QM says no observer, no existence

[nameta9]

Now let us assume for a moment that there are other bodies, which act as persons act

But that is exactly the point. As long as there are other people/communications or similar (even if fake) we retain some reference. Imagine waking up and no one is in the world anymore. You walk in a town and then everything is void of people. Now this situation (twilight zone?) would completely modify your "subjective" view of all. How long would you last ? what meaning would the "laws of physics" have in this context ? How long could you reason properly ? Now an entire civilization can be viewed as this lone "observer". It really seems to confirm the "marxist-sociological" idea that "science is a social construction".

 

[Canute]

Well, maybe exceptionally (which would then account for a lot of "supernatural" phenomena :-).
But I fail to see how we observe ourselves to be in superposed states in the "standard" situation:

In the standard situation maybe not. Maybe not even after a few beers. But do the descriptions of conscious states below not have something suggestive of superposition about them? After all, to suggest that the universe is a quantum fluctuation in a superposed state, or something like that, seems pretty uncontentious these days. When people say that reality is 'nondual' they mean something very like that it exists as a superposition of complementary appearances or aspects. Thus Jung's "no qualities, because it has all qualities."

"Nothing is the same as fullness. In the endless state fullness is the same as emptiness. The Nothing is both empty and full. One may just as well state some other thing about the Nothing, namely that it is white or that it is black or that it exists or that it exists not. That which is endless and eternal has no qualities, because it has all qualities." (Carl Jung, VII Sermones ad Moruos)

"When we encounter the Void, we feel that it is primordial emptiness of cosmic proportions and relevance. We become pure consciousness aware of this absolute nothingness; however, at the same time, we have a strange paradoxical sense of its essential fullness. This cosmic vacuum is also a plenum, since nothing seems to be missing in it. While it does not contain in a concrete manifest form, it seems to comprise all of existence in a potential form. In this paradoxical way, we can transcend the usual dichotomy between emptiness and form, or existence and non-existence. However, the possibility of such a resolution cannot be adequately conveyed in words; it has to be experienced to be understood." (Stanislav Grof, The Cosmic Game
State University of New York)

 

[vanesch]

Now this situation (twilight zone?) would completely modify your "subjective" view of all. How long would you last ? what meaning would the "laws of physics" have in this context ? How long could you reason properly ?

I don't know. You claim that an individual without contact with its peers necessarily goes bezerk. I'm not even sure of that, but let us for the sake of argument say that it is. The probable origin of this is that we are, as individuals, a social species and that somehow psychologically we do not function well if we are alone. So be it. But clearly solitary beings have no problem with that, such as leopards, who meet their "peers" only once a few years, for a copulation or so, and then go on on their own again.

Now an entire civilization can be viewed as this lone "observer". It really seems to confirm the "marxist-sociological" idea that "science is a social construction".

What goes wrong with this reasoning is that you transpose the (assumed) property of individual humans, namely that they cannot reason properly if on their own, to an entirely different animal, namely a civilisation (of which you still have to demonstrate that it even *has* a subjective experience!). There's no reason to think so, because our entire civilisation's subjective experience (if it exists!) will be "used" to live in solitude. It never met another one !

But there's something far more basic that goes wrong with this "science is a social construction". Boiling water burns your finger, whether you're alone or whether you're in a group. Rocks fall down. This is not part of a "social construction". Calculational procedures give certain results (which you can cross check by different methods yourself), and experimental procedures give also certain results, which you can also crosscheck yourself. I don't see how the agreement or disagreement between both is socially decided on matters where science is clear. I'm not talking about front level research. I'm talking about all the well-established stuff.

cheers,
Patrick.

