There are others who are far more knowledgeable in this area, but I'll have a crack. All observations show the universe to be expanding as measured by the red shift of the light coming from stars and galaxies - this is as close to a fact as you can get in this field, and yes the rate of accelleration allows cosmologists to estimate the time of the big bang. I think that some would nitpick at the word "location" as before space and time, which commenced at the big bang, the idea of location is meaningless. But as others have said, the big bang theory and the concept of all matter and energy in the universe originating from a singularity of infinite density fits all observations far better than other theories, like the steady state theory.On the OP, because the thread has become reasonably catty and I'm not really interested:
What's the alternative?
If we take as a given that the universe is expanding (which may or may not be true, but all signs point to yes; I've also read that the rate of expansion is accelerating, though how you'd measure this is beyond me), then it follows that if we track backwards through the history of time that the universe will shrink. Extrapolating from this, it follows that the totality of the universe was once in one location.
I have an extremely shoddy grasp of cosmology, but it seems that if a then b, correct?
And like others, I highly recommend Simon Singh's book.
Finally, welcome to the forum.