Aemilius,
You have it backwards, they came up with the theory of dark energy to fit the observations of the expanding universe.
Dark energy is a theory, but the expansion, deceleration, and subsequent acceleration are documented as fact. We can perceive them using telescopes. It is called the red-shift, or the Doppler effect; when planets move away from us we see their spectra stretch out and they appear more red. We can tell if they are accelerating by changes in the red shift. As we view objects at different distances (think hundreds to thousands to millions of light-years difference) we see a homogenous change in accelerations, and even going back to very very early times - near the first millions of years after the big bang we have evidence that the universe did in fact decelerate.
And no - if the universe (in reverse) decelerated, we can still mathematically see the date of singularity, it is called an asymptote [if the universe was infinite in age] - it would approach the singularity of the big bang, but slower and slower; if this were the case (which I don't know - next paragraph) the universe would have an infinite age.
I'm debating in my mind if this were possible, and by the existence of black holes I don't think it is. If you packed in an immense amount of matter in an infinitely small space, it would not slowly expand. It would either contain its mass (black hole style) or explode violently and quickly due to the electromagnetic forces.
However... gravity at that scale would be immensely powerful and could possibly contend with electromagnetic forces [hence why we have black holes to begin with - gravity becomes overpowering to repulsive forces].
I'm going to have to say, with trust in the PhD physicists out there, that they would have already seen this possibility and have dealt with it.
but - allusions video still bring up a valid, and important point. There cannot be a beginning, as far as our knowledge can grasp, of the universe, for it is a fundamental law that energy cannot be created nor destroyed - so where did the big bang come from. It is an obvious question, but from a physics stanpoint it is important. At the same time, however, it is impossible to know. The big bang would be the absolute limit of our all knowledge. There is NO science that can produce, illustrate or even attempt a model at before the big bang. Information stops in retrograde motion to the big bang. It is the end point of science.
PHEW YAY!
