Answer to Question #195587 in Quantum Mechanics for eshwa

Question

For virtual particles:

(a) [2 points] clearly define the concept of virtual particle;

(b) [2 points] name an example of such a particle with the physical context or model

in which it occurs.

(c) Extra credit [1 point] what other system(s) can be described with such a model

(other than those from Particle Physics)?

Answer 1

(a)  A virtual particle is not a particle at all. It refers precisely to a disturbance in a field that is not a particle. A particle is a nice, regular ripple in a field, one that can travel smoothly and effortlessly through space, like a clear tone of a bell moving through the air. A “virtual particle”, generally, is a disturbance in a field that will never be found on its own, but instead is something that is caused by the presence of other particles, often of other fields. Quantum mechanics allows, and indeed requires, temporary violations of conservation of energy, so one particle can become a pair of heavier particles (the so-called virtual particles), which quickly rejoin into the original particle as if they had never been there.

(b) Example involves a photon. It is not merely a ripple in the electromagnetic field, but spends some of its time as an electron field disturbance, such that the combination remains a massless particle. The language here is to say that a photon can turn into a virtual electron and a virtual positron, and back again; but again, what this really means is that the electron field is disturbed by the photon. 

(c) Other system can be described with such a model is our solar system