Virtual particals and the ZPE

[chromosome24]

can anybody explain to me virtual particals and how they related to the zero point energy?

 

[Mk]

In physics, the zero-point energy is the lowest possible energy that a quantum mechanical physical system may possess; it is the energy of the ground state of the system.

Virtual particles are particles that randomly pop in and out of existence in particle/anti-particle pairs due to weird quantum mechanical effects. At such small scales of time and space the uncertainty principle allows particles and energy to briefly come into existence, and then annihilate, without violating conservation laws.

A classic experiement showing the Casimir effect is one in which two microscopic metal bars are placed parallel to each other. What is so weird is that the bars snap together. The eplanation of the effect requires that the total energy of all of the virtual particles in the vacuum be added together, except for the ones in between. There are a lot more virtual particles outside the bars than inside, so the pressure presses them in. Although the virtual particles themselves are not directly observable in the laboratory, they do leave an observable effect: their zero-point energy results in forces acting on aforementionly arranged metal plates or dielectrics.

 

[vanesch]

A good account on the matter can be found on Wiki:

http://en.wikipedia.org/wiki/Virtual_particle

 

[Ratzinger]

this article says

It is sometimes said that all photons are virtual photons. This is because the world-lines of photons always resemble the dotted line in the above Feynman diagram: the photon was emitted somewhere (say, a distant star), and then is absorbed somewhere else (say a photoreceptor cell in the eyeball). Furthermore, in the photon's frame of reference, no time elapses between emission and absorption. This statement illustrates the difficulty of trying to distinguish between "real" and "virtual" particles as mathematically they are the same objects and it is only our definition of "reality" which is at weakness here.

Could someone comment on that?

Is it correct to say that all fundamental fields are transmitted by virtual particle, but if these fields are disturbed, so if they set in wave motion then real particle (well-defined in energy) propagate and only then energy gets exchanged?

 

[vanesch]

this article says


Could someone comment on that?

Is it correct to say that all fundamental fields are transmitted by virtual particle, but if these fields are disturbed, so if they set in wave motion then real particle (well-defined in energy) propagate and only then energy gets exchanged?

It's always the same thing that bites us!
In a Feynman graph, the "external" (initial and final state) particles are the "real" ones, and the internal ones linking them are the "virtual" ones. But then it is up to you to decide when a particle is "an initial" one, and not itself part of a bigger interaction.
So where do you say that you *have* a (real) particle, and when do you consider it to be "intermediate" ?
Always the same measurement problem!

However, in practice, a particle is real when you can consider that the only state that contributes is a classically-like one. In that case, considering it as a virtual one would not make much difference, because the only contribution in the integral over all its potential states would be the "on shell" condition (namely, the condition that it is classically-like). In other words, no significant interference with "off shell" states occurs.
In that case, you can replace the integral over all "off shell" conditions by a single value, and then you've changed the virtual particle (in the integral) by a real one.

 

[chromosome24]

tell me if i am wrong

from what i've read the near magnetic feild is compromised of virtual particles popping in and out of existence.

if this is correct how do the virtual particals of one magnetic feild react with the virtual particals of a nother attracting or opposing magnetic feild?

for example do the virtual particals of one feild appear then shoot towards the other feild before vanishing?