Question about single slit diffraction

[rob5]

This is in response to some posts to an earlier thread with this title.
In these posts one question seemed to be that the Huygens idea of scattering from points in the space between the slit edges was too mathematical and that scattering from the slit edges might provide a more realistic description of what was happening.
My thoughts on this are that the Huygens spatial points in the space between the slit edges are really air molecules and that electrons in these molecules are set in motion by the primary light source and that the interference effects observed on a receiving surface are due to the different path distances from these secondary source oscillations of electrons.
Thus if the slit edges and other parts of the screen between the primary light source and the receiver surface are painted black(which I recall has been done), scattering from these equally physical sources, in analogy to wave producing disturbances in water, could provide and alternative explanation for the observed interference effects.
This then suggests another question: Has the single slit diffraction experiment been done in a (partial)vacuum? A related question is: Do the laser beams which show up in typical laser demonstrations also show up when done in a (partial) vacuum?
Rob

 

[misskitty]

Hello Rob,

Welcome to PF. This is an interesting topic you bring up. I'd like to talk about this because my physics class is studying this right now ironically. Your reasoning seems to make sense to me. I'm not sure if I follow you in the black screen part though. What would performing an experiment, like the one you described, in a partial vacuum show? The way light travels would be altered since light can't travel through a vacuum; it would only be logical to assume that the effects of the partial vacuum would impact the way light travels.

 

[rob5]

What would a single slit diffraction experiment in a vacuum show? I think the experiment might show that there are no diffraction interference effects due to non material light waves eminating from point sources in the slit as Huygens description was interpreted before the MM experiment persuaded most physicists that no such waves could exist. (And before this Einstein had showed that the photoelectric emission of fast moving electrons from aluminum or whatever due to a source of uv light etc occurred too soon after the turning on of the source to be due to the wave theory of light)
But Feynman says that when a wave description works as in single slit and double slit diffraction etc it is mathematically tantamount to a probabilistic photon description(see his QED or vol3 of his Lectures on Physics) even though there are no actual waves of ether in a vacuum. That is all of the light phenomena explained by waves could be explained by probabilistic photons. And so without going into this mathematics, the currently accepted theory of light implies that there would be diffraction effects.
Thus the experiment would test the currently accepted theory of light.
I don't know why you say light can't travel through a vacuum eg outer space. Also Michelson or rather his collaborators after his death published the results of their earlier light speed measurement in a vacuum tube in 1935 (see http://encyclopedia.laborlawtalk.com/Albert_Michelson ).
Regarding the painted black screen and edges of the slit, I recall someone saying that they had done this to prevent reflection of light from these locations that might produce the observed diffraction effects on the receiver screen.

 

[rayjohn01]

Although light is a 'little ' effected by air the experiments are all valid in vaccuo
light does not need any of our normal media . It will diffract purely on a Geometric basis (as per Hygens wave theory ) .
The difference in QM is that there, a single photon is considered whereas Hygens did not look at single photons , he did not even know of photons .
All experiments confirm the wave and particulate nature of light ( in the human view ) --- the probable answer is that other dimensions are involved which we cannot sense or see . See theories such as string theory .
No one has ever measured a photon ( except in energy ) but not dimensionally
you have to figure that if two telescpes 10 km apart can have interference fringes ( which they do if their light is combined ) that photons must somehow be Km in width ?.
Ray

 

[rob5]

Although light is a 'little ' effected by air the experiments are all valid in vaccuo
light does not need any of our normal media . It will diffract purely on a Geometric basis (as per Hygens wave theory ) .

Yes that is what the textbooks indicate but I have not found one that describes an in vaccuo experiment like Michelsons but applied to single slit diffraction. Do you know of such an experiment?

 

[Doc Al]

In these posts one question seemed to be that the Huygens idea of scattering from points in the space between the slit edges was too mathematical and that scattering from the slit edges might provide a more realistic description of what was happening.

