i: If we recognize that in the pure energy "big bang" singularity there would be tremdious pressure, radiation pressure, as is inside the sun.
energy is thought not to engender Gravity, space tension to the same extend as does MATTER.
it is thought that the matter that formed with the expansion, expansion that was not retarded, matter & antimatter "congealed".
a slight bias in favour of MATTER has us here, but the excess energy from that anihilation of anti matter vs. matter is apart of the energy that gave
the INITIAL IMPETUS for the outward movement of space and it's matter-CONTENT outward into time.
If you think of our cosmos as a two - dimensional diaphram expanding form it's small beginning, any movement in that curved surface would generate a "centrifugal force" favoring the universes expansion. so keep moving.
so we have the initial impetus, and continuing centrifugal forces driving expansion against ever diminishing* gravitational forces wich would resist expansion.
There are theories that propose both dark matter that would slow down expansion, and dark energy that would accelerate that movement, by
it is possible these cancelling concepts might be an artifact of our mis-interpretation of the data,
after all, we can see only what happened in the past, sometimes the very distant past. but,
Any information from events before the beginning would have been obliterated in the big squeezeng of all the (now)universes' energy into the big bang singularity. so:
for all we can see, the development of the universe can be happening spontaneously, as if flying on auto pilot, like the dividing of the fertilized ovum cell(s), but:
because of the immense energy x mass x time (squared) x distance = work,--- in my mind--, it did not make itself, too much work involved.
glad to still have the time and energy to contemplate it all.
* the energy/matter content of the universe is considered constant, its "diameter" increasing. gravity is inversely proportional to the distance from the CG in this case the big bang.