I Which-path info exists = deterministic context?

[CHOP]

Let's refer to a simple double slit experiment.
It is often said: if which-path info is available, outcome is not interference pattern, but particle pattern.
What is the situation such that which-path info does exist?
If it cannot be said in a general way, what is one example of how the which-path info would manifest in nature?
thank you,

 

[DrClaude]

There needs to be an interaction between the particle and something else (usually a detector) such that it would be possible, even only in principle, to find out which slit the particle went through.

My favourite example is https://arxiv.org/abs/quant-ph/0402146, where heating up a molecule such that it emits a photon is enough to make the interference pattern even though the photon is not detected.

 

[CHOP]

excellent, thank you for your response! non interference pattern (IP) you mean i assume..

just to clarify,
there has to be the necessity of interaction for at least one of the two possibilities, on every particle-shot. Is that correct?

because,

with detector at one slit, it detects 50% of particles (which would otherwise contribute to the IP). the other 50% of particles also would otherwise contribute to the IP, but no interaction has occurred for them.

which-path info would refer to the 50% of the time where the interaction occurred.

but the real criteria (for the non interference pattern) would be what i said about necessity. Is that correct?

also, thanks for link,

 

[DrChinese]

The clearest example I cite to understand what's at play for double slit with a single photon at a time, many repeated iterations so that a pattern builds up:

Place a polarizer by each of the 2 slits. If the polarizers are parallel, there WILL be an interference pattern. If the polarizers are perpendicular (orthogonal), there will be NO interference pattern. The explanation is that the which path information is not present in one, but is present (but not learned) in the other. This result cannot be attributed to interactions with the slits, or other types of interactions with the usual photon detectors.

http://sciencedemonstrations.fas.ha...-demonstrations/files/single_photon_paper.pdf

The experiment also demonstrates what happens when the which path information is erased. Hopefully you can guess what happens.

 

[CHOP]

Place a polarizer by each of the 2 slits. If the polarizers are parallel, there WILL be an interference pattern. If the polarizers are perpendicular (orthogonal), there will be NO interference pattern. The explanation is that the which path information is not present in one, but is present (but not learned) in the other. This result cannot be attributed to interactions with the slits, or other types of interactions with the usual photon detectors.

Okay this is very interesting. Thanks for your response. So in this case there is no interaction (please correct me if wrong).

This experiment seems to be the equivalent of one using two open slits with no filters, then blocking only one slit (getting the result), then blocking only the other slit (getting the result), then putting the two results together (representing the case where filters are not oriented the same way).

If that is the equivalent, then we can say:
The experiment is just two blocked slit experiments, combined. Right?

But then, in that case: in what way is the path-info manifesting in nature? If it's not about path-info manifesting in nature, what is it about? The paper says "it is in principle knowable".

But the pattern is not really about whether knowing the path is possible, I presume. I presume it's about something else (in nature), and that something else gives rise to knowing is possible. So, what is that 'something else' ?

 

[CHOP]

actually, if that IS the equivalent, there is no need for path info to be manifesting in nature!
Is that right?

 

[PeterDonis]

in this case there is no interaction

No, that's not correct. The light is interacting with the polarizers. The fact that the results of those interactions at each slit are not recorded does not mean the interactions aren't there.

This experiment seems to be the equivalent of one using two open slits with no filters, then blocking only one slit (getting the result), then blocking only the other slit (getting the result), then putting the two results together (representing the case where filters are not oriented the same way).

I have no idea why you would think that. Remember, on each run, a single photon is passing through the experiment. You can't pass a single photon through the experiment while having two open slits, then blocking one slit and getting a result, then blocking the other slit and getting a result. The experiment has to be set up just one way, and that's it.

 

[CHOP]

No, that's not correct. The light is interacting with the polarizers. The fact that the results of those interactions at each slit are not recorded does not mean the interactions aren't there.

In what way is a photon interacting with the polarizer?
Also, I didn't say anything about recording interactions. You just brought that in from nowhere.

I have no idea why you would think that.

