The premise of "Potter and the Methods of Rationality" is what would have happened if aunt Petunia married a scientist instead, and Harry was raised in such an environment?
Is this the only difference at the branching point of the two stories (the original and the fan-fic)?
It seems, at first glance, that everything happens as it did in the original Harry Potter universe, and everyone has the same personality as in the original, until Harry arrives and the butterfly effect kicks in.
However, this does not explain why Professor Quirrel, Dumbledore and Voldemort have vastly different personalities/behavior compared to the original.
I could understand Dumbledore, as he might have been observing Harry before he turned 11, and acts accordingly.
But why does Voldemort in this universe differ so much from the original one even before really interacting with Harry??
Are there other differences between the two universes besides the husband of aunt Petunia, or it's just Harrys scar/connection having an effect on Voldemort?