Quantum Immortality Explained: Proving Life After Death?

[hadeka]

Hi all

Quantum Immortality: http://en.wikipedia.org/wiki/Quantum_immortality

I could not understand it ... does it prove life after death ?!

 

[DaveC426913]

It is merely a thought experiment which explores the implications of the MWI of QM. It proves nothing; it is merely conjecture.

In a nutshell: If the Many-Worlds Interpretation is the correct** interpretation of QM, then it could be argued that this implies immortality of a sort. If all possibilities of a life-of-lethal-experiences create their own universe, then there must be at least one universe in which the experimenters survived every near-death experience, therefore is, in a sense, immortal somehwere out there in the multiverse.

**BTW, it can't be proven or disproven, so it is philosophy, not science.

 

[Fredrik]

It certainly doesn't prove life after death.

If you try to kill yourself, there's always some probability (very tiny, but still >0) that you will fail. In quantum mechanical terms, the wavefunction of the universe (a concept that only makes sense in the many-worlds interpretation) will evolve into a state that's a superposition of you being dead and you being alive. In the many-worlds interpretation, the wave function doesn't "collapse" into one of those two options, and since the theory doesn't suggest that one of the options is more "real" than the other, the natural conclusion would be that they're both real.

Now the idea is that from your own point of view, 100% of the times when you ask yourself "am I still alive", you are alive. And some people claim that this means that from your point of view you will always fail.

This sounds like complete BS to me. In fact it's a bit too obvious that it is. It makes me suspect that I have misunderstood something.

Edit: What I said in the first long paragraph is a valid point about the MWI. I don't think that part is BS. The MWI does imply that some version of you will always continue to exist after a suicide attempt. This version of you won't notice anything different about the world around him. He will just think that the gun jammed or whatever. The part I think is BS is that stuff about "your point of view", but maybe that wasn't part of the original argument. It could be a misinterpretation that was introduced later (possibly by Tegmark).

 

[xantox]

This sounds like complete BS to me. In fact it's a bit too obvious that it is. It makes me suspect that I have misunderstood something.

Which is the exact problem you have with this part?

 

[Fredrik]

Which is the exact problem you have with this part?

Consider e.g. the statement "From Bob's point of view, there's a 100% probability that he will fail". Suppose that he goes out in the desert and kills himself by shooting himself in the gut. It will take a few days to die, but he doesn't care since according to the argument there's a 100% probability that the gun will fail.

That sounds intuitively insane, but that may not be the best counterargument. I'll try to do better. The argument isn't completely crazy, but it seems to me that the words "Bob" and "he" are references to different things. "Bob" is clearly a reference to the guy who's still alive after the suicide attempt. So Bob is a physical system that doesn't include a rotting corpse. That's why it's not the same physical system that tried to kill itself. I'll try to make that more clear.

Think of Bob's initial state as a subsystem of the universe, isolated from the rest. The "rest" includes the gun. When he tries to kill himself, he interacts with the rest of the universe. The initial state of the universe is |Bob alive>|gun loaded> and it evolves into |Bob still alive>|gun jammed>+|Bob dead>|gun discharged>.

The whole point of the MWI is the logical consequence of the fact that the final superposition represents the same physical system as the initial state: We know that one of the terms represents reality, but since there's no indication whatsoever in the theory that one of the terms is of a different kind than the other, we are forced to conclude that the theory's prediction is that there are two realities.

Recall that the word "he" refers to the physical system that tried to kill itself. According to the above, that system now consists of a guy who's still around to ask questions and a rotting corpse. So "he" doesn't refer to the same thing as "Bob".

(The reason I colored the word Bob red everywhere except in the third paragraph is that in the third, it refers to the complete physical system, not just to the survivor. All the red Bob's above are references to the survivor only. The blue Bob in the third paragraph is a reference to the corpse only).

 

[xantox]

So Bob is a physical system that doesn't include a rotting corpse. That's why it's not the same physical system that tried to kill itself. [..] Recall that the word "he" refers to the physical system that tried to kill itself.

