I Double slit - properties of slit?

[Homestar1]

In the double slit experiment, are there articles that study different slit properties (e.g. charges, magnetic fields, current, etc.)? Curious if a wave is the property of the measurement, changing the properties of the experiment may alter the output measurement.

 

[EPR]

The slits don't have any of the listed properties - charge, current and magnetic fields.

 

[Homestar1]

The slits don't have any of the listed properties - charge, current and magnetic fields.

Thanks. Am curious if anyone has set up an experiment to change these properties to see what happens and if they influence an outcome in theoretically predictable ways.

 

[DrChinese]

Thanks. Am curious if anyone has set up an experiment to change these properties to see what happens and if they influence an outcome in theoretically predictable ways.

The double slit can be done with photons, which lack charge. The purpose of the double slit setup is to demonstrate particle self-interference, which would not be affected by varying anything you mention (unless it gave any which-slit information, in which case the interference pattern would disappear).

 

[Homestar1]

Thank you!

 

[EPR]

What is the idea? Anything that can be continuously observed and measured will always act as if it was classical, even if it were extremely tiny and entirely quantum in nature. Be it atoms or elementary 'particles'. Or macro objects.

 

[Homestar1]

The double slit can be done with photons, which lack charge. The purpose of the double slit setup is to demonstrate particle self-interference, which would not be affected by varying anything you mention (unless it gave any which-slit information, in which case the interference pattern would disappear)

 

[Homestar1]

Imagine a theoretical (exploratory) concept where a particle is looked from an observer's point of view. The relative state between the co-objects would have no relative linear motion, zero velocity, and zero displacement, and the particle existed in a self-interference state (if I'm using that term correctly) but had innate circular motion (like a moon orbiting a planet without a planet). Now, when the particle is subject to measurement (now with a velocity and displacement), would it be measured as a wave?

 

[Homestar1]

To clarify, the co-objects with no relative linear motion would be the observer and the centre of the circular orbit (where the planet would be if there was one to keep the analogy).

 

[EPR]

Imagine a theoretical (exploratory) concept where a particle is looked from an observer's point of view. The relative state between the co-objects would have no relative linear motion, zero velocity, and zero displacement, and the particle existed in a self-interference state (if I'm using that term correctly) but had innate circular motion (like a moon orbiting a planet without a planet). Now, when the particle is subject to measurement (now with a velocity and displacement), would it be measured as a wave?

No, it would be measured as a 'particle' at a location. There are no waves.
Waves and wavefunctions are abstract tools for making predictions about the life of the 'particles'. It's much more complicated than that but for the level of the questions, it's enough to guide you. There are conservation laws about energy, mass, charge, momentum and they play a central role for why the quantum appears orderly when it's probed by our macroscopic devices(and supposedly our senses).

 

[DrChinese]

Imagine a theoretical (exploratory) concept where a particle is looked from an observer's point of view. The relative state between the co-objects would have no relative linear motion, zero velocity, and zero displacement, and the particle existed in a self-interference state (if I'm using that term correctly) but had innate circular motion (like a moon orbiting a planet without a planet). Now, when the particle is subject to measurement (now with a velocity and displacement), would it be measured as a wave?

To the extent such an idea could be realized: No, because a measurement of a quantum property of an electron (or photon) never shows a value that indicates it is a wave. For example, a measurement of momentum or position will always return a single value.

 

[Homestar1]

No, it would be measured as a 'particle' at a location. There are no waves.
Waves and wavefunctions are abstract tools for making predictions about the life of the 'particles'. It's much more complicated than that but for the level of the questions, it's enough to guide you. There are conservation laws about energy, mass, charge, momentum and they play a central role for why the quantum appears orderly when it's probed by our macroscopic devices(and supposedly our senses).

Thanks. I agree with seeing waves and wave functions as abstract tools. Any textbook you recommend so I can continue my studies? If I understand it right, each moment in time a particle is defined by conservation laws, but each moment changes from what was and what will be, thus appearing disordered, but within a moment of time between measures, there is order.

