Simple question. Am I right in thinking that, according to current theory, the rapid cooling occurring after the Big Bang is a direct result of the universal spatial expansion (absurd as it may seem), for the following two reasons. 1) as the (hot) particles of matter move into that new space, their relatively high linear speed is greatly reduced. They were moving very fast relative to other nearby particles, but now they're moving, with other particles, into newly created space, and so their relative velocity (relative to the other particles that also move into that now more sparsely populated space) is much less. 2) the photons also are moving into newly created space, reducing their density and also shifting them to the red in that new space.