If, as Richard Feyman insisted, nobody understands quantum mechanics

[Bob Eldritch]

MWI is, to me, very strange, almost like magic not physics, but it's a free country. Believe MWI if you want, but why?
Regards,
Reilly Atkinson

Only because MWI resolves the indeterminacy problem to the extent that you can say that in the world observed the results of any quantum experiment could not be otherwise. But then, of course, the indeterminacy is thus only pushed elsewhere as the result of the inability in determining whether or not other worlds exist where the results of quantum experiments are otherwise.

 

[JesseM]

Only because MWI resolves the indeterminacy problem to the extent that you can say that in the world observed the results of any quantum experiment could not be otherwise.

As I said in my responses to reilly and Tomsk, the lack of indeterminacy is not the main reason people like the MWI--issues like the difficulty defining the boundary between quantum systems and classical measuring-system, the difficulty understanding what it would mean to have an entire universe governed by quantum laws with no external measuring system, and the problem of avoiding nonlocality are bigger reasons. A theory whose only "problem" was indeterminacy would probably bother far fewer physicists.

 

[reilly]

My suspicions about MWI were confirmed by David Deutsch's The Fabric of Reality. He talks about parallel universes in the spirit of MWI. He talks about "shadow photons", which apparently traverse universes. I ended up spending a lot of time going through his book with a fine tooth comb. He must have written it in a hurry, the book is full of contradictions, and hardly worth reading.

But, he led me to questions like ; where are these universes; do they interact; where does the energy come from to create the parallel universes; is their creation instantaneous (relativity would disaprove), or do they expand at the speed of light? Seems to me that the collection of universes form a non-separable Hilbert Space, not a nice thing.

As I've written before, my take is that wave function collapse is purely the result of neural learning. But, why is not MWI confined to our minds -- we can certainly imagine MWI, a plausible circumstance.

There are many systems in the classical world which require stochastic dynamical equations; control theory, cascades generated by cosmic rays; random walk, and so on. I see no reason at all that a MWI approach could not be used. How about breaking a membrane and allowing two gases at different temp and pressure to interact. What's the probability that a molecule could transverse the system without a collision -- how could I measure such a case? What about Kalman Filters?

Regards,
Reilly Atkinson

 

[JesseM]

As I've written before, my take is that wave function collapse is purely the result of neural learning.

And do you think the fundamental laws governing the brain are different from the laws governing the individual particles that make it up?

 

[reilly]

[

• QUOTE=JesseM;1314060]And do you think the fundamental laws governing the brain are different from the laws governing the individual particles that make it up?[/QUOTE]

No, of course not. In fact, quantum mechanics plays a key role in vision -- converting photons into signals that travel up the optic nerve.

Why would I think otherwise? Why do you ask?
Regards,
Reilly Atkinson

 

[JesseM]

And do you think the fundamental laws governing the brain are different from the laws governing the individual particles that make it up?

No, of course not.

Then how can the "collapse" be a consequence of anything going on in the brain, as opposed to something that must be applied to the brain by an external classical measuring-device to put it in a definite state? If you treat the behavior of the brain using the same rules as other quantum systems--constructing a wavefunction for its state and letting the state evolve according to the Schroedinger equation--then you just end up predicting a the brain is in a superposition of very different macroscopic states, nothing inherent to the system itself will cause a collapse to a single classical-looking state.

 

[vanesch]

That is perhaps one of the best explanations of MWI. I particularly like your analogy with static spacetime. Is that analogy invented by you, or first introduced by someone else? If the latter is correct, can you give me the reference where this analogy has been originally introduced?

I did find this view myself, but it might very well be that there are papers on it. I got "beaten up" by some relativists when I made those statements

 

[vanesch]

My suspicions about MWI were confirmed by David Deutsch's The Fabric of Reality. He talks about parallel universes in the spirit of MWI. He talks about "shadow photons", which apparently traverse universes. I ended up spending a lot of time going through his book with a fine tooth comb. He must have written it in a hurry, the book is full of contradictions, and hardly worth reading.