I agree on the first two statements, but disagree on the last, ie. we should not equate "he" to some particular physical system / body before the experiment, but rather to some abstract property of it and its motion which corresponds to "being Bob". That is why the argument can work subjectively and why it can be said that "he" is Bob.

The desert example seem also not applicable, as the "dying Bob" state should not be allowed in the superposition, eg. the triggered device should rather annihilate the body, on a shorter timescale than the consciousness response time.

We had a similar discussion with vanesch on this other thread, https://www.physicsforums.com/showthread.php?t=198794&page=2 (posts 26-31) and similarly I didn't find at the end any basis allowing for Bob to decide he is located in some particular body rather than another.

 

[Naty1]

I could not understand it ... does it prove life after death ?!

Nobody understands exactly what either life or death is either...Just because you "die" in this universe is no proof you have "disappeared" from an infinity of other universes, if they exist. And you are "made from the stars" and your atoms will eventually be returned there to be recycled yet again, so you disperse but are in a sense immortal...

Then there is the issue of the "soul" which may or may not be essential to life...and if it is how that gets "recycled"...if it does...

 

[vanesch]

The problem with this quantum immortality is that it makes an extra hypothesis which is a priori not necessary in MWI.

In MWI, you have to distinguish between the subjective "you" and the material body support (the physical degrees of freedom of the body material). In more classical approaches, we associate a single subjective you with a single material body, so there's no point in distinguishing between both. The association is between a subjective experience, and a number of material degrees of freedom (a set of particles, say). The (single) state of that set of particles determines the subjective experience that goes with it.

In MWI, with a single set of material degrees of freedom (a single set of particles) corresponds a single quantum state (its wavefunction) but which is split into many different states (each entangled with a different state of "the environment"), and it is postulated that to each of these different quantum states (parts of the overall state) corresponds (at least one) subjective experience. So this time, to the same set of physical degrees of freedom (to the same set of particles) correspond miriads of subjective experiences. However, "you" are just one of them, and the link between subjective experience and the material world is given by the MWI equivalent of the Born rule: the probability for "you" to experience a state |psi5> is given by the relative norm of |psi5> to the other states of the same material degrees of freedom in the overall quantum state.

But now, the question is, what happens upon time evolution ? Are "you" redistributed each time ab initio over all the different quantum states that correspond to the evolving overall state, or is there some "continuity" ? That is, do you incessantly experience from moment to moment, totally different worlds, or do you "stick to your world" ? I prefer to think you do, but that's just my personal choice. That means that upon each quantum splitting of YOUR branch, you go randomly into one of the emerging branches, with probabilities given by the Born rule for THIS branching. You never visit other, parallel branches again. But that's just my favorite. The "other" branch(es) that are split off are then assigned to "new" subjective experiences, but you just continue to trace out your path through the arborescence of branchings. And now you can see it how you want: if some branches cannot support any subjective experience anymore (your body state is dead), and "you" happen to "draw" it, then I could say that this terminates "your" subjective experience. You are dead now. In the next door branch, a "new" subjective experience is created, but it is not the original "you", and so you don't experience that, in the same way as you don't experience the "other" branch in a non-fatal splitting. If that's the "rule", then quantum immortality doesn't work. You are just dead, and in a parallel world, a copy of you survives.

However, you can modify the rule, and say that you only draw from the "surviving" branches. And then, quantum immortality works the way it is displayed.

In the case you don't like to keep "subjective continuity" but redraw each time from scratch, the same can be said: or you draw only from "living states", in which case quantum immortality happens of course. Or you draw from living and dead states, in which case you have also a chance to be dead. The strange thing is that the next moment, you might draw again a branch in which you live...

So quantum theory, even in the MWI interpretation, doesn't lead unavoidably to quantum immortality.

However, if it is the case, then this could be the basis of an "improbability drive" (from Douglas Adams fame...)

