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The universe is expanding at an ever increasing rate. Virtual particles are being created and then destroyed everywhere at every moment. As space expands even faster, will a time come when these virtual particles will be ripped apart before they can destroy each other, much like what happens at gravitational event horizons. Does this mean that the universe will at this point find itself suddenly full of Hawking radiation, almost as if a new "Big Bang" had occurred?

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By appropriate coordinate transformations, the inflating universe can be described as stuff falling towards the cosmic horizon, that corresponds in this framework to a black hole event horizon with the black hole being outside the cosmic horizon. So I guess there should indeed be Hawking radiation emitted towards us from the cosmic horizon. But I dont know what would be the Hawking temperature, and therefore the energy of this radiation. –  Dilaton May 29 '13 at 14:23

2 Answers 2

Yes, cosmological horizons are expected to emit Hawking radiation. However, the temperature would be extremely low, about $10^{-30}$ K (Baez 2004 and Hu 2010). This is nothing like a Big Bang. This is all assuming dark energy that behaves like a cosmological constant. For dark energy with certain properties, you can get a Big Rip. See Adams 1997 for a more general discussion of the ultimate fate of the universe, which however was written before the discovery of dark energy.

You may also be interested in Penrose's conformal cyclic cosmology, although the theory no longer seems to be viable.

Adams and Laughlin, http://arxiv.org/abs/astro-ph/9701131

Baez, J., 2004, "The End of the Universe.", http://math.ucr.edu/home/baez/end.html

Hu, 2010, http://arxiv.org/abs/1007.4044

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I guess we are both right :). It reminds me of a Hodja tale: Hodja, a fool or judge or both in Anatolian legends lives and arbitrates in a small village. One day a villager comes and describes his complaints against another villager . Hodja listens carefully, shakes his head and says : "my friend, you are in the right".The villager who was complained against starts his defense and also convinces Hodja to say :"my friend you are in the right". –  anna v May 29 '13 at 5:47
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A third villager who had listened to both expositions exploded: "But Hodja, however can they both be right on the same controversy?" Hodja thought a bit and replied : "you also my friend are in the right". –  anna v May 29 '13 at 5:47

Have you read this simple enough article?

Once objects are bound by gravity, they no longer recede from each other. Thus, the Andromeda galaxy, which is bound to the Milky Way galaxy, is actually falling towards us and is not expanding away. Within our Local Group of galaxies, the gravitational interactions have changed the inertial patterns of objects such that there is no cosmological expansion taking place. Once one goes beyond the local group, the inertial expansion is measurable, though systematic gravitational effects imply that larger and larger parts of space will eventually fall out of the "Hubble Flow" and end up as bound, non-expanding objects up to the scales of superclusters of galaxies.

Bound states , including our galaxy which is gravitationally bound are infinitesimally affected by the expansion. Virtual states exist as mathematically useful models only in bound form. To get a real pair creation out of a virtual pair energy must be supplied so that the particle appears with mass . In current theories the expansion is not supplying energy in the local regions, where conservation laws hold .

In this article scenaria for the end of the universe are described.

Edit after the conflictin answer of Ben

You ask

Does this mean that the universe will at this point find itself suddenly full of Hawking radiation, almost as if a new "Big Bang" had occurred?

The answer is no, because at the temperature for the model estimated in Ben's answer, even if one could talk of virtual particles , even the eV energies needed for neutrino antineutrino pairs will have infinitesimally small probability of getting energy from the tail of the statistical distribution. So it will not be filled with Hawking type radiation.

As I said in the comment, even the concept of virtual particles, inextricably tied to Feynman diagrams, will have little meaning if there are no bound states. The whole Standard Model will be non existent ( quarks cannot be free), virtual particles and all, and Hawking radiation needs Feynman diagrams.

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The Big Rip scenario suggests that eventually even subatomic particles will be ripped apart. This would occur long after galaxies have turned into black holes and the black holes have evaporated. At this time there will essentially only be space and dark energy. Dark energy is theorised as being the cause of space expanding at an increasing rate, and I would imagine this would provide all the energy needed to create real pairs out of virtual pairs. Yes? –  Lionel Doolan May 29 '13 at 3:59
    
In my opinion no, at such a hypotheis , if nuclei are ripped appart, there will not longer be bound states and no virtual particles and pair creation . The whole Standard Model will be non existent ( quarks cannot be free), virtual particles and all. –  anna v May 29 '13 at 4:06
    
+1, interesting point about local conservation laws. I hadn't really considered this point before, which superficially seems to contradict the Big Rip idea. –  Ben Crowell May 29 '13 at 5:37
    
@BenCrowell the Big Rip is an interesting scenario, but it also rips the standard model and yes, lorenz invariance locally , I guess. Not that it would not be possible when one reaches such unexplored phase spaces. –  anna v May 29 '13 at 5:41

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