Curiosity Day 8 - Big bang..

So have been reading / listening to a lot of stuff around the big bang. It is funny how a lot of scientific literature treats the big bang as being the origin of the universe as a fact, while it is just a theory. Einstein in his general theory of relativity had assumed a static universe that was not expanding or contracting. To make his assumption of a static universe work, he inserted a cosmological constant in his equation to make the math work. But then Hubble came along and showed from observations that the Universe was actually expanding. This put an end to the cosmological constant and was the main underpinning of the Big Bang theory. The one assumption that the Big Bang theory makes is that it assumes that gravity will eventually cause a Big Crunch, which means that while the universe is expanding, it is doing so as a slower rate as gravity slows it down. But new data from the Hubble Space telescope has shown that the universe is actually expanding at a faster rate. So what is causing this acceleration? To make the theory work, dark energy was added to the mix. Kind of like Einstein added the cosmological constant, now we've added dark energy. But there is no evidence of dark energy and what it is etc. It exists and is strong enough to cause the universe to expand faster but cannot be detected. I have a feeling that some discovery is going to come along that is going to change our understanding. There are mathematics based theories like String and M theory that also explain the data that is observed about our universe and provides another explanation for the origin of the universe but these theories are even more difficult to prove, not to mention the extra dimensions, parallel universes etc.