Is Wave-Particle Duality Really Real? An Analysis of the Double Slit Experiment

[mintparasol]

Hi all,
I'm not trained in physics beyond high school but have a healthy interest and understand a little quantum physics and special (still grappling with general!) relativity.
Here's a quick question on a pop.science book I'm reading at the moment. The book is by Marcus Chown, it's called 'Quantum Theory Cannot Hurt You.'
In the book he makes an example of the double slit experiment we all did in high school and says that if we fire one photon at the slitted screen, we'll get an interference pattern on the rear screen. So far, so good. He then goes on to say that if we can detect the photon going thru one slit rather than the other(i.e. detect which slit the photon passed thru), that we can't possibly pick up any interference pattern at the 2nd screen due to wave/particle duality.
Is he serious? Are there experimental results that show this?

 

[Fredrik]

Yes there are tons of experiments that support that claim. (I don't have any references for that, but I'm sure Google can help you find some).

The simplest explanation by far is that QM doesn't tell you what actually happens in an experiment. It's just a set of rules that you can use to calculate the probabilities of possible results of experiments. (There are plenty of suggestions about how QM might be interpreted as a description of what actually happens, but all of them have problems).

 

[DrChinese]

To quote from a physics lecture by Professor Henry Greenside:

"Consider Young’s double-slit interference experiment but now put a linear polarizing filter in front of each slit. Then as transmission axis of one polarizer is slowly rotated about its axis while transmission axis of other polarizer is kept fixed, one finds experimentally that the bright regions become dimmer, the dark regions become brighter, until the fringes disappear into a smoothly varying region that is brightest behind the slits and gets dimmer off to the sides."

In other words: when the polarization of the light tells you which slit the photon went through, you get NO interference. That occurs when the polarizers are crossed (90 degrees offset). When they are parallel, you have no idea which way the photon went - and there IS interference on the screen.

 

[J12345]

Dr. Chinese- the only way that I could see to demonstrate that the photons 'stopped' going through the one hole is to somehow attach a photon counter to the rotated polarized slit and see if photons stopped flowing there. I also read that if one simply puts photon counters on the backside of the slits, the whole double slit image on the screen collapses- i.e.; the photons don't ' like being watched '.

 

[SimonA]

J12345 - are you attributing consciousness to particles? Bohr would just say that the measurement is the collapsing of the wave function, and that's the easy way out that physicists have followed for decades. You miss the subtle questions that we need to start asking again.

 

[DrChinese]

Dr. Chinese- the only way that I could see to demonstrate that the photons 'stopped' going through the one hole is to somehow attach a photon counter to the rotated polarized slit and see if photons stopped flowing there. I also read that if one simply puts photon counters on the backside of the slits, the whole double slit image on the screen collapses- i.e.; the photons don't ' like being watched '.

Well, the photons don't know that you aren't checking their polarization when they hit the screen... you could check that in principle. As a result, the inteference disappears. (When the polarizers are crossed, a photon can only go through one slit or the other - so detecting the polarization would tell you which.)

 

[Mentz114]

... that's the easy way out that physicists have followed for decades.

After such a sweeping and maybe slightly arrogant statement you should share your secrets and tell them where they've been going wrong.

You miss the subtle questions that we need to start asking again.

Ask away, don't be shy !

 

[Fredrik]

Another interesting experiment is to do this with C₆₀ molecules, and repeat the experiments many times with a different air pressure around the setup each time. You get a "wave" interference pattern (as if both slits are open at the same time) when you do it in a vacuum, and a "particle" interference pattern (as if only one is open at a time) when the air pressure is high. The interesting part is that you get an "intermediate" pattern when the air pressure is neither high nor very low.

The reason is that interactions with the environment (the air) changes the statistical properties of the molecules, as more and more information about the paths taken can (in principle) be inferred by performing measurements on the state of the air. This proves that "wavefunction collapse" isn't a sudden and discontinuous physical process, and that "wave-particle duality" isn't about the system being either a wave or a particle. Apparently it's a little bit of both. For more information about this, see a book or a review article about decoherence.

 

[SimonA]

After such a sweeping and maybe slightly arrogant statement you should share your secrets and tell them where they've been going wrong.

To me the arrogance is the way the transactional interpretation and bohms interpretation have been so ignored, and the defeatist Copenhagen and rediculous Many Worlds interpretations have been so embraced. It's as if modern scientists have the curiosity of old men and the dilligence of children. Upside-down in my opinion.

