"When they "rewind" this math, it leads them to the big bang. According to this theory, the universe before the Big Bang was an infinitely dense point."
That's assuming the contraction during such an imaginary rewind would go on to such tiny point. After all it was only relatively recently that they discovered that the universal expansion is increasing (dark energy and all that)! And an universe expanding faster now than in the past doesn't quite fit with the contracting down to a tiny point, me thinks.