Well, why didn't you ask, Peter? Then you'd have an idea.
Let's be productive here.

Remember, on each run, a single photon is passing through the experiment.

Yes Peter, that's how things work. Why are you assuming that I am thinking more than one photon went through?
In fact, it's always the case that one photon goes through at a time, even when you spray them.
The frequency has just been increased.

You can't pass a single photon through the experiment while having two open slits,

Wrong. Yes you can.

then blocking one slit and getting a result,

Wrong. You can even have a slit blocked. Photons still go through the open slit.

then blocking the other slit and getting a result. The experiment has to be set up just one way, and that's it.

If you want to say that something is not equivalent, then you should explain why, not just say "has to be done this way". That's not a very scientific approach.

 

[PeterDonis]

In what way is a photon interacting with the polarizer?

Um, because that's the definition of a polarizer? Something that interacts with photons in order to only allow those with a particular polarization to pass through?

Why are you assuming that I am thinking more than one photon went through?

Because that's what you described. You said:

This experiment seems to be the equivalent of one using two open slits with no filters, then blocking only one slit (getting the result), then blocking only the other slit (getting the result), then putting the two results together (representing the case where filters are not oriented the same way).

In order to do what you say seems to be equivalent, you would need to run multiple experiments, with multiple photons. There is no way to do "two open slits with no filters, then blocking only one slit (getting the result), then blocking only the other slit (getting the result)" with a single run of the experiment using a single photon. You have to make three runs, each with its own photon, in the three different configurations you describe. And no, that would not be equivalent to a single run with polarizers at the slits.

Wrong. You can even have a slit blocked. Photons still go through the open slit.

Wrong. Yes you can.

Apparently you did not grasp my point. You can do all of these things one at a time, in separate runs of the experiment. You cannot do them all at once in a single run of the experiment, which was the point I was making (see above).

 

[PeterDonis]

it's always the case that one photon goes through at a time, even when you spray them.
The frequency has just been increased.

This is not correct. It is perfectly possible to raise the beam intensity enough that the expected value of photon number at any given time is more than one.

 

[CHOP]

Um, because that's the definition of a polarizer? Something that interacts with photons in order to only allow those with a particular polarization to pass through?

I didn't ask why you think there is interaction. I asked what I asked, which is, how does the polarizer interact with the photon.
And I am talking about the photons that pass through, since only they contribute to the outcome.

Because that's what you described.

No I didn't. You are confusing things. I was talking about an equivalence. Not the experiment at hand.
But even still you are wrong, because again, even when photons are sprayed, it is ONE at a time.

In order to do what you say seems to be equivalent, you would need to run multiple experiments, with multiple photons.

Of course. Once again, why are you assuming that not multiple photons would be used? Why didn't you ask?
It is well understood that the pattern emerges after many hits, not one hit.
A single photon does not do anything toward one kind of pattern. The pattern is a statistical entity.

There is no way to do "two open slits with no filters, then blocking only one slit (getting the result), then blocking only the other slit (getting the result)" with a single run of the experiment using a single photon.

Of course. Why are you thinking a single photon can be used for more than one experiment? How can you have a photon registerer and then use that photon all over again? They are not recyclable Peter. A photon's life is finished the instant it is hits anything with mass.

And no, that would not be equivalent to a single run with polarizers at the slits.

Your version of the experiment as you described it can't be equivalent, you got that right. It can't even not be equivalent, because it can't even happen.

Apparently you did not grasp my point. You can do all of these things one at a time, in separate runs of the experiment. You cannot do them all at once in a single run of the experiment, which was the point I was making (see above).

No, it is you Peter who is simply confusing what is going on here. Again, if you had asked clarifying questions, you would have not been confused.

 

[CHOP]

It is perfectly possible to raise the beam intensity enough that the expected value of photon number at any given time is more than one.

The point is, that there is an enormous range of frequencies available, from single isolates shots to incredible rapid fire, and all of that is simply ONE at a time. As for your claim that 'it is possible' to get more than ONE at a time (in the smallest possible time interval), you realize that saying such a thing is meaningless except as saying 'they pass through the slits at the same time'? And take a guess at what the slits edges look like to a photon. If you want to say that the intensity can be made so great that two photons (or more) will pass exactly the same distance through the slit at exactly the same time, then you will need to provide evidence (of that).