Ask away, don't be shy !

How does the supposed Higgs particle give mass to itself? Why does dark matter seem like such a childish solution to a serious question ? Why does the moon spin at exactly the right speed so we only ever see one side, and why is it exactly the right size and distance from us for eclipses? Why is so much of science's funding spend on irrelevant issues where the answers are always sensational, but contradict each other year to year?

Why does physics try so hard to refute the anthropic principle that it invents billions of unseen whole universes PURELY to refute the 'stain' in the mind that the universe (and all it's amazingly consistent laws and mathematical consistency, such that a pencil and paper can predict events billions of miles away), is more than randomness from nowhere.

Until science frees itself from from post modernism and all the crap that the current education system feeds students, despite the efforts of brilliant teachers and tutors, students will continue to learn "facts", which will be proven wrong in years if not decades or even centuries. What they should learn is questions, but sadly science has become too specialised for that to be feasible anymore.

 

[Mentz114]

I don't see the world in the same way at all. You are are generalizing too much. Physics is done by a very varied and often disparate bunch of people who certainly don't agree amongst each other about everything.

despite the efforts of brilliant teachers and tutors, students will continue to learn "facts", which will be proven wrong in years if not decades or even centuries.

How else could it be ? Scientific theories are hypotheses that more or less agree with observation. If they can be replaced with improved theories then so be it.

 

[DrChinese]

To me the arrogance is the way the transactional interpretation and bohms interpretation have been so ignored, and the defeatist Copenhagen and rediculous Many Worlds interpretations have been so embraced. It's as if modern scientists have the curiosity of old men and the dilligence of children. Upside-down in my opinion.



How does the supposed Higgs particle give mass to itself? Why does dark matter seem like such a childish solution to a serious question ? Why does the moon spin at exactly the right speed so we only ever see one side, and why is it exactly the right size and distance from us for eclipses? Why is so much of science's funding spend on irrelevant issues where the answers are always sensational, but contradict each other year to year?

Why does physics try so hard to refute the anthropic principle that it invents billions of unseen whole universes PURELY to refute the 'stain' in the mind that the universe (and all it's amazingly consistent laws and mathematical consistency, such that a pencil and paper can predict events billions of miles away), is more than randomness from nowhere.

Until science frees itself from from post modernism and all the crap that the current education system feeds students, despite the efforts of brilliant teachers and tutors, students will continue to learn "facts", which will be proven wrong in years if not decades or even centuries. What they should learn is questions, but sadly science has become too specialised for that to be feasible anymore.

Next time, please consider using the tags [RANT] and [/RANT].

 

[J12345]

Dr. Chinese? how do you 'register' on your web site- there seems to be no spot to hit to register thanks

 

[Frame Dragger]

@SimonA: We get it, the elegance of the universe takes your breath away, and why not, it's all for you. *rolleyes* Anyway, you might want to consider that "counterintuitive" doesn't equal "wrong". As for your concepts of teaching, you would... what... throw the very latest theories at kids and hope they can cope? LOL Oh boy. Everyone needs a platform from which to begin their learning, and first we have to be taught HOW to learn. That's what school is about before graduate work frankly, but it seems that notion has been drowned in a torrent of your rightous indignation.

I do have a solution for you however. If you want people to learn facts that haven't been discovered yet, build a time machine. Good luck with those CTCs buddy.

 

[Dmitry67]

Another interesting experiment is to do this with C₆₀ molecules, and repeat the experiments many times with a different air pressure around the setup each time. You get a "wave" interference pattern (as if both slits are open at the same time) when you do it in a vacuum, and a "particle" interference pattern (as if only one is open at a time) when the air pressure is high. The interesting part is that you get an "intermediate" pattern when the air pressure is neither high nor very low.

The reason is that interactions with the environment (the air) changes the statistical properties of the molecules, as more and more information about the paths taken can (in principle) be inferred by performing measurements on the state of the air. This proves that "wavefunction collapse" isn't a sudden and discontinuous physical process, and that "wave-particle duality" isn't about the system being either a wave or a particle. Apparently it's a little bit of both. For more information about this, see a book or a review article about decoherence.

