far into future (ie, 1 X 10 Googols to the Googolth power years), far far past the heat death of the universe. They appear in empty (inter-galactic) space, and displace any atoms which may be present.

Question: What effects/forces would these objects experience in the dead universe, and what effect would their sudden presence have on a universe which has long since reached a stable/maximum entropy?

More specifically, would an astronaut in a modern space suit be able to survive in such an environment for more than a few seconds?

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    $\begingroup$ I recommend Stephen Baxter's book Manifold Time, which actually explores what such a concept might be like. $\endgroup$
    – Cort Ammon
    Mar 11, 2016 at 14:07
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    $\begingroup$ Very interesting question. Nice one! $\endgroup$
    – AndreiROM
    Mar 11, 2016 at 14:14
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    $\begingroup$ I smell a contradiction. You said they are able to retrieve the objects, after the heat death of the universe? A single living human means the heat death of the universe has not yet happened, simply because our breathing is a chemical reaction that produces heat/energy, not to mention the many other bodily processes that happen constantly. $\endgroup$ Mar 11, 2016 at 14:47
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    $\begingroup$ Are you saying 10^10^100 yeas from now? Because according to some theories, a new Big Bang may occur on the order of 10^10^56 years from now due to random quantum fluctuations or quantum tunneling. $\endgroup$
    – Michael
    Mar 11, 2016 at 16:28
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    $\begingroup$ He means the universe is already at heat death the instant before the astronaut appears. So, very technically, the universe would stop being at heat death when the astronaut appears and return to heat death when he returns. That would actually be a very scary situation: no light, no point of reference, no readings on your sensors or instruments, nothing. $\endgroup$
    – Pedro
    Mar 11, 2016 at 16:31

4 Answers 4


If the Grand Unification Theory is right, then there would be no atoms at all left in the universe by the time you have mentioned. This would occur due to proton decay.

By this time probably all black holes would also have evaporated due to a phenomenon known as Hawking Radiation. Maybe even photons can decay into lighter particles.

If these theories are right then there would be no universe left at all. Perhaps not even space and time. According to some theories, space and time can't exist without matter while others posit the fabric of spacetime can exist independently of the existence of matter. We just don't know yet.

If some of the theories about the core reality of matter and spacetime happen to be true, all the physical objects (including photons) would have evaporated out of existence and the very fabric of spacetime would have been wrapped by then.

Which suggests that the universe would have ceased to exist by that time.

Also read this article. I found it very informative.

Note: This article (the one mentioned above) was written in 2010. While being very interesting and informative, do not jump to any quick conclusions based only at this article. Read it to increase your general knowledge about mathematical models about the fate of universe.

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    $\begingroup$ When you stretch the time to such astronomical levels as you suggested in your question, all our current knowledge fades away into oblivion and guesswork. Basically our understanding of the fate of universe depends on a grand unification theory which would employ both quantum mechanics and general relativity. This hasn't been achieved yet ... $\endgroup$ Mar 11, 2016 at 14:31
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    $\begingroup$ "We just don't know yet" - no, but if we hang around for long enough, we may find out :) $\endgroup$ Mar 11, 2016 at 15:23
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    $\begingroup$ The emphasis was on yet in that sentence ;) $\endgroup$ Mar 11, 2016 at 15:24
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    $\begingroup$ @AvrohomYisroel Pros: You manage to survive the heat death of the universe and gather useful data. Cons: You're very, very lonely now. :-( $\endgroup$
    – corsiKa
    Mar 11, 2016 at 20:39
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    $\begingroup$ @corsiKa - "Ooh, is that a proton? No. Wait, it's not." -Repeat for the next infinity years. $\endgroup$
    – Richard
    Mar 11, 2016 at 23:19

I'm assuming you're talking about the classic heat death, rather than any of the other theories that have come about from time to time (such as the "big rip"). In this case, to all practical purposes, the post-heat-death Universe would be not much different from the vacuum of space as it exists today.

The main differences would be (i) there would be no starlight or light or matter of any kind, and (ii) there would be no detectable cosmic microwave background radiation, or indeed any detectable radiation of any kind. All the radiation is actually still there, it's just that the Universe has expanded a lot since today, and the radiation has expanded along with it, converting it to such enormous wavelengths and low intensities that it could never possibly be detected. The matter, on the other hand, really isn't there any more. It was all converted into black holes very long ago, which then evaporated into electromagnetic radiation over trillions upon trillions of years; that radiation has since been stretched out along with all the other radiation.

So the universe they find will be black - completely and utterly black beyond all conception of blackness, and cold - completely and utterly cold beyond all conception of coldness. But since space is already pretty cold and black in our time, the space suits we already have would be perfectly good for surviving in it for a time.

As for the effect the astronauts will have on the universe: well, they're emitting a lot of infra-red radiation, along with their radio signals and any visible light from lamps they have with them. That radiation will spread out from their position at the speed of light, and keep going pretty much forever, though in the general scheme of things it won't be all that long before it too is stretched out to undetectably long wavelengths and to all practical purposes disappears.

They are also very likely to leave behind them some atoms even if they make it back somehow, due to gas leaks, propellant, dust particles and what have you. In the absence of any black holes those atoms will last for quite some time, but they will probably eventually decay to electromagnetic radiation through some process or other. Though if they happen to have left a net charge there might be a few electrons left over, which can never decay because there are no protons left in the entirety of the rest of the Universe. It's a tiny mark to leave on the Universe, but it will last for all eternity.

