Quantum immortality as you describe it is not a consequence of MWI. It’s not true that every single change in an MWI universe is accompanied by branching. Branching occurs when microscopic quantum superpositions decohere, i.e. when interactions magnify microscopic superpositions into macroscopic superpositions. So branching is the consequence of a particular type of physical process: the “measurement” of a microscopic superposition by its macroscopic environment. Not all physical processes are of this type, and its not at all obvious to me that the sorts of processes usually involved in our deaths are of this sort. When someone gets run over by a bus, for example, what we’re dealing with is an already decohered macroscopic system (the bus) interacting with another decohered macroscopic system (the unfortunate victim). We’re not dealing with a microscopic superposition getting kicked up to the macroscopic scale. Now it may be the case that the actual processes that go on in the victim’s brain after the accident and determine whether she dies or not are “measurement”-type processes, but I’d need to hear an argument that this is usually the case.
Even if one’s death can be directly attributed to a measurement-type event, quantum immortality doesn’t follow. Say a person gets cancer from a single radiation event (not sure if this is possible, but I’m postulating that it is), and subsequently dies from this cancer. The radiation event is a microscopic quantum process, and his body acts as a macroscopic detector. In this case, one would get branching. One one branch he would get cancer and eventually die from it. On the other he wouldn’t get it. But even on the branch in which he dies, death is not instantaneous. He experiences both branches, not just the one in which he lives longer. So this is not a quantum immortality type situation.
One might be able to set up an artificial situation in which quantum immortality is real, but it would have to be a very carefully constructed scenario, one in which the moment of death coincides with the moment of decoherence (of course, neither of these are literal moments). I don’t think the circumstances under which most of us die are of this sort.
Okay, this is the kind of argument that, if true and correct, would actually convince me that quantum torment is not real.
My extremely limited, incomplete, and non-mathy understanding of QM makes me suspicious of your explanation because it talks about things like macroscopic measurements affecting the fundamental level of reality, and about fundamental events only happening sometimes in special circumstances.
But since my understanding is so incomplete, I don’t actually trust it. I’ll have to rely on other people who understand QM, or give Eliezer’s sequence and my physics books another shot! Since this has become such an important topic to me, I don’t think I have a choice anymore, anyway.
My extremely limited, incomplete, and non-mathy understanding of QM makes me suspicious of your explanation because it talks about things like macroscopic measurements affecting the fundamental level of reality, and about fundamental events only happening sometimes in special circumstances.
World-splitting in MWI is not a fundamental event. “Worlds” themselves aren’t fundamental objects in the theory. They are imprecisely defined macroscopic entities that emerge from decoherence. So nothing I say involves macroscopic processes affecting the fundamental level of reality.
ETA: Perhaps you’re thrown off by my use of the word “measurement” because it suggests something vaguely Copenhagish. All I mean by a measurement-type interaction is an interaction between the system and its environment that leads to einselection.
Hmmm… this post has received at least three downvotes at this point. I’m pretty confident that everything I’ve said here about the MWI is correct, but if someone thinks it isn’t, I’m very interested to hear why. So if the downvoting is attributable to perceived factual inaccuracy, could you let me know what you think the inaccuracy is? Thanks.
So branching is the consequence of a particular type of physical process: the “measurement” of a microscopic superposition by its macroscopic environment. Not all physical processes are of this type, and its not at all obvious to me that the sorts of processes usually involved in our deaths are of this sort.
I think that essentially all processes involving macroscopic objects are of this type. My understanding is that the wave function of a macroscopic system at nonzero temperature is constantly fissioning into vastly huge numbers of decoherent sub-regions, i.e., “worlds.” These worlds start out similar to each other, but we should expect differences to amplify over time. And, of course, each new world immediately begins fissioning into vast numbers of “sub-worlds.”
So, while in one world you might get run over by a bus, there is e.g. another world that separated from that one a year ago in which the bus is late and you survive. Plus huge numbers of other possibilities.
In this vast profusion of different worlds, for any given death there’s essentially always another branch in which that death was averted.
Most of his premises are approximately correct but applied incorrectly to reach an incorrect conclusion (that is the first sentence). It could be restored by injecting caveats like “for all practical purposes” and “virtually” here but the thing is the whole “Immortality” notion is already ridiculously impractical to begin with. Quantum tunneling through the bus and leaving your arm behind is only a few gagillion orders of magnitude more unlikely than winning Quantum Roulette ten times a day every day for 1,000 years. It is stupid to consider those improbable outcomes as privileged but not wrong.