 

[nameta9]

There is something deeply "arbitrary" in science. Science depends on an "observer", but in our case this observer is a human mind/body. Now if you modify this observer maybe by changing its neural circuits or the way it processes sense information or adding other sense organs you end up having a completely different observation of the universe. Now this observer+universe is a completely different system, hence science is arbitrary in that it depends on the structure of the observer. In many posts in these forums and in www.scienceforums.net I have often mentioned the fact that we may be able to modify our own neural circuits or the way our mind organizes the information or adding new sense organs since what we really have in the end is just electrical signals going into an arbitrarily evolved/designed brain. We could add trillions of new sense organs by just modifying the neural organization of our minds hence we would have an infinite number of different universes. We would use our present science to kick start the process.

 

[vanesch]

There is something deeply "arbitrary" in science. Science depends on an "observer", but in our case this observer is a human mind/body.

What I think you mean is that PERCEPTION is deeply arbitrary. But science is more than just perception: it is the construction of a mathematical representation of a hypothetical ontology that is a 1-1 mapping to its perception. Now, of course because this perception is arbitrary (up to a point), this representation can change. But I'm somehow convinced that the underlying mathematical object that is represented (in different ways) is unique - and IS in fact, the objective, ontological world.

Let me take a childish illustration of what I'm trying to say. Imagine that space is given by 3-dim Euclidean space, and that there are different creatures, with different eyes, which "see" the world as rather hyperbolical, or elliptical or rasterized or whatever. They will come up with different theories of their vision (if we limit their perception to their optical vision) with different laws according to what is "distance" and so on, but if they are analysed deep enough, one will finally notice that all those complicated objects are just inequivalent representations of 3-dim Euclidean space.

THIS underlying structure is objective, and all our possible perceptions (no matter how crazily we are wired up) are limited to representations of said underlying structure.

Now if you modify this observer maybe by changing its neural circuits or the way it processes sense information or adding other sense organs you end up having a completely different observation of the universe. Now this observer+universe is a completely different system, hence science is arbitrary in that it depends on the structure of the observer.

I just tried to argue that although "superficially" the world looks totally different, the underlying object should be the same, and with enough thought, observation and analysis, one could hope that different observer/universe systems lead to finally the same deeper understanding: these are the laws of nature, and it is the most fundamental working hypothesis of physics that these laws exist (that this mathematical object exists).

We could add trillions of new sense organs by just modifying the neural organization of our minds hence we would have an infinite number of different universes. We would use our present science to kick start the process.

yes, but they would all be limited to being representations of the mathematical object that is at the heart of the workings of the universe (this mathematical object are the "ultimate laws of nature")
The very fact that we would "use our present science to kick start the process" is the very antithesis of the statement that "science is but a social process" !

 

[Canute]

Perhaps the question is not: Is there or is there not an underlying reality? This is an all or nothing choice equivalent to the unresolved background dependent/independent paradox, which may be an undecidable metaphysical question for all we yet know. Perhaps the question could be : If one takes away all observer-actualised differences between universes, or if one take away all observers, one by one, then when at last the last one is taken away what is left?

What is really real and so would remain even if unobserved or unconceptualised? Would quantum events ever happen? Would matter still exist? Would space and time still exist? Would 'Being' still exist? How could we ever know?

 

[vanesch]

What is really real and so would remain even if unobserved or unconceptualised? Would quantum events ever happen? Would matter still exist? Would space and time still exist? Would 'Being' still exist? How could we ever know?

If nothing is there to know, the last question doesn't make sense of course. But I'd say "yes" to all the others, realising that this is an unfalsifiable working hypothesis.

I think the simplest indication that at least this is a sensible working hypothesis is: the world looks as if it had a history. By that, I mean: with all we know, from different disciplines, it really does make sense to say that the earth, for instance, is something like 5 billion years old. Too many things fit together with this picture for it just to be decided by "social convenience". You can of course not exclude the big conspiracy, that the Earth is in fact 7 minutes old, but that everything was put together TO MAKE YOU BELIEVE that you are already there for several years, and that dinosaur bones were put in the ground etc... but that is a much less fruitful hypothesis.
Things just fit together when we say that the Earth was there even before there were humans, or dinosaurs, or trilobites. And know what ? It seems to have followed about the same laws of nature than those that we socially convened upon. We cannot go back to know for sure, of course, but this hypothesis fits within what we observe as "remnants of the past", which is the best we can do.
Now from an MWI quantum view, does that mean that "the wavefunction got observed before we were here" ? You don't need that. The universe can be objectively in a quantum state where there are terms where the Earth didn't even devellop and others where the Earth did devellop, but life never formed, and others where the dinosaurs didn't get exterminated. We simply don't happen to observe that branch (and to a certain point, we couldn't, because our bodies aren't present in those branches). This view implements automatically the antropological principle in some way.