Don't get hung up on Huygen's principle. It works, but not for the handwaving arguments usually given:
http://ist-socrates.berkeley.edu/~phy7c/huygens.html

 

[rob5]

Yes why it works is the question. According to this other standard explantion, em waves or photons from the source produce oscillations of charge in the screen with the slit and if a plug is placed in the slit, secondary oscillations of charge are produced there also. Then the combined effect of these primary and secondary em waves or photons on the back side of the screen facing the receiving wall, these waves etc cancel each other out and so no field emanates from this side of the screen.
If cancellation was not complete, we could make the screen and plug a little thicker until cancellation was complete.
Thus the field at the receiver wall due to the field produced by the screen with the slit in it plus the field due to the plug in the slit plus the field produced by the source is, E(screen with slit)+E(plug) + E(source)=0. But this implies that
-E(plug)=E(screen with slit)+ E(source)
That is, if you take the plug out and subtract the field at the receiving wall due to the oscillations of charge in this plug you should get the observed pattern of light strips and dark strips.
This is the same as the Huygens argument without explicitly saying that point sources are produced in the space between the slits.
The question remains, if you do this demonstration in a vacuum, will the mathematically calculated wave effects which are mathematically equivalent to probablistic photon effects be demonstrated.
If not, then maybe the observed pattern is due to actual physical point sources, oscillating charges in the air molecules in the slit as well as to oscillations of charge in the primary light source.

 

[shyboy]

The Huygens's idea is a mathematical trick to solve the wave equation, nothing more. The first point: if there is two functions which satisfy the wave equation, then their linear combination is a solution too. The second point : by fixing the light intensity and phase on some area we have a unique light field.
So we can calculate the light field at any point a combination of fictious light sources.
If we have some media, we need to take into the account the effect of the media, but light itself does not need any media to propagate. Or, let's say, it can propagate in a physical vacuum.

 

[rob5]

The Huygens's idea is a mathematical trick to solve the wave equation, nothing more. The first point: if there is two functions which satisfy the wave equation, then their linear combination is a solution too. The second point : by fixing the light intensity and phase on some area we have a unique light field.
So we can calculate the light field at any point a combination of fictious light sources.
If we have some media, we need to take into the account the effect of the media, but light itself does not need any media to propagate. Or, let's say, it can propagate in a physical vacuum.

Yes the question here rephrased is what is the effect of the air molecule media ? The fact that light does not need any media to propagate in the vacuum of outer space and in Michelson's last light speed measurment etc indicates that the media is not necessary for light propagation in the single slit refraction experiment,
The mathematics of the wave function as you say imply that the interference effects are solely due to the movement of light as a wave (or a probabalistic photon)
But this implication of the wave theory of light applied to these interference effects has apparently never been tested directly.
The possibility exists that just as you don't see a laser beam in a vacuum you might not see the interference pattern in the single slit or double slit refraction in a vacuum.
That is the effects of light scattering from air molecules as well as the effects of light propagation in a vacuum are well known and the question is what are their contributions to these single slit and double slit diffraction phenomena?

 

[shyboy]

The light scattering on air molecules is negligible. The main effect will come from the small decrease of the light speed in the air. Nowever, if air is not uniform, as it is usually, the light will scatter on fluctuations of the air density, so the total intensity will decrease. The picture would be probably more blurry as well.

 

[rob5]

I don't know why you say the scattering from the air molecules is neglible. This is not the case when looking at a laser beam in air. But all of this is just speculation.
Maybe a test could be done at Abbess:
http://abbess.com/vac/homepage-vac.html#vacchambers-cube

whose largest vacuum chamber is 4'by4'by5'.
The tests that I recall had the wall about ten feet from the few mm slit so that the distance between intensity minima were large enough to see the differences in intensity-which may make sense considering the formula eg see http://www.drchaos.net/drchaos/Whit/Lab_Manual/node34.html

So the tests in such a vacuum chamber would somehow have to be scaled down to half this scale etc and a photograph taken of the chamber wall where the interference pattern should be. The photograph could then be enlarged. Maybe this is possible.

 

[inha]

This is not the case when looking at a laser beam in air

Laser beams don't show up in air unless the the beam is so energetic that it ionizes air.

 

[shyboy]

or the air is dusty.

 

[ZapperZ]

I don't know why you say the scattering from the air molecules is neglible. This is not the case when looking at a laser beam in air. But all of this is just speculation.
Maybe a test could be done at Abbess:
http://abbess.com/vac/homepage-vac.html#vacchambers-cube

whose largest vacuum chamber is 4'by4'by5'.
The tests that I recall had the wall about ten feet from the few mm slit so that the distance between intensity minima were large enough to see the differences in intensity-which may make sense considering the formula eg see http://www.drchaos.net/drchaos/Whit/Lab_Manual/node34.html

So the tests in such a vacuum chamber would somehow have to be scaled down to half this scale etc and a photograph taken of the chamber wall where the interference pattern should be. The photograph could then be enlarged. Maybe this is possible.

I don't get it. Are you implying that diffraction and interference patterns have NOT been observed in any kind of "vacuum"? How about, let's say, 10^-10 Torr? Would such a level be acceptable?

