[PvK]

The Expanding Universe theory is that gravity is too weak to slow down something moving quickly away that is already an astronomical distance away. Gravity gets weaker and weaker the farther something is away. There is a limit to how much its force will ever add up to beyond a certain distance, so if the distance is increasing, and effect of gravity decreasing, things can escape gravity. The question then became exactly how massive is the universe, and how far is it apart, how fast does it seem to be expanding?

However, after many years of trying to figure that out based on all sorts of assumptions (which made sense, but are still just theories), cosmologists are starting to decide that some even more basic assumptions seem to likely be not correct, such as that the rules of the universe remain constant over time and distance...

The idea that we are seeing the universe all receding at increasing speeds at great distance is all based on assumptions about how to interpret the light we see based on a mountain of theories. It's an extremely sophisticated mountain of theories, but it's still an active volcano, so to speak.

PvK