The universe is stranger than we imagine. Over an extremely large but not infinite amount of time, by sheer chance, atoms in a void could spontaneously come together in such a way as to assemble a functioning human brain.
The Boltzmann brain argument suggests that it is more likely for a single brain to spontaneously and briefly form in a void (complete with a false memory of having existed in our universe) than it is for the universe to have come about as the result of a random fluctuation in a universe in thermal equilibrium.
Fabio Pacucci explores this mind-numbing thought experiment 