 

[xantox]

[..]That means that upon each quantum splitting of YOUR branch, you go randomly into one of the emerging branches, with probabilities given by the Born rule for THIS branching. [..] The "other" branch(es) that are split off are then assigned to "new" subjective experiences, but you just continue to trace out your path through the arborescence of branchings. [..] In the next door branch, a "new" subjective experience is created, but it is not the original "you" [..]

The problem is that it is not possible to localize one instance of "you" when there are many identical ones. So, upon each quantum splitting of YOUR branch, "you" don't go randomly into ONE of the emerging branches, but you go into MANY emerging branches. It's only upon subsequent branching that each instance will become slightly different. But after the initial branching which triggered the device, both "you" are the same entity.

For this reason, just before a branching, the "you" before the branching cannot consider that the "left path" will be any more or less valid than the "right path" in order to become "your path".

As a consequence, after the branching, and since we put a roadblock on the left path, the "you" who took the right path must both consider to have survived the experience and to be still on "his path".

 

[pallidin]

Hi all

Quantum Immortality: http://en.wikipedia.org/wiki/Quantum_immortality

I could not understand it ... does it prove life after death ?!

My understanding is that this is like a "catch-22"
Only the actual participant can experience the potential quantum immortality effect as opposed to anyone else or any external instrumentation to verify its occurrence.

Thus, though a 'thought experiment", it is intrinsically un-verifiable under those terms.
This leads me to question the value of that and similar types of "thought experiments"

 

[pallidin]

Having given this more thought, I wonder if there is a way to construct a MWI quantum immortality experiment that can be verifiable.

The concept of the "quantum eraser", for example, encourages me to think that exotic experimental techniques could be developed to explore brazen ideas. In this case, though, I'm not sure. It's a tough one.

 

[Fredrik]

I agree on the first two statements, but disagree on the last, ie. we should not equate "he" to some particular physical system / body before the experiment, but rather to some abstract property of it and its motion which corresponds to "being Bob". That is why the argument can work subjectively and why it can be said that "he" is Bob.

We seem to agree that the time evolution of the state of the universe around the time of the suicide attempt can be described as

|Bob alive>_X|gun loaded>_Y ---> |Bob still alive>_X|gun jammed>_Y + |Bob dead>_X|gun discharged>_Y

where X is a physical system that includes the original Bob, and Y is everything else, including the gun. Our disagreement seems to be that I'm saying that it's the physical system X that's trying to kill itself, while you're saying that it's a proper subset of the Hilbert space of possible states of X that tries to kill itself.

Explanation of that last part: "Being Bob" is a property of the physical interactions in his body. The interactions are described by his quantum state, which is represented by a vector in the Hilbert space H(X) of possible states of the system X. So to say that the system is "being Bob" is to say that the state vector belongs to a particular proper subset B of H(X).

I think it's pretty strange to think of Bob as a subset of states rather than as a physical system. If we do, we're introducing the problem of what other subsets might be relevant. Do we e.g. have to define a subset B' of B that consist of states that represent a guy that's "alive and not dying"? Then how do we define "not dying"?

If this is what the quantum suicide argument is about, I think they should have made that clear from the start. (Maybe they did. I've only read one article about it, and I don't remember the details).

The desert example seem also not applicable, as the "dying Bob" state should not be allowed in the superposition, eg. the triggered device should rather annihilate the body, on a shorter timescale than the consciousness response time.

I disagree about the need for the whole thing to be over quickly. The only reason I can think of to treat the suicide attempt as effectively instantaneous would be to hide some of the issues, in particular the need to consider proper subsets of B.

It's obviously impossible to make the interaction instantaneous. It is however possible to make its duration so short that there's no time for any real thoughts, but that doesn't change anything important unless we really believe that there's something fundamentally different about a physical system that's conscious. What about someone who's asleep, in a coma, or clinically dead during brain surgery?

I was wrong to say that quantum immortality claims that the dying Bob is right to say that there was a 100% chance that he would fail. I'm not sure what the immortality argument really says though.

