# Do have virtual particles gravity?

1. Jan 17, 2012

### minio

First I would like to apalogize if this is not right thread for my question, but I am not sure where to put it.
If I understand it right, vaccum is actually full of virtual particles and antiparticles popping into existence and anihilating again and that always particle and antiparticle are created so it is zero sum game.
However those particles (electron, positron) also should have some gravity, right? So such event would temproarily increase gravity in that area which would affect other mass, but then they would have to be real particles, because they interact. And also vacuum should than show some gravity. Am I missing something or virtual particles have no gravity although they have mass?

2. Jan 17, 2012

### jfy4

At the risk of having this same argument again with some of my peers on this site, the answer is that virtual particles don't exist, and being gracious I'll say: yet.

3. Jan 17, 2012

### Ken G

Not to get into an argument about the reality of virtual particles, instead I would point out that they don't have to be real to exhibit gravity, in the sense that they could provide a motivation for reconciling the existence of some form of gravity that we otherwise have a hard time understanding why it's there. A classic example is the "dark energy", which appears to be a form of repulsive gravity that requires no real particles for its existence. Where does this gravity come from? No one knows, but it is not uncommon to try and associate it with a seething sea of virtual particles in the vacuum. Does it have to "come from" something real, can't it just be there, and all the "coming from" is just our efforts to understand and predict it?

The idea there is that negative pressure could produce the desired antigravity, and negative pressure means that something acquires energy when it expands. Virtual particles in vacuum would do that-- expanding vacuum just gives you more vacuum, so if the virtual particles have some "dark" energy associated with them, then more vacuum means more energy, ergo, negative pressure. Voila, antigravity. Of course, the problem is, no one knows how virtual particles, which are just supposed to move energy around, could act like they possess their own energy, and no estimates of how they might do this come anywhere close to being correct for dark energy. So we can say there are still quite a few uncertainties there, but all the same, it would appear to be a potentially interesting place to think about both virtual particles and gravity in the same breath. Most likely one could formulate an interpretation without them, but that's not the issue, there are many ways to frame physics theories using different hypothetical ontological elements along the way, we should probably have learned by now not to "marry" our ontologies. Personally, I view all physics ontology as hypothetical, but I guess that would tend to open a different argument!

Last edited: Jan 17, 2012
4. Jan 17, 2012

### Bill_K

The lesson we have learned from quantum field theory is that the fields are the primary objects, and particles are secondary, being excitations of those fields. Virtual particles are just another type of field excitation, and it's a philosophical question to debate whether they are 'real', or in fact what reality means.

To answer the original question, virtual particles carry energy and momentum, and are therefore a source of gravity. However the idea that they cause gravity to be 'temporarily increased' is false. Energy does not fluctuate, it is conserved at all times, even in the quantum world. The 'energy of the vacuum' is a constant, whose treatment involves renormalization theory.

5. Jan 17, 2012

### Ken G

But even with renormalization theory, there is not yet any sense to the concept of "energy of the vacuum"-- there's just a hope that it can be made sense of. Are we not still more than 100 orders of magnitude away from reaching that goal? And who knows if field theory, or renormalization, or even string theory, will survive that effort? Maybe the best current answer to the OP is, virtual particles have no existence outside of some theory that gives them meaning, and no theory explains the gravity of the virtual particles that theory might invoke.

6. Jan 18, 2012

### minio

Thank you for answers. So if i understand it correctly, my question might not be valid, but if would, then there is not definite answer to it now.

7. Jan 18, 2012

### Neandethal00

Sorry, I'm not trying to hijack your thread, a question about virtual particles is bugging me for sometime. Your gravity may also play some role in my question.

I can't imagine any other particles who can be more Entangled than two virtual particles. Then why don't we covert the anti-particle into a real particle also?

8. Jan 18, 2012

### Ken G

Sometimes you do-- like when an electron-positron pair annihilates into two photons, you might say that the photons are a matter/antimatter pair. But there you need two to conserve energy and momentum-- in situations where you can conserve the necessary quantities with only one photon, you can just get one virtual photon being "promoted".