 

[EPR]

Thanks. I agree with seeing waves and wave functions as abstract tools. Any textbook you recommend so I can continue my studies? If I understand it right, each moment in time a particle is defined by conservation laws, but each moment changes from what was and what will be, thus appearing disordered, but within a moment of time between measures, there is order.

There is continuity.

I am unsure if studying QM in detail will help you much, except maybe to dispel some very common misunderstaings. You'll quickly run out of answers... and definitely have many more questions.
The belief that quantum mechanics is actually how reality really works, rather than how it is a math of probability being used to describe reality with very limited information of its actual structure.
If you measure mass with the metric system, your units are in metric.
If you speak French and answer questions, most likely your answer will be in French.
If you describe reality with probabilities, with little to no real understanding of what is going on, your answer will be in probabilities.
All that this can tell you with certainty is: your answer is always going to be in the format/language you used to ask the question. This doesn't actually mean the truth IS the language/format you asked the question with.

A calculation is a calculation. Nothing more, nothing less. A calculation is not a cause of anything, it can carry no forces, it can provide no existence for anything anymore than any second hand calculation can be independent of the party that calculates it. The question quantum mechanics has failed to answer is what is actually generating the probabilities...the basis for the calculations.
If you are looking to understand how the world really works, go to a church.
I am joking but... you'll likely get more unanswered questions than you have now. And they will be more difficult to address.

 

[PeterDonis]

Moderator's note: Thread level changed to "I".

 

[PeterDonis]

Any textbook you recommend so I can continue my studies?

If you are trying to learn QM, there are many QM textbooks available, and it's probably a good idea to study several of them. I personally find Ballentine to be a good introduction. The parts of the Feynman Lectures on Physics that deal with QM might also be helpful (those are available for free online).

 

[Homestar1]

There is continuity.

I am unsure if studying QM in detail will help you much, except maybe to dispel some very common misunderstaings. You'll quickly run out of answers... and definitely have many more questions.
The belief that quantum mechanics is actually how reality really works, rather than how it is a math of probability being used to describe reality with very limited information of its actual structure.
If you measure mass with the metric system, your units are in metric.
If you speak French and answer questions, most likely your answer will be in French.
If you describe reality with probabilities, with little to no real understanding of what is going on, your answer will be in probabilities.
All that this can tell you with certainty is: your answer is always going to be in the format/language you used to ask the question. This doesn't actually mean the truth IS the language/format you asked the question with.

A calculation is a calculation. Nothing more, nothing less. A calculation is not a cause of anything, it can carry no forces, it can provide no existence for anything anymore than any second hand calculation can be independent of the party that calculates it. The question quantum mechanics has failed to answer is what is actually generating the probabilities...the basis for the calculations.
If you are looking to understand how the world really works, go to a church.
I am joking but... you'll likely get more unanswered questions than you have now. And they will be more difficult to address.

Thank you for your comments. They resonate well, very well actually. This is a quote from a manuscript (in review) of mine and when accepted (fingers crossed) you may find the work interesting. I'm brought into QM not as a destination of choice, but as a path that is leading me to be introduced to it. This quote below is NOT referring to QM but it ties very well some some of your comments, thus my new interest in QM.

"Once the properties of the physical are conceptually understood, the units of measure become less important in visualising understanding the overall representations. In fact, at a point, a conceptual visual representation can then become a guide to what can be converted into measurement using mathematical hypotheses, models, and testing."

 

[PeterDonis]

This is a quote from a manuscript (in review) of mine

Please be advised that Physics Forums is not for discussion of unpublished research. If your manuscript is published in a peer-reviewed journal, then it can be a basis for discussion.

 

[hutchphd]

You might wish to visit https://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect...I don't know.