 

[nameta9]

yes, but they would all be limited to being representations of the mathematical object that is at the heart of the workings of the universe (this mathematical object are the "ultimate laws of nature")
The very fact that we would "use our present science to kick start the process" is the very antithesis of the statement that "science is but a social process" !

True, but we are always assuming that our mental-sensory informational organization is the fundamentally true and basic one. We would modify another mind's neural circuits using our science but we would really not know how the other mind views and sees the universe unless we see "through" that new mind. And it may be that the new mind reveals completely different fundamental relationships, or even logical processes or emotions/sentiments etc. This new mind is at an equal level with ours. We are just as fundamental as any of the trillions of other possible minds. So the new mind can look at ours and say look at how unfundamental the human mind is "and they thought they knew the laws of physics". Of course there is an initial master-slave configuration in that we modify the other mind, but through the other mind we may appear just as arbitrary. It may be that there are no mathematical invariants in the end or that mathematics may just be one of many ways to organize information.

I wrote some other similar threads:


http://www.scienceforums.net/forums/showthread.php?t=6944

https://www.physicsforums.com/showthread.php?t=71298

 

[oldtobor]

What an interesting relationship with the whole concept of intelligent design and evolution. So then, what if another mind who has a more fundamental or knowledgeable view of the universe designed our mind and we are the "slave" of the master-slave configuration ? Also evolution itself somehow creates more complex organisms from simpler ones, the "hierarchy" is actually inverted from almost nothing creating a human mind. So we don't need a "master" with a better mind to "design" another as evolution shows that nothing at all evolved (designed?) us not a superior being as god.

It is like saying an inferior being can design a superior being, a modified mind can know more than its designer just as a blind process like evolution created superior minds after a long chain of events starting from carbon atoms. Simple carbon atoms in a sense "designed" by themselves and the process of evolution a mind. An inferior thing designed a superior one that knows "more" and "deeper" than the originator.

 

[vanesch]

And it may be that the new mind reveals completely different fundamental relationships, or even logical processes or emotions/sentiments etc. This new mind is at an equal level with ours. We are just as fundamental as any of the trillions of other possible minds.

Well, before playing Dr. Frankenstein yourself, you could already look at what variants of our minds "observe". Go to your nearest closed psychiatric hospital, to study "other minds with other perceptions of the world" I don't know if they produce a lot of sophisticated science on which they have social consensus (of the style "I'm Napoleon" - "No, *I* am Napoleon" ;-)

 

[nameta9]

This may end up being very important in the future when we start to modify our neural circuits. I was even thinking if we had 2 minds A and B where A sees the world as the human and B sees the world as modified mind. So A will always interpret all that B sees within its reference system and B will interpret things according to its. But a system composed of A + B could see things a bit like each but it would already be a completely different system. It is like if you take a human mind and you change its fundamental beliefs ( or even memories) like "matter is made up of atoms". It would be a completely different view of the world, hence a different system; A+B is neither really A or B.

 

[vanesch]

It is like if you take a human mind and you change its fundamental beliefs ( or even memories) like "matter is made up of atoms". It would be a completely different view of the world, hence a different system; A+B is neither really A or B.

Could it be that your B is a complete nutcracker ?
There are probably zillions of ways to make CRAZY minds. But do you have to consider a madman's propositions as just an alternate form of science ?

