B A view of the double-slit experiment

[PeroK]

What a wave is even made out of? Is water made of waves?

Water is made of water molecules. A water wave is the propagation of energy through the water. Try this:

https://www.khanacademy.org/science...ound/mechanical-waves/v/introduction-to-waves

 

[Qhmu]

Water is made of water molecules. A water wave is the propagation of energy through the water. Try this:

https://www.khanacademy.org/science...ound/mechanical-waves/v/introduction-to-waves

But the waves themselves are still just water molecules?

 

[PeroK]

But the waves themselves are still just water molecules?

The waves are motion/energy of the water molecules. You might as well ask whether the speed/kinetic energy of a car is made of car parts.

 

[Qhmu]

I might as well go to a christian forum and try to tell them how walking on water was an optical illusion, and they would start citing the bible.

Again, everyone is basically saying that a wave stops expanding/starts behaving differently the moment it gets inside an opening and doesn't collide with the walls of said opening?

 

[PeroK]

I might as well go to a christian forum and try to tell them how walking on water was an optical illusion, and they would start citing the bible.

Again, everyone is basically saying that a wave stops expanding/starts behaving differently the moment it gets inside an opening and doesn't collide with the walls of said opening?

It's only you saying that, as far as I can see. If the walls of the opening are thin, then they would have little effect. If, however, the opening was a tunnel, then the water would move constrained inside the tunnel until it emerged. This behaviour, however, is not really relevant to the diffraction, as that is what happens when the water emerges from the opening, not what happens when the water is constrained by the opening.

 

[Qhmu]

It's only you saying that, as far as I can see. If the walls of the opening are thin, then they would have little effect. If, however, the opening was a tunnel, then the water would move constrained inside the tunnel until it emerged. This behaviour, however, is not really relevant to the diffraction, as that is what happens when the water emerges from the opening, not what happens when the water is constrained by the opening.

But isn't a light wave coming from a single point source moving in all directions at the same speed? Like thinking about a circle and resizing it larger while maintaining the shape? And if it would encounter an opening of any size really, it would "try" to continue to grow inside the opening and produce interference pattern at the other side?

Sorry if i sound repetitive

 

[Ibix]

But isn't a light wave coming from a single point source moving in all directions at the same speed?

Why are you assuming a point source? Even if you assume that, have you thought about how much the wave spreads out as it passes through the slits to see how relevant this is? Consider a light source 1m away from slits made in a layer off paint 0.1mm thick on the surface of a microscope slide.

 

[Qhmu]

Why are you assuming a point source? Even if you assume that, have you thought about how much the wave spreads out as it passes through the slits to see how relevant this is? Consider a light source 1m away from slits made in a layer off paint 0.1mm thick on the surface of a microscope slide.

Well, what kind of a source ultimately isn't a point source? And if i consider what every direction means, doesn't it mean it hits even 0.1mm thick objects? It should cover all angles?

 

[ZapperZ]

Well, what kind of a source ultimately isn't a point source? And if i consider what every direction means, doesn't it mean it hits even 0.1mm thick objects? It should cover all angles?

Then you are making this even more difficult.

The simplest scenario for single-slit and double-slit diffraction is the use of "plane wave" source, i.e. either a point source that is very far away (the sun), or laser light source that has the added benefit of being a coherent light source. Even for many point source setup, using a series of optical components can easily produce such plane-wave conditions.

I am still puzzled by all this IF you are still holding on to your original picture. Unfortunately, my earlier advice to you in the sense that you need to also understand the mathematics of this seems to have been neglected. You simply can't explain or can't argue things via the hand-wavy way that you've been doing. If you think that something can be "explained" via such-and-such a manner, it must have a (i) mathematical description and (ii) valid comparison of its prediction with the results.

Both diffraction and 2-slit interference patterns are well-known. Now, go match them EXACTLY. Otherwise, what are we discussing here?

Zz.