 

[DrChinese]

Okay this is very interesting. Thanks for your response. So in this case there is no interaction (please correct me if wrong).

This experiment seems to be the equivalent of one using two open slits with no filters, then blocking only one slit (getting the result), then blocking only the other slit (getting the result), then putting the two results together (representing the case where filters are not oriented the same way).

If that is the equivalent, then we can say:
The experiment is just two blocked slit experiments, combined. Right?

But then, in that case: in what way is the path-info manifesting in nature? If it's not about path-info manifesting in nature, what is it about? The paper says "it is in principle knowable".

But the pattern is not really about whether knowing the path is possible, I presume. I presume it's about something else (in nature), and that something else gives rise to knowing is possible. So, what is that 'something else' ?

As PeterDonis indicated, there is an interaction at the polarizers. Usually for experiments like this, the input polarization is 45 degrees (mid way between V and H). Therefore any single photon that emerges is polarized either H or V (and no longer at 45 degrees). If the polarizers were aligned parallel, there is no way to distinguish the path and so there is interference.

The experiment is definitely not about doing something to one slit (such as blocking it). It is all about the relationship of the slits.

About "the pattern is not really about whether knowing the path is possible": I don't know what else it is about. If there is something else, that is speculation because that is as good a rule as I know.

I am not following your comments to PeterDonis. You might instead focus on the experiment, and trying to follow what it is telling us. It covers a lot of ground, as we are able to see how the relationship of the polarizers allows the which slit information to be encoded in the polarization. And potentially be erased at a later time. And it is not mentioned, but as you alter the difference in relative polarization between the slits, you can vary the amount of interference detected from max to min (and everything in between).

 

[DrChinese]

The point is, that there is an enormous range of frequencies available, from single isolates shots to incredible rapid fire, and all of that is simply ONE at a time. As for your claim that 'it is possible' to get more than ONE at a time (in the smallest possible time interval), you realize that saying such a thing is meaningless except as saying 'they pass through the slits at the same time'? And take a guess at what the slits edges look like to a photon. If you want to say that the intensity can be made so great that two photons (or more) will pass exactly the same distance through the slit at exactly the same time, then you will need to provide evidence (of that).

This has no relevance to the experiment. More photons, less photons, same qualitative results.

 

[CHOP]

This has no relevance to the experiment. More photons, less photons, same qualitative results.

Exactly my point.

 

[PeterDonis]

how does the polarizer interact with the photon.

If you want the details, there's plenty of information on line about various types of polarizers and how they work. You will find that all of them involve some kind of interaction between the polarizer and the photon. Which of course is what we would expect given the definition of a polarizer, as I said.

I am talking about the photons that pass through, since only they contribute to the outcome.

Yes, of course.

I was talking about an equivalence.

Then you are going to need to describe in more detail what experiment you think is equivalent, because the description you've given so far doesn't make it clear to me. Also you need to explain exactly in what respects you think this alternate experiment is equivalent to the one under discussion in this thread, because that's not clear to me either. (I see a possible clue later on in your post, which I'll remark on below, but I'd much rather you gave more details explicitly so I don't have to guess what you mean.)

even when photons are sprayed, it is ONE at a time.

No, they are not. The state of the quantum EM field emitted by the source is not an eigenstate of photon number, so it doesn't have a definite number of photons. The intensity of the source is adjusted so that the expectation value of photon number is approximately 1. But that is not the same as the source "spraying photons one at a time". The source emission process is continuous; the only discreteness is in the hits at the detector.

It is well understood that the pattern emerges after many hits, not one hit.

Yes, obviously. So perhaps what you are saying when you talk about "equivalence" is that you think the same pattern could be built up by making multiple runs with no polarizers where you randomly chose, for each run, whether slit A was blocked, or slit B was blocked. Is that what you intended?

it is you Peter who is simply confusing what is going on here. Again, if you had asked clarifying questions, you would have not been confused.