 

[rude man]

In the double slit experiment, are there articles that study different slit properties (e.g. charges, magnetic fields, current, etc.)? Curious if a wave is the property of the measurement, changing the properties of the experiment may alter the output measurement.

A particle has a wave function. The wave function completely describes everything knowable about the particle. So other parameters like momentum and energy are intrinsicall contained within this function.

This wave is a mathematical abstraction. There is no physical wave to look at; it must be derived for each situation, e.g the wave function of a single hydrogen electron. The double-slit experiment for particles was the first indication that a particle's momentum is associable with an electromagnetic wavelength - by associating the interference patterns produced by electromagnetic light of wavelength $\lambda$ with the same pattern produced by particles of known momentum.

If you disturb the slits, for example if you try to see which slit the particles entered by looking at the slits, you would need light (photons) to see it. The photons would interact with the particles. That would destroy the wave function and you'd get no interference pattern.

 

[tech99]

The double slit can be done with photons, which lack charge. The purpose of the double slit setup is to demonstrate particle self-interference, which would not be affected by varying anything you mention (unless it gave any which-slit information, in which case the interference pattern would disappear).

When I read your post this morning I thought you said phonons?
May I ask, if a photon is reflected from a sheet of metal, do the electrons in the metal move? This seems an analogous situation to discussing the material of a slit.

 

[rude man]

When I read your post this morning I thought you said phonons?
May I ask, if a photon is reflected from a sheet of metal, do the electrons in the metal move? This seems an analogous situation to discussing the material of a slit.

By the Bohr atom model, if the photon has the right energy (=hf) then an electron moves from a lower to a higher energy level. If the photon has even more energy ( energy > "work function") then an electron can actually leave the metal. Einstein won his Nobel figuring that one out.

I am not a qm physicist so can't be more precise than that.

The double slit can be done with photons, which lack charge. The purpose of the double slit setup is to demonstrate particle self-interference, which would not be affected by varying anything you mention (unless it gave any which-slit information, in which case the interference pattern would disappear).

I meant particles of finite rest mass. I believe the original double-slit experiments in regard to modern physics involved electrons. Photons didn't "exist" at that time. Light interference patterns were until then ascribed to Maxwell's electric waves.

 

[DrChinese]

May I ask, if a photon is reflected from a sheet of metal, do the electrons in the metal move? This seems an analogous situation to discussing the material of a slit.

The double slit experiment does not examine the material of the slits, which plays no significant part in the usual results. You know that because you cover each slit independently, and the sum pattern of those does not equal the interference pattern (both slits uncovered). So the slit material is not the independent variable.

Photon reflection is a complicated subject, probably outside the scope of this thread. The simplistic answer is that the reflecting photon is not a point particle that bounds off a point electron. It is more like the sum of many possible interactions with the components of the metal.

 

[tech99]

Just for my education, are you saying the vector sum pattern does not equal the interference pattern? I assume we are talking about the pattern obtained from many photons over a period of time.

 

[hutchphd]

Thanks. Am curious if anyone has set up an experiment to change these properties to see what happens and if they influence an outcome in theoretically predictable ways.

In the far field, the position of the slit (centers) determines the fine details of the interference pattern. The details of the slit shape ( form factor and number) render the larger envelope of the diffraction. This is not usually the salient part in this context and so it is largely irrelevant to the "two slit problem"

 

[rude man]

Just for my education, are you saying the vector sum pattern does not equal the interference pattern? I assume we are talking about the pattern obtained from many photons over a period of time.

Not sure what you mean by vector sum pattern.

But the interference pattern obtained from classical physics (i.e. wave nature of light) is the same as that obtained from quantum mechanics.

Experimentally, by equating the interference pattern from the classical wave theory ($\lambda$) to that left by particles of known momentum $p$, we find that $\lambda p = h$ with $h$ = Planck's constant.

And yes, the pattern is that obtained on a photoemissive screen from many photons over a period of time..

