According to some current theories, there was a single moment...somewhere between 12 and 15 billion years in the past (depending on who posted the theory)...of course there are a thousand different interpretations of the theory, and it is being revised as new discoveries are examined...but the one thing that hasn't changed is the beginning event, an explosion...Stephen Hawking is thinking that the answer lies within black holes (who incidentally is the first scientist I have ever heard of to admit one of his theories was wrong)...the theory posted on NASA's site claims an object just a few millimeters across held all the mass within the visible universe.
OK, it goes as so: The universe has an age, but no time of creation. Talking of a moment when "suddenly" there was a big bang suggest that time was passing while waiting for this big bang. There was no time, there was not even vacuum (which is very much "something" in quantum field theory). Therefore there was no black hole waiting to go boom or what ever. I get asked a lot "where was the big bang". It make sense that if the universe expanded from a point then you should be able to find that point. The correct answer is: here. I am standing in the exact place where the big bang happened... and so are you. All we space we know is that initial point and all time before the big bang was one point in a not-yet-ticking time.
In addition, the best current estimates are 13.7 billion years and this is not from theory, but observations. The theory interprets measurements (cosmic microwave background and supernova redshift measurements are the dominant) to give this age and the various estimates agree quite well, but nothing in the theory REQUIRES this age.
You must be talking about classical mechanics which is derived from Newton's laws...I understood it to be predictive physics theory...not sure about relativistic mechanics but quantum mechanics is a purely theoretical science that looks at things on the atomic level.
Quantum mechanics purely theoretical?! where do I even begin about that?....
Quantum mechanics treat individual particles, but any macro object is made of these particles. To be "correct" you need to take into account every particle that makes the "object" in classical mechanics. Given that the typical scale for the number of particles in one gram of "object" is 10^23 particles, good luck with calculating the time it takes a ball to fall to the floor. That huge number of particles is what saves Newtonian mechanics: while each particle may do crazy things, the overall mean behavior is extremely predictable. This is why you can even treat a football as a single object with macro properties derived from the most (read: incredibly) likely behavior for the particles ensemble.