Exploring Quantum Theory: Schrödinger's Cat & the Many-Worlds Interpretation

[NetMage]

Hi I was wondering if someone could better explain this. I do not quite understand the implications. Thanks for any input.


"Unlike the Schrödinger's cat thought experiment which used poison gas and a radioactive decay trigger, this version involves a lethal weapon and a device that measures the spin value of photons. Every 10 seconds, the spin value of a fresh photon is measured. Conditioned upon that quantum bit, the weapon is either deployed, killing the experimenter, or it makes an audible "click" and the experimenter survives.

The theories are distinctive from the point of view of the experimenter only; their predictions are otherwise identical.

The probability of surviving the first iteration of the experiment is 50%, under both interpretations, as given by the squared norm of the wavefunction. At the start of the second iteration, if the Copenhagen interpretation is true, the wavefunction has already collapsed, so if the experimenter is already dead, there's a 0% chance of survival. However, if the many-worlds interpretation is true, a superposition of the live experimenter necessarily exists, regardless of how many iterations or how improbable the outcome. Barring life after death, it's not possible for the experimenter to experience having been killed, thus the only possible experience is one of having survived every iteration."

 

[Joseph14]

Hi I was wondering if someone could better explain this. I do not quite understand the implications. Thanks for any input.


"Unlike the Schrödinger's cat thought experiment which used poison gas and a radioactive decay trigger, this version involves a lethal weapon and a device that measures the spin value of photons. Every 10 seconds, the spin value of a fresh photon is measured. Conditioned upon that quantum bit, the weapon is either deployed, killing the experimenter, or it makes an audible "click" and the experimenter survives.

The theories are distinctive from the point of view of the experimenter only; their predictions are otherwise identical.

The probability of surviving the first iteration of the experiment is 50%, under both interpretations, as given by the squared norm of the wavefunction. At the start of the second iteration, if the Copenhagen interpretation is true, the wavefunction has already collapsed, so if the experimenter is already dead, there's a 0% chance of survival. However, if the many-worlds interpretation is true, a superposition of the live experimenter necessarily exists, regardless of how many iterations or how improbable the outcome. Barring life after death, it's not possible for the experimenter to experience having been killed, thus the only possible experience is one of having survived every iteration."

If that is right then it doesn't mean you wouldn't be shot, rather you would be shot and then remain at the edge of death in extreme pain forever, with completely unlikely things keeping you alive. Not a pretty theory.

 

[NetMage]

Well, I'm more asking about the last paragraph. I do not understand why " if the Copenhagen interpretation is true, the wavefunction has already collapsed, so if the experimenter is already dead, there's a 0% chance of survival. However, if the many-worlds interpretation is true, a superposition of the live experimenter necessarily exists, regardless of how many iterations or how improbable the outcome. Barring life after death, it's not possible for the experimenter to experience having been killed, thus the only possible experience is one of having survived every iteration."

is true.

 

[JesseM]

Quantum suicide doesn't really follow from the MWI alone, it also requires some assumptions about consciousness and personal identity (though these assumptions may seem more 'natural' if MWI is true). For example, leaving aside the MWI, if I step into a Star Trek style teleporter that takes aparts all my atoms in one spot and rebuilds the exact same pattern of atoms in another, would you say that the person who steps out at the other end is the "same person" as the one whose atoms were taken apart, or just a "copy" with false memories, with the "original" having died? Physics can't give you an answer to this sort of question, if there even is any "true" answer. But if you accept in this sort of example that your consciousness can jump along with the pattern of your body, and that your consciousness could even "split" if the teleporter created multiple versions of the same pattern of atoms, then in that case the idea of quantum immortality seems pretty natural (I can give more detail on why 'belief that your stream of consciousness can split in two when you are copied' seems to imply quantum immortality if you want)

 

[Pio2001]

it's not possible for the experimenter to experience having been killed, thus the only possible experience is one of having survived every iteration."

I don't see much difference with the simple statement that when you are dead, you can't realize it, so it doesn't matter to kill yourself right now.

 

[cavalier3024]

Well, I'm more asking about the last paragraph. I do not understand why " if the Copenhagen interpretation is true, the wavefunction has already collapsed, so if the experimenter is already dead, there's a 0% chance of survival. However, if the many-worlds interpretation is true, a superposition of the live experimenter necessarily exists, regardless of how many iterations or how improbable the outcome. Barring life after death, it's not possible for the experimenter to experience having been killed, thus the only possible experience is one of having survived every iteration."

is true.

This is really more of a philosophical question..
But i think that what they meant is this: according to copenhagen interpretation, the wavefunction will collapse to either state at a 50% chance, so the person may or may not die. But according to the many worlds interpretation the wavefunction will collapse to both states, each at a different 'world', and the person will both die and not die, depending on which 'world' you are looking at.
now if an outside observer was looking at the experiment he would see this person die at a 50% chance (since he have equal chance to be at each 'world'). but if we are looking at it from the person's point of view then he can not experience the 'worlds' in which he died, so he will continue to experience those worlds in which he exists, as long as there is at least one copy of him still alive.

the problem with this experiment is that even if the many worlds interpretation is true and the experiment works it doesn't really prove anything.
lets say that after 100 iterations the person is still alive. according to copenhagen interpretation the chances for that are 1/2^100. according to many-worlds interpretation there will now be 2^100 worlds, and again, the chances that we are currently existing at the one world where this person didn't die are 1/2^100 as well.
in other words we can not know if he is very lucky to be alive, or if we are very lucky to be exactly on the world where he is alive.

I don't see much difference with the simple statement that when you are dead, you can't realize it, so it doesn't matter to kill yourself right now.

it is kinda different. its like saying: suppose there are many copies of you that keep multiplying all the times, does it matter if one dies?

 

[Phrak]

Long before these quantum suicide posts started showing up--before PCs, and long before Al Gore was "instrumental in bringing about the internet", I thought it would be a very bad idea to discuss this with anyone, and did not. I still think its a bad idea to spread around among a general population, with plenty of life's problems, about a theory that can't even get expectation values correct with a hefty burden of metaphysical baggage.

 

[Joseph14]

I don't see much difference with the simple statement that when you are dead, you can't realize it, so it doesn't matter to kill yourself right now.

Good point.

Also, if being alive is defined as observing, then I don't see how quantum suicide ruled out death as a possibility. If you don't observe anything it means you are dead.

 

[Joseph14]

Long before these quantum suicide posts started showing up--before PCs, and long before Al Gore was "instrumental in bringing about the internet", I thought it would be a very bad idea to discuss this with anyone, and did not. I still think its a bad idea to spread around among a general population, with plenty of life's problems, about a theory that can't even get expectation values correct with a hefty burden of metaphysical baggage.

This is a very good point. As quantum immortality has little merit to understanding quantum mechanics, I don't think it should be discussed here for the sake of people who have been confronted with the reality of suicide in a real life rather then just hand off philosophical bantering.