Comment author:gjm
14 June 2013 02:46:39PM
1 point
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I think you should analyse further. Expecting conditional on still being alive? Surely you expect that even without "quantum immortality". Expecting to find yourself still alive, and experience that? Again, what exactly do you mean by that? What does it mean to expect to find yourself still alive? (Presumably not that others will expect to find you still alive in any useful sense, because with that definition you don't get q.i.)

I expect there are Everett branches in which you live to 120 as a result of a lot of good luck (or, depending on what state you're in, bad luck). Almost equivalently, I expect there's a small but nonzero probability that you live to 120 as a result of a lot of luck. { If you live to 120 / In those branches where you live to 120 } you will probably have experienced a lot of surprising things that enabled your survival. None of this is in any way dependent on quantum mechanics, still less on the many-worlds interpretation.

It seems to me that "believing in quantum immortality" is a matter of one's own values and interpretive choices, much more than of any actual beliefs about how the world is. But I may be missing something.

Comment author:khafra
14 June 2013 03:34:42PM
0 points
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I should perhaps be more clear that I'm not distinguishing between "MWI and functionalism are true" and "quantum immortality works." That is, if "I" consciously experience dying, and my consciouness ceases, but "I" go on experiencing things in other everett branches, I'm counting that as QI.

Expecting conditional on still being alive? Surely you expect that even without "quantum immortality"...What does it mean to expect to find yourself still alive?

I'm currently making observations consistent with my own existence. If I stop making that kind of observation, I consider that no longer being alive.

Going again with the example of a 35 year old: Conditional on having been born, I have a 96% chance of still being alive. So whatever my prior on QI, that's far less than a decibel of evidence in favor of it. Still, ceteris paribus, it's more likely than it was at age 5.

Comment author:gjm
15 June 2013 02:36:31PM
0 points
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Sure. But I'm not sure I made the point I was trying to make as clearly as I hoped, so I'll try again.

Imagine two possible worlds. In one of them, QM works basically as currently believed, and the way it does this is exactly as described by MWI. In the other, there is at every time a single kinda-classical-ish state of the world, with Copenhagen-style collapses or something happening as required.

In either universe it is possible that you will find yourself still alive at 120 (or much more) despite having had plenty of opportunities to be killed off by accident, illness, etc. In either universe, the probability of this is very low (which in the former case means most of the measure of where we are now ends up with you dead earlier, and in the latter means whatever exactly probability means in a non-MWI world). In either universe, every observation you make will show yourself alive, however improbable that may seem.

How does observing yourself still alive at 150 count as evidence for MWI, given all that?

What you mustn't say (so it seems to me): "The probability of finding myself alive is very low on collapse theories and high on MWI, so seeing myself still alive at 150 is evidence for MWI over collapse theories". If you mean the probability conditional on you making the observation at age 150, it's 1 in both cases. If you mean the probability not conditional on that, it's tiny in both cases. (Assuming arguendo that Pr(nanotech etc. makes lots of people live to be very old by then) is negligible.) The same applies if you try to go halfway and take the probability simply conditional on you making the observation: MWI or no MWI, only a tiny fraction of observations you make will be at age 150.

Comment author:khafra
17 June 2013 07:03:57PM
0 points
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In either universe it is possible that you will find yourself still alive at 120

In the MWI-universe, it is probable at near unity that I will find myself still alive at 120. In the objective collapse universe, there's only a small fraction of a percent chance that I'll find myself alive at 120. In the objective collapse universe, every observation I make will show myself alive--but there's only a fraction of a percent of a chance that I'll make an observation that shows my age as 120.

If you mean the probability conditional on you making the observation at age 150, it's 1 in both cases.

The probability of my making the observation "I am 150 years old," given objective collapse, is one of those probabilities so small it's dominated by "stark raving mad" type scenarios. Nobody you've ever known has made that observation; neither has anybody they know. How can this not be evidence?

Comment author:gjm
17 June 2013 08:34:53PM
0 points
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What's the observation you're going to make that has probability near-1 on MWI and probabilty near-0 on collapse -- and probability given what?

"I'm alive at 120, here and now" -- that has small probability either way. (On most branches of the wavefunction that include your present self, no version of you gets to say that. Ignoring, as usual, irrelevant details involving positive singularities, very large universes, etc.)

"90 years from now I'll still be alive" (supposing arguendo that you're 30 now) -- that has small probability either way.

"I'm alive at 120, conditional on my still being alive at 120" -- that obviously has probability 1 either way.

"On some branch of the wavefunction I'm still alive at 120" -- sure, that's true on MWI and (more or less by definition) false on a collapse interpretation; but it's not something you can observe. It corresponds exactly to "With nonzero probability I'm still alive at 120", which is true on collapse.

Comment author:khafra
18 June 2013 12:50:33PM
0 points
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"90 years from now I'll still be alive" (supposing arguendo that you're 30 now) -- that has small probability either way.

This is the closest one. However, that's not an observation, it's a prediction. The observation is "90 years ago, I was 30." That's an observation that almost certainly won't be made in a collapse-based world; but will be made somewhere in an MWI world.

