B Does Human Observation Affect the Double Slit Experiment Results?

[vanhees71]

Yes, but then it's irrelevant for science. Science aims at the simplest models to understand what's observed in nature. We don't need the infamous angle's on a pin's heads! QT is complicated enough without any esoterics!

 

[bhobba]

As a physicist, I would say: It seems that the decoherence program might be based on a simple circular reasoning fallacy.

Ruth has similar views - but let her explain them.

However in the case of the cat in Schrodinger's cat the alive cat is entangled with the air etc around it - otherwise it would not be alive.

Thanks
Bill

 

[vanhees71]

BTW: The assumption that the state of macroscopic systems on the relevant level of accuracy (or resolution) is "decohered" is a simple observational fact. It's the reason, why classical (Newtonian or relativistic doesn't matter here) physics works so astonishingly well in a wide realm of everyday phenomena.

 

[bhobba]

Yes, but then it's irrelevant for science. Science aims at the simplest models to understand what's observed in nature. We don't need the infamous angle's on a pin's heads! QT is complicated enough without any esoterics!

Thats exactly it and what I mean when I say - why bother. Such exotica is not required.

Thanks
Bill

 

[bhobba]

BTW: The assumption that the state of macroscopic systems on the relevant level of accuracy (or resolution) is "decohered" is a simple observational fact. It's the reason, why classical (Newtonian or relativistic doesn't matter here) physics works so astonishingly well in a wide realm of everyday phenomena.

You and a number of other science advisers mention it. I have tried to find a paper that gives the details. The best I know is (other than the authors excellent textbook I often recommend of course) is the following:
https://arxiv.org/pdf/1404.2635.pdf

If anyone knows of a better one please post it and we can use that to explain it instead.

Thanks
Bill

 

[Lord Jestocost]

Of course.

Any interpretation in accord with the formalism,.even those some consider weird - like consciousness causes collapse - is scientifically valid.

What me and Vanhees try to stress is there is no need to go down paths like that - but if you want to of course you can. QM when viewed using minimalist interpretations like the Ensemble is much more 'common sense' and less weird than some try to present it.

Thanks
Bill

Interpretations of quantum mechanics: The best you can say about it is "excellent nonsense".

To me, the only honest approach towards quantum physics is an instrumentalist’s point of view: The operational formalism of quantum mechanics represents nothing else than a calculational recipe, designed to predict the probabilities of various directly observed “macroscopic” outcomes – the linkage of pointer readings with pointer readings –, and the used symbols, such as the probability amplitudes, are nothing else than intellectual tools to “calculate” these probabilities. When going beyond this by “smuggling in” classical ideas and conceptions, one begins to produce pseudo-science which is at the end based on personal psychological predispositions (implicit assumptions). Some commenters here on PhysicsForums don’t seem to grasp that their “interpretations” merely reflect their “feelings” of what “relality” “ought to be”. In case you need your "ensemble interpretation", that's o.k.. But, please, be aware that's your personal "feeling" of what "ought to be out there".

 

[bhobba]

Some commenters here on PhysicsForums don’t seem to grasp that their “interpretations” merely reflect their “feelings” of what “relality” “ought to be”. In case you need your "ensemble interpretation", that's o.k.. But, please, be aware that's your personal "feeling" of what "ought to be out there".

Sure. No issue.

Dirac would be proud of you.

But really all the ensemble is, is the formalism dressed up in the frequentest interpretation of probability - it isn't really assuming much - but yes it does assume things. After all Einstein came up with it and he was hardly in Dirac's camp - although he carried his textbook at all times as his bible on things QM related.

Pauli expressed it this way:
'Pauli complained that Dirac’s book did not reveal the crucial fact that quantum mechanical measurements require real and solid measuring devices that follow the laws of classical physics; measurements in the atomic and subatomic realm are not processes that merely involve mathematical symbols and formulae. While the classical nature of the measurement apparatus was an important element in Pauli’s and Bohr’s conception of quantum mechanics, it was not a point appreciated by Dirac.'

I have said it before, and will say it again, Dirac was the odd man out as far as the early pioneers go - he had ideas more like yours, even though that's not often emphasized. When forced to comment he would say some Copenhagen stuff, but really for him the formalism was the thing.

Thanks
Bill

 

[nnope]

Alot of QM questions end up discussing consciousness but has anyone ever actually asked what consciousness is from a biological viewpoint. Is there just the auto assumption that its a magical thing that has an affect?