 

[tech99]

Than you, I was just clarifying the comment in #22 about the two signals not adding.
By the way, using classical wave theory the slits are electrically coupled together I believe, but I have not seen it mentioned.

 

[rude man]

Than you, I was just clarifying the comment in #22 about the two signals not adding.
By the way, using classical wave theory the slits are electrically coupled together I believe, but I have not seen it mentioned.

No. They're just slits in an otherwise impenetrable wall. In the Young experiment (to which you refer), electricity plays no part.

In QM, don't try to associate charge with electrons. Electrons are often used because they're tiny and their initial momentum can easily be set. QM applies to ALL particles, charged or not, even including (in theory) cannon balls! (Maybe this doesn't apply to subatomic particles; I don't know).

 

[PeroK]

Than you, I was just clarifying the comment in #22 about the two signals not adding.
By the way, using classical wave theory the slits are electrically coupled together I believe, but I have not seen it mentioned.

Double slit interference can be seen with water waves, for example, where there is no electromagnetic aspect.

If you've not seen something mentioned, then by definition it's your idea.

 

[AdvaitDhingra]

In the double slit experiment, are there articles that study different slit properties (e.g. charges, magnetic fields, current, etc.)? Curious if a wave is the property of the measurement, changing the properties of the experiment may alter the output measurement.

The distance that separates the slits is a factor, as is the distance from the slits to the wall at the back. Magnetic fields, charge etc. is not taken into account. If you are talking about the double slit experiment with light, then these two factors have no meaning, as light is not influenced by an electric or a magnetic field. It is a different story with electrons, where if you try to observe which slit the electron went through using electromagnetic radiation (light) of a short wavelength (i.e. a precise measurement of which slit the electron went through), the interference pattern disappears, as you disturb the electron by observing it. If you increase the wavelength, the interference pattern returns yet the precision is so bad, that you no longer know which slit it went through. I would think the same applies with an electric or magnetic field.

Very good question by the way.

 

[akhmeteli]

In the double slit experiment, are there articles that study different slit properties (e.g. charges, magnetic fields, current, etc.)? Curious if a wave is the property of the measurement, changing the properties of the experiment may alter the output measurement.

Journal of Applied Physics 100, 074322 (2006) (https://aip.scitation.org/doi/abs/10.1063/1.2357000?journalCode=jap) or accessible version https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1060&context=mrsecfacpubs

"In the course of our previous qualitative study an unexpected broadening of the diffraction peaks was observed.27 We show that the broadening of the diffraction peaks is affected by the type and thickness of metallic coating"

The reason is the "image charges" in the screen with which electrons interact depend on the electric properties of the screen.

 

[rude man]

The double-slit experiment is traditionally performed with a non-conducting screen.
Electrons bombarding metal might suggest the photoelectric or some other secondary effect such as what the authors determined. Anyway, not germane to the canonical experiments investigating double-slit interference, or single-slit (Fraunhofer) diffraction, patterns (correlating wave and particle theory results).

 

[akhmeteli]

The double-slit experiment is traditionally performed with a non-conducting screen.
Electrons bombarding metal might suggest the photoelectric or some other secondary effect such as what the authors determined. Anyway, not germane to the canonical experiments investigating double-slit interference, or single-slit (Fraunhofer) diffraction, patterns (correlating wave and particle theory results).

Could you provide references to your statement "The double-slit experiment is traditionally performed with a non-conducting screen"? For example, https://iopscience.iop.org/article/10.1088/1367-2630/15/3/033018 uses silicon nitride coated with gold. And anyway, even if the screen is made of a dielectric, its electric properties, such as permittivity (or refraction index, for photons), would certainly have an effect on the interference.

 

[DrChinese]

The double slit experiment is an example of interference (when which-slit information is NOT available) vs. non-interference (which slit information IS available, whether or not used to determine which-slit).