Just as a reference, if this discussion continues, this is how I'd like to express the time evolution of the state of the universe when we let it take a while:

|Bob alive>_X|gun loaded>_Y ---> |Bob not dying>_X|gun jammed>_Y + |Bob dying>_X|gun discharged>_Y

---> |Bob still alive>_X|gun jammed>_Y + |Bob dead>_X|gun discharged>_Y

 

[xantox]

I think it's pretty strange to think of Bob as a subset of states rather than as a physical system. If we do, we're introducing the problem of what other subsets might be relevant. Do we e.g. have to define a subset B' of B that consist of states that represent a guy that's "alive and not dying"? Then how do we define "not dying"?

I would certainly not include my hair in the description of myself, especially since I tend to lose many of them. But also in my brain, there must be a majority of degrees of freedom not bearing the "being myself". While we do not have the necessary knowledge to identify them, there is certainly such a subset. "Not dying" can be defined for the needs of the thought experiment in a larger way as simply not disrupting the whole body eg by nuclear fission.

I disagree about the need for the whole thing to be over quickly. The only reason I can think of to treat the suicide attempt as effectively instantaneous would be to hide some of the issues, in particular the need to consider proper subsets of B.

The basic reason for the quick timing is making sure that no instance of the experimenter will experience the forbidden branch, or that will ruin the whole experiment. The probability that Bob can observe that branch must be zero. This includes not hearing a bang, or not suffering for a few seconds. If the timing is quick, as you said no conscious experience can develop, then ensuring that the "myself" system can't experience his own presence in the forbidden branch. Possibly there are other problems in cutting the brain evolution at any random time, but one supposes they can be solved so that the end of the "myself" evolution in the forbidden branch can be perfectly plugged in the evolution of the other branch without any discontinuity. Indeed performing the experiment while sleeping could be an additional measure, though the experimenter could prefer to be conscious to make sure the device is operated correctly.

 

[Fredrik]

I would certainly not include my hair in the description of myself, especially since I tend to lose many of them. But also in my brain, there must be a majority of degrees of freedom not bearing the "being myself". While we do not have the necessary knowledge to identify them, there is certainly such a subset.

That's actually not the kind of subset I'm talking about. I'm not talking about splitting the Hilbert space into subspaces that represent different degrees of freedom, so I am including the hair or whatever in the system X. I'm talking about a subset B of vectors in H(X) that represent versions of Bob that we would consider conscious. Note that for every vector in B that e.g. has the spin of some electron in your foot pointing up, there's another one with that spin pointing down.

Now correct me if you think I'm wrong, but I think that's the sort of subset of H(X) that would represent the "being Bob" property of the system X.

The basic reason for the quick timing is making sure that no instance of the experimenter will experience the forbidden branch, or that will ruin the whole experiment. The probability that Bob can observe that branch must be zero.

But why? Why not just wait until sufficient time has passed, so that we know that the system is described by the last superposition in #12.

This includes not hearing a bang, or not suffering for a few seconds. If the timing is quick, as you said no conscious experience can develop, then ensuring that the "myself" system can't experience his own presence in the forbidden branch.

I really don't see why a "conscious" physical system should be treated differently than one that's not.

 

[Fredrik]

The problem with this quantum immortality is that it makes an extra hypothesis which is a priori not necessary in MWI.

You didn't make it really clear what the extra hypothesis is. Can you express it as a sentence?

 

[vanesch]

You didn't make it really clear what the extra hypothesis is. Can you express it as a sentence?

That the "choices" of a subjective experience are limited to the "living" branches and cannot end up in a "dead" branch.

It makes the difference between: "I got a twin, but he died" and "I got a twin, but I died".

What quantum immortality actually needs, is: "I got a twin, and upon the death of my body, I became my twin".

 

[vanesch]

The problem is that it is not possible to localize one instance of "you" when there are many identical ones. So, upon each quantum splitting of YOUR branch, "you" don't go randomly into ONE of the emerging branches, but you go into MANY emerging branches. It's only upon subsequent branching that each instance will become slightly different. But after the initial branching which triggered the device, both "you" are the same entity.