Ok, I just asked one above. And if you're going to take that attitude, I could just as well respond that if it was clear to you that I was confused, you could have gone ahead and just explained what you actually meant, instead of complaining that I hadn't asked.

 

[CHOP]

thank you for that explanation

The experiment is definitely not about doing something to one slit (such as blocking it). It is all about the relationship of the slits.

i wouldn't say it's about the relationship of these polarized slits. i would say, the relationship of these slits bares a relation with the relation of the slits in all the different variations of the experiment, whose results are likewise. That what these polarizers are doing, is at a deep fundamental level, what other de-cohering methods do, or what even masks are doing. I know this experiment is not about blocking, not in its appearance at least.

About "the pattern is not really about whether knowing the path is possible": I don't know what else it is about. If there is something else, that is speculation because that is as good a rule as I know.

Agreed, all else would be speculation. But let's not forget what we are saying when we say "its about it being possible to know the path". We're not saying that one causes the other, only that this pattern and our being able to know path, corresponds.

And in fact, it's not even that strange. Because they correspond in just the way they would, had those been baseballs (with our eyes closed). That is, they better correspond! Or else we'd have a real problem. Because how could we get the IP in the context that the path is determinable? So yes, we better get the PP if the path is knowable.

Neither is the strangeness that we get a different pattern when we can't know the path. We better not be able to know the path if we got a different pattern! Or else contradict the path. So in a way, things are pretty good (they could have been crazy). I think the problem is really the IP. Making sense of it.

I think it may be helpful to approach the IP, from the mindset that we didn't even know that the pattern changes when measurement at slit, or further upstream. Didn't even know it's related to info being available. Just thinking in terms of "What is it about nature such that this is the appropriate result for everything up to molecules?"

And it is not mentioned, but as you alter the difference in relative polarization between the slits, you can vary the amount of interference detected from max to min (and everything in between).

Right, this is (likely) due to that, as you vary the difference, you vary the probability that polarization is H (or V) for a given photon. That would be the same kind of thing as reducing the light sprayed over the slits electrons pass through, to explore how the IP flows in and out of PP (and vice versa), as in Feynman's writings. Where the frequency of photon/electron collision determines (proportionately) the result.

 

[DrChinese]

i wouldn't say it's about the relationship of these polarized slits.
...
And in fact, it's not even that strange. Because they correspond in just the way they would, had those been baseballs (with our eyes closed). That is, they better correspond! Or else we'd have a real problem. Because how could we get the IP in the context that the path is determinable? So yes, we better get the PP if the path is knowable.
...
Neither is the strangeness that we get a different pattern when we can't know the path. We better not be able to know the path if we got a different pattern!
...
I think it may be helpful to approach the IP, from the mindset that we didn't even know that the pattern changes when measurement at slit, or further upstream. Didn't even know it's related to info being available.
...
Where the frequency of photon/electron collision determines (proportionately) the result.

I still don't see where you are going. You asked for an example of which path information existing, and I provided that. In that experiment, it is the relationship of the polarizers (parallel or crossed) that controls the pattern - nothing else is being varied. But I don't see the relevance of baseballs, strangeness, or where in the stream the patterns form, or the frequency of collisions (of what I am not sure).

If a particle could have gone through either/both slits, there will be an interference effect.

 

[CHOP]

You asked for an example of which path information existing, and I provided that.

I didn't say you didn't offer that. I thanked you for it. Not sure what's the issue.

In that experiment, it is the relationship of the polarizers (parallel or crossed) that controls the pattern - nothing else is being varied.

Right, that's just how the experiment works. I think you are thinking in a way I am not. You are thinking in the sense of "What here is associated with which pattern" -- relative orientation of filters. Whereas, when I think of what "controls" the pattern here, I am not interested in associations.

I want to know the deep down reason (likely something very abstract) which is enabling that this experiment you offer can alter the pattern, by altering relative orientation of filters. The same deep thing that enables all kinds of DS experiments to alter the pattern by altering their own unique parameters.