Wow
i did not not know that nice part about the PRESSURE
Thank you

 

[Dunce]

I admit I'm biased, so I apologize if I offend anybody. It seems to me at least, that most of these crazy QM experiments can be pretty easily and logically explained. When we speak of an "observer", we don't literally mean just a mechanical eyeball or something like that. In order to gain a quantum measurement, the object being measured has to physically interact with a classical object, which will the measurements obtained. Quantum information changes when information is transformed into a classical "measurement". For example, with the double slit experiment, the "observer" is a piece of film in which the particles travel through. The object behaves differently when "observed", but people seem to ignore that physical interactions are taking place.

The fact that we so willingly accept that a particle spins in both directions at the same time until measured, is a little bit absurd. If you're in space viewing Earth from the North Pole, the planet is rotating in the opposite direction compared to anybody viewing it from the South Pole. How can we tell which "pole" we're viewing when we "look" at a particle? Quantum Physics aren't as magical as they can be when we stop making assumptions.

 

[Frame Dragger]

I admit I'm biased, so I apologize if I offend anybody. It seems to me at least, that most of these crazy QM experiments can be pretty easily and logically explained. When we speak of an "observer", we don't literally mean just a mechanical eyeball or something like that. In order to gain a quantum measurement, the object being measured has to physically interact with a classical object, which will the measurements obtained. Quantum information changes when information is transformed into a classical "measurement". For example, with the double slit experiment, the "observer" is a piece of film in which the particles travel through. The object behaves differently when "observed", but people seem to ignore that physical interactions are taking place.

The fact that we so willingly accept that a particle spins in both directions at the same time until measured, is a little bit absurd. If you're in space viewing Earth from the North Pole, the planet is rotating in the opposite direction compared to anybody viewing it from the South Pole. How can we tell which "pole" we're viewing when we "look" at a particle? Quantum Physics aren't as magical as they can be when we stop making assumptions.

You do realize that the term "spin" is a term of art and does not literally refer to a particle spinning about an axis? The term was chosen because of a mathematical similarity, just as "colour" and "quark" were rather whimsical. Beyond that, explain the following: You take a single buckyball, or a Rubidium atom, and pass it through the double slit. It STILL forms an interfernece pattern as would be expected from quantum behaviour. Again... counterintuitive does not mean "wrong".

 

[mintparasol]

To quote from a physics lecture by Professor Henry Greenside:

"Consider Young’s double-slit interference experiment but now put a linear polarizing filter in front of each slit. Then as transmission axis of one polarizer is slowly rotated about its axis while transmission axis of other polarizer is kept fixed, one finds experimentally that the bright regions become dimmer, the dark regions become brighter, until the fringes disappear into a smoothly varying region that is brightest behind the slits and gets dimmer off to the sides."

In other words: when the polarization of the light tells you which slit the photon went through, you get NO interference. That occurs when the polarizers are crossed (90 degrees offset). When they are parallel, you have no idea which way the photon went - and there IS interference on the screen.

In other words, when you cross polarity by 90 degrees you get no interference. This proves nothing at the quantum level

 

[DrChinese]

I admit I'm biased, ...

The fact that we so willingly accept that a particle spins in both directions at the same time until measured, is a little bit absurd. If you're in space viewing Earth from the North Pole, the planet is rotating in the opposite direction compared to anybody viewing it from the South Pole. How can we tell which "pole" we're viewing when we "look" at a particle? Quantum Physics aren't as magical as they can be when we stop making assumptions.

Welcome to PhysicsForums, Dunce!

We all have bias, and a lot of that comes from assumptions. It actually turns out that your view - which is considered a "classical" one - has more assumptions than the standard quantum mechanical perspective. So it is not the seasoned scientists making assumptions, it is you.

It turns out that in the double slit experiment, for example, you would expect that the particle either goes through one slit or the other. Yet as mentioned above: all I have to do is put polarizers on each slit and set them certain ways, and I can make the interference disappear. This corresponds to knowing which-slit, and cannot be explained classically because it requires you to abandon your initial assumption that the particle (or whatever is it) only went through one slit or the other. Obviously, the interference effect is evidence to the contrary.

To make this clear, consider the following two setups A and B, which are identical except for the settings of the polarizers in front of each slit. In each case, the source beam is polarized to 0 degress and the L (left) slit has a +45 degree polarizer. The R slit has a ++45 degree polarizer in the A setup but has a -45 degree polarizer in the B setup. Sorry for the crude drawing...

