Qualia and Quantum Mechanics

  • Thread starter Varon
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  • #51
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I know they are using a subtle approach to their weak measurements, that's not the point I'm making. I'm saying that no matter how they do it, the "average trajectories" they get are obviously the same as the streamlines of what we would call the "photon fluxes" in a completely classical limit where they are just the energy flux in a classical wave going between two slits. So I could easily draw their exact same figure with entirely classical measurements of an entirely classical wave. So their result (that figure) is nothing the least bit surprising. So what is their claim? That somehow the "weak measurements" are telling us something more than the exact same figure made purely classically? I see no evidence for that claim at all, if you have the exact same output as a classical approach, you don't have any additional information there, you just have a much more complicated way of extracting the same information.

The other way to get that same figure is to send one photon through at a time, and just let it hit a detector on a wall that is at variable distances from the slits, running the experiment over and over. Normalize the patterns on all those walls to have zero divergence, and draw the stream lines. Same picture again, still no trajectories of any individual photons, just an aggregate of different detector realities uniting to make a pretty picture.
You are saying a classical wave (without any particle) can also produce the same results. Ok.
Try to use pure wave on the following description (see below). What is counterpart to "photon polarization" or "Photons that enter the calcite perpendicular to the surface pass straight through" or "Photons that enter at a shallower angle follow a longer path through the calcite". Can you put pure wave into a calcite? See below:

Excerpt from http://scienceblogs.com/principles/2011/06/watching_photons_interfere_obs.php [Broken]

"How do you only measure a tiny bit of the momentum? Isn't that a "little bit pregnant" sort of contradiction? The system they used for this is really ingenious: they use the photon polarization as a partial indicator of the momentum. They send their original photons in in a well-defined polarization state, then pass them through a calcite crystal. Calcite is a "birefringent" material, which changes the polarization by a small amount depending on the amount of material the photon passes through.

Photons that enter the calcite perpendicular to the surface pass straight through, and travel a distance equal to the thickness of the calcite. Photons that enter at a shallower angle follow a longer path through the calcite (think of it like cutting a loaf of French bread on the bias-- the angle-cut pieces are longer than the thickness of the loaf), and thus experience a greater change in polarization. The polarization of an individual photon then depends on the angle it took through the calcite, which tells you the direction of its momentum. The magnitude of the momentum is determined by the wavelength, which is the same for all the photons, so this gives you the information you need for the trajectory."
 
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  • #52
Ken G
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You are saying a classical wave (without any particle) can also produce the same results. Ok.
Try to use pure wave on the following description (see below). What is counterpart to "photon polarization" or "Photons that enter the calcite perpendicular to the surface pass straight through" or "Photons that enter at a shallower angle follow a longer path through the calcite". Can you put pure wave into a calcite? See below:
I'm saying the details of how they generate that figure doesn't matter, what matters is its information content, which I can get in much easier ways. Let me ask if you agree that the "average trajectories" that they plot are indeed exactly the same as we would get via my method #2 above-- running one photon at a time through exactly their configuration, and just putting the wall at different distances, and collect the aggregate detections. Then build up a concept of the aggregate photon flux by taking those measurements, normalizing the total detection numbers to be a constant total for every wall distance used (zero divergence), and then drawing the "field line density" for that divergenceless detection field? That's exactly how we would generate a concept of "aggregate photon flux" in this very two-slit experiment, in a completely classical limit of many iterations of slightly different experimental setups (the distance to the wall being the sole variable).

If we can agree that I can get the exact same figure my way, with no subtle "weak measurements", then the question to ask is: what additional information are they extracting with their clever measurements if they end up with the exact same figure I get?

Note that it makes no difference how clever their measurements are-- if they can tell which slit the photon went through, they won't get that photon to participate in an interference pattern anywhere. That is all the CI needs to hold.
 
  • #53
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Wish this thread is in QM Forum so the quantum physicists can challenge your claim or comment. Anyway. Why don't you participate anymore at the QM Forum. Are you bored there, Ken?
 
  • #54
Ken G
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Nah, just busy! You're right, this really should be over there at this point. Hopefully someone will start a thread on this experiment over there, but my guess is, the fact that the result looks just like what anyone would call the photon flux pattern in a two-slit experiment, it won't create much of a stir. My opinion is, these folks have simply created a very roundabout way to measure what is easily construed as a classical wave energy flux distribution.
 
