universe starts as singularity - more entropy - less gravity - things move apart - universe expands.
I think the universe still is a singularity.
It only appears not to be so by those who are in it.
That is why every particle is at the center of the Big Bang,just as they were at the Big Bang.
They are separated by time and momentum but have never reall moved relative to the universe’s event horizon.
That explanation is not based on physics. Gravity is an acceleration: the rate of distance per time squared. The only way an object can accelerate is by a force acting upon it such as gravity.
An object moving through space at a constant velocity has no acceleration. Therefore no force is acting upon it. To change its velocity, there must be an acceleration. To get that acceleration, a force must act upon the moving object.
The velocity at which the universe is expanding is increasing. That means there is an increase in acceleration. That increase can only come about due to a force.