If it is, then may I recommend that you visit your neighborhood synchrotron center and ask them how they select the photon energy/wavelength/frequency that they wish to work with. I mean, they don't call these things interferometer, diffractometer, etc. for nothing. And these things ARE in the vacuum beamline, thankyouverymuch!

Zz.

 

[rob5]

We are obviously not accelerating electrons or protons or such here and we are not talking about electron diffraction here. So I don't think the single slit (light) diffraction experiment in vacuuo has been done at some neighborhood synchroton center. But if you know of such a case or that it has been done somewhere please tell us what you know.

 

[ZapperZ]

We are obviously not accelerating electrons or protons or such here and we are not talking about electron diffraction here. So I don't think the single slit (light) diffraction experiment in vacuuo has been done at some neighborhood synchroton center. But if you know of such a case or that it has been done somewhere please tell us what you know.

Who says anything about "electron diffracton"?

When the electron bunches in a synchrotron passes through a series of undulators or wigglers, it generates a SPECTRUM of light depending on the spacing in those insertion devices. This spectrum is then sent to the experimental beamlines that uses the LIGHT (not the electrons!) for varous purposes, but they have to SELECT what frequency they want! So they have to use various things such as an inteferometer, etc. etc... These are nothing more than a glorified diffraction slits that can similarly be found in an undergraduate labs.

All of these are done in vacuum!

Zz.

 

[ZapperZ]

I think this is a good opportunity to get rid of some strange misconception that people may have on what a "synchrotron center" is. A synchrotron center is a LIGHT SOURCE! Various centers are called The Advanced Photon Source, Advanced Light Source, National Synchrotron Light Source, etc. Their sole purpose is to generate light of all differnt kinds that researches use to perform their work! The range of light can be from IR, to UV, to visible, and all the way to very hard X-ray! The range of research work performed at one of these centers range from material science to basic physics to biological to medicine, etc.

There are many of these centers all over the world, because it has become one of the most important and useful TOOL in doing a huge amount of crucial research. Info on ALL the synchrotron centers throughout the world can be found at

http://www.lightsources.org/cms/

Most, especially here in the US, have either open days, or can arrange for a tour. Go see one!

Zz.

 

[rob5]

Who says anything about "electron diffracton"?

When the electron bunches in a synchrotron passes through a series of undulators or wigglers, it generates a SPECTRUM of light depending on the spacing in those insertion devices. This spectrum is then sent to the experimental beamlines that uses the LIGHT (not the electrons!) for varous purposes, but they have to SELECT what frequency they want! So they have to use various things such as an inteferometer, etc. etc... These are nothing more than a glorified diffraction slits that can similarly be found in an undergraduate labs.

All of these are done in vacuum!

We are talking about ONE diffraction slit a few mm wide not many a few angstroms wide as in a crystal diffraction pattern for xrays produced by a synchroton or whatever.
We are talking about the existence or non existence of secondary radiation sources in the vacuous space of the one slit that produce or don't produce the same sort of diffraction pattern observed when light passes through the one slit in air. The alternation of dark and light stips is similar to that produced by two slits and similar in the sense that there are dark and light spots for crystal diffractors where there are many slits and holes etc. but that tells us nothing about what happens when only one slit is considered.
However if you know of a synchroton center that has a 10 ft long vacuum tube that could be used for a simple visible light single slit diffraction experiment please tell us.

 

[ZapperZ]

We are talking about ONE diffraction slit a few mm wide not many a few angstroms wide as in a crystal diffraction pattern for xrays produced by a synchroton or whatever.
We are talking about the existence or non existence of secondary radiation sources in the vacuous space of the one slit that produce or don't produce the same sort of diffraction pattern observed when light passes through the one slit in air. The alternation of dark and light stips is similar to that produced by two slits and similar in the sense that there are dark and light spots for crystal diffractors where there are many slits and holes etc. but that tells us nothing about what happens when only one slit is considered.
However if you know of a synchroton center that has a 10 ft long vacuum tube that could be used for a simple visible light single slit diffraction experiment please tell us.

OK, so NOW, you've lost me.

1. I'm guessing that we have finally straighten you out that synchrotron centers produce LIGHT and not "electrons" that participate in some "diffraction".

2. You want "ONE diffraction slit a few mm wide" REGARDLESS of the wavelength of light, and expect to see diffraction pattern no matter what?

3. The thing that I don't understand is this. Can you look up ANY elementary derivation of, let's say, the Fraunhoffer diffraction pattern of a single slit, and point to me where in that derivation is the factor in which it makes a difference if it was done in air or in vacuum. In fact, I will put it to you that ALL of the physics involved was done by assuming a dispersonless medium, which is a vacuum! I will also put it to you that if you check any modern optics text, the diffraction pattern is actually a Fourier transform of the SLIT GEOMETRY. It means that doing this in air or vacuum is irrelevant! I could do this in glass and all I will alter is the separation between the patterns!

