Probability waves are the quantum mechanics theory that, if an object hasn't been observed, it can be several things at once. It if you think about it, it completely disproves the plot of back to the future. My theory is that in order for the plot to work, the "good" home he returned to would NOT be a changed reality but an alternate one. This means that his original family would never see him again, and since he was able to meet all his siblings, which means that there was another alternate marty whom he never met, and the one with the "good" home and eastwood ravine was probably vaporized by a flying teacup and nobody noticed.
I read about probability waves on a Q&A with Richard A. Watson:
WHICH I CANNOT FIND.....