But I don't see the relevance of baseballs, strangeness, or where in the stream the patterns form, or the frequency of collisions (of what I am not sure).

Well, again, I think it's because you are very focused on specifically the operation of this one experiment. Not really thinking about it in a bigger context.

With regard to "where in the stream the pattern forms", well, it forms wherever the measurement took place. If measurement takes place between source and slits, or around slits, you get PP. If you measure downstream the slits you get IP (you're the screen in that case).

With regard to collisions, i was simply bringing attention to something Feynman wrote (I thought you'd already know it so I didn't explain it much). It relates to what you said about how the IP vanishes (smoothly) as a difference of relative orientation of filters is (smoothly) altered:

Feynman talked about photons used to measure electrons at the slits, and how the intensity of the light relates to how pronounced the IP effect comes out (instead of the PP effect). That's according to there being less frequent photon-electron collisions as intensity drops.

That's the same thing as what you were saying about varying filter orientations: 'more and more electrons get by without collision' is the same kind of circumstance as 'more and more photons get through with alike polarization'.

If a particle could have gone through either/both slits, there will be an interference effect.

Of course, similar to a block/unblocked slit.
But the question is... WHY is nature this way? WHY couldn't it be that we got PP when we made available the other slit? Doesn't that fascinate you?

 

[Nugatory]

I want to know the deep down reason (likely something very abstract) which is enabling that this experiment you offer can alter the pattern, by altering relative orientation of filters.

First, the short answer: Nobody knows.

The longer answer:
Consider the quantum mechanical explanation of the slits+polarizers experiment. QM says that the probability of an incident photon producing a dot at a given point on the screen is calculated by summing the amplitudes of all possible paths to that point. Interference happens because the contributions from the various paths add destructively at some points and constructively at others.

Important digression: "Photon" is not to "dot on screen" as "bullet" is to "bullet hole". What's above is a statement about how we calculate the probability of the photon being detected (that's what "make a dot" means in this context) at a particular point on the screen. There's nothing here that requires us to think in terms of the photon going through one or both slits, following multiple paths, or doing anything except making that dot.​

When paths through both slits are possible, the contributions will add in such a way that dots are more likely to appear in some areas and not others, and over time the interference pattern will build up. When paths through only one slit are possible, then the same calculation of summing the contributions through the possible paths tells us that a single-slit diffraction pattern will build up.

If we place polarizers at each slit, 90 degrees apart, this summing of contributions from all possible paths still works. Any photon behind the barrier will be polarized either horizontally or vertically; when we sum the contributions of all the paths available to it we'll only be considering the paths through the the slit with the appropriate polarizer setting. Any other interaction that changes things in a way that which-path information is available will have the same effect; we're considering the contributions from possible paths, and saying that which-path information is available is just another way of saying some paths aren't contributing to the calculation.

OK, so that's what QM says about the double-slit. However, you will have noticed this doesn't do much at all for the question that you've asked: Why is it that way? The computational recipe works really really well, but what's really going on? What's the "deep down reason" why these calculations work? Now we're back to the short answer: Nobody knows. Quantum mechanics tells us, with exquisite accuracy, how the universe behaves but not why it behaves that way.

Something similar has happened in other branches of physics in the past. For example: Boyle discovered the relationship (Boyle's Law) between volume, pressure, and temperature of a quantity of gas in a sealed container in the 17th century. But why does Boyle's Law work? What's the "deep-down" reason? It wasn't until the 19th century that statistical mechanics developed to the point that we could predict the behavior of ideal gases from first principles to answer that "Why?"

Likewise, it possible that some deeper theory will eventually explain why quantum works so well. But without a serious proposal for such a theory, the discussion can only be idle speculation. Until then: QM works; it tells us more about how the universe we live in works than any other theory; and it's not able to tell us why it works.

 

[CHOP]

Nugatory, thank you very much for your detailed post and for honing in on where my concerns are,

First, the short answer: Nobody knows.