 

[Canute]

Vanesch - You wrote "In MWI quantum view, does that mean that "the wavefunction got observed before we were here" ? You don't need that. The universe can be objectively in a quantum state where there are terms where the Earth didn't even devellop and others where the Earth did devellop, but life never formed, and others where the dinosaurs didn't get exterminated. We simply don't happen to observe that branch... "

Doesn't this imply that the branch we are in had to be observed to be actualised. If it existed in the past then this was because it was observed, if it was not observed in the past then it 'was' in a superposed state and it is our current observations that create our evolutionary past.

This seems relevant here, regarding the . Speaking of the consistent histories approach to quantum cosmology Lee Smolin writes:

"While the ‘classical’ world we observe, in which particles have definite positions, may be one of the consistent worlds described by a solution to the theory, Dowker and Kent’s results showed that there had to be an infinite number of other worlds too. Moreover, there were an infinite number of consistent worlds that have been classical up to this point but will not be anything like our world in five minutes’ time. Even more disturbing, there were worlds that were classical now that were arbitrarily mixed up superpositions of classical at any point in the past. Dowker concluded that, if the consistent-histories interpretation is correct, we have no right to deduce from the existence of fossils now that dinosaurs roamed the planet a hundred million years ago."

Lee Smolin
Three Roads to Quantum Gravity (44)

On the importance of social organisation to the systemisation of our knowledge, or on science as social process, Tobias Dantzig, in his book "Number -The Langauge of Science" (worth a read on some of these issues IMO - it was a favourite of Einstein) writes:

"Of the absolute and immutable world which exists outside our consciousness we know only through theological speculations: accepting it or rejecting it are alike futile to a natural philosophy. But just as futile and sterile is the acceptance of the crude reality of our senses as the arch-reality, the only reality. It is convenient for a systematic exposition, to be sure, to regard the newly born child, or the primitive man, or the animal, as the embodiment of such an arch-reality. We can go still further and imagine, as did Helmholtz, Mach and Poincare, an intelligent being who has been deprived of all but one of his senses, say sight, and speculate on the type of universe that such a being would construct. Such speculations are tremendously fascinating in that they allow free rein to our power of resolving our sensations into their constituents, and then regarding the concept as a synthesis of these arch-sensations. But to accept such a synthesis as reality, as the reality, has, to my way of thinking, one fatal defect: it postulates the existence of an individual intellect; whereas the very process of coordinating these sensations involves thought, which is impossible without the vehicle language, which in turn implies an organized exchange of impressions, which in turn presupposes a collective existence for human beings, some form of social organisation."

Tobias Dantzig
Number - The Langauge of Science

 

[Canute]

Vanesch - you wrote - "In MWI quantum view, does that mean that "the wavefunction got observed before we were here" ? You don't need that. The universe can be objectively in a quantum state where there are terms where the Earth didn't even devellop and others where the Earth did devellop, but life never formed, and others where the dinosaurs didn't get exterminated. We simply don't happen to observe that branch... "

Doesn't this imply that the branch we are in had to be observed to be actualised? If it existed in the past then this was because it was observed, if it was not observed in the past then it 'was' in a superposed state and it is our current observations that create our evolutionary past.

Speaking of the consistent histories approach to quantum cosmology Lee Smolin writes:

"While the ‘classical’ world we observe, in which particles have definite positions, may be one of the consistent worlds described by a solution to the theory, Dowker and Kent’s results showed that there had to be an infinite number of other worlds too. Moreover, there were an infinite number of consistent worlds that have been classical up to this point but will not be anything like our world in five minutes’ time. Even more disturbing, there were worlds that were classical now that were arbitrarily mixed up superpositions of classical at any point in the past. Dowker concluded that, if the consistent-histories interpretation is correct, we have no right to deduce from the existence of fossils now that dinosaurs roamed the planet a hundred million years ago."