The material of the screen has little or nothing to do with this critical element of the experiment. Ditto for the slit material. There might be some minor effects as akmeteli indicates, but these are obviously not the independent variables of study interest.

 

[hutchphd]

The material of the screen has little or nothing to do with this critical element of the experiment. Ditto for the slit material. There might be some minor effects as akmeteli indicates, but these are obviously not the independent variables of study interest.

I reiterate my previous remarks #18 and strongly agree that the details don't relate to the premise of the OP question

In other contexts this question is of interest for example Hans Bethe's seminal paper:
http://www.physics.miami.edu › Bethe1944

 

[rude man]

And anyway, even if the screen is made of a dielectric, its electric properties, such as permittivity (or refraction index, for photons), would certainly have an effect on the interference.

I'm not sure what percentage of emitted electrons make it thru the slits but any that don't are absorbed in,or reflected by, the slit screen. They will not affect the interference pattern. Only electrons that make it thru the slits are recorded on the phosphorescent screen downstream.

You're raising some good questions that I can't adequately answer, such as what if a mag field is applied at the slits on electrons.

What I can tell you is that the two-slit experiment using electrons as opposed to photons/light waves was seminal in launching qm, and that it did not knowingly involve any properties of the slit material.

(BTW I hope we're on the same page "screen-wise".There is the screen housing the slits and there is the phosphorescent screen recording where the electrons land. In past posts I used "screen" to mean the slit screen.)

 

[Nugatory]

There is the screen housing the slits

You can save yourself just a ton of grief by calling that a "barrier"

 

[rude man]

You can save yourself just a ton of grief by calling that a "barrier"

10-4. 'Barrier' it will be from now on.

 

[akhmeteli]

I'm not sure what percentage of emitted electrons make it thru the slits but any that don't are absorbed in,or reflected by, the slit screen. They will not affect the interference pattern. Only electrons that make it thru the slits are recorded on the phosphorescent screen downstream.

I am trying to say that electrons passing through a slit at some distance from the edge of a slit are also affected by the slit screen (they interact with their image charges, which depend on the properties of the slit screen).

 

[PeroK]

I am trying to say that electrons passing through a slit at some distance from the edge of a slit are also affected by the slit screen (they interact with their image charges, which depend on the properties of the slit screen).

You're proposing different interrefence patterns depending on the composition of the barrier with the slits?

In fact, we can simplify the experiment to a single slit: you're proposing different single-slit diffraction based not only on the width of the slit but the composition of the barrier?

 

[akhmeteli]

You're proposing different interrefence patterns depending on the composition of the barrier with the slits?

In fact, we can simplify the experiment to a single slit: you're proposing different single-slit diffraction based not only on the width of the slit but the composition of the barrier?

That is correct. Please see the reference in my post #30 in this thread.

 

[PeroK]

That is correct. Please see the reference in my post #30 in this thread.

I guess what we have (for single-slit diffraction) is:

1) The heuristic explanation using the HUP for position and lateral momentum.

2) A better analysis in terms of the electron being in an infinite square well for a short time as it passes through the slit.

3) A more exact analysis in terms of how precisely (or imprecisely) the barrier provides an infinite square well potential - which may depend on the material of the barrier.

Is that about it?

 

[akhmeteli]

I guess what we have (for single-slit diffraction) is:

1) The heuristic explanation using the HUP for position and lateral momentum.

2) A better analysis in terms of the electron being in an infinite square well for a short time as it passes through the slit.

3) A more exact analysis in terms of how precisely (or imprecisely) the barrier provides an infinite square well potential - which may depend on the material of the barrier.

Is that about it?

I am not sure. There can be dynamic aspects as well, as an electron spends a finite time near the slit. Something about dispersion relation for the barrier material.

