Virtual particles and accelerated expansion

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Discussion Overview

The discussion revolves around the concept of virtual particles and their relationship to the accelerated expansion of the universe, particularly in the context of inflation and potential future scenarios like the Big Rip. Participants explore theoretical implications and the nature of dark energy, as well as the conditions under which particles might emerge from the vacuum of space.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants reference a textbook claim that during inflation, virtual particles become real due to rapid expansion, questioning if this could occur again if the universe's expansion accelerates beyond the speed of light.
  • There is curiosity about the whereabouts of antiparticles during this process, with participants seeking clarification on their role in the context of accelerated expansion.
  • One participant suggests that the expansion of space cannot continue indefinitely at inflationary speeds, implying a limit based on different inflation models.
  • Another participant introduces the Big Rip scenario, noting its dependence on the nature of dark energy and suggesting that while expansion could accelerate indefinitely, it would not affect gravitationally bound objects.
  • Concerns are raised about the implications of the Big Rip, with references to a Wikipedia article describing catastrophic outcomes for cosmic structures, leading to speculation about whether this would lead to a new inflationary phase.
  • Some participants express skepticism about the Big Rip's plausibility, suggesting that it is losing support in the scientific community.
  • One participant posits that if dark energy density remains constant, it would not lead to a Big Rip, while another counters that the final state of a Big Rip would be a singularity, diverging distances to infinite values.
  • There is a suggestion that the current accelerated expansion is already happening, albeit at a lower rate, and that it will lead to a finite temperature in the distant future.

Areas of Agreement / Disagreement

Participants express a variety of views on the implications of accelerated expansion and the Big Rip scenario, with no consensus reached on the nature of dark energy or the future of cosmic expansion. Disagreement exists regarding the plausibility of the Big Rip and the conditions under which inflationary processes might repeat.

Contextual Notes

Participants acknowledge that the discussion is speculative and dependent on various cosmological models, with limitations in the current understanding of dark energy and its effects on the universe's expansion.

skydivephil
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In my textbook, "Universe" by Friedman et al it says the following:
"During inflation, however , the universe expands so fast that particles were rapidly separated from their corresponding antiparticles. Deprived of the oppurtunity to recombine and annhilate, these virtual particles became real particles in the real world. In this way, the universe was flooded with particles in the real world"

What I was wondering is that if the expansion of the universe continues to accelerate to the point its faster than the speed of light, wouldn't this process happen again?
 
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skydivephil said:
In my textbook, "Universe" by Friedman et al it says the following:
"During inflation, however , the universe expands so fast that particles were rapidly separated from their corresponding antiparticles. Deprived of the oppurtunity to recombine and annhilate, these virtual particles became real particles in the real world. In this way, the universe was flooded with particles in the real world"

If only someone could explain where are those antiparticles.

skydivephil said:
What I was wondering is that if the expansion of the universe continues to accelerate to the point its faster than the speed of light, wouldn't this process happen again?

How would you define universe that is expanding faster then light? Remember that V=Ho*D, so for any positive Ho, there is a distance at which recession is superluminal.
 
Calimero said:
If only someone could explain where are those antiparticles.



How would you define universe that is expanding faster then light? Remember that V=Ho*D, so for any positive Ho, there is a distance at which recession is superluminal.

Im not a cosmologist, just about to start studying astronomy and doing some pre course reading. But I guess I mean that the rate of the expansion of space is the same as as during the proposed inflationary epoch.
 
Well, let's hope that it can't happen. Exact answer why it can't happen, would depend on particular model of inflation that you are willing to accept (quantum tunneling, slow roll inflation, etc).
 
So presumably then the expansion of space cannot continue to accelerate indefinitely but has some limit to stop it from expanding at the speeds during the inflationary epoch?
 
Are you familiar with Big Rip scenario? Its plausibility would depend on exact nature of dark energy. Try to google it.
On the other hand there is possibility that expansion can indefinitely accelerate, but it wouldn't affect gravitationally bound objects.
 
Calimero said:
Are you familiar with Big Rip scenario? Its plausibility would depend on exact nature of dark energy. Try to google it.
On the other hand there is possibility that expansion can indefinitely accelerate, but it wouldn't affect gravitationally bound objects.

I am familiar with the big rip, the wikiepdia article
http://en.wikipedia.org/wiki/Big_Rip
implies everything is torn apart during the big rip:
"About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the solar system would be gravitationally unbound. In the last minutes, stars and planets would be torn apart, and an instant before the end, atoms would be destroyed"
is this wrong ?
 
skydivephil said:
I am familiar with the big rip, the wikiepdia article
http://en.wikipedia.org/wiki/Big_Rip
implies everything is torn apart during the big rip:
"About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the solar system would be gravitationally unbound. In the last minutes, stars and planets would be torn apart, and an instant before the end, atoms would be destroyed"
is this wrong ?

Wouldn't that just bring us back to the start, where inflation was so fast that it prevented virtual particle pairs from recombining and thus flooding the universe with particles all over again? If that's the case, how would we know which iteration of inflation we were in?
 
friend said:
Wouldn't that just bring us back to the start, where inflation was so fast that it prevented virtual particle pairs from recombining and thus flooding the universe with particles all over again? If that's the case, how would we know which iteration of inflation we were in?

Well that's exactly what my opening post was wondering.
 
  • #10
skydivephil said:
I am familiar with the big rip, the wikiepdia article
http://en.wikipedia.org/wiki/Big_Rip
implies everything is torn apart during the big rip:
"About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the solar system would be gravitationally unbound. In the last minutes, stars and planets would be torn apart, and an instant before the end, atoms would be destroyed"
is this wrong ?

Question is if dark energy density remains constant over time, like in the case of simple cosmological constant, or does density increase over time, which would lead to more acceleration and eventually to big rip. For some reasons that are out of the scope of this thread, and which would be regarded as pure speculation by mentors, I personally believe that density is constant.

It appears that, generally, big rip is loosing support anyway.

friend said:
Wouldn't that just bring us back to the start, where inflation was so fast that it prevented virtual particle pairs from recombining and thus flooding the universe with particles all over again? If that's the case, how would we know which iteration of inflation we were in?

No. Final state of big rip is singularity, distances diverge to infinite values. There is no mechanism that can prevent that. Inflation, fortunately, ends with reheating.
 
  • #11
skydivephil said:
What I was wondering is that if the expansion of the universe continues to accelerate to the point its faster than the speed of light, wouldn't this process happen again?
Yes, it's happening now, albeit at a much lower rate. As time goes forward to infinity, assuming a cosmological constant, the universe will approach a finite but very low temperature due to this interaction.
 

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