Re: Can real particles be changed to virtual particles?

Hi Chris,

virtual particles are particles that cannot be detected. they are not "on the mass-shell". what does that mean? electromagnetic interaction, for example is transmitted by photons. real photons have a rest mass equal to zero, i.e. its energy squared E^2 is equal to momentum squared times velocity of light squared, E^2=p^2 c^2. for particles with rest mass m, we have the formula E^2 = m^2 c^4 + p^2 c^2. if you want an interaction the particles propagating that interaction should transfer energy and/or momentum. at the interaction vertex we demand energy-momentum conservation. the only way to satisfy energy and momentun conservation is that -in case of elektromagnetism - E^2 is not equal to p^2 c^2, but less or greater. the energy difference is borrowed via the uncertainty principle. but you can "borrow" energy only for a very short time, the virtual particle has to be absorbed by that time. the heavier virtual particles are the shorter is the reach of the interaction propagated by these virtual particles. for more detail see for example Some Frequently Asked Questions About Virtual Particles. virtual particles can not be transformed into real particles, virtual particles can be absorbed by real particles, and then something happens to that particle. it may change into another particle. in other words a virtual particle may "decay" into real particles. also a real particle can emit a virtual particle and change into a different particle. for example take the emission of a photon by an electron. let us consider the electron flying around with engergy E_0 and momentum p_0, suddenly emitting a photon with energy E^2=p^2 c^2. the electron's energy after emission is E_0-E. after a short calculation one sees that momentum is not conserved. demanding conservation of energy and momentum, means that the photon is a virtual one, which cannot be observed. in case of the breaking radiation i have described, the virtual photon has to be absorbed by some heavy atomic nuclei and reemitted.

i hope this answer helps you,
Michael