It's human nature we explain the world in the simplest way we can. In earlier times, people thought the world was flat.... seemed to make sense at the time. Now, in the age of Hubble deep field telescopes, quantum physics, and general relativity... our observations are more advanced, even if our human reasoning isn't.
So, why is the Big Bang theory widely accepted? Here are the main observations:
- The universe appears to be expanding.
- 'Cosmic microwave background radiation' was predicted by the Big Bang, and is in fact observed.
- An abundance of light elements in the universe (called nucleosynthesis) is predicted by the Big Bang & observed.
Now for a few challenges posing scientists regarding the Big Bang theory:
- The expansion of the universe seems to be accelerating.
- The universe is expanding uniformally around us, so either: the universe is expanding uniformally from everywhere(then where's the center?), or we are at the center of the universe (sounds like pre-Copernicus thinking to me)
If there's one conceptual/philisophical problem I have with the Big Bang... it's that it implies a finite universe & a creation, which forces one to ask more questions. I'm sure the Pope would have an answer for you... in fact the Big Bang theory was proposed by a preacher. However, I see no reason to mix religion & science. Considering Occam's' Razor (the most important rule of thumb for science in my opinion), a finite universe over-complicates everything by forcing one to ask questions like: "where did the matter come from? why was it the amount of matter it is? why was it located where it was?". An infinite universe is pure & simple (albeit mind boggling, but just look at the night sky for a minute & you'll understand infinite).
From what I can tell... Einstein did everything possible to explain away the Big Bang (cosmological constants & what-not). I feel ok not agreeing with the scientific majority, if I'm in that sort of company. Everyone knows Einstein was genius... but it wasn't just a genius of logic & math, it was a creative 'think outside the box' genius. Hell, he invented "Space-Time" & realized that matter bends space-time to cause gravity. It took me a while to even comprehend that!
When you get to this area of theoretical physics/science... you have to bring in philosophy to some degree. Why do we have the laws of physics that we do (gravity, weak/strong nuclear, electromagnetic)? Why does the speed of light = 299 792 458 m/s instead of 57? As for the observation that the universe is expanding.... Quantum mechanics shows that laws of the universe break down at the subatomic level, so who's to say the laws of the universe don't also break down at the multi-galaxy level? (the earth appeared flat, but duh -it wasn't from the macro-view).
String theory (and attempts at a 'grand unified theory') propose ideas about how & why the rules of our universe exist. In my opinion, Occam's Razor would prescribe that 'infinite' is the answer at all levels. In fact, there is an alternative to the Big Bang theory which accepts the infinite AND explains all the observations... I've seen it referred to as the Brane Collision theory. It basically implies that in an infinite mesh of alternate universe's membranes (each with their own properties)... a collision between membranes could cause a 'reset' of matter much like the Big Bang, but without the finite expansion from a singularity.