A. Inteference IS seen
...======
... Source
...== | ==
... |
... V
== /L/ = /R/ ==

.===Screen===B. NO Interference seen
...======
... Source
...== | ==
... |
... V
== /L/ = \R\ ==

===Screen===

In both cases A and B above, the amount of light that is detected on the screen is the same. And that amount is half of the light that would go through if there were no polarizers in front of the L and R slits. In other words, the polarizers filter out half the light. In the classical view, where does the interference originate? And why does it disappear if we cross the polarizers?

Regardless of whether you advocate the particle or wave perspective, your answers will not be consistent. On the other hand, quantum mechanics explains the A results based on a superposition of states which gives rise to interference terms. But there are no interference terms when the polarizers are crossed. So QM relies on a mathematical formalism rather than an "intuitive" description.

 

[DrChinese]

In other words, when you cross polarity by 90 degrees you get no interference. This proves nothing at the quantum level

Sure it does. See my A/B example in the above post. You can see that the only difference between the A and B setups is that the R slit polarizer is rotated 90 degrees. This provides the answer to the "which slit" question - at least in principle (you don't need to actually know this information, it is enough that you *could* know it). That is enough to eliminate the interference. There is NO chance that a particular photon polarized at 0 degrees could pass through both a +45 polarizer and a -45 degree polarizer in the quantum mechanical view. The operative formula is the COS^2(L-R) rule, where L-R=90 degrees so that the result is 0 and there is no interference.

On the other hand, in the classical perspective, there IS a chance that any particular photon polarized at 0 degrees could pass through both a +45 polarizer and a -45 degree polarizer. Do you see why? The rule is different because the probability is resolved independently for each slit, unlike in the quantum view in which it is the relative angle of the L and R slits is important. So now you get COS^(L-0)*COS^(R-0) and there should be some interference because the result is .25 which is >0.

In other words, the quantum view considers both the L and R slits as a system, while the classical view considers each slit separately. You see the same kind of things with entangled photons, which is a much better example than the double slit. But either way, it is a quantum effect although the traditional Young setup itself (not the example I gave which is modified) is sometimes considered a classical wave example too.

 

[Frame Dragger]

@DrChinese: You have no idea how happy I am that you showed up.

 

[DrChinese]

@DrChinese: You have no idea how happy I am that you showed up.

 

[Agent M27]

Very interesting DrChinese! I am reading Feynmans QED right now, and I just passed the section dealing with the double slit experiment. In this section he covers the obvious of not being able to predict through which slit the photon travelled, but he also covers an experiment which will alter/remove the interference pattern by changing the distance between the two slits. He did not however, cover the bit about polarization, which sounds like a cute trick to the layman mind. To the original poster, this is a great read and it is actually not all that difficult to comprehend. I suggest it as an intro to QM so to speak.

DrChinese: I fully understand what happens in a given two slit experiment, but I am at a loss as to why. Your experiment of polarization sounds like it is narrowing it down to a why, but is there more to it? I surely don't accept that the photon is conscious of the experiment or "observer", but aside from the ability to calculate it's probability amplitude, is there a reason it is in superposition? I am starting David Bohms Quantum Theory next, so my knowledge base is minimal. Thanks and have a great day!

Joe

 

[mintparasol]

Sure it does. See my A/B example in the above post. You can see that the only difference between the A and B setups is that the R slit polarizer is rotated 90 degrees. This provides the answer to the "which slit" question - at least in principle (you don't need to actually know this information, it is enough that you *could* know it). That is enough to eliminate the interference. There is NO chance that a particular photon polarized at 0 degrees could pass through both a +45 polarizer and a -45 degree polarizer in the quantum mechanical view. The operative formula is the COS^2(L-R) rule, where L-R=90 degrees so that the result is 0 and there is no interference.

On the other hand, in the classical perspective, there IS a chance that any particular photon polarized at 0 degrees could pass through both a +45 polarizer and a -45 degree polarizer. Do you see why? The rule is different because the probability is resolved independently for each slit, unlike in the quantum view in which it is the relative angle of the L and R slits is important. So now you get COS^(L-0)*COS^(R-0) and there should be some interference because the result is .25 which is >0.

In other words, the quantum view considers both the L and R slits as a system, while the classical view considers each slit separately. You see the same kind of things with entangled photons, which is a much better example than the double slit. But either way, it is a quantum effect although the traditional Young setup itself (not the example I gave which is modified) is sometimes considered a classical wave example too.