The longer answer:
Consider the quantum mechanical explanation of the slits+polarizers experiment. QM says that the probability of an incident photon producing a dot at a given point on the screen is calculated by summing the amplitudes of all possible paths to that point. Interference happens because the contributions from the various paths add destructively at some points and constructively at others.

Right. Which is an elegant explanation, beautiful really.

Important digression: "Photon" is not to "dot on screen" as "bullet" is to "bullet hole". What's above is a statement about how we calculate the probability of the photon being detected (that's what "make a dot" means in this context) at a particular point on the screen.​

​

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Yes, nicely pointed out. It can be thought of as spontaneous 'flashes' on screen, but corresponding (by time, etc) to had they arose from trajectories.​

​

I mean, there cannot be a flash any sooner than the soonest that an actual trajectory would have caused a hit. Please confirm? If not true, that would be absolutely nuts, in my view. I think there has to be agreement with what's true had these been trajectories - the disagreement is exclusive to the frequency of 'hits' at specified screen regions. Correct?​

​

This disagreement is essentially what is making very difficult (perhaps impossible) the notion of trajectories (CM). Correct, or is there something else as well? But there is something to be said on that, I think. There is a sense in which 'trajectories' are not being violated. What's violated is the frequency distribution they 'typically' yield.​

​

To stress what I mean, it's as if things ARE classical, but where it's classical in a kind of 'modified' way.​

​

Example: you watch, from your dock, a duck crossing a pond. It does it all the time, but you never in one sitting see the whole uninterrupted route, because, for example, your coffee sometimes gets cold, so you go into warm in, then come back out. So you can 'see' the whole route in your mind, but there are sections less vivid in your mental visual. There is a bias here. That's the modification.​

​

I have a question: is it ever the case (in any situation of the IP result, in any experiment) where the 'low frequency' regions are NOT 'low frequency', but are factually, absolutely (indisputably) regions of ZERO probability? If that were true, that would also be nuts to me. If true, can you say where it occurs?​

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There's nothing here that requires us to think in terms of the photon going through one or both slits, following multiple paths, or doing anything except making that dot.​

right.

When paths through both slits are possible, the contributions will add in such a way that dots are more likely to appear in some areas and not others, and over time the interference pattern will build up. When paths through only one slit are possible, then the same calculation of summing the contributions through the possible paths tells us that a single-slit diffraction pattern will build up.

right. elegant. so, given a certain type of particle (let's say electron), there is an optimal setup as far as the getting vividness of the IP on the screen. In general, you wouldn't want the slits too large because then you need a much greater frequency to compensate the 'dulling' of the effect caused by large slits (I expect), right? Narrow slits, situated where frequency is greatest (straight ahead of source) --That would be ideal setup, as far as vividness of IP, correct? Also, where slits are at equal angles to center source (ideal, but not required) Correct?

If we place polarizers at each slit, 90 degrees apart, this summing of contributions from all possible paths still works. Any photon behind the barrier will be polarized either horizontally or vertically; when we sum the contributions of all the paths available to it we'll only be considering the paths through the the slit with the appropriate polarizer setting.

right, thanks for mentioning that. key information there, as far as there being a 'what's' considered.

Any other interaction that changes things in a way that which-path information is available will have the same effect; we're considering the contributions from possible paths, and saying that which-path information is available is just another way of saying some paths aren't contributing to the calculation.

excellent. thank you for saying that, that helps remove some doubt in my head. this is related to why i saw the blocked case as not different from everything else.

OK, so that's what QM says about the double-slit. However, you will have noticed this doesn't do much at all for the question that you've asked: Why is it that way?

right, but power to QM. it's elegant and beautiful, and is obviously right on the EDGE of the issue.

The computational recipe works really really well, but what's really going on? What's the "deep down reason" why these calculations work? Now we're back to the short answer: Nobody knows.

Thank you for your efforts toward addressing me, i appreciate that.

 

[CHOP]

Example: you watch, from your dock, a duck crossing a pond.

Just to clarify:

The less vivid slabs of the route correspond to the times you left the pond, but are still there (in your mental image) because you saw them sometimes. Whatever is controlling when, during that route, you 'typically' get up to warm the coffee, is what creates the bias of vividness, distributed along the duck's route.

