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Virtual Pairs and the Fate of the Universe

  1. Dec 14, 2004 #1
    I was thinking... virtual particle-antiparticle pairs created just inside the event horizon of the universe continuously adding mass to the universe at an ever increasing rate as the event horizon expands and accelerates... How does this effect the mass/topology of the universe and could this eventually close the universe? Am I misunderstanding something?
  2. jcsd
  3. Dec 14, 2004 #2


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    Welcome to these Forums Hellburner! An interesting question.

    GR states empty (of electro-magnetic fields etc.) vacuum has zero density, a quantum approach would suggest that it is full of virtual particles of potentially huge energy density. So you can take your choice.

    Normally cosmology takes a GR approach, at least until you get to the initial 'singularity' or worry about Dark Energy, in this cosmological case the expanding universe does not impinge on virtual pairs and they in turn have no effect on the expansion of the universe.

    However if you now do think about DE then this energy density could be made up of Zero Point Energy of virtual pairs in the false vacuum. There is then what is known as the "Lambda problem", a mismatch of around 10^140 or so (depending on who you read) in density expectations between quantum theory and that required to 'fix' GR cosmology. These virtual pairs are then required to have a double effect, they add mass to the universe conveniently making the cosmological density up to the critical density, and they effect the dynamics of the expansion making it accelerate (at times!).

    However these are not virtual particles being created along the event horizon, they are just there, everywhere. I think you must be thinking of Hawking radiation from a Black Hole in your post #1.

    Last edited: Dec 14, 2004
  4. Dec 14, 2004 #3
    Or it might be that there is some sort of conservation law requiring that whatever mass is lost behind the present cosmological event horizon be compensated for by the creation of new particles by the Zero Point Energy of the quantum fields. I suppose if this effect were real, then it could be traced all the way back to the creation of the very first particles (whether massive or not). It seems to me that particles in and of themselves represent the perpetuation of some sort of structure and form contrary to the effects of entropy which seems to want to obliterate structure. I wonder if a conservation of entropy or information could be responsible the structures that evolve as the universe expands. I think of space expanding before any particle was created, and I suspect that somehow that the expansion of space itself is responsible for how the first particle inside the universe came to be.
  5. Dec 14, 2004 #4


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    If I understand correctly you are talking about the particles created due to the existence of a cosmological event horizon in a deSitter spacetime, same as the particles created due to a Hawking horizon in a Schwarzschild spacetime, or due to a Rindler horizon in case of an accelerated observer in a Minkowski spacetime.

    In such a case the observer located within the cosmological event horizon detects a thermal distribution of particles (most of them photons). The energy density of photons depends on the temperature (Stefan-Boltzmann law), which in turn depends on the area of the horizon. In an exponentially expanding universe (which will be the fate of our universe, as currently believed) the event horizon remains at a constant distance from the comoving observers (at the Hubble sphere) and thus does not change its area. This means that the energy density of the particles created by the event horizon will remain constant in time.

    Since this energy density will be also very small (I recall John Baez made a calculation of the temperature which is available somewhere in his web), its influence will be negligible. However, if the universe is exactly flat and remains flat until then (a very improbable coincidence), then every slight perturbation in its energy density will change its curvature. Although it will expand forever due to the action of the dark energy (which, due to its high energy density, accelerates the expansion regardless of the curvature), its geometry will change with this slight perturbation and space may evolve in a different way.
    Last edited: Dec 15, 2004
  6. Dec 15, 2004 #5
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