I say “seems to imply” because its not really clear what Copenhagen does or does not imply, because it doesn’t really make predictions in every circumstance.
Copenhagen implies that when we make a measurement, the value we measure is in fact the one true value. In particular, there are not other worlds where the measurement returned other values. This is precisely the thing that distinguishes it from many worlds, which suggests that there are other worlds where the measurement returned other values.
By accepting that only one value of the measurement actually happens, you reject the possibility of one human civilization, where one thing was measured, interfering with a different human civilization, where a different thing was measured (because you don’t believe the other human civilization even exists).
That is not a prediction, it is a postdiction, and it is a postdiction that Copenhagen and MWI agree on. And that is, when you make a measurement, the result you get is the only result you get in the world that you are in. Copenhagen and MWI agree on this.
MWI implies that you could interact with other worlds where there was a different outcome, at least in principle. This is not a postdiction because we have never engineered such an intricate situation , and MWI and Copenhagen don’t agree on it. In fact this was proposed as a test of MWi vs. Copenhagen; build a quantum computer, upload a human into it, and then run the experiment I described above (to my knowledge, this is actually the first proposed use of a quantum computer).
Actually this isn’t really an “in principle” thing. If we ignore gravity (I suspect that if we understood gravity correctly we wouldn’t have to) and assume the universe has finitely many degrees of freedom, MWI predicts that all of these world lines will eventually converge in the future. It will just be a long time in the future, after all order in the universe has eroded and entropy is decreasing again. This is clearly not what Copenhagen says. In Copenhagen, it is possible that we never again return to the state of the universe at the big bang. In MWI this is not possible, because all systems with finitely many degrees of freedom are periodic.
I say “seems to imply” because its not really clear what Copenhagen does or does not imply, because it doesn’t really make predictions in every circumstance.
Copenhagen implies that when we make a measurement, the value we measure is in fact the one true value. In particular, there are not other worlds where the measurement returned other values. This is precisely the thing that distinguishes it from many worlds, which suggests that there are other worlds where the measurement returned other values.
By accepting that only one value of the measurement actually happens, you reject the possibility of one human civilization, where one thing was measured, interfering with a different human civilization, where a different thing was measured (because you don’t believe the other human civilization even exists).
That is not a prediction, it is a postdiction, and it is a postdiction that Copenhagen and MWI agree on. And that is, when you make a measurement, the result you get is the only result you get in the world that you are in. Copenhagen and MWI agree on this.
MWI implies that you could interact with other worlds where there was a different outcome, at least in principle. This is not a postdiction because we have never engineered such an intricate situation , and MWI and Copenhagen don’t agree on it. In fact this was proposed as a test of MWi vs. Copenhagen; build a quantum computer, upload a human into it, and then run the experiment I described above (to my knowledge, this is actually the first proposed use of a quantum computer).
Actually this isn’t really an “in principle” thing. If we ignore gravity (I suspect that if we understood gravity correctly we wouldn’t have to) and assume the universe has finitely many degrees of freedom, MWI predicts that all of these world lines will eventually converge in the future. It will just be a long time in the future, after all order in the universe has eroded and entropy is decreasing again. This is clearly not what Copenhagen says. In Copenhagen, it is possible that we never again return to the state of the universe at the big bang. In MWI this is not possible, because all systems with finitely many degrees of freedom are periodic.