Well, it's not what creates the bias - it's what the bias is. The key is that there is, on average, a certain range of time that you're absent.

How that relates to the 'classical seems still present' notion: the fact that you do see the whole route corresponds to flashes do occur everywhere trajectories land. And, the fact that certain slabs of the route are more often seen, corresponds to certain regions of screen more often flashed. That is what I meant by 'modification' of the classical.

 

[DrChinese]

This disagreement is essentially what is making very difficult (perhaps impossible) the notion of trajectories (CM). Correct, or is there something else as well? But there is something to be said on that, I think. There is a sense in which 'trajectories' are not being violated. ...

Trying to describe, by inference, what happens when a particle is not being observed is a quick way to get into a hole. You may as well say that when there IS interference, the particle goes through 1 slit and one slit only. No one knows for sure, even though classical logic implies that it does!

 

[CHOP]

You may as well say that when there IS interference, the particle goes through 1 slit and one slit only. No one knows for sure, even though classical logic implies that it does!

No, I wouldn't say it the way you have just suggested. The way you have suggested is not a working way. You have basically made a contradictory statement. You say it went through one slit, and also say there was interference. Well, there can't be interference (that 'activity') if the particle went through one slit. So, the word "interference" has to be discarded, and replaced with "interference pattern" - the name that was given to such an outcome.

So, that brings us the following suggestion: "When there IS an interference pattern, the particle goes through 1 slit" (note: I won't add "and one slit only", because I don't see the need for the specification - there is no reason to think that a particle can go through two slits). So yes, now we have a working suggestion - all we needed to do was take the contradiction out of it.

But I am pretty sure I can guess what you are thinking: you are thinking "But it's still a contradiction". Well, if you feel that way, I can appreciate that you do, but I cannot appreciate that it is a contradiction. Because it is not one. That said, there might be a way to phrase it, which would make there actually be a contradiction. That said, even if there was a phrasing that contradicted itself, it wouldn't rebut what I have actually said in the post.

 

[DrChinese]

So, that brings us the following suggestion: "When there IS an interference pattern, the particle goes through 1 slit" (note: I won't add "and one slit only", because I don't see the need for the specification - there is no reason to think that a particle can go through two slits). So yes, now we have a working suggestion - all we needed to do was take the contradiction out of it.

The only contradiction is when you assert that "everything" goes through a single slit. "Something" goes through both slits when there is interference. We know that from the experiment I cited, where which-path information is encoded (and later, erased). We don't know what goes where, we just know that both slits contribute to the outcomes when there is interference.

 

[CHOP]

This statement:
"Something goes through both slits when there is interference"
is problematic.
Let's break it up into the two problems:

1.
Again, if you mean (by 'interference') the activity of interfering, which happens before a particle registers at screen, then you have to show that such activity has occurred.

2.
Until then, I will assume that (by 'interference') you mean the so called Interference Pattern. That is, you are saying this:
"Something goes through both slits when there is an interference pattern"

That has not been shown. It is just a way of conceptualizing what is going on. A kind of story. It may seem that you got out of the issue by changing the word 'particle' to the word 'something', but that is kind of like changing your signature on a paper you don't want to sign - it doesn't work.

The fact is, you are asserting that there is 'motion' by saying the thing 'goes through' both slits. Only it is less apparent that you have created a contradiction, because you swapped 'particle' for something more vague ('something').

 

[CHOP]

It seems the key point, this:
It can always be said that this one particle has gone through a slit. It would be wrong to say that only if: where it landed contradicted where it was said to come from (and CM determines that).

The problem arises when we talk in terms of a quantity of particles going through the slit. That is (it appears) we cannot say: "Each of all the particles have gone through a slit".

But isn't it interesting that we can't say that? Look how close it is to saying the first thing (which can be said).

The first statement 'doesn't care' about quantity, but nevertheless speaks of one instance (of the quantity). That means the first statement is equivalent to the second statement.