I'm just a lay nut so I won't even pretend to understand the math. It's still one photon going thru one slit, resulting in no interference. There's nothing counter-intuitive or esoteric about it, you won't get an interference pattern if you don't get the same photon(s) going thru both slits. If you change the operation of one of the slits by the means described in this thread and elsewhere, you won't get an interference pattern on the 2nd screen. This proves nothing other than the fact that the same light source must pass unimpeded thru both slits in order to produce an interference pattern on the 2nd screen.
I'm sorry, but this is the emperor's new clothes. Yes, it proves that light has wavelike properties and that a single photon can pass thru 2 slits, so what? A single low frequency waveform in the audio spectrum will also pass thru 2 slits in a screen, resulting in an interference pattern that can be detected at the rear of the screen. We could probably ascribe a whole lot of QM to soundwaves as well if we wished, but what would be the point?

 

[DrChinese]

I'm just a lay nut so I won't even pretend to understand the math. It's still one photon going thru one slit, resulting in no interference. There's nothing counter-intuitive or esoteric about it, you won't get an interference pattern if you don't get the same photon(s) going thru both slits. If you change the operation of one of the slits by the means described in this thread and elsewhere, you won't get an interference pattern on the 2nd screen. This proves nothing other than the fact that the same light source must pass unimpeded thru both slits in order to produce an interference pattern on the 2nd screen.
I'm sorry, but this is the emperor's new clothes. Yes, it proves that light has wavelike properties and that a single photon can pass thru 2 slits, so what? A single low frequency waveform in the audio spectrum will also pass thru 2 slits in a screen, resulting in an interference pattern that can be detected at the rear of the screen. We could probably ascribe a whole lot of QM to soundwaves as well if we wished, but what would be the point?

Well at least you are thinking about it...

I would be interested in a demonstration of a classical wave effect which eliminates all interference when partial polarizers (or classical equivalent) are present in a setup similar to the double slit. You use the example of audio, and I think a careful consideration of your analogy will demonstrate that the interference will NOT be eliminated after all - as it would need to be to match light in a double slit.

Of course there is a lot more to the story on the quantum side anyway. If light were waves (only) then a lot of things would be different (in contradiction to experiment - see for example: http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf" ). If light polarization operated as you imagine, things would be different with entangled particle pairs (in contradiction to experiment).

You may not be aware of all of the experiments out there (who is?), but you might want to at least ask before talking about the emperor's clothes. The double slit is just one piece of the puzzle.

 

[Frame Dragger]

I'm just a lay nut so I won't even pretend to understand the math. It's still one photon going thru one slit, resulting in no interference. There's nothing counter-intuitive or esoteric about it, you won't get an interference pattern if you don't get the same photon(s) going thru both slits. If you change the operation of one of the slits by the means described in this thread and elsewhere, you won't get an interference pattern on the 2nd screen. This proves nothing other than the fact that the same light source must pass unimpeded thru both slits in order to produce an interference pattern on the 2nd screen.
I'm sorry, but this is the emperor's new clothes. Yes, it proves that light has wavelike properties and that a single photon can pass thru 2 slits, so what? A single low frequency waveform in the audio spectrum will also pass thru 2 slits in a screen, resulting in an interference pattern that can be detected at the rear of the screen. We could probably ascribe a whole lot of QM to soundwaves as well if we wished, but what would be the point?

Speaking of sound, as we discuss this, a "sonic black hole" has been created in a lab, and is being studied as an analogy for the event horizon of a gravitic black hole. In fact, they are waitng to see if phonons are emitted (as expected) in a fashion similar to what you'd expect with photons on the boundry of a Black Hole (i.e. hawking radiation) which is a quantum theory that mimics a classical thermodynamic process. So... yes... there is that attribution to sound, but as DrChinese pointed out it's the DUAL nature of quanta such as photons that cause the results you find in the double-slit experiment.

Moreover, before you simply ascribe this quantum behaviour to light alone, it's simply not that limited. Carbon60 (buckyballs! wheee), and single Rubidium atoms have been used and you still find expected quantum behaviour. I wouldn't lead with, "I'm a lay nut", and move right into comparing the (constantly evolving) world of modern theoretical physics (and QM in particular) to a blindness to the simple truths of Newton's classical laws.

The big issue here is that the wave-particle duality is a TRUE duality and not just "this is a particle with some wave-like propertiers" or visa versa. Like it or not, again and again tests show that one photon, or one atom DOES pass through more than one aperture. Like it or not, intuitive or not.

