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Virtual Particle Density in Expanding Space Time

  1. Apr 17, 2009 #1
    Please have pity on a poor ignorant layperson struggling for understanding... and keep in mind that I am mathematically impotent. I am trying to wrap my mind around the concept of expanding space-time with regard to quantum foam. Could someone please explain whether the "density" of quantum foam decreases in an area of "expanded" space. Does the distribution of virtual (transient) point particles become more diffuse relative to less expanded space? Is there less potential information content?
  2. jcsd
  3. Apr 17, 2009 #2
    Feeble....it's not your problem, it's still one for science!!!

    The cosmological constant is believed to remain constant....it's called "cosmological" because the energy density remains constant everywhere in the universe....which is CRAZY!!!! Einstein did not really believe it!!! Then, later he did.

    I don't claim to understand it and likely nobody does...but dark energy is presumed to be a source of negative pressure causing an accelerating universe.

    You can try wikipedia at http://en.wikipedia.org/wiki/Cosmological_constant#Cosmological_constant_problem

    for some explanation, but ultimately it is still a significant mystery....."something from nothing"

    I can think of some vague explanations: quantum foam is a natural occurrence that powers everything....or maybe quantum foam is the pathway from other more high energy environments 'leaking' into ours...and on and on...but those are just personal speculations.....nobody even knows if the "big bang" was a one time unique event, an incredibly rare quantum foam instability...or whether such irregularities go on right in front of our noses with an infinite number of universes spawned every moment....
  4. Apr 17, 2009 #3
    Thanks Naty. I found your Wikipedia source interesting. But again... and please pardon my ignorance... given that the negative pressure produced by the dark energy causes accelerating expansion of the universe, how does that relate to the "density" of the quantum foam within the expanded space? If space of volume X expands to volume Y, does the distribution of quantum foam remain constant and correspondingly "expanded"... or rather, does the expanded volume of Y allow for greater quantum foam content?

    I suppose what I'm really looking for is an understandable definition of "expanded space" with regard to it's potential information content.
  5. Apr 17, 2009 #4


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    I agree you are asking a question that never seems to get properly answered. And it is unaffected whether we are talking old fashioned "coasting to a halt" inertial expansion of spacetime or new wave, dark energy accelerated, expansion.

    If more space is being created, there would seem to have to be some cost attached. In your terms, the zero point foam could not be diluted or stretched thinner. So more of it would be manufactured. At least it would naively seem.

    For old fashioned inertial expansion, I believe the books are balanced because expansion creates a gravitational potential. So the positive energy of moving things apart is exactly matched by the negative desire to move things back together.

    In GR terms, the balance of positive and negative "curvature" would add to a flat zero.

    This would seem to explain why from the point of view of energy book-keeping, a flatly expanding (but cruising to an elastic halt) universe is not costing anything. More foamy expanse can be created freely without adding to the existing energy content.

    But still, there would seem to be questions about the accounting for the creation of the foamy expanse at some level. And I have not come across clear statements of how this might be best handled.
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