According to the Big Bang theory, the universe is continuously expanding. Is there no limitation to the expansion of the universe? Explain your arguments.

Question

Accepted Answer

The expansion of the universe is not necessarily unlimited; it depends on the average density of the universe compared to the critical density. If the average density is less than the critical density, gravity cannot stop the expansion, so the universe will keep expanding forever (open universe). If the average density equals the critical density, the expansion gradually slows down and eventually stops (flat universe). If the effect of gravity remains strong even after the speed of celestial bodies becomes zero, the universe will stop expanding, start contracting, and eventually collapse into a single point (closed universe, ending in a Big Crunch). So whether the expansion has a limit depends on how much matter (density) the universe contains.