 

[Qhmu]

Then you are making this even more difficult.

The simplest scenario for single-slit and double-slit diffraction is the use of "plane wave" source, i.e. either a point source that is very far away (the sun), or laser light source that has the added benefit of being a coherent light source. Even for many point source setup, using a series of optical components can easily produce such plane-wave conditions.

I am still puzzled by all this IF you are still holding on to your original picture. Unfortunately, my earlier advice to you in the sense that you need to also understand the mathematics of this seems to have been neglected. You simply can't explain or can't argue things via the hand-wavy way that you've been doing. If you think that something can be "explained" via such-and-such a manner, it must have a (i) mathematical description and (ii) valid comparison of its prediction with the results.

Both diffraction and 2-slit interference patterns are well-known. Now, go match them EXACTLY. Otherwise, what are we discussing here?

Zz.

Even a plane wave coming from the sun "stretches" sideways? But you are correct, there is no point in trying to explain anything if we don't speak the same language e.g. math. Simply visualizing scenarios and trying to explain something based on that won't do any good to anyone.

Now please excuse me, i go play some guitar and/or videogames.

 

[ZapperZ]

Even a plane wave coming from the sun "stretches" sideways?

I do not know what this phrase mean.

If you are asking if plane waves will undergo diffraction, the answer is yes. Otherwise, this "stretches sideways" is an ambiguous description.

Zz.

 

[Nugatory]

Again, everyone is basically saying that a wave stops expanding/starts behaving differently the moment it gets inside an opening and doesn't collide with the walls of said opening?

A wave follows the same behavioral rules everywhere because it always obeys the same differential equation; this equation let's you calculate the evolution of the wave at a given time and place based on its amplitude nearby and a moment earlier. The amplitude of the wave inside a solid barrier is necessarily zero at all times, so of course the evolution of the wave at points near the barrier - including those in a small opening in the barrier - will be different than if the barrier weren't there and that amplitude were not zero.

This behavior has nothing to do with "colliding" with the walls or bouncing off them... but to see what it is you have to actually get comfortable with the math. That's a non-trivial investment of time, typically an entire semester during the second year of an undergraduate physics bachelor's degree program and using a textbook like https://www.amazon.com/dp/0070048606/?tag=pfamazon01-20

 

[Qhmu]

I do not know what this phrase mean.

If you are asking if plane waves will undergo diffraction, the answer is yes. Otherwise, this "stretches sideways" is an ambiguous description.

Zz.

"The plane wavefront is a good model for a surface-section of a very large spherical wavefront; for instance, sunlight strikes the Earth with a spherical wavefront that has a radius of about 150 million kilometers (1 AU)." -Wikipedia

What i was trying to say is that a spherical/circular wavefront appears planar when it actually isn't

And by stretching i meant the wavefront getting larger by distance traveled, and even 0.1mm could be considered a distance?

 

[ZapperZ]

"The plane wavefront is a good model for a surface-section of a very large spherical wavefront; for instance, sunlight strikes the Earth with a spherical wavefront that has a radius of about 150 million kilometers (1 AU)." -Wikipedia

What i was trying to say is that a spherical/circular wavefront appears planar when it actually isn't

And by stretching i meant the wavefront getting larger by distance traveled, and even 0.1mm could be considered a distance?

If you do a simple experiment here on earth, you'd be hard-pressed to detect the spherical effect of the light from the sun. Many of my students managed to do a lot of optics experiment by using sunlight and taking it as plane waves. The results are very accurate! After all, do you consider the gravity from Alpha Centauri when you calculate all the forces acting on an object here on earth? Get real!

If you mean divergence of the light path, why don't you try it yourself? Take a large aperture (large than the wavelength of visible light, which shouldn't be difficult), and figure out how much it "stretches" after 0.1 mm.

Zz.

 

[Qhmu]

If you mean divergence of the light path, why don't you try it yourself? Take a large aperture (large than the wavelength of visible light, which shouldn't be difficult), and figure out how much it "stretches" after 0.1 mm.