For this reason, just before a branching, the "you" before the branching cannot consider that the "left path" will be any more or less valid than the "right path" in order to become "your path".

Observationally, you're right. But imagine that there is a perfect twin of you, somewhere in a perfect copy of your environment. That's a very similar situation, and your argument would also apply: there's no distinguishing between that twin of yours, and yourself. Hey, maybe there IS such a place right now. Imagine that the next split second, that twin is killed. You're not. You're not even aware of that. Now, imagine again that the next split second, YOU are killed. Do you really think that "you" still live on as your twin ?

As a consequence, after the branching, and since we put a roadblock on the left path, the "you" who took the right path must both consider to have survived the experience and to be still on "his path".

Yes, but the hypothesis here is that your subjective experience can jump from the left to the right. That's the extra hypothesis.

 

[xantox]

I'm talking about a subset B of vectors in H(X) that represent versions of Bob that we would consider conscious.

OK then, indeed such a subset is relevant. And the experiment simply consists in isolating those "versions" out of the deadly branches, by making sure there is no version experiencing an intermediate event such as "I'm about to die", as if it was the case, it cannot be established that the experiment worked. The experiment must work as follows: if the nuclear weapon is not armed, then the experimenter must observe 50% "white shot" triggers. If the nuclear weapon is armed, then the experimenter must observe 100% no-triggers.

I really don't see why a "conscious" physical system should be treated differently than one that's not.

It should be not. But it must be stressed that the conscious system is NOT the complete physical system out there, it is just a name for an abstract property, more or less like "A" is a name for some pattern of photons reaching the eye, no matter their spins or wavelenghts, and no matter it was drawn with ink, LCD pixels, or stars, so that you may have in principle very different systems sharing that exact same property of interest.

 

[xantox]

What quantum immortality actually needs, is: "I got a twin, and upon the death of my body, I became my twin".

I agree that it needs this extra bit, which must be the result of a theory of mind. But in my view, an extremely abstract theory of mind (eg an extremely basic assumption, simply considering the mind a property of the body), is sufficient in this regard to also imply the truth of your statement.

Observationally, you're right. But imagine that there is a perfect twin of you, somewhere in a perfect copy of your environment. That's a very similar situation, and your argument would also apply: there's no distinguishing between that twin of yours, and yourself. Hey, maybe there IS such a place right now. Imagine that the next split second, that twin is killed. You're not. You're not even aware of that. Now, imagine again that the next split second, YOU are killed. Do you really think that "you" still live on as your twin ?

Yes, absolutely, since there is no way to label the first case as being different from the second. If you cannot distinguish between your twin and yourself, there is no meaning at all in using two nouns. The two cases you present are a single one, as "you" are both, there is no "you" and "a twin". So, who is killed has absolutely no importance and makes no difference at all.

 

[Fredrik]

That the "choices" of a subjective experience are limited to the "living" branches and cannot end up in a "dead" branch.

If we have to add this as an extra postulate of quantum mechanics to get the quantum immortality argument to hold, then the argument isn't worth much in my opinion.

 

[xantox]

If we have to add this as an extra postulate of quantum mechanics to get the quantum immortality argument to hold, then the argument isn't worth much in my opinion.

It's rather a postulate of a theory of mind (since we're arguing about the fate of minds). However it's a very simple postulate, just making sure we consider the mind a property of a physical system and not some super-natural entity.

 

[vanesch]

Yes, absolutely, since there is no way to label the first case as being different from the second. If you cannot distinguish between your twin and yourself, there is no meaning at all in using two nouns. "You" are both, there is no "you" and "twin". So, who is killed has absolutely no importance and makes no difference at all.

I'd prefer by far that it is my twin that is killed, you know ...

But that's because I'm a dualist.

 

[xantox]

I'd prefer by far that it is my twin that is killed, you know ...

But that's because I'm a dualist.

Ah! :-) that is you don't accept the basic assumption that the mind is a property of the body? You consider the mind some super-natural stuff?