4. This is something ANYONE can try (in fact, shouldn't one have already done this in intro physics labs?). Look at the diffraction pattern from a single slit. Then, using the SAME slit width, do this for 2 slit interference. Compare the two patterns. You will see more bright-dark-bright-dark-etc pattern, but if you pay attention, this pattern is MODULATED by the pattern made by the SINGLE slit pattern! I could do this for 3, 4, 5, gazillion slits. If I pay attention to the modulation, I can easily deduce the pattern made by just ONE slit without having to DO the 1-slit diffraction experiment. Having worked at the NSLS for 3 years doing photoemission spectroscopy, I had to adjust the interferrometer all the time when I change the incoming photon energy from the ring. And I'll be damned if the modulation isn't there. Now unless you are claiming some new physics here, I will put it to you that I don't have to do any single-slit experiment to know what a single-slit diffraction pattern would look like simply based on such modulation.

5. 10 foot vacuum pipe? Do you have any idea how BIG each one of these synchrotron centers are? The APS is a ring that is 3/4 of a mile in circumference! Each of the beamline pipe from the ring is 10 to 20 meters long! 10-foot vacuum pipe is child's play!

Zz.

 

[rob5]

OK, so NOW, you've lost me.


2. You want "ONE diffraction slit a few mm wide" REGARDLESS of the wavelength of light, and expect to see diffraction pattern no matter what?

Yes and no. One diffractions slit but preferably with visible light and a few mm wide single diffraction slit.

3. The thing that I don't understand is this. Can you look up ANY elementary derivation of, let's say, the Fraunhoffer diffraction pattern of a single slit, and point to me where in that derivation is the factor in which it makes a difference if it was done in air or in vacuum.

No. All texts that I have seen say there should be no difference because the cause of the diffraction pattern is the difference in distances from point sources on wave fronts in the ether between the edges of the slit( and that there is a mathematical equivalence between the ether wave description of light and the quantum electrodynamic probabalisitic photon description)
But a number of people like myself have wondered if the cause is due in part or wholly to oscillations of charge in air molecules in the slit as well as in the primary light source. A vacuum version of the experiment would clarify this.

 

[ZapperZ]

Yes and no. One diffractions slit but preferably with visible light and a few mm wide single diffraction slit.

But you're forgetting one important thing. You do not observe any significant diffraction pattern when the size of the slit is LARGER than the size of the wavelength! So you can't just arbitrarily set a slit size without even considering the nature of the light you're dealing with!

No. All texts that I have seen say there should be no difference because the cause of the diffraction pattern is the difference in distances from point sources on wave fronts in the ether between the edges of the slit( and that there is a mathematical equivalence between the ether wave description of light and the quantum electrodynamic probabalisitic photon description)
But a number of people like myself have wondered if the cause is due in part or wholly to oscillations of charge in air molecules in the slit as well as in the primary light source. A vacuum version of the experiment would clarify this.

That would be VERY strange when "oscillations of charge in air molecules" does not enter the formulation of such a thing. It means the MEDIUM is playing an active part in this thing. It also means this phenomenon is UNIQUE only to light passing in a medium. Yet, we see the same thing not only for light, but others too!

Again, I don't need to do a "1-slit" version of this to know that such a thing occurs even in vacuum simply based on what I have personally observed. But since you are the one who is trying to formulate your own ideas, I suppose the burden of proof lies with you. Just be aware that optical conductivity (i.e. how light passes through a medium where polarization, phonon modes, and other effects are present) is a well-known and well-studied area of condensed matter physics. If you are trying to use "oscillations of charge in air molecules" as a basis of the diffraction pattern, you have a HUGE body of knowledge that will come down severely on you.

Zz.

 

[rob5]

But you're forgetting one important thing. You do not observe any significant diffraction pattern when the size of the slit is LARGER than the size of the wavelength! So you can't just arbitrarily set a slit size without even considering the nature of the light you're dealing with!

1) Of course. That is why I am talking about mm size slits and visible light and 10 foot distances from the slit to the observation wall.

That would be VERY strange when "oscillations of charge in air molecules" does not enter the formulation of such a thing.

2)Again we agree. But we have no evidence as to how much of the diffraction pattern is due to air molecules and how much is due to point sources of ethereal wave fronts of their probabilistic photon counterparts in the space between the slits.




Again, I don't need to do a "1-slit" version of this to know that such a thing occurs even in vacuum simply based on what I have personally observed.

3) If you mean the two slit version implies the one slit version, I disagree.

But since you are the one who is trying to formulate your own ideas, I suppose the burden of proof lies with you.

4)I'm not trying to prove anything. Just pointing out that there is no direct proof of single slit diffraction in a vacuum. So far no one here has proven otherwise.

Just be aware that optical conductivity (i.e. how light passes through a medium where polarization, phonon modes, and other effects are present) is a well-known and well-studied area of condensed matter physics. If you are trying to use "oscillations of charge in air molecules" as a basis of the diffraction pattern, you have a HUGE body of knowledge that will come down severely on you.

5)Just the opposite. there is no direct knowledge about single slit diffraction in a vacuum and their is a lot of direct knowledge of light scattering by air molecules etc..

 

[ZapperZ]

But you're forgetting one important thing. You do not observe any significant diffraction pattern when the size of the slit is LARGER than the size of the wavelength! So you can't just arbitrarily set a slit size without even considering the nature of the light you're dealing with!

1) Of course. That is why I am talking about mm size slits and visible light and 10 foot distances from the slit to the observation wall.

That would be VERY strange when "oscillations of charge in air molecules" does not enter the formulation of such a thing.

2)Again we agree. But we have no evidence as to how much of the diffraction pattern is due to air molecules and how much is due to point sources of ethereal wave fronts of their probabilistic photon counterparts in the space between the slits.

No, we DON'T agree! I was pointing out the the formulation of the diffraction pattern WOULD BE STRANGE IF it includes the oscillation of charge in air molecules, which you implied. The formulation that produces the faunhoffer pattern DOES NOT include such things. And we have those patterns ANYWAY!. If I do this in a medium (and not just air), I'll get the same thing but with different interference pattern spacings due to the different index of refraction! Is this such a surprising thing?

Again, I don't need to do a "1-slit" version of this to know that such a thing occurs even in vacuum simply based on what I have personally observed.

3) If you mean the two slit version implies the one slit version, I disagree.

And why would you disagree? You'll understand if I don't just accept your word for it. You simply missed my whole explanation why on I can deduce a single-slit pattern from a 2-slit, 3-slit, 4-slit, multiple slit interference pattern. Obviously you didn't think my explanation of the modulation of the interference pattern had any significance. I strongly suggest you go back and redo these simple experiments and verify them for yourself.

But since you are the one who is trying to formulate your own ideas, I suppose the burden of proof lies with you.

4)I'm not trying to prove anything. Just pointing out that there is no direct proof of single slit diffraction in a vacuum. So far no one here has proven otherwise.

There are plenty. You are just not aware of them, the same way you thought synchrotron centers does "electron diffraction". If there's already clear evidence that your knowledge on this is incomplete, what's there to say it is also incomplete elsewhere, such as here? You have shown ZERO evidence or even a posible impetus for why doing this in vacuum would not produce the same result.

Just be aware that optical conductivity (i.e. how light passes through a medium where polarization, phonon modes, and other effects are present) is a well-known and well-studied area of condensed matter physics. If you are trying to use "oscillations of charge in air molecules" as a basis of the diffraction pattern, you have a HUGE body of knowledge that will come down severely on you.

5)Just the opposite. there is no direct knowledge about single slit diffraction in a vacuum and their is a lot of direct knowledge of light scattering by air molecules etc..

... and that is why we make use of optical conductivity in matter to study other things. We know A LOT about it. However, you seem to have missed the fact that practically ALL of the origin of optical conductivity problems STARTS off with the scenario for transmission/reflection etc in VACUUM! Look at any E&M or Optics text and confirm for yourself that the very first few chapters of those texts treats EM waves in VACUUM as the SIMPLEST case. What did you think the permittivity and permeability of "free space" was for? AIR?

Again, you have shown almost no understanding of why a diffraction pattern occurs from a single slit (refer to a modern optics text for Fourier transform of the slit, or a QM explanation that it is a manifestation of the uncertainty principle). Doing it in air, or vacuum, or glass, or water has nothing to do with it! Even doing it with light/photons is irrelevant! This point, somehow, simply escapes you.

Zz.

 

[rob5]

No, we DON'T agree! I was pointing out the the formulation of the diffraction pattern WOULD BE STRANGE IF it includes the oscillation of charge in air molecules, which you implied. The formulation that produces the faunhoffer pattern DOES NOT include such things. And we have those patterns ANYWAY!.

1)No such patterns have ever been seen in a vacuum. Only the claim that there are dark strips where ethereal waves or their qed counter parts interfere destructively and light strips where these waves interfere constructively. The claim is based as you say on confirmations of the wave equation in other contexts like Michelson's speed of light experiments in a huge vacuum tube. But it remains a claim because no one has done the single slit diffraction experiment in a vacuum.

If I do this in a medium (and not just air), I'll get the same thing but with different interference pattern spacings due to the different index of refraction! Is this such a surprising thing?

2)No of course not. But the pattern in air and the supposed pattern in a vacuum would be nearly the same if the theoretical claim is true. I suspect that in a good partial vacuum there will be no visible diffraction pattern for a single slit and that for a less evacuated tube the diffraction pattern will start to become visible.

And why would you disagree? You'll understand if I don't just accept your word for it. You simply missed my whole explanation why on I can deduce a single-slit pattern from a 2-slit, 3-slit, 4-slit, multiple slit interference pattern. Obviously you didn't think my explanation of the modulation of the interference pattern had any significance.

3) The single slit case has lines from points on supposed wave fronts in the space between the slit edges while the double slit case has lines from the centers of each of the two slits that are used to calculate the positions of the dark and light stripes observed on the wall beyond the slit or slits.
You could have the latter case without implying the former but if you assume the given theory of course then both cases are implied.

There are plenty[of experiments that imply single slit diffraction works in a vacuum] You are just not aware of them,

4) I am aware of all of the experiments that are explained by the standard wave theory and qed theory and that the standard theory implies that single slit diffraction works in a vacuum. But neither one of us is aware of any demonstartion of single slit diffraction in a vacuum.

... and that is why we make use of optical conductivity in matter to study other things. We know A LOT about it. However, you seem to have missed the fact that practically ALL of the origin of optical conductivity problems STARTS off with the scenario for transmission/reflection etc in VACUUM! Look at any E&M or Optics text and confirm for yourself that the very first few chapters of those texts treats EM waves in VACUUM as the SIMPLEST case. What did you think the permittivity and permeability of "free space" was for? AIR?

5) You are simply repeating the statement that the standard theory implies single slit diffraction works in a vacuum. Agreed But NO experiment has been done that directly shows the single slit diffraction works in a vacuum

 

[jtbell]

rob5, could you please preview your postings before actually posting them, and fix the quoting as necessary? The stuff you're quoting isn't getting set off properly from your own stuff, which makes your postings difficult to read.

Insert a [ quote=whowroteit ] at the beginning of each quoted section (if there isn't one there already), and a [ /quote ] at the end. (I had to insert blank spaces between the brackets so the forum software wouldn't interpret this example as a quotation itself... take out the blanks when you do it.)

Thanks in advance...

 

[ZapperZ]

3) The single slit case has lines from points on supposed wave fronts in the space between the slit edges while the double slit case has lines from the centers of each of the two slits that are used to calculate the positions of the dark and light stripes observed on the wall beyond the slit or slits.
You could have the latter case without implying the former but if you assume the given theory of course then both cases are implied.

1. Double slit patterns have MODULATIONS in the dark-bright-dark-bright fringe pattern.

2. The MODULATIONS MATCHES that seen when only ONE slit of the same width is used.[1]

3. Do you understand (1) and (2) above?

4. If you do, then you'll understand that without a single slit diffraction pattern, a bunch of STRANGE things will happen to the 2-slit, multiple slits "interference" pattern!

Zz.

[1] http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/mulslid.html

 

[rob5]

1. Double slit patterns have MODULATIONS in the dark-bright-dark-bright fringe pattern.

2. The MODULATIONS MATCHES that seen when only ONE slit of the same width is used.[1]

3. Do you understand (1) and (2) above?

4. If you do, then you'll understand that without a single slit diffraction pattern, a bunch of STRANGE things will happen to the 2-slit, multiple slits "interference" pattern!

Zz.

[1] http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/mulslid.html

In the single slit case there are no obstacles between the points from which lines are drawn to the wall where the bright and dark strips and the shading between these are observed.
But still you get the alternating pattern of bright and dark strips due to interference of different path lengths as you do with lines drawn from the two slits.
This is somewhat surprising unless you assume that waves emanate from points on wave fronts in the space between the single slit edges. If you don't assume this you can still get the double slit diffraction pattern.
Thus I would expect the double slit diffraction experiment works in a vacuum but the single slit does not because waves cannot emanate from points on ethereal wave fronts but waves can emanate from oscillations of charge in air molecules.
Of course the standard theory says that you will get single slit diffraction in a vacuum for all the reasons we have discussed. But this has never been shown directly.