So, the second statement is not (actually) a problem, even though it seems has to be wrong.

If we want to 'force' a statement that fails, we have to get away from the specification that we are talking about a single instance. That is, we have to talk in terms of "many going through". That is, where we treat the case as a whole that is not divisible.

The beautiful thing is this: now finally, when we have managed to force a claim that fails, we have not (actually) succeeded. Because a quantity is not something that goes through a slit.

That is: Yes, it's true that "many did not go through a slit" - because many is not something that moves. So we are right that the claim is false, but it's not false in the way we expected it to be.

If what I have said is right, it shows how incredibly subtle (and non intrusive) the quantum mechanical effects are. Our attempts to 'generate' a claim that fails, is our suspecting that one should.

But, I think, none will.

 

[DrChinese]

Only it is less apparent that you have created a contradiction, because you swapped 'particle' for something more vague ('something').

A photon is NOT a particle, it is a quantum particle - and many here prefer not to call it any kind of particle. It cannot be described by the language you are using. That is the point of the experiment, to demonstrate that every permutation of a classical explanation (as a particle) is refuted.

Obviously, the slit edges don't cause interference. Multiple photons (going through at the same time as a group) are not needed to create interference (by colliding). There is no interference where only 1 slit is open. There is no interference when both slits are open but you have a which-slit marker in place. There is interference when the which-slit marked is later removed, which allows the paths coming through both slits to again interfere as predicted by QM.

So it seems to me you are in denial of the basic facts, and are clinging to a description with a classical element (which is obscured by the semantics of your examples).

 

[CHOP]

A photon is NOT a particle, it is a quantum particle - and many here prefer not to call it any kind of particle. It cannot be described by the language you are using. That is the point of the experiment, to demonstrate that every permutation of a classical explanation (as a particle) is refuted.

"Photon not particle" makes no difference. All kinds of particles can be used in this experiment. Not sure why you are putting so much emphasis on what to call a photon. You can call a photon what you like - I make the same points regardless. The point was, that you are treating the thing in a classical way by saying that it "goes through both slits" creating contradiction. Just because this is 'housed' in QM does not excuse that description. In fact, it conflicts with it, because you imply a motion and some kind of strange thing doing that motion, and doing it only when there is no detectors (or equivalent) stationed at the slits. That's not QM, that's making up stories (until it is supported with evidence, or reason). In fact, I was quite surprised.

If you check what I have been saying, you will see that I have not been making stories about what 'is happening'. I have only been analyzing things. Very careful with my language (very, very, careful). In fact, it is because I am so careful that I noticed your language was problematic. What I have done is thought -- about this, pointing out interesting observations along the way, about what can and cannot be said, showing exactly what's not classical, exactly what is. Asking questions, praising the mathematics, offering analogies to help convey things. The irony is that I would embrace your classical object that 'moves through both slits' if I had any wish at all to think in such terms. Fact is, I just think a lot and am (and have been) very interested in this, and am not afraid to juggle the issues in various ways.

Obviously, the slit edges don't cause interference. Multiple photons (going through at the same time as a group) are not needed to create interference (by colliding).

I didn't say that slits are doing anything to the photons and cause interference. Not at all. I also didn't say that multiple photons are needed to create interference. In fact, there have been posts showing that I understand very well, that this is (easily) done (and is done) with one at a time. I even said that when they are sprayed, it is still one at a time. Also, I did not say that photons collide. These ideas I do not know where they are coming from. In fact, photons can't collide with each other. It has become very clear to me that you are not understanding what I was saying at all. But apparently you are also not noticing that you may not be understanding.

So it seems to me you are in denial of the basic facts, and are clinging to a description with a classical element (which is obscured by the semantics of your examples).

Okay, so when you don't follow someone's concepts, don't even see how they corrected you, even when you have acknowledged that you don't see where they are going, even when they pointed out (earlier) to you (in plain English) that there is a big difference in what the both of us consider to be the problem -- after all of that (all those signs) you trust your judgement here enough, to lay out this nonsense, about where I'm at.

Good Luck to you,

 

[PeterDonis]

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