Well, the amplitudes would change: all possible universes "exist", but their existence is not binary, it has a complex amplitude. And the norms of the amplitude

Well, the amplitudes would change: all possible universes "exist", but their existence is not binary, it has a complex amplitude. And the norms of the amplitudes of all universes sum to one. So basically if you have three universes, at time t you might have A:0.5, B:0.25, C:0.25, and then at time t+1 you might have A:0.30, B:0.40, C:0.30. Thus the "flow" of time is really just the flow of amplitudes from certain branches to certain others. The idea that something does not "exist or not exist", but rather "exists at amplitude 0, amplitude 0.5, amplitude -i, etc." is kind of a mind screw, but that's the suggestion. This being said, there might be a steady state or fixed point where all amplitudes remain constant. Not sure how we could know if there is one or if we're in it, but that would be interesting.