 

[ZapperZ]

In the single slit case there are no obstacles between the points from which lines are drawn to the wall where the bright and dark strips and the shading between these are observed.
But still you get the alternating pattern of bright and dark strips due to interference of different path lengths as you do with lines drawn from the two slits.
This is somewhat surprising unless you assume that waves emanate from points on wave fronts in the space between the single slit edges. If you don't assume this you can still get the double slit diffraction pattern.
Thus I would expect the double slit diffraction experiment works in a vacuum but the single slit does not because waves cannot emanate from points on ethereal wave fronts but waves can emanate from oscillations of charge in air molecules.
Of course the standard theory says that you will get single slit diffraction in a vacuum for all the reasons we have discussed. But this has never been shown directly.

Of course, you claim there is something MORE beyond the "standard theory", despite the fact that optical conductivity in dispersive material is well-known. What this "more" is, and how it can reproduce all the observations, remain a mystery just like any quackery.

You have conveniently IGNORED the point I made about the modulations of the 2-slit, multi-slit intensity. This can only imply you have no clue how they work and why they are important.

Fine. If you think the "single slit" diffraction pattern hasn't been done in vacuum, go ahead and do this, send your result into a peer-reviewed journal and CLAIM that this is the first EVER investigation of light passing through a single slit. But when they look at you sideways when you propose to someone who has access to a vacuum line to do this, don't tell me that I didn't warn you.

Zz.

 

[rob5]

Let me take back what I said before " Thus I would expect the double slit diffraction experiment works in a vacuum but the single slit does not"

I don't expect this. I must have been imagining in phase light sources at each slit but this is not what is done. That is the light coming from a source behind the two slits spreads out as a wave in the vacuous or air filled medium and then produces points of in phase interference in the medium in the space between the slits which serve as secondary sources just as in the case of single slit diffraction.
Thus in both the single slit case and the double slit and multiple slit cases I would not expect the alternating pattern of light and dark stripes etc to occur if their is a vacuum in the space between the slits. That is , I think it is the oscillation of charge in the air molecules or other molecules between the slits that become secondary sources at points where there is in phase interference of influence from the primary light source. The points where there is out of phase interference of influences from the primary light source produces no such oscillations.
The result is that the image on the wall or screen of light from the primary and these variously distant secondary sources shows an alternating pattern of light and dark where in phase and out of phase influences occur on the wall or screen.

 

[ZapperZ]

Let me take back what I said before " Thus I would expect the double slit diffraction experiment works in a vacuum but the single slit does not"

I don't expect this. I must have been imagining in phase light sources at each slit but this is not what is done. That is the light coming from a source behind the two slits spreads out as a wave in the vacuous or air filled medium and then produces points of in phase interference in the medium in the space between the slits which serve as secondary sources just as in the case of single slit diffraction.
Thus in both the single slit case and the double slit and multiple slit cases I would not expect the alternating pattern of light and dark stripes etc to occur if their is a vacuum in the space between the slits. That is , I think it is the oscillation of charge in the air molecules or other molecules between the slits that become secondary sources at points where there is in phase interference of influence from the primary light source. The points where there is out of phase interference of influences from the primary light source produces no such oscillations.
The result is that the image on the wall or screen of light from the primary and these variously distant secondary sources shows an alternating pattern of light and dark where in phase and out of phase influences occur on the wall or screen.

Why stop at 2-slit? Why not also say that multi-slit inteference such as from a diffraction grating is also not detected in vacuum? I mean, let's go all the way, since this thread is almost ripe for the TD section as it is already.

Zz.

 

[Doc Al]

Thus in both the single slit case and the double slit and multiple slit cases I would not expect the alternating pattern of light and dark stripes etc to occur if their is a vacuum in the space between the slits.

Why not just try it and see? Go to the nearest High School or College physics department--any place with a bell jar, vacuum pump, and laser would do--and ask them to set it up. (Or do it yourself, if you have access to a lab.) A bell jar isn't exactly high vacuum, but you should be able to reduce the air pressure by a factor of 100 or so. That should be enough.

 

[rob5]

Why stop at 2-slit? Why not also say that multi-slit inteference such as from a diffraction grating is also not detected in vacuum?


