I was told that perfect vacuum is impossible as virtual photons, permitted by the uncertainty principle, and undergo pair production to produce a particle-antiparticle pair, and they annihilate before the time limit set by the uncertainty principle.
I was also told that some sort of particle must be present near a photon in order for it to undergo pair production (normally a nucleus) due to momentum conservation. a) what is this particle in a 'vacuum'? b) let's say there is a particle nearby when the photon undergoes pair production. Then the particle would have gained some momentum during the pair production process. When the particle and antiparticle annihilate, the particle would still carry some momentum; surely this is not allowed because the energy that the universe 'loaned' must all be 'paid for' at the end as photons, isn't it?
due to momentum conservation, when a particle and its antiparticle annihilate they produce more than one photon - is this okay in terms of 'borrowing' and 'paying back'?
when a virtual photon first appears, wouldn't it violate momentum conservation? from zero to whatever the momentum the photon carries