Big Bang

• If the universe began as a singularity, why was it so hot? (as evidenced by cosmic background radiation)
• Why is the universe uniform on a macroscopic scale? Most notably, radiation is very nearly the same from every direction is space indicating that heat is coming to us from all directions equally rather than one direction as one would expect from a singularity.
• Why did the universe start expanding at a critical rate that would allow it to continue to be expanding at nearly the same critical rate today?
• What is the origin of the density fluctuations that must have existed in order to form clumps of matter in galaxies surrounded by empty space? An exploding infinitely small, infinitely dense singularity should be very uniform in how it distributes matter.

Hawking investigated the quantum effects of the past and believes that the universe never began nor will it end, it just is. That is to say, space-time has no boundaries, yet it is still finite. This is pretty hard to grasp because we cannot really comprehend this a 4 dimensional world. The example Hawking uses is that it's like the earth, which in two dimensions has no boundaries (you can go around and around without reaching a boundary) but it does have a finite size. The tricky part is extrapolating this concept to 4 dimensions instead of 2 :)

The normal drill if you want to explore the early World is to get a huge telescope and look at distant objects; a galaxy 20 million light years away gives you an indication if what a galaxy looked like 20 million years ago.

This is impossible in principle for the early universe, as when it was a youngster the Big U was opaque to EM radiation.

This allows theories like inflation (which was invented to fill discrepancies in the Big Bang model) to be put forward, rather than questioning the BB model itself.
This kind of shenanigans (postulating theories that can't be verified) is rife in cosmology.
That's what turned me off it after I got my degree.

Well, that and the math.

This fine-tuning, along with many other examples, has led to a consensus among physicists: The initial conditions of our universe really are astounding.

Unfortunately, there isn't any better name than "big bang" that is as short, because nothing in human experience carries anything even close to the proper amount of precision.

Evidences for the Big Bang:

• The cosmic background radiation. It fits, in all manner, exactly what the Big Bang model would predict. There used to be some aspects in the radiation that appeared to conflict with the Big Bang, but when analysed further there only was more evidence.
• Universal expansion. In astronomy there is a law called "Hubble's Law", which basically says that far away objects are usually moving away from us. It has been verified time and time again, and it serves as a good evidence for the Big Bang. (If we extrapolate backwards in time we find all the visible matter coming from a small point)
• The abundance of light elements - not all have been turned into heavier ones as we would happen in an old universe

(We now have the ability to explain the big bang right up to t = 0, using string theory. Unfortunately, it is a very difficult theory to test. But it is a start - we are no longer needing to rely on wild speculations.)

Non-utilitarian artifacts, such as complex cave paintings, (the Chauvet,) Venus statues, as well as more effective hand-axes, have been dated back to 50,000 years ago.

The big bang theory concludes that these artifacts indicate that during this time we became distinctly human; the artifacts must be linked to a sudden change in the process of human evolution, as well as the birth of full-blown language.

However, it is good to keep in mind that absence of evidence is not evidence of absence.