[MtnClimber]

Just off the top of my head there are many theories and this article points out evidence for and against each being correct. The competing theories from my recall:

Open Universe or Closed Universe - does the universe expand forever or eventually collapse due to gravity.

Expanding Universe or Static Universe and is there expanding space-time - Is the universe expanding or is it essentially fixed with unknown things that make it look like it is expanding. And is the fabric of space expanding.

[chiller]

.."expand forever or eventually collapse due to gravity."

....only to explode again sending all elements on their merry way to continue the cycle.

[Boogieman]

Just about every possible alternative has already been ruled out. The atheist/materialists were desperate to find an alternative but they have consistently been stymied by experimental results, or mathematical and metaphysical impossibilities that arise from other theories.