That hasn't and I doubt will EVER be proven. We can't be certain that the big bang happened. I never said the universe is infinite. The universe may be growing, it may not. They're all theories.
Unfortunately, we will probably never know 100% if the Big Bang ever happened because there is that moment in "time" that humans still can't see past. I'm not saying that I don't think it happened either. However, whether or not we ever actually find the answer to if, we will still have the questions of how and why.
According to inflation theories, backed up by observations of the cbr. The universe is finite, however space it's self is infinite. The best possible explanation is that this infinite space is filled with an infinite amount of universes.
I can't believe Monty Python's "Galaxy" song hasn't been referenced yet. https://m.youtube.com/watch?v=jsgExTttJ2Y
Sounds like a Lawrence Krakpot theory. Let me guess, the universe was made from nothing, but nothing is something?
I have an bigger theory... What if all we see is from our brain? Maybe you guys are fake ??!!? Maybe this game is totally fake!?!?!!?
There are limits to the universe's size. Otherwise physicists would not be able to make claims regarding the number of atoms in the universe. Therefore we can say that physicists don't regard the universe as infinite. If it were infinite then that would imply that it has existed for an infinite amount of time, because in order to be spread across an infinite distance, something requires an infinite amount of time to travel that distance. As we all know, the universe is only 13.7 billion years old. If the universe existed for an infinite amount of time, then that would mean that we would be able to see an infinite distance into the universe, but we can't. We can only see approximately 13.7 billion light years away.
It's almost certainly growing. We have telescopes that we can point in the sky and we can tell that the light is mostly red shifted, meaning the wavelengths of light are stretched out because most objects are moving away from us. It's simple physics. It's likely that the big bang occurred because we know that initially the universe was moving away from itself extremely quickly, then started to slow down due to gravity, then sped up most likely due to dark energy (not much is known about it other than it fits well into physics equations - it's been theorized to be a property of empty space). Some theories are more probable than others. The universe is definitely expanding.