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In Hawking's radiation, virtual particles respond to intense gravitational tidal forces with pairs being ripped apart. One crosses the event horizon and the other escapes.

On the other hand, in normal space, virtual particles wink into and out of existence faster than can be observed.

My first question is could virtual particles' momentary existence collectively create a gravitational field which might giving rise to effects we attribute to dark matter?

Secondly, could intergalactic space affect virtual particle pair creation / destruction differently than galactic space?

thokiro
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Keith Reynolds
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    Black holes don't emit charged particles but photons, so the pair production picture is awfully poor. Virtual particles aren't particles, at all. They are elements of a mathematical perturbation series that is being used by theorists to describe quantum fields. Even Feynman warned against interpreting the perturbation series as actual physical events. Do mathematical formulas gravitate? No... or maybe by as much as the paper and the ink gravitate. – CuriousOne Feb 02 '16 at 22:49
  • Can perturbative effects be described by perturbation theory? Yes. Medieval astronomers did that, already, when they introduced epicycles. Are epicycles therefor fundamental physics? No. – CuriousOne Feb 03 '16 at 00:03
  • But virtual particles do give rise to observable, affects like the Casimir effect where virtual particle radiation pressure differences due to excluded frequencies result in a net external pressure on two conductive plates. I had to correct my spelling errors. – Keith Reynolds Feb 03 '16 at 02:04
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    @KeithReynolds These observable effects are caused by processes in quantum fields. Virtual particles are a tool to calculate these processes. In principle you can make the calculations using some other approach, without the virtual particles. – mpv Feb 04 '16 at 16:18

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First have a look at my answer to Black holes and positive/negative-energy particles for some background on Hawking radiation. The pairs of virtual particles analogy is just an analogy and not what actually happens. In fact virtual particles don't really exist in the way that real particles do - see this article by Matt Strassler for more on this.

But your question does touch upon a mystery in quantum field theory so it's worth a bit of discussion. In QFT the vacuum has a zero point energy, however since in QFT we only ever measure energy differences this zero point energy has no immediate physical effect. However like everything in quantum mechanics the zero point energy is subject to the uncertainty principle so repeated measurements of the vacuum energy will return different answers. These fluctuations in the measured vacuum energy are what is normally modelled by virtual particles. Let me emphasise once again that these virtual particles are a computational device. The energy fluctuations are real, and lead to phenomena like the Casimir effect, but they aren't really due to particles jumping in and out of existence.

The mystery comes when we move to general relativity because although in QFT we are only interested in energy differences, in GR it is the absolute value of the energy density that curves spacetime. The problem is that if we attempt to calculate the gravitational effect of the vacuum energy the answer we get is 120 orders of magnitude too big.

Currently there is no good explanation for this discrepency and we have to admit we don't understand what is going on here. The pragmatic approach, favoured by many (most?) of us, is to assume that for some reason that we'll discover soon vacuum energy doesn't gravitate and the problem goes away.

Finally we should note that even if vacuum energy did gravitate it would not behave like dark matter but instead it would behave like dark energy and cause an exponential expansion of the universe.

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John Rennie
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    "These fluctuations in the measured vacuum energy are what is normally modelled by virtual particles." - I'm afraid I don't know what that is supposed to mean in any precise sense. How does a "virtual particle" - a line in a Feynman diagram in a perturbative expansion - model a "fluctuation" - the simple fact that the standard deviation of things may be non-zero? The Casimir effect can by purely explained by the fact that the vacuum energy inside a confined space varies with the size of the space, you don't need to talk about "fluctuations" at all. – ACuriousMind Feb 03 '16 at 16:17
  • Perhaps the sign of an inconsistency somewhere that cannot be removed without a lot a new assumptions. –  Feb 03 '16 at 16:18
  • I freely admit my answer takes considerable liberties in an attempt to give a popular science level explanation. Anyone who thinks it takes unacceptable liberties should downvote and I will respond by deleting my answer. Obviously I think any distortions of the truth are acceptable otherwise I wouldn't have posted it, but I'm willing to go with the majority opinion. – John Rennie Feb 03 '16 at 16:39
  • Is there reason to believe certain vacuum energies inaddition to those with a wavelength less than the plank scale should be excluded? Thus avoiding the huge discrepancy. And im having a problem understanding that if they do gravitate, how it would cause the universe to expand – Keith Reynolds Feb 03 '16 at 17:32
  • @KeithReynolds: for why vacuum/dark energy causes expansion see this answer of mine. You'll have to clarify your first question as I'm not sure what you mean. – John Rennie Feb 03 '16 at 17:40
  • The Vacuum_catastrophe page you linked to said "several assumptions are made that have no grounds in observation or established theory. These include the assumption that quantum field theory acts as a natural and effective field theory down to the Planck scale and the assumption that vacuum energy gravitates." What if it were not applied down to the plank scale, but for some reason yet to be determined, the scale was set much higher. – Keith Reynolds Feb 03 '16 at 17:50
  • @KeithReynolds: you need to post a fresh question to do justice to this, but for example supersymmetric cancellations can cut off the contributions above some hypothetical supersymmetry scale. The trouble is that scale must be greater than a few TeV or we would have evidence for it from the LHC. Even a few TeV still creates a vacuum energy many orders of magnitude greater than observed. You can of course suggest any random cut-off you want, but without any physical justification you are effectively just moving the problem around. – John Rennie Feb 03 '16 at 17:58
  • Of the possibilities that fall within observational limits, were left with either it does not gravitate and/or there is a vary large cutoff scale that the effective field theory does not apply too. Rather than suggesting any random cutoff point, it might be helpful to look at what is excluded and possible with in current observation. If that proposed limit generates prediction that we see on a cosmic scale, then there may be a connection. – Keith Reynolds Feb 03 '16 at 18:14