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Quantum foam in general

  1. Feb 8, 2007 #1
    (i am at first year and absolutly have no idea of what qm says)

    does the quantum foam exists only in our spacetime, or it necessarily exist in all...places?
    i was guessing about to deny the existance of vacuum in general, like "vacuum cannot exist because quantum foam is evrywhere at evry level".
    if what i say makes any sense, is quantum foam general and present at evry scale?
  2. jcsd
  3. Feb 9, 2007 #2
    hi born2perform,

    quantum foam, the way ive heard it used, describes the structure of space time on quantum scales. In general relativity, space time is described as a smooth 4-d manifold that curves in response to energy density. When you bring in ideas from quantum mechincs such as particle - anti particle pairs being able to pop out of the vacuum briefly and then annahilate with eachother this ruins the smoothness. Those particles have an energy density and cause bumps and wiggles in spacetime that are always appearing and disappearing. The smaller the patch of spacetime you look at, the more extreme the deviations from smoothness can be. This is what quantum foam is, and so yes it exists everywhere but only on the tiniest scales.
  4. Feb 9, 2007 #3
    Note that the vacuum of quantum physics is not "so vacuum" but only the energy level you fix as the lower...
  5. Feb 9, 2007 #4
    i really wish to have my questions answered:

    -is quantum foam or whatever u call it also in other "universes", i mean other spacetimes, with other geometries; for example in a flatland, or in a 18734+1 dimensions land... does it necessarily exist evrywhere?

    -is it at evry scale? for example at 10^-2378562134875623478956234875 m?

    Last edited: Feb 9, 2007
  6. Feb 9, 2007 #5
    What do you mean exactly? because quantum foam is what allday has written, but..

    - if you consider quantum gravity, quantum states of spacetime are described through spin foam that is pregeometric, so if you want in principle it exist always... even in different universe!

    - if you do a quantistic construction in order to quantize spacetime, there would be quanta of spacetime, i.e. a minimal lenght below which have no sense to talk about distance... you cannot play to ask "what there are below?" infinite times!
  7. Feb 9, 2007 #6
    i was thinking about non-existance of vacuum because of quantum foam.
    can vacuum be 100% denied because of quantum foam?
  8. Feb 9, 2007 #7
    in physics for every system you want to study, you must choose the right instruments of knowledge considerig first of all order of magnitude...
    what you call vacuum in classical physics isn't the same object of quantum physics... so I wouldn't deny vacuum at all! even if you can keep in mind that at a fundamental level "vacuum" is not equivalent to say "nothing" but it's only a certain level of energy, at which a lot of quantum fenomenology can happen!
  9. Feb 9, 2007 #8


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    As so often, and as Francesca pointed out, your question is to imprecise to allow an actual answer.
    Also, misconceptions.

    What is a place is, is defined by a spacetime which is defined by a spinfoam.

    Then is there a place where there is no spinfoam is like asking, was there are time when there was no time? The question is circular and in trying to give it meaning you are invariably going to introduce ambiguities upon which the correct answer (yes, no, unknown at present) depends.
  10. Feb 9, 2007 #9
    You seem to be asking, "can nothing exist?"

    If it exists it isn't nothing, is it?

    If a universe has nothing in it, is it a universe?

    This is pure sophomore philosophy and while it can be fun and dizzying to pursue these circular kinds of paradox, it isn't likely to be revealing of any truth.

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