Different scientific theories for the same thing? If such a situation exists they are not believed.I told you why. You can have differing theories for the same thing. Why can't you accept that? The "beginning" of the universe is an excellent example. Not all theories can be right, maybe none are. IF you choose to believe one it's by faith, not science.
Again, no one believes a scientific theory that will never be proven. Well not if they know how the system works. They accept that by scientific consensus it is the best present knowledge/explanation.
Show me someone who believes they know how the universe began, that will be a crank. It's not likely to be a scientist.