 

[vanesch]

Ah! :-) that is you don't accept the basic assumption that the mind is a property of the body? You consider the mind some super-natural stuff?

Mmm, this is more philosophy than anything else but ok, because it is related to this thing (after all, before discussing quantum immortality, we have to define what mortality is), let's go. I'm convinced by the dualist arguments that strictly materialist considerations cannot explain all aspects of subjective experience, and in essence, cannot explain the very existence of subjective experience. Now, this wouldn't have anything to do with physics if it weren't for MWI and related things, but because in this view, an essential part is played by the difference between what is objectively happening and what is subjectively experienced, one cannot avoid entering in these considerations, although it is always a bit awkward to talk about that in a physics forum, because it easily drifts off into discussions that have nothing anymore to do with the theory at hand.

Do I think that there are some ghostly creatures (souls) that float around in "ghost space" and decide or not to "inhabit" a body ? No. Not at all. However, I think that on top of the evolution of the wavefunction, there emerges a structure of entities which are subjective experiences. They are "rooted" in the objective (wavefunction) world, but they are not entirely described by it. In other words, on top of the objective evolution of the wavefunction, emerges an arborescence of "new things", which are subjective experiences, and your subjective experience is one of them, and mine is too. Of course, we are "driven" by the objective wavefunction, but its arborescence is not visible in the wavefunction. No physical experiment, no observation, nothing which has purely to do with the wavefunction will demonstrate anything of that arborescence, and in that sense, it is not open to scientific inquiry.

What is of course open to scientific inquiry is the behavioural aspect of the wavefunction, including all aspects of a body. I don't believe that the emergent entity (subjective experience) has any influence on the wavefunction (on the body state). So you can do all tests you want on a body, it will act *as if* there was no subjective experience. But that doesn't prove that there isn't any.

This is of course an old philosophical debate, and the more classical view of it can be seen as follows. In a more classical view, there is no "arborescence" of subjective experiences, but just isolated "lines", where a subjective experience "emerges" when a body is starting to live (consciously) and "ends" when the body dies (or becomes unconscious). Dualists say that there are such "lines", materialists say that there ain't any. Behavioristically, there is no distinction. And because of the simple, separated, individual "lines" in this case, the discussion is entirely separated between the physics of the body, and an eventual "subjective experience". There's no need to talk about that in classical physics. If (as I do) we assume that the emergent property "subjective experience" has no influence on the underlying material structure, the body, then there is no way to behaviouralistically find out whether such an experience actually exists. And this impossibility is usually called "the hard problem" in philosophy. There's observationally, hence scientifically, no way to distinguish between the body in a materialist view and in a dualist view. And the physicist doesn't need the consideration.

But in MWI, things are different. Here, to a same "body" (material degrees of freedom, hilbert spaces), there correspond now many subjective experiences: one (or more! Many minds) for each substate that is entangled with a different environment. It is the only way to explain that what we "experience" is a classically looking world (a substate) while objectively our body exists in many classically-looking but different states at the same time.
And moreover the number of these subjective experiences changes (increases) constantly. So in a certain respect, MWI doesn't even make any sense without a form of dualism: we need to "assign" a subjective experience to each classically-looking body state. Of course, MWI can explain the correct interactions that determine the body states' evolution, and, most importantly, show that they cannot depend upon what happens "in other branches", but at the end of the day, it doesn't explain why we only experience ONE of these branches. If subjective experience were nothing else but a "property of the body" then I would have to experience all my bodystates simultaneously without of course being aware when I would be in one, that the others existed. Nevertheless, this is not what I experience. I experience a single bodystate, and there is a clear continuity in it. I don't "jump around and forget". Of course as this is a subjective experience, I can not "materialise it", and a strictly materialist analysis of the wavefunction would in fact be able to show how this post emerged from physical processes in my brainstate which actuated my fingers to type all this (and my copies would do similar things in different branches). There is an untransgressable window between the subjective experience which I "am" and the physical state of my body from which it emerges.

