When you break in a game of pool, the moment you set your cue ball in motion, all the collisions of the balls, and final resting points are immediately determined. We may not have the information required to calculate it intellectually, but nonetheless, everything that happens on that table was determined the moment you applied force to that cueball.
Perhaps our Universe is a much larger example of that scenario. The moment the big bang occurred, every particles trajectory was determined, from then until now, and until the end of time, and consciousness is merely an illusion. Our consciousness is not making the choices, it is merely observing the choices the physical brain is making and 'feeling' like it is making them. But in fact, every physical, electrical event occurring in your brain is a result of the previous event, and the previous, and so on, and so on.
We may never have the ability or information required to accurately gauge it, but every thing that is as it is right now, every atom, every particle, every wave, is a result of a causal event, which could theoretically be traced all the way back to the initial math of the Big Bang.
So the idea would be that whatever caused the Big Bang in the first place will inevitably happen again, and when it does, this exact universe, and ever event that occurred in it, will reoccur again. And when that chain of events reaches our current present, you'll be right back here again, living out your mortal years, oblivious to the fact that you've been here and done this an infinite amount of times.