I never read it, but I find Deutsch close to a sect guru, with what I know of him.

But, he led me to questions like ; where are these universes; do they interact; where does the energy come from to create the parallel universes; is their creation instantaneous (relativity would disaprove), or do they expand at the speed of light?

You don't ask that question when, say, an electron is in a superposition of two position states, don't you ? You don't ask: where did the energy, lepton number etc... come from to have now an electron at position x1 and another (?) electron at position x2.

As I've written before, my take is that wave function collapse is purely the result of neural learning. But, why is not MWI confined to our minds -- we can certainly imagine MWI, a plausible circumstance.

Well, I could give a speculative answer to that question, but maybe this will lead us too far astray. I would say that a mind cannot at the same time have the "impression of free will" and be aware of a superposition of "states of awareness", because in that case, he could (have the impression to) act according to things observed in different branches. But if that is the case, then the physical interaction resulting from such a decision would introduce a coupling between two terms in the wavefunction, which is impossible for a linear time evolution operator. With a linear time evolution operator, you're not supposed to be able to interact with other terms. So, or you cannot be "aware" of them, or you would necessarily have the impression that you cannot "freely decide what to do".
For instance, imagine that you had a "multi-world" awareness, and you were doing a quantum experiment with the state |a> + |b>, where you measure quantity A and you'd have outcome a or outcome b.
You could say, "if I see a in one world, and b in another, I press the red button, but if I see only a, I press the green button".
Clearly, in MWI, you would both see the a and the b outcome then, and you'd push the red button.
If the incoming state would be state |a>, you'd press the green button.
But you're not supposed to be able to do this!

Indeed, let us look at the unitary evolution:
|nobutton>|a> evolves into |greenbutton>|a>
but |nobutton>(|a> + |b>) should evolve into |redbutton>(|a>+|b>).

But this can never be happening with a purely unitary time evolution operator (the |a> part should evolve into |greenbutton>|a> in any case).

There are many systems in the classical world which require stochastic dynamical equations; control theory, cascades generated by cosmic rays; random walk, and so on. I see no reason at all that a MWI approach could not be used.

MWI is not there to "explain" the randomness. It is there to explain the apparent clash between projection and unitary evolution.

 

[reilly]

Then how can the "collapse" be a consequence of anything going on in the brain, as opposed to something that must be applied to the brain by an external classical measuring-device to put it in a definite state? If you treat the behavior of the brain using the same rules as other quantum systems--constructing a wavefunction for its state and letting the state evolve according to the Schroedinger equation--then you just end up predicting a the brain is in a superposition of very different macroscopic states, nothing inherent to the system itself will cause a collapse to a single classical-looking state.

But I know several things: the brain, on an atomic scale is huge, and very complex. The brain is a classical system -- networks of non-linear electrical devices (neurons). The generation of neural pulses and neural transmission are well understood, described as they are by the Hodgkin-Huxley Eq. There's really no more practically important quantum superposition in the brain than there is in a door bell.

Note that the human mind can effectively be in what might be called a superposition of ideas. That is, "Will I make the next light?" and "What's the probability that an electron can traverse a a slab of crystal, many angstroms thick, without any collisions. That is, I can imagine both making the light and not making the light. When I get there, and say we are talking green, then our "neural pattern " collapses to " made it"-- and that's generically true for any probability situation. In other words, collapse is connected with a change of knowledge. By the way, this approach to QM came from Sir Rudolph Peierls, one of the early and prolific workers in QM, for which he won a Nobel Prize -- no crackpot he. Also, Prof. Wigner was sympathetic to Peierls poit of view.

Where is it written that QM must explain the Measurement Problem?


Regards,
Reilly Atkinson

Regards,
Reilly Atkinson

 

[Mike2]

Note that the human mind can effectively be in what might be called a superposition of ideas...In other words, collapse is connected with a change of knowledge.