From a medical science point of view consciousness isn't a thing other than the active awareness of the brain. Its not some kind of soul it is just the activity within the brain. When you look to observe anything, using your eyes for example all that happens is the light hits the rods and cones, transfers to ganglia cells, then to the optic chiasm and ganiculate nucleas after which it enters the occiptal lobe for interpretation.

How does this process or that of any other of the senses impose any kind of outwardly influence on quantum systems or otherwise. The only thing I can think that might have any semblence of influence is the magnetic field of the brain and that is too small.

 

[laymanB]

If we believe that a macroscopic object can be in two places at the same time and in the same relation, then we need different axioms to construct our laws of logic and language. Maybe our axioms don't work in the subatomic realm and that's why people debate what the interpretations "really" mean. How would someone who takes a non-realist interpretation of quantum physics explain the existence and evolution of the universe, prior to life on Earth, without using a decoherence chain of causality?

 

[itfitmewelltoo]

It is unfortunate that the word "observe" is used because it implies that it is the existence of the human being that is the necessary element. It isn't. It is the interaction with the measurement device that is the necessary element.

 

[DarioC]

Very well put itfitmewellputtoo. Somewhere in the forum I would like to post a question about the affect of the distance between the slits in the double slit experiment when using actual physical slits. I suspect there is some information to be found there. Likely already done, but I have not seen the info/results/etc.
DC

 

[Nugatory]

Very well put itfitmewellputtoo. Somewhere in the forum I would like to post a question about the affect of the distance between the slits in the double slit experiment when using actual physical slits. I suspect there is some information to be found there. Likely already done, but I have not seen the info/results/etc.

You don't need any quantum mechanics for that. Ordinary classical wave theory will let you calculate how the interference pattern varies as the separation between the slits (and their width, which you didn't mention but is just as important) varies.

 

[DarioC]

Thanks, point well taken. Have to break out the books and/or look around online for how to calculate/understand that particular aspect of the subject.
Oh, I did error in not saying that I am specifically interested in learning about the pattern when it is a single photon or particle at at a time.
DC

 

[Jon Richfield]

The answer to all three of your questions is "yes, correct".
... the video camera recording was actually in a superposition and had not yet collapsed.

A better response to this kind of claim (i.e., a claim that only human consciousness can collapse the wavefunction, etc.) is that, since it is inherently untestable (I've just explained how it can explain away any possible test result you can imagine), it's not a scientific claim.

I understand the concept as you put it, but am increasingly dissatisfied with it as a point of view. Just for starters think of various combinations of multiple human observers, instrumentation etc. At which point does observer A (human or artificial, organic or inorganic, conscious or otherwise, as long as it records relevant evidence) say that observer B (human or artificial, organic or inorganic, conscious or otherwise, as long as it records relevant evidence etc.) has collapsed all relevant wave functions, including her/s own? Are we to assume that consciousness cannot be in any kind of superposition, but that no "unconscious thing" such as a camera, can collapse wave functions?

I don't see how any physical description implies, recognises, explains, or otherwise deals with "consciousness" whatsoever in any sense relevant to that discussion.

I reckon that a view based on information theory is far more helpful, but given that it has nothing to do with homework or the content of textbooks, and given the strictures on exploratory discussion in this forum, I have no idea where or how to discuss or enquire on the concept.

 

[Johan0001]

Science Advisor Gold Member laymanB said: ↑ How does such a device interact with the "light wave"? To add to PeterDonis' answer: there are a number of approaches. I like one in which the slits have polarizers in front. a. Orient the polarizers PERPENDICULAR, and it is possible to identify which slit the light goes through by its polarization. Regardless of whether you check the light's polarization or not, there will be NO interference pattern on the screen. b. Orient the polarizers PARALLEL, and it is impossible to identify which slit the light goes through by its polarization. There WILL be an interference pattern on the screen. Obviously, it is a bit difficult to assert that the individual polarizer itself modified the momentum of each light particle so as to collapse the interference. Because there are polarizers present in both a. and b. It is only the relative orientation that is a factor.

Reference https://www.physicsforums.com/threads/double-slit-and-measurement.930286/

Hi Dr Chinese

In the above setup , could you help me interpret the following outcomes.

1. Assume we start in the PARALLEL polarizer position , sending single photons say 10000 over a period of time.
We will see an interference pattern.

2. If we turn one of the polarizers by 1 degree and repeat the experiment ?
How would the interference pattern change , on the detection screen.

