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May16-10, 01:03 AM
In a free field theory, the true ground state of the theory, |Omega>, corresponds with |0>, the eigenstate of the number operator. [...]However, in an interacting field theory, like QED, |0> is no longer equal to |Omega>.
That's correct, but I'm still a little hazy on how this shows that virtual particles are a real, nonperturbative phenomenon, rather than an artifact of a perturbative calculation.