 

[SimonA]

@SimonA: We get it, the elegance of the universe takes your breath away, and why not, it's all for you. *rolleyes* Anyway, you might want to consider that "counterintuitive" doesn't equal "wrong". As for your concepts of teaching, you would... what... throw the very latest theories at kids and hope they can cope? LOL Oh boy. Everyone needs a platform from which to begin their learning, and first we have to be taught HOW to learn. That's what school is about before graduate work frankly, but it seems that notion has been drowned in a torrent of your rightous indignation.

I do have a solution for you however. If you want people to learn facts that haven't been discovered yet, build a time machine. Good luck with those CTCs buddy.

I think people like you blind children from science. Kids love mystery, and quantum physics is, precisely, 99.9% pure mystery. You may want to cling to the mathematical formalism as a safety blanket, but mystery and the dilligent search for truth is exciting to other types of people.

 

[conway]

Just so there is no misunderstanding, I think someone should point out that even in classical physics, the interference pattern disappears if you have crossed polarizers in front of the alternate slits. There's nothing really mysterious about it.

 

[Frame Dragger]

I think people like you blind children from science. Kids love mystery, and quantum physics is, precisely, 99.9% pure mystery. You may want to cling to the mathematical formalism as a safety blanket, but mystery and the dilligent search for truth is exciting to other types of people.

So, your argument against an entire branch of theoretical and experiemental physics (with not a little evidence to show that the correct trackis being taken) is that people like me are teaching CHILDREN Quantum PHYSICS... and blinding them to your version of science? Who are these children that people like me are teaching QM?! I want to meet them, because they're either children of the bloody corn, or geniuses beyond all measure. Anyway, children are raised to believe in cults, religions (not that I percieve a difference), the certainty of atheism (another religion in SOME cases) and yet they manage to think for themselves if the quality of their mind is fine enough. I would be more concerned about the children who have that capacity, but are destroyed by circumstances such as poverty, partial or total abandonment, abuse, etc. That way, future generations can examine this issue long after we're dead and come to their own conclusions which lead to more questions.

Oh, and I doubt many people find the mathematics of QM very comforting. I for one find it downright upsetting in many of its implications, but that doesn't keep me from examining it. If you need to be PROTECTED from thoughts and theories, science, teaching, etc... these would not be endevours for you. Beyond that, while this is a thread about the double-slit experiment, you do realize that the evidence supporting the validity many parts of current Standard Model does exist, right?

That bit out of the way, I think that one of the better points of the scientific method is that such matters are presented as open to revision and change as experimental evidence and new theoretical thinking evolves. In that sense, it's rather hard to stifle someone's desire for scientific inquiry by posing them some of the greater unsolved problems of the world beyond our immediate experience. This, and the fact that the book is HARDLY closed on Quantum Physics.

 

[inflector]

The big issue here is that the wave-particle duality is a TRUE duality and not just "this is a particle with some wave-like propertiers" or visa versa. Like it or not, again and again tests show that one photon, or one atom DOES pass through more than one aperture. Like it or not, intuitive or not.

I'm still with John Bell on this one. The de Broglie-Bohm pilot wave theory fits the measured data just as well and offers an alternative explanation that doesn't require a photon or atom to pass through both apertures at once. It does require that a wave pass through both apertures but not the photon or the atom.

What the tests SHOW is interference patterns and lack thereof under differing circumstances. While it is certainly the case that most physicists believe as you do that photons and atoms are necessarily both particles and waves, there are some that do not and they are not quacks. John Bell was not a Quack.

 

[Frame Dragger]

I'm still with John Bell on this one. The de Broglie-Bohm pilot wave theory fits the measured data just as well and offers an alternative explanation that doesn't require a photon or atom to pass through both apertures at once. It does require that a wave pass through both apertures but not the photon or the atom.

What the tests SHOW is interference patterns and lack thereof under differing circumstances. While it is certainly the case that most physicists believe as you do that photons and atoms are necessarily both particles and waves, there are some that do not and they are not quacks. John Bell was not a Quack.

There is a whole thread dedicated to this issue, and in that Dr. Chinese has already posted a more interesting and insightful argument in support of The Standard Model vs. dBB than I possibly can. https://www.physicsforums.com/showthread.php?t=283740 Enjoy. As this debate is well established and doesn't really need to be rehashed here, you can simply assume I'm in the camp that doesn't believe in a contorted theory which accomplishes nothing, but ease the minds of people who can't accept the more uncomfortable implications of the standard interpretation of the SQM.

