People often say that the particles in ground state of interacting fields are virtual (for instance, from youtube video "What is 'Nothing'?" by Sabine Hossenfelder). However, from my understanding, this vacuum $|\Omega>\ \propto lim_{t\rightarrow \infty \ }e^{itH} |0>$ is different from the non-interactive vacuum $|0>$. I tend to think that $|\Omega>$ has non-zero expectation value in particle number of a specific particle type. If so, then isn't it wrong to call those particle virtual?
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