QM & Consciousness: Has Theory Been Disproven?

[atyy]

Okay, if you want to conflate the macroscopic/microscopic distinction with the conscious/nonconscious distinction, then I agree with you. But the reason I like the macroscopic/microscopic distinction is that it doesn't rely on unmotivated distinctions between say, a conscious human and an unconscious recording device. I don't think that distinction serves any purpose. You can replace a human observer by a machine, and nothing about QM changes, as far as I can see.

On the other hand, I see the macroscopic/microscopic distinction as unsatisfying, for other reasons. For one thing, the cutoff is pretty arbitrary.

Yes. Actually, Landau and Lifshitz are closer to your view, and they don't like to state the measurement problem using the term "observer". They prefer to say QM assumes the classical world, and so it is no longer true in QM that we have a most fundamental theory from which the less fundamental theory emerges, rather the classical world is fundamental although it is also a limit of quantum mechanics.

I don't object to that. However, using the "observer" to formulate the measurement problem is also traditional. I don't think there is much difference between titling the thread "QM and Consciousness" or "QM and the Observer" or "QM and Common Sense" or "QM and the classical/quantum cut".

 

[maline]

If the universe starts off in macroscopic state ss, then after time tt, it will be in state s′s' with probability Pρs(t)(s′)P_{\rho_s(t)}(s')

Uh, don't you mean "...will be measured to be in state..." ? That's all the standard formalism is willing to claim!

 

[julcab12]

At first it is really hard to shallow but i guess ill just accept it as it is -- experimental limit/withstood test upon test. If someone is drenched with the classical logic(like me^^) then it would be very difficult to entertain QM since classical ensemble is not forgiving with things that doesn't respect it. Oddity/weird phenomenon in the macroworld is always solved classically and explained it very well but that is not the case for quantum world. Uncertainty and non correlation is inherent to QM, by that regards; it wouldn't make sense(quantum) to even consider measurement problem and collapse to be a problem at all.

"Quantum Mechanics In Your Face"
http://media.physics.harvard.edu/video/?id=SidneyColeman_QMIYF

 

[stevendaryl]

Uh, don't you mean "...will be measured to be in state..." ?

No, I don't mean that.

 

[maline]

Uh, don't you mean "...will be measured to be in state..." ? That's all the standard formalism is willing to claim!

No, I don't mean that.

My point is that you are making a claim that goes beyond standard QM. For instance, MWI is (claimed to be) compatible with standard QM, but not with objective descriptions of macroscopic classical states.

 

[stevendaryl]

My point is that you are making a claim that goes beyond standard QM.

I don't think it makes any different testable claims, though.

Standard QM says the wave function gives probabilities for results of measurements, and I think that's completely problematic. What is a "measurement"? Making sense of what a measurement is requires an enormous amount of machinery and brings up philosophical questions about consciousness and so forth and for absolutely no benefit that I can see.

 

[craigi]

Thank you, I'm not very knowledgeable of physics beyond an AP physics class I took back in high school (which was over a decade ago), so if I'm wrong on anything feel free to correct me. I've been reading a lot of science/physics related books recently and thought it would be fun to throw some of my ideas on here and see what people who are well versed in physics have to say about it.

That's another thing that isn't going to fly well here. We don't discuss personal theories. That isn't to say thst we can't discuss what you are curious about, every physicist has ideas. The key is to be careful to phrase things in the appropriate way.

 

[stevendaryl]

Standard QM says the wave function gives probabilities for results of measurements, and I think that's completely problematic. What is a "measurement"? Making sense of what a measurement is requires an enormous amount of machinery and brings up philosophical questions about consciousness and so forth and for absolutely no benefit that I can see.

It seems to me that for something to count as a "measurement" of a property, there has to be a persistent macroscopic record created. So the concept of measurement already involves the concept of macroscopic differences.

 

[maline]

What is a "measurement"?

Anything that you think is a measurement, is one! That's the advantage of treating QM as just a calculating tool- you always can work out what your predicted observations are, without worrying about sticky definitions.

