Posted: Oct 01, 2011 2:25 pm
mizvekov wrote:
And as that book I quoted made this point, there is another way to claim that a particle is virtual, and that is to say that it does not obey the m2c4 = E2 − p2c2 relationship, or what he says about the particles being "off mass shell". Eg, the particles can violate energy conservation for short periods of time by not having the "correct" mass. As more "incorrect" the mass of the particle is, the more likely it is for it to be destroyed by destructive interference, and so less time it is expected to live.
But the weird thing of this account is that you cannot say that any particles are "real" either, they are only approximately (sometimes to a ridiculously high degree) real.
You can make an argument that the word "particle" is different in QFT than what it is in classical physics, and I would agree. In QM, a particle behaves more like a wave packet. But even in that prescription, at higher and higher energies ( smaller and smaller distances) the wave packet is almost synonymous with a particle. And hence, we can talk about the mass of a particle, we never speak of the mass of a wave.
NB: String theorists will argue that, at even smaller scale (planck scale), you get strings.