The whole concept of the big bang, losing it's momentum and that gravity falls upon itself, drawing the Universe together again, is part of the theorem. Eventually the Universe will crash upon itself, and thus start the cycle all over again.
That's why it's a zero theorem. Nothing matters in the end.
The Big Bang/Big Crunch cosmology seems to have fallen out of favour, as physicists try to reconcile quantum mechanical concepts with general relativity.
(The Big Bang/Big Crunch model is just one of three possibilities, that follow from applying general relativity to the entire universe and making some massive assumptions to simplify the maths. The other two possible solutions are the Big Bang/Endless Expansion a.k.a Heat Death universe, and the Steady State universe. Which of the three is "correct" depends on the total mass of the universe, which unfortunately is estimated to be almost the exactly value that divides the three solutions from one another. But I digress.)
These days, physicists are trying to reconcile general relativity with quantum mechanics, giving theories like Loop Quantum Gravity and Brane Theory. If these theories are right, then the universe didn't start with what 's technically a "Big Bang": in fact, Loop Quahtum Gravity predicts that there could've been "precursor" universes to our own, and that information could have leaked through the 'not quite' BB into our universe, and from our universe (via the 'not quite' Big Crunch) into the next one.
I'm beginning to lose interest in cosmology. There are so many possible models, and such a paucity of data, that I think the truth might be beyond our grasp. (Then again, I'm just an outsider looking in.) I should note that Stephen Hawking thinks that Brane Theory coupled with the Anthropic Principle should be enough to answer any question we might reasonably ask of Cosmology.)
I guess the old "memory effect" hypothesis of homeopathy just wasn't convincing the modern punters, hence the need for this new level of craziness. (Mind-blowing video!)