 

[stevendaryl]

Anything that you think is a measurement, is one! That's the advantage of treating QM as just a calculating tool- you always can work out what your predicted observations are, without worrying about sticky definitions.

My point is that there is no advantage that I can see to using the concept of measurement. What you're really doing is setting up a composite system so that microscopic differences in state of one subsystem are amplified to make macroscopic differences in the state of another subsystem.

 

[maline]

there is no advantage that I can see to using the concept of measurement.

We can speak with full confidence about measurement results, but not about objective reality, even macroscopically. MWI just might be true!

Also, as you pointed out, "macroscopic" is not well defined. "Measurement", on the other hand, does not need to be defined- it's just the fact that you have results to speak of.

 

[stevendaryl]

We can speak with full confidence about measurement results, but not about objective reality, even macroscopically.

I don't agree. To me, the certainty that I measured spin-up when I did a Stern-gerlach experiment on an electron is no more (or no less) certain than the claim that the moon is at such-and-such a location relative to the Earth.

MWI just might be true!

But in MWI, measurement results are not certain, either.

Also, as you pointed out, "macroscopic" is not well defined. "Measurement", on the other hand, does not need to be defined- it's just the fact that you have results to speak of.

But "having results to speak of" is a more complicated concept than "macroscopic", it seems to me. Results implies macroscopic facts.

I suppose that you could say that it's unnecessary to assume that all macroscopic facts have definite values; it's enough just to assume that measurements do. But in practice, there is no difference in the implications.

 

[bhobba]

The Von Neumann chain is 'cut' once it reaches it's final destination, which is the conscious observer who determines the final outcome-giving certainty.

Why do you believe its final destination is a conscious observer? Why can't it, for example, be a photographic plate in the double slit? Are you seriously proposing observations would not have occurred until conscious observers appeared? It really is a very weird, and if you think critically about it, rather silly view.

In modern times the chain is cut after decoherence. That's the error Von-Neumann made. There is a place that's different - just after decoherence.

Thanks
Bill

 

[maline]

But in MWI, measurement results are not certain, either.

They are certain in a subjective, utilitarian, sense. I know that this is the result that "he whom I can now call 'I' " got. That's why many-worlds is an interpretation of QM, rather that an alternative model.

 

[bhobba]

I don't agree. The measurement problem has several aspects, and decoherence helps with some of them, such as how the measurement basis is selected. But the more fundamental ontological problem, if I understand correctly, goes something like this:

The measurement problem has, with our current knowledge of decoherence, morphed to why do we get any outcomes at all. Its not an issue for the logic of the theory because its primitive is observations - its only an issue if you want look deeper. Some people are worried by it, others, like me, don't particularly care. All theories have primitives not explained by the theory - that observations are QM's primitives concerns me not in the least.

Thanks
Bill

 

[maline]

There is a place that's different - just after decoherence

When you say it's "different", do you mean in an ontological sense, or just in the practical sense- that that's the point beyond which we can forget about interference effects?

 

[bhobba]

When you say it's "different", do you mean in an ontological sense, or just in the practical sense- that that's the point beyond which we can forget about interference effects?

I mean it in the sense that just after decoherence is a defined point in time. That was the issue that worried Von-Neumann. The only place that was different is the conciousness of a conscious observer that why he introduced the concept - we now know different.

Thanks
Bill

 

[Fredrik]

I think what all these replies assume is that the measurement problem has at least one solution, ie. Bohmian Mechanics or MWI can be considered "consensus" quantum mechanics.

My view on the "measurement problem" is that it's partially answered by decoherence calculations, and that the rest of it consists of misguided expectations about what a theory is supposed to do.

As long as the measurement problem has not been solved or is asserted not to matter, the observer retains fundamental status. One may argue whether the observer is the same as consciousness, but that is semantics. Neither are explained in terms of more fundamental things, so they are just names for objects that fundamentally postulated, so one can call it the "observer" or "consciousness" or "pink fairies". "Consciousness" is not a terrible term, because bhobba and Weinberg's preferred term is "common sense", and Witten calls it "consciousness".

