Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Virtual particles and accelerated expansion

  1. Sep 14, 2010 #1
    In my text book, "Universe" by Friedman et al it says the following:
    "During inflation, however , the universe expands so fast that particles were rapidly seperated 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, wouldnt this process happen again?
  2. jcsd
  3. Sep 14, 2010 #2
    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.
  4. Sep 14, 2010 #3
    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.
  5. Sep 14, 2010 #4
    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).
  6. Sep 14, 2010 #5
    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?
  7. Sep 14, 2010 #6
    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.
  8. Sep 14, 2010 #7
    I am familiar with the big rip, the wikiepdia article
    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 ?
  9. Sep 14, 2010 #8
    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?
  10. Sep 14, 2010 #9
    Well thats exactly what my opening post was wondering.
  11. Sep 14, 2010 #10
    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.

    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.
  12. Sep 15, 2010 #11


    User Avatar
    Science Advisor

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook