The double slit experiment

Foundations of physics and/or philosophy of physics, and in particular, posts on unresolved or controversial issues

Re: The double slit experiment

Postby Xray » Fri May 09, 2014 4:20 pm

AFAICT, the Bertlmann chapter is complete.

But the eBook here is Bell (1987), not Bell (2004). So the opening reference to Alain Aspect is, to me, misleading.

The eBook page numbers are 10 higher that the hard-copy because the hard-copy numbers the Preface etc (i) to (x). The eBook numbers them 1-10.

HTH, Xray
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Re: The double slit experiment

Postby gill1109 » Fri May 09, 2014 11:07 pm

Xray wrote:AFAICT, the Bertlmann chapter is complete.

But the eBook here is Bell (1987), not Bell (2004). So the opening reference to Alain Aspect is, to me, misleading.

The eBook page numbers are 10 higher that the hard-copy because the hard-copy numbers the Preface etc (i) to (x). The eBook numbers them 1-10.

HTH, Xray

Which eBook where is the first edition? The one on Amazon Kindle right now is the second edition. Also available direct from Cambridge University Press.

Yes Bertlmann is the same in preprint versions and in print.
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Re: The double slit experiment

Postby gill1109 » Fri May 09, 2014 11:12 pm

How distant are the two slits in the two slit experiment? Seems to me they should each be cut in a separate piece of (whatever) and the two pieces should be slightly separated and mounted on such a sturdy frame that vibration can hardly move from one half to the other half. Then there should be a kind of curtain behind the gap between the two pieces so that nothing goes through the gap. Finally, one should arrange that each slit can be closed independently of the other by two other kind of curtains...

Just a thought experiment!

Hasn't the two slit experiment been done with bucky balls and with slits which are further apart from one another than in the experiments with photons? Well, bucky balls would give more momentum on colliding with the walls of the slits so the problems simply get scaled up.
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Re: The double slit experiment

Postby Ben6993 » Sat May 10, 2014 3:55 am

Following on from the idea of using soft curtains, a different idea is to connect the slits to vibrators and so apply random noises to the slits. Increasing the strength of the noise should decrease the sharpness of the interference pattern if the pattern is affected by linear momentum transfer at the slits. (This surely has already been tried?)

However, the slits would not be vibrating in isolation as the air would be set vibrating too. So do this in a vacuum. The vacuum can possibly, maybe far-fetchedly, be a BEC superfluid, and if the slits somehow divide the vacuum into separate parts, then two BECs come together between the slits and the screen. Two BECs coming together are well known to create interference patterns, and BEC interference would not be affected by the vibrators.

Using added noise at the slits would still not tell me whether a diluted interference effect was caused by linear momentum from the slits or of interference within the vacuum as the two effects, if any, would be compounded.
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Re: The double slit experiment

Postby jreed » Sat May 10, 2014 6:37 am

These arguments about the screen assembly are exactly what Stopes-Roe was writing about in his Nature article. He couldn't understand how the screen assembly was acting as a whole. Lande gave a reply to this, but he just said essentially that an understanding of it will probably appear at some time in the future. I don't believe this. To use phonons to explain it will depend on the bulk modulus of the material, thickness, mounting rigidity and many other things. The diffraction pattern, on the other hand only depends on the width of the slits and the distance between them. As I said when all this started, this theory just moves the trouble (interference patterns) from the electrons, where it is calculated using the wave function obtained by solving Schroedinger's equation to the slit assembly. Now the interference calculation has been moved to another place, the screen, where it must again be found using quantum principles (phonons are quanta of the mechanical assembly). I don't find either theory more locally realistic. What has been gained?
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Re: The double slit experiment

Postby gill1109 » Sat May 10, 2014 7:12 am

jreed wrote:These arguments about the screen assembly are exactly what Stopes-Roe was writing about in his Nature article. He couldn't understand how the screen assembly was acting as a whole. Lande gave a reply to this, but he just said essentially that an understanding of it will probably appear at some time in the future. I don't believe this. To use phonons to explain it will depend on the bulk modulus of the material, thickness, mounting rigidity and many other things. The diffraction pattern, on the other hand only depends on the width of the slits and the distance between them. As I said when all this started, this theory just moves the trouble (interference patterns) from the electrons, where it is calculated using the wave function obtained by solving Schroedinger's equation to the slit assembly. Now the interference calculation has been moved to another place, the screen, where it must again be found using quantum principles (phonons are quanta of the mechanical assembly). I don't find either theory more locally realistic. What has been gained?

Nicely said.
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Re: The double slit experiment

Postby minkwe » Sat May 10, 2014 9:30 am

gill1109 wrote:Seems to me they should each be cut in a separate piece of (whatever) and the two pieces should be slightly separated and mounted on such a sturdy frame that vibration can hardly move from one half to the other half.

Richard, you are not understanding that we are talking about dynamics at the atomic level. You can not prevent atomic vibrations with what you call "Sturdy frame", which itself is made up of atoms. That is why you keep misunderstanding and thinking that photons/electrons are interacting with the whole slit assembly.
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Re: The double slit experiment

Postby minkwe » Sat May 10, 2014 9:35 am

Ben6993 wrote:Following on from the idea of using soft curtains, a different idea is to connect the slits to vibrators and so apply random noises to the slits. Increasing the strength of the noise should decrease the sharpness of the interference pattern if the pattern is affected by linear momentum transfer at the slits. (This surely has already been tried?)

Not as far-fetched as you may think. You have to apply the right vibrations though not just any type of vibrations. And indeed this has been done, (in a crystal), by adding forced vibrations, new diffraction peaks appear. I'll dig up the article.
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Re: The double slit experiment

Postby minkwe » Sat May 10, 2014 10:02 am

jreed wrote: Lande gave a reply to this, but he just said essentially that an understanding of it will probably appear at some time in the future.

So, then Lande's explanation is not the same as mine, as I provide the mechanism and it is not with the "whole slit assembly".

I don't believe this. To use phonons to explain it will depend on the bulk modulus of the material, thickness, mounting rigidity and many other things.

You still have to appreciate that the dynamics of an atom in the slit can be determined by the structure of the whole, so that a completely local interaction between an impinging particle and a single atom will contain information about the whole, without the interaction itself being with the whole slit assembly. Diffraction patterns are only produced by combining multiple different interactions of millions of different particles with different atoms of the slit ensemble, spread out over time, at different times in their oscillation cycles. That is why the pattern builds up over time. There is no interaction with the "whole slit assembly", rather the particles sample the time varying dynamics of the different particles of the slits. They dynamics, which in-turn is determined by the structure of the whole slits. Most of the confusion is introduced by naively believing that a single particle produces a diffraction pattern. It does not. A single particle samples one vibrational state of one atom at one given moment in time (the relevance of the Fourier transform then becomes quite clear).

The diffraction pattern, on the other hand only depends on the width of the slits and the distance between them.

It also depends on the momentum of the incoming particles. At least you admit that the electrons do not play a major part in the diffraction pattern, contrary to the claims of Feynman and the like, who instead say the diffraction pattern is produced by electrons interfering with themselves. Obviously false.
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Re: The double slit experiment

Postby minkwe » Sat May 10, 2014 10:07 am

As I said when all this started, this theory just moves the trouble (interference patterns) from the electrons

You still have not said where the trouble is in my explanation. You think if phonons are involved, it must be an interaction involving the whole slits, but as I've explained above, this is not the case. The dynamics of a pendulum depends on the weight of the ball, and the length of the rope. Yet if the ball hits another ball during its oscillation cycle, you won't say the interaction was with the whole pendulum, including the rope and the support. Yet If you have a lot of similar pendulums collide with a lot of different balls at different points during their oscillation cycles and record the momentum transferred, you will in the end be able to capture the full dynamics of the pendulum which is a property of the whole pendulums (including the rope), from only local interactions of the ball.

Now the interference calculation has been moved to another place, the screen, where it must again be found using quantum principles(phonons are quanta of the mechanical assembly). I don't find either theory more locally realistic. What has been gained?

Yes you apply quantum mechanical principles to phonons. So what? It doesn't mean you can not explain the experiment in a completely non-mystical manner as I've done. QM is just an information theory for calculating experimentally observed probabilities. You can apply QM principles to the stock market, I guess that makes the stock market mystical then according to your line of argument?