Yes, of course the observer is consciousness. Science requires theories to be falsifiable. A theory is falsified by verifying that the relative frequency of a specific outcome is different from what the theory has predicted. "Outcomes" are by definition states (of some object) that can easily be distinguished by a human observer. So the "fundamental status" of consciousness/observers is a rather trivial consequence of the fact that the rules of science have been chosen by humans who are conscious when they make their observations.

 

[bhobba]

My view on the "measurement problem" is that it's partially answered by decoherence calculations, and that the rest of it consists of misguided expectations about what a theory is supposed to do.

Well said.

Thanks
Bill

 

[stevendaryl]

My view on the "measurement problem" is that it's partially answered by decoherence calculations, and that the rest of it consists of misguided expectations about what a theory is supposed to do.

Well, the notion of what a scientific theory is supposed to do has shifted over time. Once upon a time, it was about understanding the world. Later, this shifted to modeling the world (and the models themselves might be mathematically complex, so they don't necessarily help much when it comes to "understanding" in the psychological sense). But after QM, the goals shifted once again to merely being able to make quantitative predictions about experiments, and forget about modeling the world.

A lot of people act as if it were unreasonable to ever want more than that, but I think that's a matter of making lemonade out of lemons. If the best you can do is make quantitative predictions, then you convince yourself that you never wanted anything else. But people don't go into science to make predictions. They go into science to understand the world.

 

[bhobba]

A lot of people act as if it were unreasonable to ever want more than that,

Of course its not unreasonable. Its just unreasonable to demand there MUST be more.

Thanks
Bill

 

[stevendaryl]

Of course its not unreasonable. Its just unreasonable to demand there MUST be more.

Well, you could say it's unreasonable to demand that the world be comprehensible, at all. Why should it be?

 

[tom aaron]

Of course its not unreasonable. Its just unreasonable to demand there MUST be more.

Yes. This is difficult for humans to accept. We always assume there is something still hidden behind the curtain. If not a god then some balanced equation that all the variables plug into.

 

[craigi]

Well, you could say it's unreasonable to demand that the world be comprehensible, at all. Why should it be?

Because as sentient beings we require comprehensibility. What would we be if the world weren't comprehensible? We certainly wouldn't be having this discussion.

 

[atyy]

My view on the "measurement problem" is that it's partially answered by decoherence calculations, and that the rest of it consists of misguided expectations about what a theory is supposed to do.

That's fine and reasonable. But I would ask, what happens if experiment does verify that Bohmian mechanics is a more accurate description of reality? Would your position then be that all theories are falsifiable anyway, and the motivation for looking for solutions to the measurement problem like Bohmian mechanics were misguided?

Yes, of course the observer is consciousness. Science requires theories to be falsifiable. A theory is falsified by verifying that the relative frequency of a specific outcome is different from what the theory has predicted. "Outcomes" are by definition states (of some object) that can easily be distinguished by a human observer. So the "fundamental status" of consciousness/observers is a rather trivial consequence of the fact that the rules of science have been chosen by humans who are conscious when they make their observations.

But the interesting thing is that the outcome is not the quantum state of an object. That is why quantum mechanics is different from classical physics.

 

[Derek Potter]

That's another thing that isn't going to fly well here. We don't discuss personal theories. That isn't to say thst we can't discuss what you are curious about, every physicist has ideas. The key is to be careful to phrase things in the appropriate way.

Sometimes this goes too far though. Debating the onticity of the wavefunction, for example, is something which in any other science would be laughed out of the room "If your fossils, Mr Paleontogist, are not something to do with real animals, what is the point in digging them up and arranging them to look like skeletons? Why not just say the little bits of mineral that happen to look like bones are the only reality?" But here it tends to be regarded with great suspicion and discussing whether one should abandon realism or merely adapt what one believes to be real is labelled "philosophy" and off-topic. I do not like the heavy-handed moderation but I do understand that Admin wants to keep the forum productive. In their eyes!

 

[Derek Potter]

...the rules of science have been chosen by humans who are conscious when they make their observations.