  • #55
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Nah, just busy! You're right, this really should be over there at this point. Hopefully someone will start a thread on this experiment over there, but my guess is, the fact that the result looks just like what anyone would call the photon flux pattern in a two-slit experiment, it won't create much of a stir. My opinion is, these folks have simply created a very roundabout way to measure what is easily construed as a classical wave energy flux distribution.
But even though the experiment didn't make simultaneous position and momentum measurement. At least what it shows is that between measurement, the particle exists! There is a variant of the Copenhagen where they state that in between measurements. The particle is not even in spacetime. A second variant believe the particle turning into pure wave. So you mean this experiment didn't refute this second variant where the particle just turns into pure wave in between measurement? And it only refutes this variant where particles are not located in spacetime in between measurement?
 
  • #56
apeiron
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If we can agree that I can get the exact same figure my way, with no subtle "weak measurements", then the question to ask is: what additional information are they extracting with their clever measurements if they end up with the exact same figure I get?
The difference here is surely that the photon path is (weakly) observed. Yes, there is absolutely no surprise in the result. But the point was there could have been, with an actual observation.

For instance, the photons could all have come through just a single slit or tunneled through the barrier or whatever. Or been pure wave as Varon says. Not likely outcomes. But the only way to rule them out is observation.

The fact that each path is the average of some 32,000 events makes it very averaged. But still, this seems like new information.
 
  • #57
Ken G
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I can accept that the observation achieves a concept of "photon lines of flux" via a different observation strategy than the most obvious way to do it (with variable wall distances), and who knows if it might have obtained a different result, but it would have been very surprising if it had. From the point of view of "information is surprise", I'd have to say getting the exact same result that classically aggregated "photon flux lines" would give can't be much in the way of new information. The experiment allows us to go on imagining that a classical wave-energy flux is the same thing as an aggregated discrete photon flux, but that's just what we would have imagined already. I can't say what has actually been learned here, but I certainly don't see it as a challenge to the CI stance that "individual particles do not follow trajectories unless they are observed in such a way as to establish a trajectory," nor that "particles don't participate in interference patterns if you know which slit they went through", but you can create a concept of aggregate photon fluxes, and draw streamlines consistent with that, and still have the interference pattern.

The prevailing point is that drawing photon "lines of flux" is just not the same thing as drawing individual photon trajectories, though the two are easily confused. I'd say what they have mostly done is found a very complicated and subtle way of making it easier to fall into that confusion.
 
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  • #58
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I can accept that the observation achieves a concept of "photon lines of flux" via a different observation strategy than the most obvious way to do it (with variable wall distances), and who knows if it might have obtained a different result, but it would have been very surprising if it had. From the point of view of "information is surprise", I'd have to say getting the exact same result that classically aggregated "photon flux lines" would give can't be much in the way of new information. The experiment allows us to go on imagining that a classical wave-energy flux is the same thing as an aggregated discrete photon flux, but that's just what we would have imagined already. I can't say what has actually been learned here, but I certainly don't see it as a challenge to the CI stance that "individual particles do not follow trajectories unless they are observed in such a way as to establish a trajectory," nor that "particles don't participate in interference patterns if you know which slit they went through", but you can create a concept of aggregate photon fluxes, and draw streamlines consistent with that, and still have the interference pattern.

The prevailing point is that drawing photon "lines of flux" is just not the same thing as drawing individual photon trajectories, though the two are easily confused. I'd say what they have mostly done is found a very complicated and subtle way of making it easier to fall into that confusion.

Hi Ken, There is an active thread in the QM Forum that discusses precisely this... and many people are confused about it. I shared them your view that pure classical EM wave can produce the same result and some agree, some disagree. So pls. visit the thread and participate, here's the link.


https://www.physicsforums.com/showthread.php?t=503861&page=10

Thanks.
 