Zz.

Or just shine it straight at the wall?

 

[ZapperZ]

Or just shine it straight at the wall?

Have at it!

Zz.

 

[tech99]

If you want to understand diffraction you need to let go of ray optics and study light as a wave. Huygens' Principle would be a good place to start. You'll need to be able to do integration for anything more than idealised cases.[/QUOTE]
Although Huygen's Principle gives the right answer, are we certain that the observed effects are not actually caused by radiation by currents flowing in the obstruction or slit edges? I am not sure on this one.
Any beam of restricted width must have been passed through a hole, so edges are always present.

 

[ZapperZ]

If you want to understand diffraction you need to let go of ray optics and study light as a wave. Huygens' Principle would be a good place to start. You'll need to be able to do integration for anything more than idealised cases.
Although Huygen's Principle gives the right answer, are we certain that the observed effects are not actually caused by radiation by currents flowing in the obstruction or slit edges? I am not sure on this one.
Any beam of restricted width must have been passed through a hole, so edges are always present.

Again, this is getting to be ridiculous. This is because the 2-slit interference effects can be seen in other types of setups!. Superconducting quantum inteference devices exhibit such properties. One can also do an analogous 2-slit interference using an interferometer! Look ma, no slits!

So to tie this effect and observation specifically to the interaction of the slits and their edges fails spectacularly when the same effect is observed elsewhere without the use of any slits!

Why doesn't this fact sink in?

Zz.

 

[tech99]

Again, this is getting to be ridiculous. This is because the 2-slit interference effects can be seen in other types of setups!. Superconducting quantum inteference devices exhibit such properties. One can also do an analogous 2-slit interference using an interferometer! Look ma, no slits!

So to tie this effect and observation specifically to the interaction of the slits and their edges fails spectacularly when the same effect is observe elsewhere without the use of any slits!

Why doesn't this fact sink in?

Zz.

Sorry to be obtuse, I was thinking about diffraction rather than interference between waves. I will read up on your suggestions.

 

[Qhmu]

Here i present to you this ridiculous "simulation" of the image in my head about waves that i can't seem to unsee:



It is a fun toy to play with if anything

Isn't divergence a linear "thing"? If it is, any divergence at all should cause the wavefront to expand inside the slit?

Edit: Okay now I'm confusing myself even more, shouldn't you get electrons at the other side if the slits were made of metal and if you hit the slit walls with photons?

 

[ZapperZ]

Here i present to you this ridiculous "simulation" of the image in my head about waves that i can't seem to unsee:



It is a fun toy to play with if anything

Isn't divergence a linear "thing"? If it is, any divergence at all should cause the wavefront to expand inside the slit?

Edit: Okay now I'm confusing myself even more, shouldn't you get electrons at the other side if the slits were made of metal and if you hit the slit walls with photons?

Once again, you don’t get it. What is the PATTERN you get after all this? Does it match the diffraction pattern to a T?

If it doesn’t, then why would this “simulation” be relevant here?

This is starting to feel like talking to a wall (pun intended).

Zz.

 

[Qhmu]

Once again, you don’t get it. What is the PATTERN you get after all this? Does it match the diffraction pattern to a T?

If it doesn’t, then why would this “simulation” be relevant here?

This is starting to feel like talking to a wall (pun intended).

Zz.

And you seem to take everything literally but the text.

"ridiculous "simulation" of the image in my head"

How is "Zz." relevant?

 

[ZapperZ]

And you seem to take everything literally but the text.

"ridiculous "simulation" of the image in my head"

But again, how is this relevant to the TOPIC that you have created, and how is this relevant to the issue at hand? I still do not know if you are aware of why there is such a major shortcoming with the picture that you have. And the fact that you keep coming back to it, and even attempted another "simulation" is puzzling.

