Actually, we can see a tiny fraction in time after the big bang as the light from this event is only reaching us now, and our most powerful telescopes can look directly at what the universe looked like then. The big bang is generally proven by analysis of the cosmic background radiation left over from the explosion. So, it’s a lot more than just a theory. Please be careful of falling for the ignorance trap. i.e. If you don’t understand the science, assuming that therefor it’s not real. In our age of internet, there are too many people assuming that because they can use google, they are experts. Google does not make one an expert. Let me illustrate. To derive the mathematics of the orbital for the hydrogen atom (our simplest atom) took me 15 years of education and oodles of very complex math (schroedinger’s equations) to get to the point where I could do that. If someone else can’t do that, it doesn’t mean that it’s not real. Just saying…be careful of drawing incorrect conclusions…