According to the quantum fluctuation concept, a particle and its corresponding antiparticle appear out of nothing only to annihilate and emit some energy in the form of electromagnetic waves.
Does this only happen in vacuum? From where do the particles get the energy to come into being in the first place? Does this effect involve only electrons and quarks (and thus positrons and antiquarks) or protons and neutrons too?
The particle and antiparticle pair don't emerge from nothing, but rather the field (e.g. lepton field for electrons and positrons) that permeates the vacuum over all space. So pair creation an annihilation isn't tied to the vacuum but to the quantum field, and it happens everywhere - not just in an experimental vacuum. I.e it happens in the nucleus of an atom, which is far form being a vacuum in the sense you mean, and the cloud virtual pairs are responsible for the majority of the mass of the nucleus. You could have a virtual proton sure, or even a Boltzmann brain, but the suppression of the probability of finding a large particle is huge
Where they get the energy from - the zero-point energy of the quantum field, of which they are excitations of. They are energetic fluctuations of their corresponding particle field.
