New version of double-slit experiment

[universecode]

That's fine. Just keep in mind that several users in this thread are physicists and publish papers.

Apologies if I offended anyone somehow, didn't mean to.

It just does not work. If you start with the actual physics (the calculations), this is directly obvious. If you start with Feynman diagrams, it is hard to forget that wrong idea.

Consider this, for example: for every possible process, if you have any chance to draw Feynman diagrams, you have an infinite number of Feynman diagrams. And all of them contribute to every process. So how do you find out "which diagram happened"? You cannot. Not even in principle, because "this diagram happened" is not a meaningful concept.

Well, sure, isn't that the problem when you assume that outcome is created in the act the measurement? At which point you will have infinite number of past histories, infinite number of diagrams to consider etc.

What if you assume what I am postulating that outcome is created at the act of emission or each next junction is decided at the previous junction on the diagram?
Past history becomes irrelevant at each junction. Am I completely off the mark here?

 

[Nugatory]

What if you assume what I am postulating that outcome is created at the act of emission or each next junction is decided at the previous junction on the diagram?
... Am I completely off the mark here?

That seems like a logical enough starting point. It's intuitive; it's consistent with our experience with classical particles, even very small ones; and it's consistent with much of the semi-classical thinking (for example, the Bohr atom and the photoelectric effect) that preceded the formal development of quantum mechanics.

It's not easy (impossible in principle?) to falsify this line of thinking with experiments that involve only one particle at a time.

However, that line of thinking also suggests that if two photons are emitted in the same event, then the results of a measurement of either photon will be determined at the emission event. That experiment has been done many times, and the results are unequivocal: there is no way to describe the subsequent behavior of both particles based on their state at the time of emission.

Google for "Bell's Theorem", "EPR paradox", and "Alain Aspect".

 

[universecode]

However, that line of thinking also suggests that if two photons are emitted in the same event, then the results of a measurement of either photon will be determined at the emission event.

Thanks, may I just clarify that this event would always imply entanglement as we know it at present?

 

[Nugatory]

Thanks, may I just clarify that this event would always imply entanglement as we know it at present?

If we both understand the question that you're asking, then the answer is "yes".

But it would be well to remember that any time you hear someone speak of "two entangled particles" they're playing a bit fast and loose with the language. It would be more accurate to speak of "a single quantum system with two properties that we can measure".

 

[universecode]

If we both understand the question that you're asking, then the answer is "yes".

But it would be well to remember that any time you hear someone speak of "two entangled particles" they're playing a bit fast and loose with the language. It would be more accurate to speak of "a single quantum system with two properties that we can measure".

Exactly, thank you, I am going to do some more thinking about the Bell's theorem from another angle...

 

[DrChinese]

1. Has there ever been a high level discussion arguing why taking Feynman diagrams literally is a terrible idea not worth pursuing under any circumstances?

Nugatory already mentioned, but I will give you a counter-example to Feynman diagram. There is not one that explains how particle entanglement works. That is because such diagrams are local realistic, but QM as a whole is not.

2. Past history becomes irrelevant at each junction. Am I completely off the mark here?

Yes, off the mark. That does not actually follow from QM either. An example is entanglement swapping, in which case the decision to entangle 2 particles can be made AFTER the particles are detected. If you follow the space time diagram, both past and future are relevant to the description and effects are best described as flowing in both forward and backward time directions. (You might expect this because entanglement is a counterexample in 1.)

I do think your decision to look at Bell's Theorem from more angles is a good one. (Yes a totally predictable comment... )

 

[universecode]

I do think your decision to look at Bell's Theorem from more angles is a good one. (Yes a totally predictable comment... )

Thanks, your comments are finally useful to my objective.
Anyway, I just read your version of Bell's theorem proof to make sure we are talking about the same thing.
Are you absolutely certain about your version?

Let's have a look at the first and the main assumption:

a. ASSUME that a photon has 3 simultaneously real Hidden Variables A, B and C at the angles 0 degrees, 120 degrees and 240 degrees per the diagram above. These 3 Hidden Variables, if they exist, would correspond to simultaneous elements of reality associated with the photon's measurable polarization attributes at measurement settings A, B and C. In other words, each hidden variable gives us the answer to the question "will this photon pass through a polarizer lens set at a specific angle?" Presumably, this information is SOMEHOW encoded definitely in the photon at the time it is created (sort of like an instruction set) and does NOT depend in any way on the polarizer lens itself (which is encountered at a later time).