 

[hutchphd]

There is an entire science niche devoted to LEED (Low Energy Electron Diffraction) mostly to investigate the surfaces of solids including conductors. There is nothing of fundamental interest about wave-particle fru-fru in any these studies and papers. I think my name may be on one of them from long ago (I used to analyze atomic beams diffracting from surfaces but electrons were just a passing discussion).
This is interesting physics but no big deal. The fact that surfaces are approximately two dimensional is what is really interesting. Don't get me started.

 

[gentzen]

There is an entire science niche devoted to LEED (Low Energy Electron Diffraction) mostly to investigate the surfaces of solids including conductors. There is nothing of fundamental interest about wave-particle fru-fru in any these studies and papers.

What exactly are you trying to say here?

That you don't see wave-particle duality effects in the measurement data? That depends, the wave effects are often quite dominant (and "undesired") for transmission data. Those occur in practice when you have manufactured a wedge to measure the stopping power at different thicknesses in order to validate your models. Wave effects (or rather phase effects) also occur in backscatter data (this time "desired"), when used to measure dislocaltions, defects, or stress via channeling contrast.

Or do you mean that the models themselves don't include the wave effects? For this part the reply would be a bit more complicated. The model certainly contain a variety of direct local quantum effects, including parts where electrons are indistinguishable Fermions, and parts where the electrons are distinguishable for various reasons. On the other hand, the mixing of wave and particle effects as seen in the measurement results described above is still active research. But even there I don't understand which point you are trying to make with your statement.

 

[DrChinese]

What exactly are you trying to say here?

That you don't see wave-particle duality effects in the measurement data? That depends, the wave effects are often quite dominant (and "undesired") for transmission data. Those occur in practice when you have manufactured a wedge to measure the stopping power at different thicknesses in order to validate your models. Wave effects (or rather phase effects) also occur in backscatter data (this time "desired"), when used to measure dislocaltions, defects, or stress via channeling contrast.

...

Answering for hutchphd (who is certainly capable of addressing this without me), and stating the orthodox line:

The presence or absense of "wave-particle duality" is not dependent on the slit's composition. Several posters have implied the opposite, that such composition has not been sufficiently researched (with respect to duality).

On the other hand: it is well known that there are "some" edge effects, but again quantum interference itself is not dependent on those. Could edge effects be exaggerated to the point that interference completely disappears? Even if that were possible, it wouldn't change anything important we learn from the double slit experiment. It would simply be a completely different experiment.

 

[gentzen]

Answering for hutchphd (who is certainly capable of addressing this without me)

Thanks for your answer. It enabled me to learn that "LEED (Low Energy Electron Diffraction)" is actually a specific imaging technique where an energy filter is used to exclude those electrons that lost energy during inelastic scattering events (typically interactions with electrons from the valence or conduction band). So it makes sense that hutchphd called it "an entire science niche". I had misinterpreted LEED as the study of the actual scattering and diffraction of the low energy electrons (inside of the sample), and was a bit surprised why that should be a niche.

After learning this, I first worried whether those measurements I knew using wave effects in backscatter data to measure dislocations, defects, or stress were also done using an energy filter. Had I really always missed that? But after checking some more, my impression is that most of them didn't use an energy filter. So wave effects are still strongly visible even without energy filtering. But the relation between energy filtering and visibility of wave effects is cool: Of course, after an electron lost (a mostly random bigger amount of) energy, its wave length is changed, and therefore its contribution to a diffraction pattern becomes mostly noise.

And that relation between inelastic scattering and lost coherence also makes it clearer how the mixing of wave and particle effects can be included in the models. Only the elastic part of the model must directly take care of the coherence and the structure of the solid. This is great, because it is clear (at least in principle) how to do this, and existing work has focused on that part. And the inelastic part can then be used to estimate the loss of coherence for a given distance.

This is a nice step forward compared to a discussion I had some weeks ago, where someone suggested that the inelastic part would also need to take care of the coherence. My arguments why I thought that the elastic part was more important were only partly convincing. (It was clear that I had no idea what to do with the inelastic part, and that weakened my arguments significantly.)