In this view, my "subjective experience line" is following a specific path throughout the arborescence that emerges on top of the wavefunction branching, and that line had a beginning, and will have an end. The lines that are split off (twins) are simply OTHER subjective experiences, new ones, which emerge at the moment of the split. Maybe I'm one of those too. As my memories and so on are materially determined, I cannot distinguish between "starting my experience yesterday but with the memories of an old body" and "actually having lived all that time". But I will go my way, and I will reach my end. It is not because *another* subjective experience emerges, that *I* will live it, as I already don't do it when I don't die. I don't "live the experiences" of my twins. I only live one. So I don't see how I would start "living those others" when my line comes to an end.

Things are much easier in a classical settings because they are all single lines with a clear starting point and a clear end.

There.

 

[atyy]

If (as I do) we assume that the emergent property "subjective experience" has no influence on the underlying material structure, the body, then there is no way to behaviouralistically find out whether such an experience actually exists. And this impossibility is usually called "the hard problem" in philosophy. There's observationally, hence scientifically, no way to distinguish between the body in a materialist view and in a dualist view. And the physicist doesn't need the consideration.

Hmmm, I think some sort of dualism is necessary even "classically". We could say an emergent property like the phases of water has no impact on the underlying material structure, so we don't really need to ask if the distinction between water and steam exist. Since the thermodynamic limit of an infinite number of particles doesn't really exist, it's us that made up the distinction (and just like consciousness if you go round the critical point the distinction doesn't exist even in theory ). But I have to admit that even so, it's not clear to me if such a point of view will help the MWI experience become more "subjective".

 

[Fra]

I didn't follow the detailed reasoning on the "mortality/immortality" part but I made the following reflection skimming this.

an essential part is played by the difference between what is objectively happening and what is subjectively experienced

This sequence is a key theme that I see repeated in many contexts. In particular when one discusses what is observable and what is not. It seems to me at least that it's obvious that what observations by definition are subjective, because they relate to a specific choice of observer. But often one sees the idea that this subjective view a real physical view, and that the physical view must be observer invariant, in the sense that the physical observables are things that all observers agree upon.

But then the question arises how the "correct" objectivity is established by any ONE real observer (which is the practical real life situation we are stuck with). It's almost that sometimes the fact that real observers are a nuisanse that just makes life hard for the physicists, but even the physicists is an observer.

I like Rovelli's RQM idea that whatever objective RELATION that exists between the subjective views, is something that must be negotiaded or communicated. And this observer-observer communication is nothing but the ordinary physical interactions of nature.

To me this suggest that a clear distinction between objective events and subjective events simply doesn't exists, because even the supposedly objective relations of subjective eventes must be described by some subject. So objectivity is thus emergent from subjevtivity.

I think a key difference that seems to divide thinkers is what is more fundamental, the subjective view of a REAL LIFE observer or real life system, or the supposed objective relations (where the question is, how to find a physical basis for describing the objectivity when it seems to be a fact that the world is composed of a collection of interacting subjective observers?)

/Fredrik

 

[xantox]

I'm convinced by the dualist arguments that strictly materialist considerations cannot explain all aspects of subjective experience, and in essence, cannot explain the very existence of subjective experience.

Yes, indeed this explains entirely our different conclusions in regards to the experiment.

However, I think that on top of the evolution of the wavefunction, there emerges a structure of entities which are subjective experiences.

This evokes an interesting and original approach where Descartes' view of a connection between the res extensa and the res cogitans meet the Bohm intepretation of QM.

My own view, if that could be of interest, is that dualism is false, that reality is one, and that it is physical. We don't need two entities to explain our lack of knowledge. I suspect the temptation of dualism is the result of sort of overreacting to the difficulty of solving the hard problem you mentioned. One wants to solve it at all costs, including by cheating, so that it is extremely difficult to invoke rational arguments against dualism.

On the other side, materialists also most often fail to understand what their materialism does mean or imply, and they tend to solve those same hard problems too fast too, by considering there are no problems to start with, sometimes even saying silly things like minds do not exist at all, which ends up making dualists more correct than them in most cases.

