Do virtual particles have any velocity?

Assyrian said:

When virtual particles pop into existence in the quantum foam do they have velocity, even zero velocity? I am wondering how they would appear from a different relativistic inertial frame? If they had a preferred inertia it would suggest a preferred reference frame. Is this one of the areas where quantum mech and relativity aren't reconciled. Or am I just sniffing ether?

Click to expand...

Two things make me say "yes". First there is no such thing as "zero velocity". At least not in an absolute sense. All velocities are relative and no matter how fast a particle of matter is moving there is a frame of reference where it has a velocity of zero.

Second Hawking Radiation is due to virtual particles where one falls into a black hole and its partner has enough energy not to fall into a black hole. In other words it even has a relative velocity to black holes.


As you can see my answer would be yes.

Assyrian said:

When virtual particles pop into existence in the quantum foam do they have velocity, even zero velocity? I am wondering how they would appear from a different relativistic inertial frame? If they had a preferred inertia it would suggest a preferred reference frame. Is this one of the areas where quantum mech and relativity aren't reconciled. Or am I just sniffing ether?

Click to expand...

It's almost funny that you asked if they have any velocity, because that's more or less correct: they have any velocity.

When you make a QFT calculation with virtual particles, the result involves a sum (integral) over all of the quantum possibilities for the momentum of the virtual particle(s). For instance, for a simple Feynman graph like the one pictured at the right here, the dotted line represents the virtual particle, which is transferring an amount of momentum, k, from one particle to another (the two solid lines). To calculate the total cross section, it would involve an integral on k from -infinity to infinity, allowing the possibility for the virtual particle to take on any value for the momentum. Since that covers all possible momenta, I think this would not be affected significantly by shifting to a different relativistic frame.

Assyrian said:

So are quantum foam virtual particles actual particle particle interactions or just virtual with an infinite range of possible velocities

Click to expand...

The quantum vacuum does not really involve any real particles. A 'real particle' is one that has a line that extends out of the Feynman graph. So vacuum graphs are disconnected 'bubble graphs', and yes the virtual particles there could take on any momentum values.

unless it is collapsed by interaction with an actual particle in it own frame of reference?

Click to expand...

Right. A virtual particle can get 'promoted' to a real particle through some other interaction, whether it's a particle zipping by, or a gravitational effect like the Hawking Radiation Subduction Zone mentioned.

Impressive.

Assyrian, are you going back to graduate school for another Ph.D. ?

Assyrian said:

When virtual particles pop into existence in the quantum foam do they have velocity, even zero velocity?

Click to expand...

I'd say that essentialsaltes covered the basics from a theoretical perspective, but I like to point out a problem in that particular theoretical perspective. The notion of "popping into existence" is a pure misnomer. At the time of our original experiments, nobody knew that neutrinos had mass, and passed through every experiment we ever built by the billions per second. There is "kinetic energy" in every "vacuum" we've ever constructed on Earth. Energy isn't being "popped into existence", it's being "redirected" within a moving ocean of kinetic energy. The concept it's just "popping into existence" is actually a misnomer, albeit a popular one. From the perspective of existing forms of kinetic energy however, it's not a position that can be demonstrated, mostly due to the fact that we cannot remove all the kinetic energy from inside of any vacuum.