3. If we continued to change the polarize by 1 degree , until the angle between the polarizers were 45 degrees.
How would the pattern then look.

4 Finally if we get to PERPENDICULAR polarizers we would get the 2 distinct ''collapsed" pattern.My actual question , is , at what point can we say that the 'knowing which way' the photon went through , caused "collapse".
If indeed such a physical phenomenon of ''collapse'' really exists?

I understand that the angle between the polarizers determine the probability outcome of the results , but where would , if any "collapse"
fit into this setup, if any?

Regards

Johan

 

[laymanB]

Science Advisor Gold Member laymanB said

LOL. I don't have such qualifications. I am just a layman, as per my moniker, who wants to accurately understand what modern science says. Thanks for trying to promote me though.

 

[DrChinese]

2. If we turn one of the polarizers by 1 degree and repeat the experiment ?
How would the interference pattern change , on the detection screen.

3. If we continued to change the polarize by 1 degree , until the angle between the polarizers were 45 degrees.
How would the pattern then look.

4 Finally if we get to PERPENDICULAR polarizers we would get the 2 distinct ''collapsed" pattern.

My actual question , is , at what point can we say that the 'knowing which way' the photon went through , caused "collapse".
If indeed such a physical phenomenon of ''collapse'' really exists?

I understand that the angle between the polarizers determine the probability outcome of the results , but where would , if any "collapse"
fit into this setup, if any?

Great questions!

Yes, our knowledge of "which slit" can be varied from 0% to 100% simply by rotating the polarizers a little at a time. Thus the visible pattern shifts from interference to no interference. Like many quantum phenomena, these blended setups are a bit counter-intuitive. (For example you can have photon pairs that are 50% entangled, or high but limited certainty for both position and momentum.)

So at what point do we cause collapse? Is there a tipping point? I guess when we have a better physical model of collapse (assuming there is such a thing), we could answer that. In the meantime: there is no specific point at which collapse can be said to occur, but it can vary as I described.

 

[PeterDonis]

At which point does observer A (human or artificial, organic or inorganic, conscious or otherwise, as long as it records relevant evidence) say that observer B (human or artificial, organic or inorganic, conscious or otherwise, as long as it records relevant evidence etc.) has collapsed all relevant wave functions, including her/s own?

Before we can address this question, we first need to figure out whether "collapse" is something that actually happens at all (as opposed to being an artifact of the way humans currently undertstand QM, which is incomplete). Which means we need to come up with some kind of physical model of "collapse" that makes predictions different from the predictions of standard QM, and then run the experiments to see which one is right.

There are some proposed "collapse" models (e.g., the GRW model) that at least move in this direction, but so far, AFAIK, every one that leads to some kind of experimental test is already falsified by our current knowledge (for example, AFAIK all of the versions of the GRW model that are currently testable would, if they were true, have led to different results than were actually observed in lots of QM experiments we've already run). But that doesn't change the requirement (for a model that makes testable predictions different from standard QM). It just means the requirement is very difficult to meet, which means it will probably be quite some time before we can make real progress in this area.

 

[Boing3000]

When going beyond this by “smuggling in” classical ideas and conceptions, one begins to produce pseudo-science which is at the end based on personal psychological prédispositions (implicit assumptions).

You don't seem to realize that you are yourself smuggling unscientific misconception into your meta analyse of the meta analyse of QM.
Let's stick to non-pseudo meta science. This is QUANTUM mechanic. All statements about QM are made about classical FACT (not ideas, nor conceptions). Those facts are some "beep" here and there, in so many form, in so many totally classical apparatus. I call them event(s).

Some commenters here on PhysicsForums don’t seem to grasp that their “interpretations” merely reflect their “feelings” of what “relality” “ought to be”.

Actually, I have learned a lot here reading people being able to embrace MANY "interpretations", and use them to expand knowledge and probe hypothesis. Both about new experimental testing, or even simply on the internal coherence of the theory.

In case you need your "ensemble interpretation", that's o.k.. But, please, be aware that's your personal "feeling" of what "ought to be out there".

Your personal feeling seems to be that there "ought to be" no better explanation out there. I found that hypothesis very un-scientific.

You don't throw an "ensemble" into a double slits. There is no such things as an "ensemble" in nature. Your implicit interpretation is the source of the "consciousness" nonsense. The experiment start with the first quanta and ends with the last one. The ensemble is in ones head.
Thinking that all that happens in between is merely non-exciting and should be ignored, and only some probability assignable to ensemble element is existing, is a strong (and even if useful) but too chastising statement.