So make it relevant and answer this question: Do you still think that diffraction of light AND the double-slit interference can be explained using this bouncing-off-the-slits-walls picture?

Zz.

 

[Qhmu]

So make it relevant and answer this question: Do you still think that diffraction of light AND the double-slit interference can be explained using this bouncing-off-the-slits-walls picture?

Zz.

That's what I'm thinking, yes. Only thing that's different from shooting a laser at the wall and shooting it through a hole is the amount of surfaces said laser can interact with.

I'm just going to leave it here now, there's no need to make a fuss about it. I apologize to you for being so dense.

 

[ZapperZ]

That's what I'm thinking, yes. Only thing that's different from shooting a laser at the wall and shooting it through a hole is the amount of surfaces said laser can interact with.

So let me get this right just in case I misunderstood what you said here. You STILL think that this bouncing-off-the-slits-walls is a valid explanation for the single-slit diffraction and the double-slit interference? After ALL that have transpired here, and the fact that you can't show the result of your simulation and how it matches the diffraction pattern, you are still holding on to this model?

Then there is nothing else for me to do here either, because I have just proven that I've been talking to a wall. I definitely have better things to do.

 

[Qhmu]

So let me get this right just in case I misunderstood what you said here. You STILL think that this bouncing-off-the-slits-walls is a valid explanation for the single-slit diffraction and the double-slit interference? After ALL that have transpired here, and the fact that you can't show the result of your simulation and how it matches the diffraction pattern, you are still holding on to this model?

Then there is nothing else for me to do here either, because I have just proven that I've been talking to a wall. I definitely have better things to do.

Because i see it would be utterly pointless to make a computer "model" of interference pattern and present it to you without providing maths or explanations, but in case you ever feel the need to waste more of your time, here's an example of a double-slit-pattern done with only bouncing behavior, just watch where my balls land *giggle*:

 

[ZapperZ]

Because i see it would be utterly pointless to make a computer "model" of interference pattern and present it to you without providing maths or explanations, but in case you ever feel the need to waste more of your time,...

No, I don’t, because you haven’t learned anything.

Zz.

 

[Nugatory]

Edit: Okay now I'm confusing myself even more, shouldn't you get electrons at the other side if the slits were made of metal and if you hit the slit walls with photons?

There's no such thing as hitting the walls with photons - photons aren't like little objects that move around until they hit something and a beam of light is not photons moving by the way a stream of water is water molecules moving by. These light waves are electrical and magnetic fields evolving according to the differential equation derived from Maxwell's equation.

 

[Ibix]

Because i see it would be utterly pointless to make a computer "model" of interference pattern and present it to you without providing maths or explanations, but in case you ever feel the need to waste more of your time, here's an example of a double-slit-pattern done with only bouncing behavior, just watch where my balls land *giggle*:

Your pattern is dependent on the thickness of the wall. This is not the case for diffraction. Try again with the wall as thin as you can make it.

Your pattern is dependent on the existence of significant curvature of your incident pattern. This is not the case for diffraction. Try again with a slit separation of 0.5mm and your particles radiating from a point eight light minutes - 1.4×10¹¹m - away. Or even 1m.

Your pattern is dependent on the symmetric distribution and separation of your particles. This is not the case for diffraction. Try again, displacing the particles to the left by 1/4 of their initial separation.

Your pattern is dependent on the angle of incidence of your particles. This is not the case for diffraction (more precisely, it simply changes the scale and location of the pattern). Try again with particles incident at 30° to the vertical.

Furthermore, your simulation has no analog to wavelength, which is critically important to the scale of a diffraction pattern.

You cannot explain diffraction with ray optics. Ray optics is a mathematically simple approximation to wave optics, and the approximation falls apart under these circumstances. Worse, you aren't even simulating ray optics, as there is no analog to refraction in this particles-move-in-straight-lines model.

You said in your first post that you were here to ask questions. I don't understand why you bother if you are just going to ignore the answers.