Quantum immortality as you describe it is not a consequence of MWI. It’s not true that every single change in an MWI universe is accompanied by branching. Branching occurs when microscopic quantum superpositions decohere, i.e. when interactions magnify microscopic superpositions into macroscopic superpositions. So branching is the consequence of a particular type of physical process: the “measurement” of a microscopic superposition by its macroscopic environment. Not all physical processes are of this type, and its not at all obvious to me that the sorts of processes usually involved in our deaths are of this sort. When someone gets run over by a bus, for example, what we’re dealing with is an already decohered macroscopic system (the bus) interacting with another decohered macroscopic system (the unfortunate victim). We’re not dealing with a microscopic superposition getting kicked up to the macroscopic scale. Now it may be the case that the actual processes that go on in the victim’s brain after the accident and determine whether she dies or not are “measurement”-type processes, but I’d need to hear an argument that this is usually the case.
Even if one’s death can be directly attributed to a measurement-type event, quantum immortality doesn’t follow. Say a person gets cancer from a single radiation event (not sure if this is possible, but I’m postulating that it is), and subsequently dies from this cancer. The radiation event is a microscopic quantum process, and his body acts as a macroscopic detector. In this case, one would get branching. One one branch he would get cancer and eventually die from it. On the other he wouldn’t get it. But even on the branch in which he dies, death is not instantaneous. He experiences both branches, not just the one in which he lives longer. So this is not a quantum immortality type situation.
One might be able to set up an artificial situation in which quantum immortality is real, but it would have to be a very carefully constructed scenario, one in which the moment of death coincides with the moment of decoherence (of course, neither of these are literal moments). I don’t think the circumstances under which most of us die are of this sort.
Okay, this is the kind of argument that, if true and correct, would actually convince me that quantum torment is not real.
My extremely limited, incomplete, and non-mathy understanding of QM makes me suspicious of your explanation because it talks about things like macroscopic measurements affecting the fundamental level of reality, and about fundamental events only happening sometimes in special circumstances.
But since my understanding is so incomplete, I don’t actually trust it. I’ll have to rely on other people who understand QM, or give Eliezer’s sequence and my physics books another shot! Since this has become such an important topic to me, I don’t think I have a choice anymore, anyway.
Thanks for the reply.
World-splitting in MWI is not a fundamental event. “Worlds” themselves aren’t fundamental objects in the theory. They are imprecisely defined macroscopic entities that emerge from decoherence. So nothing I say involves macroscopic processes affecting the fundamental level of reality.
ETA: Perhaps you’re thrown off by my use of the word “measurement” because it suggests something vaguely Copenhagish. All I mean by a measurement-type interaction is an interaction between the system and its environment that leads to einselection.
Hmmm… this post has received at least three downvotes at this point. I’m pretty confident that everything I’ve said here about the MWI is correct, but if someone thinks it isn’t, I’m very interested to hear why. So if the downvoting is attributable to perceived factual inaccuracy, could you let me know what you think the inaccuracy is? Thanks.
I have an objection to this:
I think that essentially all processes involving macroscopic objects are of this type. My understanding is that the wave function of a macroscopic system at nonzero temperature is constantly fissioning into vastly huge numbers of decoherent sub-regions, i.e., “worlds.” These worlds start out similar to each other, but we should expect differences to amplify over time. And, of course, each new world immediately begins fissioning into vast numbers of “sub-worlds.”
So, while in one world you might get run over by a bus, there is e.g. another world that separated from that one a year ago in which the bus is late and you survive. Plus huge numbers of other possibilities.
In this vast profusion of different worlds, for any given death there’s essentially always another branch in which that death was averted.
And then there’s the branch with extremely small amplitude that separated 30 seconds ago where the bus explodes form proton decay.
I don’t think you have any factual inaccuracies.
Most of his premises are approximately correct but applied incorrectly to reach an incorrect conclusion (that is the first sentence). It could be restored by injecting caveats like “for all practical purposes” and “virtually” here but the thing is the whole “Immortality” notion is already ridiculously impractical to begin with. Quantum tunneling through the bus and leaving your arm behind is only a few gagillion orders of magnitude more unlikely than winning Quantum Roulette ten times a day every day for 1,000 years. It is stupid to consider those improbable outcomes as privileged but not wrong.