There is at least one situation in which you might expect something different under MWI than under pilot-wave: quantum suicide. If you rig a gun so that it kills you if a photon passes through a half-silvered mirror, then under MWI (and some possibly reasonable assumptions about consciousness) you would expect the photon to never pass through the mirror no matter how many experiments you perform, but under pilot-wave you would expect to be dead after the first few experiments.
I’m not convinced there’s a real difference there.
In both cases you expect that in no experiment you observe (and survive) will the gun fire and kill you. In both cases you expect that an independent observer will see the gun fire and kill you about half the time. In both cases you expect that there is some chance that you survive through many experiments (and, I repeat, that in all those you will find that the gun didn’t fire or fired in some unintended way or something) -- what actual observable difference is there here?
In the pilot wave theory, the probability that you will witness yourself surviving the experiment after it is performed say 1000 times is really really small. In MWI that probability is close to 1 (provided you consider all future versions of yourself to be “yourself”). So if you witness yourself surviving the experiment after it is performed 1000 times, you should update in favor of MWI over pilot wave theory (if those are the two contenders).
I am skeptical of the existence of any clearly definable sense of “the probability that you will witness yourself surviving the experiment” that (1) yields different answers for Everett and for Bohm, and (2) doesn’t have excessively counterintuitive properties (e.g., probabilities not adding up to 1).
Probability that any you looking at the outcome of the experiment after 1000 runs sees you alive? 1, either way. Probability that someone looking from outside sees you alive after 1000 runs? Pretty much indistinguishable from 0, either way.
You only get the “probability 1 of survival” thing out of MWI by effectively conditionalizing on your survival. But you can do that just as well whatever interpretation of QM you happen to be using.
If I find myself alive after 1000 runs of the experiment … well, what I actually conclude, regardless of preferred interpretation of QM, is that the experiment was set up wrong, or someone sabotaged it, or some hitherto-unsuspected superbeing is messing with things. But if such possibilities are ruled out somehow, I conclude that something staggeringly improbable happened, and I conclude that whether I am using Everett or Bohm. I don’t expect to go on living for ever under MWI; the vast majority of my measure doesn’t. What I expect is that whatever bits of my wavefunction survive, survive. Which is entirely tautological, and is equivalent to “if I survive, I survive” in a collapse-y interpretation.
Anthropomorphically forcing the world to have particular laws of physics by more effectively killing yourself if it doesn’t seems… counter-productive to maximizing how much you know about the world. I’m also not sure how you can avoid disproving MWI by simply going to sleep, if you’re going to accept that sort of evidence.
(Plus quantum suicide only has to keep you on the border of death. You can still end up as an eternally suffering almost-dying mentally broken husk of a being. In fact, those outcomes are probably far more likely than the ones where twenty guns misfire twenty times in a row.)
In fact, those outcomes are probably far more likely than the ones where twenty guns misfire twenty times in a row.
It’s quite a bit less likely, but if quantum immortality changes the past (when you’re on the border of life and death, it’s clear the gun didn’t misfire), then it would just keep you from running the experiment in the first place.
There is at least one situation in which you might expect something different under MWI than under pilot-wave: quantum suicide. If you rig a gun so that it kills you if a photon passes through a half-silvered mirror, then under MWI (and some possibly reasonable assumptions about consciousness) you would expect the photon to never pass through the mirror no matter how many experiments you perform, but under pilot-wave you would expect to be dead after the first few experiments.
I’m not convinced there’s a real difference there.
In both cases you expect that in no experiment you observe (and survive) will the gun fire and kill you. In both cases you expect that an independent observer will see the gun fire and kill you about half the time. In both cases you expect that there is some chance that you survive through many experiments (and, I repeat, that in all those you will find that the gun didn’t fire or fired in some unintended way or something) -- what actual observable difference is there here?
In the pilot wave theory, the probability that you will witness yourself surviving the experiment after it is performed say 1000 times is really really small. In MWI that probability is close to 1 (provided you consider all future versions of yourself to be “yourself”). So if you witness yourself surviving the experiment after it is performed 1000 times, you should update in favor of MWI over pilot wave theory (if those are the two contenders).
I am skeptical of the existence of any clearly definable sense of “the probability that you will witness yourself surviving the experiment” that (1) yields different answers for Everett and for Bohm, and (2) doesn’t have excessively counterintuitive properties (e.g., probabilities not adding up to 1).
Probability that any you looking at the outcome of the experiment after 1000 runs sees you alive? 1, either way. Probability that someone looking from outside sees you alive after 1000 runs? Pretty much indistinguishable from 0, either way.
You only get the “probability 1 of survival” thing out of MWI by effectively conditionalizing on your survival. But you can do that just as well whatever interpretation of QM you happen to be using.
If I find myself alive after 1000 runs of the experiment … well, what I actually conclude, regardless of preferred interpretation of QM, is that the experiment was set up wrong, or someone sabotaged it, or some hitherto-unsuspected superbeing is messing with things. But if such possibilities are ruled out somehow, I conclude that something staggeringly improbable happened, and I conclude that whether I am using Everett or Bohm. I don’t expect to go on living for ever under MWI; the vast majority of my measure doesn’t. What I expect is that whatever bits of my wavefunction survive, survive. Which is entirely tautological, and is equivalent to “if I survive, I survive” in a collapse-y interpretation.
Anthropomorphically forcing the world to have particular laws of physics by more effectively killing yourself if it doesn’t seems… counter-productive to maximizing how much you know about the world. I’m also not sure how you can avoid disproving MWI by simply going to sleep, if you’re going to accept that sort of evidence.
(Plus quantum suicide only has to keep you on the border of death. You can still end up as an eternally suffering almost-dying mentally broken husk of a being. In fact, those outcomes are probably far more likely than the ones where twenty guns misfire twenty times in a row.)
It’s quite a bit less likely, but if quantum immortality changes the past (when you’re on the border of life and death, it’s clear the gun didn’t misfire), then it would just keep you from running the experiment in the first place.