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The metaphor of virtual particles that inhabit all of space is used to explain quantum fluctuations. This ceases to be just a metaphor due to the effects of gravity as clumps of any energy (not just matter) in space can give rise to gravitational effects. For example, this is one possible explanation for the cosmological constant.

How can we know that virtual particles exist everywhere in space and not just locally around individual particles or our universe as a whole? Of course, this question may only be meaningful if our universe is actually finite and not infinite (or experiences lonely clumps of matter in vast gulfs of space).

If virtual particles exist locally around the particles that we are using to observe them and not globally then the density of virtual particles would have to rise in value when we put two particles close together to conserve energy. So, I think it might violate conservation of energy if virtual particles did not exist globally. However, maybe there might be tricky ways around this. For example, maybe while the density of virtual particles wouldn't rise the volume of space they occupy would.

Also, a different explanation for the cosmological constant than virtual particles would have to be provided but I do not consider that a real problem because the predicted cosmological constant due to virtual particles disagrees violently with the one observed in reality anyways.

Also, the region of space in which virtual particles occur around a particle would either have to be very big (so that the universe has a great big ball of virtual particles surrounding it and pulling it outwards slightly) or very small (so that there is not a lot of extra gravity pulling things together) [I am not sure this approach would work as I have not calculated how much extra gravity even the very smallest amount of virtual particles would provide].

Maybe it is not possible to prove that virtual particles are a global or local phenomena and we can only rely upon Ockham's razor here.

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  • $\begingroup$ I don't understand what you mean. The zero-point energy is just the lowest energy state of a system. It is a property of a system, not a property of space, so what do you mean when saying that it is "local"? $\endgroup$ – glS Mar 1 '15 at 14:32
  • $\begingroup$ You're right. I am mixing up some concepts. I will edit the question to be clearer. $\endgroup$ – Steven Stewart-Gallus Mar 1 '15 at 18:14
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When I read your post :

so that the universe has a great big ball of virtual particles surrounding it and pulling it outwards slightly

I worry that you might think the universe is a giant 3D ball of matter sitting inside an infinite 3d space. That would indicate that we have to be far from an edge (since we don't see an edge), which harks way back to assuming we are somehow lucky/special enough to be at (or near) the center of the universe.

To address your question about what happens where there aren't particles. Firstly radiation can spread out, so there can be light everywhere, just very low power low amplitude. So if you consider photons to be particles, then there might not be any natural place with a true vacuum.

But regardless, we can't do a direct measurement of a particle free locations because that would bring particles there. So you'd have to make a model and compare your model's predictions to observations. There are people that do that. And they are professionals that have been working for a long time, so their models have already been adjusted to deal with specific observations. If your model is new, you might have to make lots of modifications before your models performs as well. And then finally we get to questions of simplicity.

If your model has lots and lots of freely adjustable parameters that need to be adjusted just right to make it agree with observations as well as other people's models, then probably no one will be impressed. There are simply too many ways to make models like that, and no good reason to prefer one over the many many others.

If you start with a strong reason that was compelling before you started, then people might like it. If you have parameters that aren't freely adjustable (such as things related to observations that have already been done, like physical constants, masses of known particles, etc.) then that's fine.

Finally, since you brought up size. One of the virtual particles you might consider are virtual photons, and they come in lots of different frequencies, so lots of different wavelengths, so if you restrict them to a region then you might exclude the long wavelength ones, thus specifically challenging (contradicting observations about) soft photon transitions. Your model might be dead in the water just for that. Also, restricting them to a finite region might require too many high frequencies particles so depend on high energy quantum effects, so not really truly addressed by the current standard effective theories.

Finally, many people might want to solve quantum gravity first, then use it to pursue a question like yours.

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