  • #59
apeiron
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The prevailing point is that drawing photon "lines of flux" is just not the same thing as drawing individual photon trajectories, though the two are easily confused. I'd say what they have mostly done is found a very complicated and subtle way of making it easier to fall into that confusion.
Speaking up for ontology, I would say that there is equal danger in the "hey, anything could be happening" view. So I see this as evidence that reality is grainy, resolvable in an approximate way, but never in an absolute way.

Saying reality is determinate and saying it is constrained are two different things. And implying it is fundamentally unconstrained is another thing yet again.

So this experiment increases the evidence in support of a constraints-based view of ontology, and goes against both determinism and the "well, if its not determined, it could be anything" alternative.

CI accepts the epistemic divide between observers and observables. But it is ontically agnostic. It has no theory about "observers". This has to be unsatisfactory in the long run.

Systems science already has developed semi-mathematical theories about constraints and degrees of freedom. It is an ontic framework that can generalise the relationship between observers and observables.
 
  • #60
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  • #61
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I'm saying the details of how they generate that figure doesn't matter, what matters is its information content, which I can get in much easier ways. Let me ask if you agree that the "average trajectories" that they plot are indeed exactly the same as we would get via my method #2 above-- running one photon at a time through exactly their configuration, and just putting the wall at different distances, and collect the aggregate detections. Then build up a concept of the aggregate photon flux by taking those measurements, normalizing the total detection numbers to be a constant total for every wall distance used (zero divergence), and then drawing the "field line density" for that divergenceless detection field? That's exactly how we would generate a concept of "aggregate photon flux" in this very two-slit experiment, in a completely classical limit of many iterations of slightly different experimental setups (the distance to the wall being the sole variable).

If we can agree that I can get the exact same figure my way, with no subtle "weak measurements", then the question to ask is: what additional information are they extracting with their clever measurements if they end up with the exact same figure I get?

Note that it makes no difference how clever their measurements are-- if they can tell which slit the photon went through, they won't get that photon to participate in an interference pattern anywhere. That is all the CI needs to hold.
Ken, Expert in the forum I referred to above didn't agree that you could get the same figure by your method. If you have time, pls go there so you can discuss your view as it is QM forum. Here at philosophy, Quantum Mechanic is not here... only armchair philosophers or metaphysicists who hold totally newtonian views as you agreed before, or in case you really missed the original paper and it produced new stuff... at least you know so.
 
  • #62
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Now you are getting into the variants of Copenhagen. In "purist" Copenhagen, that of Bohr, the opposite is true-- nothing is quantum, there is no "quantum world." There is only the world of our observations-- the entire quantum realm is something just imagined, whatever we need to do the calculation to get the right prediction. von Neumann is bridging from the empiricist Copenhagen view to the rationalist many-worlds view, and his is the only one that I have a hard time seeing the consistency of. That seems to be the thrust of your issue too, but Bohr would not have had that problem.
Ken. We are discussing now about your statement "the entire quantum realm is something just imagined" in the QM forum thread https://www.physicsforums.com/showthread.php?t=494788&page=11

A person my_wan is confused by certain meaning of your statement. He said for example: (See message starting #165)

"Again, this is highly dependent on what is meant by "no" quantum world. Is Ken referring to nonexistent in the sense that our everyday world of observations is all there is because the quantum world is nothing more than that same world, or is it an existential nonexistence? It appears to me Ken is flirting with the existential version here, but even that is tricky. Because what exactly about it is existentially nonexistence if it is merely the world we experience? This I tried to qualitatively formulate previously by showing how even the limited frame dependent notion of space and time disappears at a fundamental level. So I need more to even guess at Ken's response."

So pls. go to that thread and clarify your confusing views. Thanks.

https://www.physicsforums.com/showthread.php?t=494788&page=11
 
  • #63
Ken G
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First of all, they are not my confusing ideas, I am explaining Bohr's perspective. Which I agree with, and do not find confusing. But I'll do it on that thread, yes.
 
  • #64
Evo
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Ken, Expert in the forum I referred to above didn't agree that you could get the same figure by your method. If you have time, pls go there so you can discuss your view as it is QM forum. Here at philosophy, Quantum Mechanic is not here... only armchair philosophers or metaphysicists who hold totally newtonian views as you agreed before, or in case you really missed the original paper and it produced new stuff... at least you know so.
Telling people to go to another forum? This thread is closed.
 

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