By considering vacuum as superfluid quantum space (SQS), the relativistic phenomena described in special and general relativity are reproducible and explainable thanks to the mere action of gravity, considered as a flow of space quanta which are absorbed by massive bodies (by fermions, on subatomical scale, according to a previous work of mine), suggesting how to merge relativity with QFT. A superfluid reformulation of Einstein's equivalence principle is proposed and several hints in favour of the actual existence of SQS are discussed. Furthermore, the motion of light in vacuum is consequently reinterpreted as motion through SQS, for which mathematical and physical similarities suggest how photon might be described as a special spin-1 phonon occurring in SQS.