The solution of the hard problem must be in the understanding of the complexity of the "myself" system, it cannot be in the contemplation of such elementary questions of whether matter=mind or not. One wants to know which is the winning move of an enormous chess game, not to hear there is no winning move (because "I can't understand it"), or there is no game (because "there are only atoms").

Of course, MWI can explain the correct interactions that determine the body states' evolution, and, most importantly, show that they cannot depend upon what happens "in other branches", but at the end of the day, it doesn't explain why we only experience ONE of these branches. If subjective experience were nothing else but a "property of the body" then I would have to experience all my bodystates simultaneously without of course being aware when I would be in one, that the others existed.

I don't understand it. Why you should need to experience all body states simultaneously, since your mind is not a "Schrodinger's mind" but the property of a decohered system?

 

[Fredrik]

I've been trying to formalize some of the ideas in the quantum immortality scenario and the possibility (also mentioned in this thread) that I already have an identical copy somewhere in the universe and one of us gets killed. I think it's interesting to see how the statements we've been using in the discussion should be expressed as precise statements about vectors, subsets, subspaces, etc.

I'll use the notation H(X) for the Hilbert space of possible states of the physical subsystem X. U is the universe, so H(U) is the Hilbert space of possible states of the universe. (That makes sense in the MWI).

I'm a subset F of the Hilbert space H(S) of possible states of a subsystem S of the universe. The subsystem S is my brain and some part of the environment. It doesn't seem to matter how much of the environment we include in S. F is the set of state vectors in H(S) that represent me being alive and still "me" somewhere in S. The statement "Fredrik is alive and still himself" means that the projection of the state vector of the universe onto the subspace H(S) is in the subset F.

The statement that there's another Fredrik (dead or alive, looking like me or like Mr. T), in this universe or in another MWI branch, means there's another subspace H(S') of H(U) that's isomorphic to H(S). Let's call the isomorphism that maps H(S) onto H(S') T. The statement that we are both alive at the same time means that the projection of the state vector of the universe onto H(S) is in F and that the projection of the (same) state vector of the universe onto H(S') is in T(F).

So what does it mean to kill one of us? It means to to change the state vector of the universe so that only one of those projections is in the right subspace. Am I still alive after the Fredrik in S has been killed? That depends on how we interpret the "I". If "I" refers to the class of subsets {F,T(F)}, then yes I'm still alive. If "I" refers specifically to the subset F, then no I'm dead.

This is a lot like the barn-and-pole paradox in SR. The original question doesn't make sense until we provide more information, and when we do we find that the answer can be both yes or no, depending on what information we provide.

Disagreements in discussions about these things seem to be caused by different intuitive opinions about what the "I" should refer to. I'm not convinced that one option is more correct than the other.

 

[xantox]

The original question doesn't make sense until we provide more information, and when we do we find that the answer can be both yes or no, depending on what information we provide. Disagreements in discussions about these things seem to be caused by different intuitive opinions about what the "I" should refer to. I'm not convinced that one option is more correct than the other.

I agree that it is extremely important to rephrase the pieces of the problem more precisely in terms of the underlining theories, and as we said above there are two of them: MWI and one's theory of mind, and I don't think it is possible nor it does have any meaning to try to separate these two sides.

By the way, you should put the emphasis on the dynamics of the quantum state, since the "I" should be rather considered a time evolution, and yes I consider that the "I" must refer to the class {F,T(F)}, and that there is absolutely no reason to refer just to F since we talk about an abstract property. Not only the same "I" could look like Mr. T, it could even look like a network of drums and bouncing wood spheres and be absolutely the same.

About how much of the environment to include, it should be enough of it to properly describe the decoherence of the system (as the "I" is quite probably purely classical).

 

[flying fish]

I also think that Quantum Suicide is more likely to work if you happen to be a sub-atomic particle (or perhaps a uranium atom shooting neutrons at yourself).