What exactly in my explanation is mystical or "trouble"? I still haven't heard one thing which is.
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Re: The double slit experiment

Postby minkwe » Sat May 10, 2014 6:00 pm

minkwe wrote:
Ben6993 wrote:Following on from the idea of using soft curtains, a different idea is to connect the slits to vibrators and so apply random noises to the slits. Increasing the strength of the noise should decrease the sharpness of the interference pattern if the pattern is affected by linear momentum transfer at the slits. (This surely has already been tried?)

Not as far-fetched as you may think. You have to apply the right vibrations though not just any type of vibrations. And indeed this has been done, (in a crystal), by adding forced vibrations, new diffraction peaks appear. I'll dig up the article.


Found it. http://journals.aps.org/prb/abstract/10 ... vB.27.2264
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Re: The double slit experiment

Postby minkwe » Sat May 10, 2014 6:11 pm

Another interesting very recent article:
http://journals.aps.org/prl/abstract/10 ... 111.103201

Momentum Transfer to a Free Floating Double Slit: Realization of a Thought Experiment from the Einstein-Bohr Debates
We simultaneously measured the momentum transferred to a free-floating molecular double slit and the momentum change of the atom scattering from it. Our experimental results are compared to quantum mechanical and semiclassical models. The results reveal that a classical description of the slits, which was used by Einstein in his debate with Bohr, provides a surprisingly good description of the experimental results, even for a microscopic system, if momentum transfer is not ascribed to a specific pathway but shared coherently and simultaneously between both.

Their results fully support my explanation, although they themselves interpret the results with a bit of mysticism in their discussion.
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Re: The double slit experiment

Postby jreed » Sun May 11, 2014 10:11 am

But, on this same web site, there are the following two paragraphs:

"A particle passes through a single slit and then through one opening of a double slit. Can the pathway of the particle be determined without destroying the interference structure? This was a question first debated by Einstein and Bohr as they tried to understand the newly developed ideas of quantum physics. Einstein argued that classical physics was sufficient; you could determine the particle’s path by measuring the momentum transfer imparted from the deflection of the particle by the first slit. Bohr claimed instead that the slits, as well as the particle, behave as quantum objects, whose position and momentum are uncertain—we can either know which path the particle takes through the slit maze, or how long the path is, but not both.

So who was right? Writing in Physical Review Letters, Lothar Schmidt and colleagues, from Goethe University in Germany, show that Bohr was right. In their experiments, the team replaced the slits with hydrogen-deuteron molecular ions and bombarded them with helium atoms. As the atoms collided with the ions, an electron was exchanged between the atom and the ion. By measuring this exchange they could determine the positions and orientation of the atoms and ions. The scattering of the atoms was consistent with Bohr’s view; you need a quantum description of the slits and particles to understand the results. However, the results could still be correctly predicted using classical slits, but only if the particle simultaneously passed through both holes of the double slit and transferred half of its momentum to each path. – Katherine Thomas"

Can you explain this with your theory?
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Re: The double slit experiment

Postby minkwe » Sun May 11, 2014 10:39 am

jreed wrote:But, on this same web site, there are the following two paragraphs:

"A particle passes through a single slit and then through one opening of a double slit. Can the pathway of the particle be determined without destroying the interference structure? This was a question first debated by Einstein and Bohr as they tried to understand the newly developed ideas of quantum physics. Einstein argued that classical physics was sufficient; you could determine the particle’s path by measuring the momentum transfer imparted from the deflection of the particle by the first slit. Bohr claimed instead that the slits, as well as the particle, behave as quantum objects, whose position and momentum are uncertain—we can either know which path the particle takes through the slit maze, or how long the path is, but not both.