Well, this does not apply to my postulates! Nothing in my proposal would contradict Bell's theorem conclusions because I do not assume hidden variables as defined by Bell.
I thought I was very clear in explaining my point but I guess not, so let me repeat it:

a) at the point of emission (i.e., at each junction on Feynman's diagram) a photon knows where all particles in the universe are (whatever "location" means, if anything);
b) it constructs a probability distribution on the whole of the universe assigning a probability to each such particle;
c) it draws randomly from that constructed probability distribution;
d) and then it gets absorbed by the particle drawn at the previous step after some time.

The key point here is b) - when decision is made at the point of emission it incorporates the knowledge of the existence of future detector at that moment.
State of the particle in my proposal is obviously dependent on measurement and does not exist without it - the key difference is that it is created at emission not at the measurement itself.

 

[Nugatory]

Well, this does not apply to my postulates! Nothing in my proposal would contradict Bell's theorem conclusions because I do not assume hidden variables as defined by Bell.
...
The key point here is b) - when decision is made at the point of emission it incorporates the knowledge of the existence of future detector at that moment.
State of the particle in my proposal is obviously dependent on measurement and does not exist without it - the key difference is that it is created at emission not at the measurement itself.

So you've just been talking about a transactional interpretation all along? The interpretations that propose that the state of a system can be affected by detector settings that haven't yet been made work just fine. As with any other interpretation, they cannot be falsified by experiments because they make no predictions that differ from the predictions of any other interpretation.

 

[universecode]

So you've just been talking about a transactional interpretation all along? The interpretations that propose that the state of a system can be affected by detector settings that haven't yet been made work just fine. As with any other interpretation, they cannot be falsified by experiments because they make no predictions that differ from the predictions of any other interpretation.

Thanks, if that's what it is then I'll try to find and read what others have said about it already...

Anyway, I think it does make different predictions, at least theoretically.
Consider single photon source and two detectors as explained in my latest version of the experiment.
As far as I understand, theories predict that probability of hitting those detectors will be different dependent on their location with respect to the source, if there is absolutely nothing else in the vicinity of the experiment.

So, if we somehow could fool the nature a bit by dislocating a detector during the photon's "flight" theories would predict different probability of hitting such detector, is this correct?
I predict the probability would be the same as if nothing changed and the detector has stayed where it was all the time required for the photon to reach the detector from the source.

Obviously, as it has already been mentioned, even if this is in a vacuum with nothing around, the photon could be appearing and disappearing or interacting with vacuum infinite number of times hence adjusting its outcome according the detector dislocation.
But I would like to think this is not what's happening for the following reason. If the same experiment is left on its own with the source being switched off, would detectors keep registering photons appearing from nowhere? If all setup correctly - probably not. Hence even if there are photons appearing from vacuum they would not be relevant to our experiment.

 

[Nugatory]

So, if we somehow could fool the nature a bit by dislocating a detector during the photon's "flight" theories would predict different probability of hitting such detector, is this correct?

no. The only thing that matters is the position of the detector when the interaction happens, not the way by which the detector came to be in that position or how it moved around before the interaction.

 

[universecode]

no. The only thing that matters is the position of the detector when the interaction happens, not the way by which the detector came to be in that position or how it moved around before the interaction.

Is there a definite proof of such fact? I'd like to analyse how the conclusion was made.

 

[universecode]

If what I am postulating is even remotely correct, it would explain something that is truly mind-boggling - the true origin of the ubiquitous Normal Distribution.

It is well known that the mean of two or more random variables independently drawn from the same distribution is distributed approximately normally, irrespective of the form of the original distribution. If a distribution is constructed on the whole universe at each emission and the next step/event is decided by randomly drawing from it then it is natural that what we are observing is the mean of these processes which is found to be Normal.

Can other theories predict this?

 

[Nugatory]

Is there a definite proof of such fact? I'd like to analyse how the conclusion was made.

Bell experiments have been done with the detector angles selected and set after the emission event. The results are as predicted by QM and the same as if the detector angle was set before the emission event.

 

[universecode]

Bell experiments have been done with the detector angles selected and set after the emission event. The results are as predicted by QM and the same as if the detector angle was set before the emission event.

Thanks, have you got a link to this particular experiment, so I could analyse it in details, please?

 

[DrClaude]

Thanks, have you got a link to this particular experiment, so I could analyse it in details, please?