Lee Smolin
Three Roads to Quantum Gravity (44)

On the importance of social organisation to the systemisation of our knowledge, or on science as social process, Tobias Dantzig, in his book "Number -The Langauge of Science" (worth a read on some of these issues IMO - it was a favourite of Einstein) writes:

"Of the absolute and immutable world which exists outside our consciousness we know only through theological speculations: accepting it or rejecting it are alike futile to a natural philosophy. But just as futile and sterile is the acceptance of the crude reality of our senses as the arch-reality, the only reality. It is convenient for a systematic exposition, to be sure, to regard the newly born child, or the primitive man, or the animal, as the embodiment of such an arch-reality. We can go still further and imagine, as did Helmholtz, Mach and Poincare, an intelligent being who has been deprived of all but one of his senses, say sight, and speculate on the type of universe that such a being would construct. Such speculations are tremendously fascinating in that they allow free rein to our power of resolving our sensations into their constituents, and then regarding the concept as a synthesis of these arch-sensations. But to accept such a synthesis as reality, as the reality, has, to my way of thinking, one fatal defect: it postulates the existence of an individual intellect; whereas the very process of coordinating these sensations involves thought, which is impossible without the vehicle language, which in turn implies an organized exchange of impressions, which in turn presupposes a collective existence for human beings, some form of social organisation."

Tobias Dantzig
Number - The Langauge of Science

 

[nameta9]

no observer, no existence, problem has no solution. The observer is a billion neurons with lungs, oxygen, mental states, 10 years higher education etc. The observer is very complex. There is nothing elementary in "elementary particle physics". Each "human mind" is irreducibly different to each other in the sense that a physicist would say that the electrons are the fundamental particles, a psychologist would say mind comes first and mental states are more fundamental, a marxist would say money, power, social relations is really behind all. In reality each position is irreducible, they can be mixed but then you have a different system. Our limits are in our irreducible minds, paradigms. We can't really know how another mind feels sees without being the other mind completely, but then we would no longer be ourselves hence no way to know. If you mix the minds it is neither yours or the others.

 

[vanesch]

Doesn't this imply that the branch we are in had to be observed to be actualised? If it existed in the past then this was because it was observed, if it was not observed in the past then it 'was' in a superposed state and it is our current observations that create our evolutionary past.

Yes, almost. And all those other branches still exist too in this view, and our branch "existed" amongst others, so we didn't "create" it. We *picked* it. It is as if you step on a train, and you say that you "created" the train because if you would have picked another one, you wouldn't see this one.

Speaking of the consistent histories approach to quantum cosmology Lee Smolin writes:

"While the ‘classical’ world we observe, in which particles have definite positions, may be one of the consistent worlds described by a solution to the theory, Dowker and Kent’s results showed that there had to be an infinite number of other worlds too. Moreover, there were an infinite number of consistent worlds that have been classical up to this point but will not be anything like our world in five minutes’ time. Even more disturbing, there were worlds that were classical now that were arbitrarily mixed up superpositions of classical at any point in the past. Dowker concluded that, if the consistent-histories interpretation is correct, we have no right to deduce from the existence of fossils now that dinosaurs roamed the planet a hundred million years ago."

Lee Smolin
Three Roads to Quantum Gravity (44)

Who am I to critique Lee Smolin of course But I think he misses the point that the branch with the dinosaurs was there already (amongst many other ones). So we DO have the right to conclude that dinosaurs roamed the world, IN THE BRANCH WE PICKED NOW.

cheers,
patrick.

 

[Canute]

Are you saying that we create the history of this branch in retrospect, as Dowker suggests may be the case, or, rather, that consciousness was present at all times in the history of this branch, doing the picking?

Would you agree that saying that all possible branches existed in the past is the same as saying that all branches (with a finite probability of existing) were at that time superposed?

 

[vanesch]

Are you saying that we create the history of this branch in retrospect, as Dowker suggests may be the case, or, rather, that consciousness was present at all times in the history of this branch, doing the picking?

No, I'm saying that the branch (= term in the superposition) was present all the time, and that your consciousness picks out that term NOW.

Would you agree that saying that all possible branches existed in the past is the same as saying that all branches (with a finite probability of existing) were at that time superposed?

Yes, and they still are in superposition.