"I'm alive at 120, here and now" -- that has small probability either way. (On most branches of the wavefunction that include your present self, no version of you gets to say that.)

"small probability either way" only applies if I want to locate myself precisely, within a branch as well as within a possible world. If I only care about locating myself in one possible world or the other, the observation has a large probability in MWI.

Comment author:wedrifid
14 June 2013 03:08:08PM
0 points
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It seems to me that "believing in quantum immortality" is a matter of one's own values and interpretive choices, much more than of any actual beliefs about how the world is.

## Comments (174)

BestI think you should analyse further. Expecting

conditional on still being alive? Surely you expect that even without "quantum immortality". Expectingto find yourself still alive, and experience that? Again, what exactly do you mean by that? What does it mean to expect to find yourself still alive? (Presumably not that others will expect to find you still alive in any useful sense, because with that definition you don't get q.i.)I expect there are Everett branches in which you live to 120 as a result of a lot of good luck (or, depending on what state you're in, bad luck). Almost equivalently, I expect there's a small but nonzero probability that you live to 120 as a result of a lot of luck. { If you live to 120 / In those branches where you live to 120 } you will probably have experienced a lot of surprising things that enabled your survival. None of this is in any way dependent on quantum mechanics, still less on the many-worlds interpretation.

It seems to me that "believing in quantum immortality" is a matter of one's own values and interpretive choices, much more than of any actual

beliefs about how the world is. But I may be missing something.I should perhaps be more clear that I'm not distinguishing between "MWI and functionalism are true" and "quantum immortality works." That is, if "I" consciously experience dying, and my consciouness ceases, but "I" go on experiencing things in other everett branches, I'm counting that as QI.

I'm currently making observations consistent with my own existence. If I stop making that kind of observation, I consider that no longer being alive.

Going again with the example of a 35 year old: Conditional on having been born, I have a 96% chance of still being alive. So whatever my prior on QI, that's far less than a decibel of evidence in favor of it. Still, ceteris paribus, it's more likely than it was at age 5.

Sure. But I'm not sure I made the point I was trying to make as clearly as I hoped, so I'll try again.

Imagine two possible worlds. In one of them, QM works basically as currently believed, and the way it does this is exactly as described by MWI. In the other, there is at every time a single kinda-classical-ish state of the world, with Copenhagen-style collapses or something happening as required.

In either universe it is possible that you will find yourself still alive at 120 (or much more) despite having had plenty of opportunities to be killed off by accident, illness, etc. In either universe, the probability of this is very low (which in the former case means most of the measure of where we are now ends up with you dead earlier, and in the latter means whatever exactly probability means in a non-MWI world). In either universe, every observation

youmake will show yourself alive, however improbable that may seem.How does observing yourself still alive at 150 count as evidence for MWI, given all that?

What you mustn't say(so it seems to me): "The probability of finding myself alive is very low on collapse theories and high on MWI, so seeing myself still alive at 150 is evidence for MWI over collapse theories". If you mean the probability conditional on you making the observation at age 150, it's 1 in both cases. If you mean the probability not conditional on that, it's tiny in both cases. (Assuming arguendo that Pr(nanotech etc. makes lots of people live to be very old by then) is negligible.) The same applies if you try to go halfway and take the probability simply conditional on you making the observation: MWI or no MWI, only a tiny fraction of observations you make will be at age 150.In the MWI-universe, it is probable at near unity that I will find myself still alive at 120. In the objective collapse universe, there's only a small fraction of a percent chance that I'll find myself alive at 120. In the objective collapse universe, every observation I make will show myself alive--but there's only a fraction of a percent of a chance that I'll make an observation that shows my age as 120.

The probability of my making the observation "I am 150 years old," given objective collapse, is one of those probabilities so small it's dominated by "stark raving mad" type scenarios. Nobody you've ever known has made that observation; neither has anybody they know. How can this not be evidence?

What's the observation you're going to make that has probability near-1 on MWI and probabilty near-0 on collapse -- and probability given what?

"I'm alive at 120, here and now" -- that has small probability either way. (On most branches of the wavefunction that include your present self, no version of you gets to say that. Ignoring, as usual, irrelevant details involving positive singularities, very large universes, etc.)

"90 years from now I'll still be alive" (supposing arguendo that you're 30 now) -- that has small probability either way.

"I'm alive at 120, conditional on my still being alive at 120" -- that obviously has probability 1 either way.

"On some branch of the wavefunction I'm still alive at 120" -- sure, that's true on MWI and (more or less by definition) false on a collapse interpretation; but it's not something you can observe. It corresponds exactly to "With nonzero probability I'm still alive at 120", which is true on collapse.

This is the closest one. However, that's not an observation, it's a prediction. The observation is "90 years ago, I was 30." That's an observation that almost certainly won't be made in a collapse-based world; but will be made

somewherein an MWI world."small probability either way" only applies if I want to locate myself precisely, within a branch as well as within a possible world. If I only care about locating myself in one possible world or the other, the observation has a large probability in MWI.

You are correct.