I said that it applies to multislits. The question is about the need for molecules of air or something, as in an xray crystal, between the slits.
The light source acts on these molecules between the slits after a delay which is greater for points further from the source and at points one period greater there is in phase addition and at points half a period greater there is out of phase cancellation of the influence of light.
The same thing applies to the points of the image wall or screen beyond the slit or slits and that produces the alternating bright and dark stripes or spots.
Now suppose you do a single slit diffractions experiment in a partial vacuum and you find there is no such diffraction pattern but rather a pattern that suggests light moved from the source to the image wall or screen in a straight line.
Then as you add more air to the partial vacuum you find that a diffraction pattern becomes more and more evident.
The conclusion would be that light can move in a vacuum but cannot move as a wave(having the interference properties of waves) unless there is a material medium.
But this experiment has never been done.

 

[ZapperZ]

Why stop at 2-slit? Why not also say that multi-slit inteference such as from a diffraction grating is also not detected in vacuum?


I said that it applies to multislits. The question is about the need for molecules of air or something, as in an xray crystal, between the slits.
The light source acts on these molecules between the slits after a delay which is greater for points further from the source and at points one period greater there is in phase addition and at points half a period greater there is out of phase cancellation of the influence of light.
The same thing applies to the points of the image wall or screen beyond the slit or slits and that produces the alternating bright and dark stripes or spots.
Now suppose you do a single slit diffractions experiment in a partial vacuum and you find there is no such diffraction pattern but rather a pattern that suggests light moved from the source to the image wall or screen in a straight line.
Then as you add more air to the partial vacuum you find that a diffraction pattern becomes more and more evident.
The conclusion would be that light can move in a vacuum but cannot move as a wave(having the interference properties of waves) unless there is a material medium.
But this experiment has never been done.

Terrific! Now we have finally the ultimate admission of ignorance.

May I suggest that you visit the SAME synchrotron facilities that I have suggested, and asked them how a "monochromator" works. Then ask them where they placed this device. After you've convinced yourself, then look at their inteferometer, their diffractometer, and the rest of the devices along the vacuum beamlines.

My guess is, you won't. But I would LOVE to be proven wrong here. You appear to not want to make ANY effort to double check your claim, even after I've given you a source to go look. There are plenty of evidence. You are just ignorant of them.

Zz.

 

[rob5]

Terrific! May I suggest that you visit the SAME synchrotron facilities that I have suggested, and asked them how a "monochromator" works. Then ask them where they placed this device. After you've convinced yourself, then look at their inteferometer, their diffractometer, and the rest of the devices along the vacuum beamlines.

If you know how these things work, then you probably know that they are not vacuous and molecules in these devices contain oscillating charged particles. The evacuated tubes containing electron beams are something else.
You said in a previous post that I should do this experiment because it is so easy to do with a small bell jar vacuum. I don't think so. I saw a company,Abesse, that made a 4ft by 4ft by 5ft and possibly tubes that would be 10 ft by 1 ft by 1ft which would be better to duplicate the typical single slit, of a few mm, diffraction experiment with visible light.
The point is that it can be done but that it has never been done. And therefore that the single slit and double slit diffraction experiments do not prove that light moves as a wave in a vacuum.

 

[ZapperZ]

Terrific! May I suggest that you visit the SAME synchrotron facilities that I have suggested, and asked them how a "monochromator" works. Then ask them where they placed this device. After you've convinced yourself, then look at their inteferometer, their diffractometer, and the rest of the devices along the vacuum beamlines.

If you know how these things work, then you probably know that they are not vacuous and molecules in these devices contain oscillating charged particles. The evacuated tubes containing electron beams are something else.
You said in a previous post that I should do this experiment because it is so easy to do with a small bell jar vacuum. I don't think so. I saw a company,Abesse, that made a 4ft by 4ft by 5ft and possibly tubes that would be 10 ft by 1 ft by 1ft which would be better to duplicate the typical single slit, of a few mm, diffraction experiment with visible light.
The point is that it can be done but that it has never been done. And therefore that the single slit and double slit diffraction experiments do not prove that light moves as a wave in a vacuum.

First of all, it was doc al who suggested it, not me.

Secondly, "oscillating molecules in these devices"?

You have shifted your position so often, it is no longer clear WHAT you are claiming. You first claim that only the single slit hasn't been done in vacuum, after I pointed out how they select the frequency of light to use. Then when I point out that it is way too easy to show the single-slit diffraction pattern simply based on the modulations of the intensity of the interference slit, you now are claiming that ALL interference effects have not been seen in vacuum.

And now, without even bothering to figure out what a monochromator is, how it works, and what exactly it produces, you have already dismissed it. Keep in mind, you are doing this without a SINGLE quantitative model that uses your "guesses" to that this cannot happen in vacuum, etc.

I recommend that this thread go into the TD section where, hopefully, it'll meet with a quick death.

Zz.