What I grossly mean is this:

t1 = 5 billion years ago
|psi_universe(t1)> = |earth formation> + |Bearth formation> + |binary star formation>

(I consider 3 "branches": namely one where the Earth formed, one where another planet (much bigger) formed, and one where there were no planets, but instead of the sun, a binary star system formed)

t2 = 150 million years ago:

|psi_universe(t2)> = (|dinosaurs> +|giant trilobites>+|nolife>) + (|instable solar system> + |wonky life>) + |binary star>

The parentheses indicate possible evolutions from the previous branches.

t3 = 65 million years ago:

|psi_universe(t3)> = ({|dinosaurs dead> + |dinosaurs still around>} +|giant trilobites>+|nolife>) + (|instable solar system> + |wonky life>) + |binary star>

etc...

t4 = 1945

|psi_universe(t4)> = ({|dinosaurs dead, hitler wins WWII> + |dinausaurs dead, hilter looses WWII> + |dinosaurs still around>} +|giant trilobites>+|nolife>) + (|instable solar system> + |wonky life>) + |binary star>


t5 = today

|psi_universe(t5)> = ({|dinosaurs dead, hitler wins WWII> + |dinausaurs dead, hilter looses WWII, you look at physics forum> + |dinosaurs still around>} +|giant trilobites>+|nolife>) + (|instable solar system> + |wonky life>) + |binary star>

You happen to be in the highlighted branch. That's all.

cheers,
Patrick.

 

[Canute]

I'm still not sure what you consider to be the role of consciousness in all this. Do you mean that this branch is "highlighted" by consciousness, that consciousness picks from amongst the possibilities and actualises one of them? Or do you mean that all the possible branches or universes exist forever in superposition, as a cosmic wave-function, all of them as real as this one, and that we just happen to find ourselves here in this one? I suppose the question is: Would this branch exist if consciousness did not exist?

 

[vanesch]

all of them as real as this one, and that we just happen to find ourselves here in this one?

That's the essence of the MWI view indeed. I don't "believe" in it, I just find it the interpretation that comes closest to the ACTUAL quantum formalism. All the rest supposes some extra physics (except the also acceptable, purely epistemological view that all we do is scratch symbols on a sheet of paper, crank out numbers and observe that they correspond to readings on measurement apparatus, without giving a meaning or reality to any of this - but I personally don't like to think of things that way because it is a big "inspiration killer" !). I'm HOPING for some extra physics, but as long as we don't have such extra physics, I stick to what the actual formalism tells us ; I don't see how to do anything else, honestly.

cheers,
Patrick.

 

[vanesch]

Would this branch exist if consciousness did not exist?

I'd say: why not ?

 

[Tournesol]

That's the essence of the MWI view indeed. I don't "believe" in it, I just find it the interpretation that comes closest to the ACTUAL quantum formalism.

The actual formalism requires use of Born rule, and that is quite
tricky for MWI poponents to justify.

 

[Canute]

I'd say: why not ?

Hmm. I'd say: why? And also how? I though MWI depended on observers having a role, but maybe I'm wrong on that one.

 

[vanesch]

I though MWI depended on observers having a role, but maybe I'm wrong on that one.

MWI is of course encompassing a lot of flavors, but I think that they all agree on these points (I'm a bit a heretic amongst MWI, you'll see):

1) the state of the system (universe...) is given by the wavefunction, and it evolves according to the unitary Schroedinger equation, period (no collapse).

2) Observers manage to observe only ONE term in the wavefunction

All the different flavors try to extablish 2) FROM WITHIN the unitary formalism ; I'm convinced that this is doomed (that's my MWI-heresy) and that you have to postulate it externally.

But MWI is "less" observer-dependent than observer-collapse theories, because MWI postulates that the state of the universe follows its deterministic evolution equation, independent of what might be observed or not ; collapse models, where the observer actively collapses the wavefunction, have of course a specific dynamical role for the observer, which happens to modify the wavefunction of the entire universe.

