This is a transfer in the ability of a probability field to manifest itself and is analogous to photons and neutrinos. Classical physics has defined light as a massless wave-particle which transfers energy from one atom to another. In probability field theory, we see that since particles do not really exist but are rather probability patterns, the transfer of energy from one MPF to another really involves a transfer of probability from one field to another. This probability is neither created nor destroyed in the transfer. Mass can transfer to energy and back by changing from a spike in the probability field to a transfer of probability to other probability fields.
Gravity is seen as a warping of spacetime in on itself.
It is a form of macroscopic geometry. MPFs tend to accumulate in areas of higher warping of spacetime. This in turn tends to increase the degree of warping of spacetime. Gravity is geometry of the macroscopic. It attracts both the peaks and troughs of the probability fields.