 

[inflector]

You might enjoy this discussion as well:

https://www.physicsforums.com/showthread.php?t=304724

I was simply trying to point out to the OP that there are alternative explanations to the SQM.

 

[DrChinese]

Just so there is no misunderstanding, I think someone should point out that even in classical physics, the interference pattern disappears if you have crossed polarizers in front of the alternate slits. There's nothing really mysterious about it.

I am not sure about that actually being the case. What element of a classical explanation leads to that conclusion? Let's consider the wave perspective as being the operative picture, since that has the potential for interference. The source is vertically polarized (0 degrees) and the polarizers are either +45/+45 (Parallel) or +45/-45 (Crossed). You get full interference in the Parallel mode and NO inteference in the Crossed mode. I say any classical explanation will predict SOME interference in the Crossed mode. Now, why do I claim that?

Clearly, the polarizer stops half of the waves coming through. And clearly, the Parallel mode should transmit the light through both polarizers under both the quantum or classical views. But, as with Bell's Theorem, the classical picture adds an extra assumption not present in the quantum view. That assumption being realism. That assumption means that there must be a real value for that wave passing through the polarizers in either the Parallel or Crossed modes - even if it is only tested in a single mode at a time.

A little thought will give you these statistical requirements of such a theory.

a. The usual cos^2(theta) rule - i.e. Malus. This applies to each slit separately, and must apply at other angles than +/-45 degrees such as +/-30 degrees etc.

b. You also must have the prediction of no interference when the polarizers are Crossed. And this must apply at ALL angle settings, not just +45/-45! For example, it must true at +30/-60, +40/-50, ... i.e. whenever the difference is 90 degrees.

There are NO datasets which can meet both of these requirements consistently. You can make it appear to work for +45/-45 alone but then it will not work for +30/-60 etc. I.e. it will not work for all possible values for the polarizers simultaneously. And that violates the realism requirement, which QM does not need to respect.

If there were light waves, the classical picture will end up predicting (once you allow for realism) that sometimes there would be light that would pass through BOTH slits even in the Crossed mode. Such waves would be polarized out of phase coming out of the slits. But I don't believe you would have complete cancellation in that situation. There would be some interference effects leftover. My thinking could be wrong on that, but there is definitely no dataset that meets the requirements a. and b. above, i.e. a classical realistic description for passing through the slits.

 

[DrChinese]

Just to add to my prior post: I think the situation could probably be formulated into an inequality using logic from Bell's Theorem. Basically it is now the same situation, in which the 2 slits are the analog of Alice and Bob.

And of course we are completely disregarding the obvious contradictions in the purely wave picture involved with a classical description. Such as the fact that the photon can only be detected at one slit or the other, and never both as you would expect.

 

[Frame Dragger]

Just to add to my prior post: I think the situation could probably be formulated into an inequality using logic from Bell's Theorem. Basically it is now the same situation, in which the 2 slits are the analog of Alice and Bob.

And of course we are completely disregarding the obvious contradictions in the purely wave picture involved with a classical description. Such as the fact that the photon can only be detected at one slit or the other, and never both as you would expect.

Not to mention experimental evidence showing that while light has wave-like properties, it is subject to the effects of gravity as predicted by GR. There really is a fairly impressive near intersection between QM and GR, which promises to breed something new if they can be reconciled. Classical Mechanics consitantly takes it in the theoretical pants from QM. Who knows, we could get lucky and confirm The Higgs Mechanism through the LHC and end this debate. That would be... refreshing. Then again, Classicists might still find a theory sufficiently contorted so as to be familiar while competing with QM (in the minds of some at least). Such is the case, in my view, with dBB, and the issue we're having here re: the DS experiment!

 

[conway]

If there were light waves, the classical picture will end up predicting (once you allow for realism) that sometimes there would be light that would pass through BOTH slits even in the Crossed mode. Such waves would be polarized out of phase coming out of the slits. But I don't believe you would have complete cancellation in that situation. There would be some interference effects leftover.

There are no interference effects of that kind between light waves that are polarized 90 degrees to each other. Classical EM predicts that the pattern on the screen will simply be the sum of the patterns from the individual slits. The same as QM predicts.