Now, true MWI-ers hope that "observer" will be some kind of emergent phenomenon within the unitary QM evolution, but, as I said, I think this is impossible.

cheers,
Patrick.

 

[vanesch]

The actual formalism requires use of Born rule, and that is quite
tricky for MWI poponents to justify.

This is correct, and that's where I think that MWI goes wrong, in fact. I think the Born rule is needed as an extra postulate (and that all "derivations" of the born rule sneaked it in through the back door).
But that doesn't do away with the possibility (taken on by MWI proponents) that the wavefunction evolves unitarily, period. (no ontological projection postulate).

If you then let your consciousness "associate" with a term in the wavefunction, according to the Born rule, by postulate, you solve what MWI-ers do not succeed in deriving.

So the Born rule becomes the "evolution of (non-physical) consciousness", while the Schroedinger equation is the "evolution of the physical wavefunction".

It solves at least the issue of why certain interactions collapse the wavefunction, when you call them observation, while those same interactions evolve unitarily if you don't call them "observation".

 

[Canute]

Are you suggesting that the "collapse" of the wave function is not "out there" but rather in consciousness, and that "out there" there is no collapse?

 

[vanesch]

Are you suggesting that the "collapse" of the wave function is not "out there" but rather in consciousness, and that "out there" there is no collapse?

In a way, yes. It appears to us that there is "collapse" because we are now only associated to ONE term in the wavefunction, and as thus, can only couple significantly to this single term. The other terms, except for very very peculiar dynamics, will remain "orthogonal" for ever and we'll never observe their effect anymore. We can then, from our point of view, just take out that term alone and pretend that it is the entire wavefunction: the wavefunction, from our point of view, has "collapsed" into this single term.
Epistemologically of course, this IS a collapse. But if you insist on an ontology (such as I try to do), I'd say that there is a difference between: "the state doesn't collapse, but to us, it appears to do so" (which means that the observer, in the end, does NOT do something to the wavefunction), and "the observer collapsed the wavefunction (of the universe)" - I feel too modest to claim so :-)

cheers,
Patrick.

 

[El Hombre Invisible]

In a way, yes. It appears to us that there is "collapse" because we are now only associated to ONE term in the wavefunction, and as thus, can only couple significantly to this single term. The other terms, except for very very peculiar dynamics, will remain "orthogonal" for ever and we'll never observe their effect anymore. We can then, from our point of view, just take out that term alone and pretend that it is the entire wavefunction: the wavefunction, from our point of view, has "collapsed" into this single term.
Epistemologically of course, this IS a collapse. But if you insist on an ontology (such as I try to do), I'd say that there is a difference between: "the state doesn't collapse, but to us, it appears to do so" (which means that the observer, in the end, does NOT do something to the wavefunction), and "the observer collapsed the wavefunction (of the universe)" - I feel too modest to claim so :-)

cheers,
Patrick.

When you say the wave function continues uncollapsed 'out there', and collapse is purely a property of observation, do you mean that the wave function is completely unaltered by that observation?

I mean, if you looked in the box to see that Shrodinger's cat was dead, then came back an hour later and looked again... could it be alive?

 

[vanesch]

When you say the wave function continues uncollapsed 'out there', and collapse is purely a property of observation, do you mean that the wave function is completely unaltered by that observation?

No, it is not completely unaltered of course, because measurement is always associated with an interaction (of the device with the system). So you will introduce some unitary evolution associated with that interaction ; it is even exactly that interaction which will give rise to the "split" of the terms (and the obligation of choosing again "one term" to live in, according to the Born rule). "Ideal" measurements (pre-measurement interactions a la von Neumann) however, limit the interaction to entangling the state of the measurement system with the different eigenstates of the system under study, without altering first the state of the system under study.