So who was right? Writing in Physical Review Letters, Lothar Schmidt and colleagues, from Goethe University in Germany, show that Bohr was right. In their experiments, the team replaced the slits with hydrogen-deuteron molecular ions and bombarded them with helium atoms. As the atoms collided with the ions, an electron was exchanged between the atom and the ion. By measuring this exchange they could determine the positions and orientation of the atoms and ions. The scattering of the atoms was consistent with Bohr’s view; you need a quantum description of the slits and particles to understand the results. However, the results could still be correctly predicted using classical slits, but only if the particle simultaneously passed through both holes of the double slit and transferred half of its momentum to each path. – Katherine Thomas"

Yep "Katherine Thomas" says that, even the original authors interpret their results that way as I mentioned above. Just because they authors couldn't think of an explanation similar to mine doesn't mean it is not the correct one. They tried a naive "semi-classical" explanation which assumes that the dynamics of a single atom is independent of the dynamics of the molecule. When that didn't work, they conclude that the interaction must be with the whole molecule. They can't imagine a different explanation so they conclude that quantum mechanics is the only one that is possible. A fallacious argument. It's similar to assuming that since the interaction of the two pendulums at one end of Newton's cradle, does not completely explain the observed results, it must be that the first pendulum interacts with the whole cradle instantaneously.

Their results show clearly that. diffraction is a momentum transfer phenomenon, contrary to what some people continue to believe.
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Re: The double slit experiment

Postby jreed » Sun May 11, 2014 3:28 pm

minkwe wrote:
Their results show clearly that. diffraction is a momentum transfer phenomenon, contrary to what some people continue to believe.


Do you have a copy of this paper? I'd like to get a closer look at it so I could understand what they did better.
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Re: The double slit experiment

Postby gill1109 » Sun May 11, 2014 11:42 pm

jreed wrote:
minkwe wrote:
Their results show clearly that. diffraction is a momentum transfer phenomenon, contrary to what some people continue to believe.


Do you have a copy of this paper? I'd like to get a closer look at it so I could understand what they did better.

Yes, but is it a classical momentum transfer phenomenon or a quantum momentum transfer phenomenon?
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Re: The double slit experiment

Postby jreed » Mon May 12, 2014 5:59 am

gill1109 wrote:
jreed wrote:
minkwe wrote:
Their results show clearly that. diffraction is a momentum transfer phenomenon, contrary to what some people continue to believe.


Do you have a copy of this paper? I'd like to get a closer look at it so I could understand what they did better.

Yes, but is it a classical momentum transfer phenomenon or a quantum momentum transfer phenomenon?


I'm sure it will be momentum transfer by Duane's quantum rule. Does anyone have a copy of this paper, or is Minkwe so sure of his theory that he can dismiss the synopsis of Katherine Thomas as being wrong without knowing any of the details of the experiment or the theory behind it?
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Re: The double slit experiment

Postby Heinera » Mon May 12, 2014 6:17 am

jreed wrote:
jreed wrote:I'm sure it will be momentum transfer by Duane's quantum rule. Does anyone have a copy of this paper, or is Minkwe so sure of his theory that he can dismiss the synopsis of Katherine Thomas as being wrong without knowing any of the details of the experiment or the theory behind it?


It's this one, I guess:

http://www.atom.uni-frankfurt.de/public ... 013PRL.pdf
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Re: The double slit experiment

Postby jreed » Mon May 12, 2014 6:26 am

Heinera wrote:
It's this one, I guess:

http://www.atom.uni-frankfurt.de/public ... 013PRL.pdf


Yes, that's the one. Thanks very much for the reference. Maybe this will make this experiment easier to understand and sort out the differing theoretical approaches.
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Re: The double slit experiment

Postby gill1109 » Mon May 12, 2014 8:27 am

jreed wrote:
Heinera wrote:
It's this one, I guess:

http://www.atom.uni-frankfurt.de/public ... 013PRL.pdf


Yes, that's the one. Thanks very much for the reference. Maybe this will make this experiment easier to understand and sort out the differing theoretical approaches.


The abstract:
Schmidt et al wrote:We simultaneously measured the momentum transferred to a free-floating molecular double slit and the momentum change of the atom scattering from it. Our experimental results are compared to quantum mechanical and semiclassical models. The results reveal that a classical description of the slits, which was used by Einstein in his debate with Bohr, provides a surprisingly good description of the experimental results, even for a microscopic system, if momentum transfer is not ascribed to a specific pathway but shared coherently and simultaneously between both.


The conclusion:
Schmidt et al wrote:As an alternative to a quantum mechanical description of the slits, our results show that a classical description of the slits according to Einstein’s original viewpoint of the thought experiment is still possible. In that case one has, however, to assume a delocalized nonclassical interaction.


In other words, a classical explanation is possible, but it needs non-locality.
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