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    $\begingroup$ "Though if they happen to have left a net charge there might be a few electrons left over, which can never decay because there are no protons left in the entirety of the rest of the Universe" -- if they do that then there must be a matching positive charge somewhere else in the rest of the future Universe. Namely, the positive imbalance that results from them re-appearing in the present day with fewer electrons than they left with! $\endgroup$ Mar 11, 2016 at 18:12
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    $\begingroup$ "completely and utterly cold beyond all conception of coldness" - a vacuum isn't cold. There's nothing in it to be cold. If you were in a vacuum, you'd have to worry far more about overheating than about getting too cold. $\endgroup$
    – Rob Watts
    Mar 11, 2016 at 19:48
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    $\begingroup$ @RobWatts: well, the heat death universe is cold in the sense that if you were in thermal equilibrium with it then your temperature would be extremely low (zero point energy or whatever -- there's no cosmic background radiation worth anything). It doesn't feel cold because you'll be nowhere near thermal equilibrium with it until long after you're dead. $\endgroup$ Mar 11, 2016 at 21:46
  • $\begingroup$ @SteveJessop excellent point! So eventually all trace of them will be lost after all! $\endgroup$
    – N. Virgo
    Mar 12, 2016 at 1:39
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    $\begingroup$ @Nathaniel: I was wondering about that, and also whether it could happen even without time travel, that a positive and a negative charge get separated in that way. $\endgroup$ Mar 12, 2016 at 14:59

The simple answer is that we just don't know.

The most likely thing is that you would appear in the hardest vacuum ever measured, living inside your space suit for a while, and then disappear.

Once you disappear the slightly energized area where you shed a bunch of atoms and photons and suchlike will gradually disperse and return back towards heat-death in a brief and feeble pulse of somethingness against the vast nothingness.

On the other hand though if the entire universe has stopped existing by then...well that clearly can't have happened since you've traveled to something...

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    $\begingroup$ Why would you disappear? What would cause that to happen? $\endgroup$
    – Michael
    Mar 11, 2016 at 16:26
  • $\begingroup$ That would be good for the story's plot. The fact that you traveled somewhere means you just confirmed something that was previously impossible to test. It would be like going into a black hole's event horizon and coming back out intact. $\endgroup$
    – Pedro
    Mar 11, 2016 at 16:38
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    $\begingroup$ @Michael: Tim doesn't mean the heat death medium will cause you to disappear, he just means the premise of the question. The object is sent forward in time and then retrieved. So from the POV of the destination it appears and then disappears. $\endgroup$ Mar 11, 2016 at 18:09
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    $\begingroup$ Yep, @SteveJessop got it in one :) $\endgroup$
    – Tim B
    Mar 11, 2016 at 19:01

More specifically, would an astronaut in a modern space suit be able to survive in such an environment for more than a few seconds?

Oh that poor astronaut.

In addition to the other excellent answers about the state of the universe (or lack of a state) that far in the future, there's also the problem of The Big Rip.

The expansion of the universe is accelerating. This means the space between everything is getting bigger like the surface of an expanding balloon, except that surface is 3 dimensional space. If it keeps accelerating, as it appears to be, eventually it will be accelerating so fast to overcome the fundamental forces that hold things together.

First, gravity will be overcome. Galaxies will fall apart. Then solar systems. Then stars and planets and other bodies held together by gravity will disintegrate.

Then electromagnetic bonds between molecules will be overcome and complex structures, such as people, will be torn apart. Then the molecules themselves will be ripped apart into atoms. Then their electrons will be lost.

Eventually the acceleration will become so fast the strong nuclear force will not be able to hold atoms together. Then protons and neutrons will be pulled apart into quarks...

You get the idea. Ultimately, if the acceleration continues, the universe will be expanding faster than the speed of light. (This is ok because "the speed of light" is actually the maximum speed of information transfer between two points in space, space itself has no such limitation). At this point no information can be transferred between two points in space, they're moving apart too fast. The universe is dead.

What does this mean for our time traveling astronaut? They're immediately torn into a cloud of fundamental particles expanding in all directions faster then the speed of light. Good epitaph. Same thing for any instruments you send.

That is all according to our current understanding and much of it is hypothetical. That understanding has changed in the last few decades due to the "discovery" of Dark Energy and Dark Matter which make up about 95% of the energy in the universe.

Dark Matter we're sure exists, we can see its gravitational effects, but we don't know what it is, but we do have some candidates. On the other hand, Dark Energy we have no idea what it might be. "Dark Energy" is really a placeholder for "the universe is expanding too fast and we don't know why".

In reality the answer is right now we're not confident about what the distant universe will look like because we don't know what about 95% of the universe is.

  • $\begingroup$ The acceleration is due to a decrease in density holding it back with regular gravity. The "big rip" idea is long past being viable and is only repeated in the science shows because it sounds cool. $\endgroup$
    – JDługosz
    Mar 12, 2016 at 21:27
  • $\begingroup$ @JDługosz No, the Big Rip is definitely a possibility. Here's Professor of Physics Ed Copeland of the University of Nottingham talking about Dark Energy and the Big Rip. He'll do a better job than I will explaining why the Big Rip is on the table. That video is from 2014, very recent. He starts talking specifically about current observations supporting the Big Rip at about 15:00, though hopes they're wrong. $\endgroup$
    – Schwern
    Mar 12, 2016 at 22:10

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