For instance:
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.81.5039 (if you don't have access, see http://arxiv.org/abs/quant-ph/9810080)

 

[DrChinese]

Well, this does not apply to my postulates! Nothing in my proposal would contradict Bell's theorem conclusions because I do not assume hidden variables as defined by Bell.
I thought I was very clear in explaining my point but I guess not, so let me repeat it:

a) at the point of emission (i.e., at each junction on Feynman's diagram) a photon knows where all particles in the universe are (whatever "location" means, if anything);
b) it constructs a probability distribution on the whole of the universe assigning a probability to each such particle;
c) it draws randomly from that constructed probability distribution;
d) and then it gets absorbed by the particle drawn at the previous step after some time.

The key point here is b) - when decision is made at the point of emission it incorporates the knowledge of the existence of future detector at that moment.
State of the particle in my proposal is obviously dependent on measurement and does not exist without it - the key difference is that it is created at emission not at the measurement itself.

No problem, this is consistent with a number of existing QM interpretations. Exactly as we have said in this thread any number of times. Such interpretations are not local realistic.

See post #43 for example. And #55.

 

[universecode]

Such interpretations are not local realistic.

Thanks, is it good, bad or what does it imply that I may not be aware of?

See post #43 for example. And #55.

I wish I could figure out what I should be looking at from those posts - could you please be more specific with precise arguments that relate to my line of thinking?

 

[DrChinese]

1. Thanks, is it good, bad or what does it imply that I may not be aware of?

I wish I could figure out what I should be looking at from those posts - could you please be more specific with precise arguments that relate to my line of thinking?

I don't know how to be more specific than the post itself:

There are 2 issues here, already alluded to by others.

1. Your ideas about the path histories is considered "interpretation dependent". They are mostly right in a few interpretations but not supported by others.

2. The predictions of your "interpretation" are simply the same as all others in this case. If the photon's paths are not prohibited (constrained), they are allowed and interference occurs. Moving something before or after the photon goes by in a path makes no difference.

So while you might wonder as to the result, it doesn't really make for much of an experiment when a null result is predicted by every interpretation.

So your "hypothesis" matches those made by others in various interpretations which are known to not run afoul of Bell. Because to be viable, no interpretation can be "local realistic. So your ideas are fine. And as referenced by DrClaude and mentioned by Nugatory and myself, the location of the target doesn't matter except as of the time of detection.

 

[universecode]

So while you might wonder as to the result, it doesn't really make for much of an experiment when a null result is predicted by every interpretation.

Thanks for repeating, but I still don't get what you are talking about.

Let's go step by step with simple true or false answers to avoid confusion.

Assume you have a universe (which is the same as ours but there is very little in it) and it contains only a source of photons and few detectors in random places. The source emits photons one by one which are detected by the detectors. Do you agree that (generally, apart from special equivalent locations) every detector has different probability of observing photons emitted from this source?

 

[Nugatory]

Do you agree that (generally, apart from special equivalent locations) every detector has different probability of observing photons emitted from this source?

Yes, of course. That's what QM predicts in all interpretations, that's also the classical prediction for the intensity of light, and it's a result that all experiments so far have confirmed (although of course the experiments cannot be done in this hypothetical completely isolated universe - instead we calculate and validate upper bounds on the errors introduced by not being completely isolated).

 

[universecode]

Yes, of course. That's what QM predicts in all interpretations, that's also the classical prediction for the intensity of light, and it's a result that all experiments so far have confirmed (although of course the experiments cannot be done in this hypothetical completely isolated universe - instead we calculate and validate upper bounds on the errors introduced by not being completely isolated).

Thanks, good, let's continue with our hypothetical universe and shuffle all the detectors, so they are all in different locations now. The source stays the same and continues emitting photons.
Will each detector have the same probability of detecting photons as it had before?

 

[DrChinese]

Thanks, good, let's continue with our hypothetical universe and shuffle all the detectors, so they are all in different locations now. The source stays the same and continues emitting photons.
Will each detector have the same probability of detecting photons as it had before?

Generally, the probabilities will change.

 

[universecode]

Generally, the probabilities will change.

Thanks.
Nugatory, would you confirm this answer?
You seem to be quite good at elaborating your arguments, so I just want to seal this answer before proceeding further.

 

[Nugatory]

Thanks.
Nugatory, would you confirm this answer?
You seem to be quite good at elaborating your arguments, so I just want to seal this answer before proceeding further.

So far so good...

 

[universecode]

Good, now if we return all detectors to where they were originally, will they again start observing photons each with the same probability they respectively had originally?