An assertion which, I feel, lacks compelling evidence :)

 

[atyy]

I mean it in the sense that just after decoherence is a defined point in time. That was the issue that worried Von-Neumann. The only place that was different is the conciousness of a conscious observer that why he introduced the concept - we now know different.

I don't think von Neumann made a mistake there. In decoherence you still have to choose the factorization, so who is choosing the factorization? If it is not subjective ocnsciousness, can the factorization be chosen objectively and consistently? In fact, there are strong arguments that a factorization can be chosen objectively and consistently - that is what the hidden variables of Bohmian Mechanics do - they choose a finest factorization and compose all other factorization from the finest factorization. So Bohmian Mechanics solves (in all test cases to date) the factorization problem.

Basically, I don't think your emphasis on decoherence without explicit mention of the additional assumptions like hidden variables or Many-Worlds can justify saying that von Neumann was in error. His error was not the von Neumann chain, that was simply one way of stating the measurement problem that exists if hidden variables are not possible, which was certainly a positive contribution.

 

[Derek Potter]

Because as sentient beings we require comprehensibility. What would we be if the world weren't comprehensible? We certainly wouldn't be having this discussion.

Sure we would. The Lizard people - in whose computer we are merely simulations - live in a vastly more complex world totally incomprehensible to us. But for fun they feed us data taht make us think we understand stuff - and then throw a curved ball, like the PE effect, to make us think again.

 

[craigi]

Sometimes this goes too far though. Debating the onticity of the wavefunction, for example, is something which in any other science would be laughed out of the room "If your fossils, Mr Paleontogist, are not something to do with real animals, what is the point in digging them up and arranging them to look like skeletons? Why not just say the little bits of mineral that happen to look like bones are the only reality?" But here it tends to be regarded with great suspicion and discussing whether one should abandon realism or merely adapt what one believes to be real is labelled "philosophy" and off-topic. I do not like the heavy-handed moderation but I do understand that Admin wants to keep the forum productive. In their eyes!

There's a problem here in that "real" means many different things in physics. This leads to prescisely the problem which you're talking about. When the ontology of the wavefunction is debated, it's not comparable to whether fossils are real, but it's easy to see how the confusion arises. I'd recommend staying away from the word "real" altogether, unless it's for well defined and acknowleged concept.

 

[atyy]

Sometimes this goes too far though. Debating the onticity of the wavefunction, for example, is something which in any other science would be laughed out of the room "If your fossils, Mr Paleontogist, are not something to do with real animals, what is the point in digging them up and arranging them to look like skeletons? Why not just say the little bits of mineral that happen to look like bones are the only reality?" But here it tends to be regarded with great suspicion and discussing whether one should abandon realism or merely adapt what one believes to be real is labelled "philosophy" and off-topic. I do not like the heavy-handed moderation but I do understand that Admin wants to keep the forum productive. In their eyes!

Reality is not real. Reality is just a tool to predict the outcomes of observations :)

 

[Derek Potter]

There's a problem here in that "real" means many different things in physics. This leads to prescisely the problem which you're talking about. When the ontology of the wavefunction is debate, it's not comparable to whether fossils are real. I'd recommend staying away from the word "real" altogether, unless it's for well defined and acknowleged concept.

If you can give a couple of examples of what "reality" means then I might agree with you. As far as I know, none of them deviate from "reality = that which exists", the debate is totally to do with what exists, not its manner of existing.

 

[Derek Potter]

Reality is not real. Reality is just a tool to predict the outcomes of observations :)

Wonderful. All the most difficult problems of (the forbidden p-word) solved by physicists who refuse to say what their symbols mean.

 

[atyy]

Wonderful. All the most difficult problems of (the forbidden p-word) solved by physicists who refuse to say what their symbols mean.

Physicists are not real. Physicists are just a tool to predict the outcomes of measurements. P = Physics :)

 

[craigi]

Real means "exists".

In the english language yes, but let me give you a non-exhaustive list of the ways it's used in QM. The real part of a complex number, objectively real, subjectively real, ontologically real, counterfactual definite, a measurable property.

And then people like yourself use the word loosely to mean "exists".

Can you see why it causes confusion?