Why do we have to have Dark Energy to explain the expansion of the universe? If, for whatever reason, 10^-33 seconds after the BB, the universe started to expand very rapidly, what force could stop this expansion? Wouldn't all celestial bodies be moving through space almost indefinitely, unless a force that I can't think of, starts to slow them down(planets are rotating around our sun for this very same reason, right)?
Well, the issue is that the rate at which the universe is expanding is increasing. Also, something that could potentially slow down the expansion of the universe is this little thing known as 'gravity'.
I would think this little thing called gravity would decrease in strength with the ever expanding universe.