Perhaps we are deceived in thinking that our mathematical models describe actual reality, when they are really a description of our understanding (perception) of it. Our equations are inventions of our minds just as much as our observations. So collapse of the wave function may be just a feature of the math, not reality itself.[/url]

 

[Anonym]

Where is it written that QM must explain the Measurement Problem?

This is the content of A.Einstein erroneous requirement to the completeness of the Quantum Theory (5-th Solvay Congress). It is Classical Physics must explain the Measurement Problem. It is exactly as in case of Maxwell ED vs Newtonian Mechanics. The less general theory must be reformulated to fit the more general theory and not vice versa. The measurement apparatus obey laws of classical physics. The proper generalization of classical physics (wave mechanics) is required to include the existent formulation and to provide the natural explanation of the collapse of wave function.

Regards, Dany.

P.S. Please give me reference to mentioned paper by R.Peierls.

 

[JesseM]

But I know several things: the brain, on an atomic scale is huge, and very complex. The brain is a classical system -- networks of non-linear electrical devices (neurons). The generation of neural pulses and neural transmission are well understood, described as they are by the Hodgkin-Huxley Eq. There's really no more practically important quantum superposition in the brain than there is in a door bell.

I agree, but what's the theoretical explanation for this? The goal of reductionist physics is to find the most basic laws of the universe, and then understand higher-level laws as emerging from the more basic ones...a reductionist would say that all the laws of chemistry should in principle be derivable from quantum physics (quantum electrodynamics might be sufficient), even though in practice it would be very difficult and only some fairly simple situations like hydrogen atoms have been "reduced" in this way. But there doesn't seem to be any fundamental problem with the idea of such a derivation, whereas the whole issue of collapse and the need for external classical measuring-devices seems to pose a fundamental problem for deriving the classical world from quantum laws. Even if you reject reductionism and imagine that the universe operates according to a sort of patchwork of different laws in different situations, surely nature must have some well-defined rules for the precise conditions where one set of laws is overridden by another set, we don't expect nature to rely on the sort of fuzzy verbal distinctions that we do, that would seem to be a kind of anthropomorphism.

Note that the human mind can effectively be in what might be called a superposition of ideas. That is, "Will I make the next light?" and "What's the probability that an electron can traverse a a slab of crystal, many angstroms thick, without any collisions. That is, I can imagine both making the light and not making the light. When I get there, and say we are talking green, then our "neural pattern " collapses to " made it"-- and that's generically true for any probability situation. In other words, collapse is connected with a change of knowledge.

But in the classical world there is no "interference" between possibilities, you are free to imagine that each object was definitely in one state or another before you observed it. This is like a "mixed state" in QM, which is quite different from a "pure state".

Where is it written that QM must explain the Measurement Problem?

Well, if you want a coherent picture of the universe as a whole, something needs to explain it. I had thought that when you said "my take is that wave function collapse is purely the result of neural learning", you were suggesting some sort of explanation.

 

[Hurkyl]

Perhaps we are deceived in thinking that our mathematical models describe actual reality, when they are really a description of our understanding (perception) of it. Our equations are inventions of our minds just as much as our observations. So collapse of the wave function may be just a feature of the math, not reality itself.

If we had a theory that perfectly described everything we could possibly perceive, then what more could we possibly want? Things that have no perceptible effects are scientifically irrelevant.

 

[Anonym]

Well, if you want a coherent picture of the universe as a whole, something needs to explain it. I had thought that when you said "my take is that wave function collapse is purely the result of neural learning", you were suggesting some sort of explanation.

Bravo! Reilly, you see now where you arrived “after spending time moving lead bricks around for shielding for electron scattering experiments, and working extensively with data from such experiments”. Congratulations!

In addition, go into the street and find “the living and dead cat (pardon the expression) mixed or smeared out in equal parts.”

Regards, Dany.