 

[Nugatory]

Good, now if we return all detectors to where they were originally, will they again start observing photons each with the same probability they respectively had originally?

If we've managed not to mess something up in all the moving around, yes. So far we're in accord with all interpretations of quantum mechanics and also the classical prediction for particles other than photons (and the only reason I make that exception is that there is no classical prediction for the behavior of photons).

 

[universecode]

If we've managed not to mess something up in all the moving around, yes. So far we're in accord with all interpretations of quantum mechanics and also the classical prediction for particles other than photons (and the only reason I make that exception is that there is no classical prediction for the behavior of photons).

Thanks, suppose all our detectors are around 1 light-hour away from the source and in both cases we have been observing a photon registered by one of the detectors consistently every 2 hours plus-minus 10 minutes. Would such observation contradict anything?

 

[Nugatory]

Thanks, suppose all our detectors are around 1 light-hour away from the source and in both cases we have been observing a photon registered by one of the detectors consistently every 2 hours plus-minus 10 minutes. Would such observation contradict anything?

By "both cases" you mean before we moved the detectors and after we put them back?
Not yet, as long as the source and detectors are at rest relative to one another, "around 1 light-hour away" means that the differences in the distances are small compared with ten light-minutes, "consistently" means that we ran long enough to get statistically significant results, and probably some other reasonableness assumptions that I've missed.

The non-Poisson distribution of the arrivals would be a very strong hint that that someone was turning the light on and off back at the source.

 

[DrChinese]

Thanks, suppose all our detectors are around 1 light-hour away from the source and in both cases we have been observing a photon registered by one of the detectors consistently every 2 hours plus-minus 10 minutes. Would such observation contradict anything?

We are assuming that the setup leads us to this consistent observation for the sake of the example.

 

[universecode]

By "both cases" you mean before we moved the detectors and after we put them back?

Yes

Not yet, as long as the source and detectors are at rest relative to one another, "around 1 light-hour away" means that the differences in the distances are small compared with ten light-minutes, "consistently" means that we ran long enough to get statistically significant results, and probably some other reasonableness assumptions that I've missed.

The non-Poisson distribution of the arrivals would be a very strong hint that that someone was turning the light on and off back at the source.

Thank you, excellent explanation with right assumptions.

Now, may I confirm something that I think will be very useful for anyone who might decide to read this so they can clearly understand what's going here.

The fact of switching the source on/off is completely independent from the probabilities eventually observed at each detector. Regardless of how diabolical the operator decides to behave the probabilities after sufficiently long run will tend to be the same as if there were no operator and the source was just controlled by a timer which switches the source on every two hours and then off 10 minutes after switching on?

 

[DrChinese]

Again, we are assuming your setup for the sake of discussion. We wouldn't want to get derailed on points that have nothing to do with the topic*. *which is rapidly eluding me...

 

[universecode]

nothing to do with the topic*.
*which is rapidly eluding me...

Patience is a virtue - I am sure you know that :)

Let me also make a small correction. Previously I said:
"... we have been observing a photon registered by one of the detectors consistently every 2 hours plus-minus 10 minutes..."

I am correcting that to the following:
"... we have been observing a photon registered by one of the detectors consistently within 10 minute interval past every 2 hours ..."
i.e., we receive a photon within 10 minutes past 1.00am, then a photon within 10 minutes past 3.00 am and so on.

Does this change anything we have already confirmed?

If not, then is it safe to assume that after sufficiently long run required to build appropriate statistics to estimate probabilities (which is what we do in both cases of having detectors in one or the other sets of locations) we can be certain that this is what actually happens i.e., the source is predictable in a sense that it does emit a photon within 10 minute interval past every two hours?

 

[DrChinese]

Patience is a virtue - I am sure you know that :)

So is getting to the point.

Clearly, we are willing to accept your scenario AS LONG AS there is nothing in it that leads to some violation of some other relevant issue. The longer you drag it out, the more it seems that such is what you have in mind.

Specifically: A setup in which ANY exact number N of photons is likely during some interval T at several spots is not so simple to prepare and may have significant caveats. But again, let's assume that is the expectation for the sake of discussion.

 

[universecode]

So is getting to the point.

Not in theoretical sciences! There are theorems that take dozens if not hundreds of pages to prove and every line is a key line. Rushing the argument is not a virtue here.

Let's ponder a bit about recent statements and I would like to hear views of others before moving on...

 

[diggnforgold]

Where is the original thread? I would like to know the particulars of the new take on the double slits experiment!