If the system under study is in the state: a |1> + b|2> and you measure the 1/2 property (|1> and |2> are the eigenstates of the measurement operator), then you get, in an ideal pre-measurement interaction:
|m0> (a|1> + b|2>) evolves into a|m1>|1> + b|m2>|2>

A "dirty" measurement could first evolve |1> and |2> into different things, such as |A> and |B> and we'd have:
|m0> (a|1> + b|2>) evolves into a|m1> |A> + b|m2> |B>

This gives you the same measurement results, but the state after the "dirty" measurement is not the projection anymore of the state onto the "measurement eigenvector".

I mean, if you looked in the box to see that Shrodinger's cat was dead, then came back an hour later and looked again... could it be alive?

No, because the second time you look, you *remember* the result of the first measurement, so your brain is still entangled with the "dead cat" term, and you now re-measure that result. The state of your brain remembering "dead cat yesterday" is a complicated quantum state, which is essentially orthogonal to the state where you remember "live cat yesterday", and its evolution from yesterday to today will keep that essentially orthogonal under MOST possible time evolutions. This orthogonality suppresses completely the possible term in which you "remember dead cat yesterday" AND "live cat today". It is this EFFECTIVE orthogonality which makes that you cannot "switch branches" and that once in a branch (a term of the wave function), you're stuck with it for the rest of your days - so that you can just as well only work with that single term (projection).

But *in principle* one could evolve your brain states and all that goes with it (what you wrote down on paper, etc...) "dead cat yesterday" and "live cat yesterday" into two NON-orthogonal states (by un-doing the measurement interaction), and, indeed, "ressurect" the cat. However, in order to do so, you'd have to FORGET that you saw the cat dead yesterday, so you wouldn't feel any contradiction in seeing the cat live today. Such an evolution is far far far beyond our technical means, but it is, in principle, possible and that is what MWI distinguishes, as a physical theory, from any "collapse" theory.
The microscopic version, where we DO have the technology, is called "delayed quantum erasure". We don't do it with brains, but simply with photons.

cheers,
Patrick.

 

[El Hombre Invisible]

No, it is not completely unaltered of course, because measurement is always associated with an interaction (of the device with the system). So you will introduce some unitary evolution associated with that interaction ; it is even exactly that interaction which will give rise to the "split" of the terms (and the obligation of choosing again "one term" to live in, according to the Born rule).

So when that wave function (one in which two states are possible) is altered after measurement, is it altered such that the measured state is the only possible state, or is it just more probable than before? I assume the latter, since the former would constitute a collapsed wave function, no?

No, because the second time you look, you *remember* the result of the first measurement, so your brain is still entangled with the "dead cat" term, and you now re-measure that result. The state of your brain remembering "dead cat yesterday" is a complicated quantum state, which is essentially orthogonal to the state where you remember "live cat yesterday", and its evolution from yesterday to today will keep that essentially orthogonal under MOST possible time evolutions. This orthogonality suppresses completely the possible term in which you "remember dead cat yesterday" AND "live cat today". It is this EFFECTIVE orthogonality which makes that you cannot "switch branches" and that once in a branch (a term of the wave function), you're stuck with it for the rest of your days - so that you can just as well only work with that single term (projection).

Well, what if the second measurement is made by someone else? If it is the 'dead cat yesterday' state that ensures the state evolves into 'dead cat today' when I look again, then if I don't look again today but someone else does, they don't have that brain state of the cat being dead yesterday to stop them remembering the cat being alive today (assuming I didn't tell them).

Another few questions, related to both of the last points. If the wave function can be altered by detection, can it not be altered by non-conscious detection? Say, the photon detector in the cat experiment?

Also, do not the indiviual components of the system have their own wave functions, such as the photon detector in the cat experiment? For instance, if the photon detector can record if it detects a photon, then up until that lone photon is actual emitted towards it, the detector must surely be in a state of 'no detection' - because so far there is nothing to be detected. In which case, at what point can the wave function collapse into one of several states? Once the photon is emitted? Once it reaches the mirror? Once it reaches the detector?

Sorry if I don't really get it. I'll be getting more into this anyway soon, but it'll be good to have some kind of grounding. And to talk about it on this forum in the meantime of course.