 

[Lord Jestocost]

All statements about QM are made about classical FACT (not ideas, nor conceptions).

Your implicit interpretation is the source of the "consciousness" nonsense.

What the heck is now a "classical FACT"? And what is exactly my "implicit interpretation"?

 

[Boing3000]

What the heck is now a "classical FACT"? And what is exactly my "implicit interpretation"?

"Quantum phenomena do not occur in a Hilbert space. They occur in a laboratory"

Your implicit interpretation is that QM can tell something about what a photon will do when send into two slit. QM cannot. Saying that nobody should be interested by this problem is "your" interpretation, called "shut-up and calculate", that posit the extravagance of the existence of some probability space (and nothing else).
But there is a chance I get you wrong...

 

[vanhees71]

I guess, by "classical fact" some philosphers mean simply observed measurement results. Instead of calling them in the straight-forward way they make in attempt to sound more intellectual rather than using clear understandable language ;-)). SCNR.

 

[vanhees71]

"Quantum phenomena do not occur in a Hilbert space. They occur in a laboratory"

Your implicit interpretation is that QM can tell something about what a photon will do when send into two slit. QM cannot. Saying that nobody should be interested by this problem is "your" interpretation, called "shut-up and calculate", that posit the extravagance of the existence of some probability space (and nothing else).
But there is a chance I get you wrong...

QM, or rather QED, precisely tells you what a photon will do when send through a double slit. Hitting the detector/photo plate, it will leave a spot with a probability given by the corresponding probability distribution for hitting the photoplate at the observed position. With a single photon, of course you cannot check, whether the predicted probability distribution is correct. For that you have to create an ensemble of single photons large enough to let you measure the corresponding pattern on the photoplate and check whether it confirms your prediction.

 

[Boing3000]

QM, or rather QED, precisely tells you what a photon will do when send through a double slit. Hitting the detector/photo plate, it will leave a spot with a probability given by the corresponding probability distribution for hitting the photoplate at the observed position.

Exactly, and I find quite bizarre that you qualify "hitting the plate (anywhere) and leave a spot", a precise statement.

With a single photon, of course you cannot check, whether the predicted probability distribution is correct.

That's the point, isn't it ?

For that you have to create an ensemble of single photons large enough to let you measure the corresponding pattern on the photoplate and check whether it confirms your prediction.

This is fine, and useful "mind trick". Certainly one that will ultimately be useful to build some fancy macroscopic apparatus, or obtain useful information from a huge number of event.

Now, imagine you are that cat, in that box. You need a theory to help you escape alive. I don't think even you will be satisfied to bet on bets.

 

[vanhees71]

It's not a mind trick but an observational fact. QED is among the best confirmed theories of physics ever!

 

[zonde]

QM, or rather QED, precisely tells you what a photon will do when send through a double slit.

What a photon does is realm of interpretations. I think you ascribe too much to bare QM and QFT.

 

[vanhees71]

I ascribe as much to QM and QFT what these theories predict concerning measurable quantities. In the case of a typical double-slit experiment using single photons it predicts the detection probability at any position on the screen, no more no less. This is the minimal interpretation of the formalism that is consistent with observations.

 

[Lord Jestocost]

Your implicit interpretation is that QM can tell something about what a photon will do when send into two slit. QM cannot.

My attitude towards quantum theory is a simple one: Quantum theory cannot answer questions regarding the intrinsic nature of “phenomena” which we think to “observe”.

 

[vanhees71]

What do you mean by "intrinsic nature of phenomena"? Imho QT precisely describes what we observe. If this was not the case, there'd be a kind of crises, hopefully leading to a new even better theory. This happened exactly around 1900 when it became clear that classical physics cannot describe what has been observed around this time (black-body spectrum, specific heat of solids at low temperatures, spectral lines of atoms etc. etc.) and that a new theory had to be worked out, leading finally to modern QT around 1925-27 (Heisenberg, Born, Jordan with matrix mechanics, Schrödinger with wave mechanics, Dirac with the general formalism and field quantization for the em. field).

 

[Lord Jestocost]

What do you mean by "intrinsic nature of phenomena"?

Saying "quantum theory cannot answer questions regarding the intrinsic nature of 'phenomena'" means nothing else than saying "quantum theory deals only with object-subject relations". You cannot dissect it further on.