Understanding Double Slit Interference in Electron Diffraction

[Mentz114]

Would you care to answer my questions with at least a minimal amount of detail?

Can you delve with me into the actual fact - or at least interpretation - of [QM] science -or must we both remain astray in the land of rhetoric?

I’ll leave it up to your next post to educate, or to refract.

I presume it will be the latter, as you do not appear to hold any true communicable knowledge besides, "trust me."

Well I wouldn't want to 'refract' so I'll try to answer your original questions.

I seem to understand what's going on with the slit experiment, although what was the purpose of that machine gun example? Is the electron gun alway swung around drunkenly like that? I'm thinking that was just some type of transitional illustration to get people ready for the wave description.

I think the idea is that you spray the slits with bullets. The ones that go through the slits don't make interference bands. The ones that don't go through are irrelevant.

I'm not sure I'm clear on exactly why the quantum is supposed to go through either slit, as in, doesn't it bounce around the "box" before eventually making it's way through the slits if it is aimed directly at the center between the slits?

We can ignore quanta that don't get to the screen behind the slits.

Does quantum tunneling come into play here?

No. The idea is that the quanta go through the slits, not tunnel through the barrier.

How about some type of wavefront compression or field that causes the quanta of energy to split apart into antipairs before going through both slits and coming back on the other side. Can a normal quantum collide with a virtual particle?

No. Electrons don't split. A particle can't become a 'pair'. As I said, not necessary or correct.

That probably doesn't even make sense.

Hmmm. I'm tempted...

 

[bill cosby]

Well I wouldn't want to 'refract' so I'll try to answer your original questions.

I think the idea is that you spray the slits with bullets. The ones that go through the slits don't make interference bands. The ones that don't go through are irrelevant.

Thank you. I understand this much, as it is seems to abide by common sense. I was active duty USMC for 8 years (and still am IRR – being deployed again in two months to Afghanistan [enlisted, BTW – not an officer]) and understand very much about spraying things with bullets ).

What happens to the photons/electrons that do not go through the splits initially? They certainly “refract” around their area, right?

I've taken statistics courses (I have a BS in CompEng) and have an understanding of both the bullet and probability functions - but I am still blurry on exactly how the particles that enter the two slits can converge into an area of greater probability than directly in front of the slits. With the waves, it seems intuitive, but I have not seen any mathematical formulas describing the particle interaction yet. It seems to me that those particle interactions with two open slits are not actually possible - but I obviously don’t know. I have taken Calc III, so if you can show me any formulas, I would love to see them.

No. The idea is that the quanta go through the slits, not tunnel through the barrier.

Ah, I see. I've read that there is a phenomenon called quantum tunneling (which I learned about while taking a course on solid state devices within the military) where there is a certain probability whereas quanta may actually tunnel through a barrier. Does that not apply in this case, and if not, can you please explain how? I am guessing that it is only fractionally relevant in this case and would not amount to any increase in the interference pattern, is this correct? It would appear that this is merely a novel effect as to which the absolute effects can not fully be explained under current theory. Can you tell me if I am at least partially correct?

No. Electrons don't split. A particle can't become a 'pair'. As I said, not necessary or correct.

I was confused at this point as I've read that an electron in a bubble chamber was hit with UV light and underwent some type (I'm new at this) of quantum fractional division where the electron divided its charge into three separate packets that were allowed to move through the discrete paths in the a bubble chamber. I do not at all understand the implications of that, and have not been able to find much more data on it. I've also read that at SLAC in around... 1997-- ?? they forced two photons to collide to create an electron-positron pair that annihilated into a photon again. I am still not sure if this constitutes a virtual particle, virtual photon, or just a superposition of a photon. Can you please explain this to me?

My appreciation will increase in as your explanation approaches infinty.

 

[Mentz114]

Hi Bill,
the problem with this is that you've hi-jacked the original posters (OP) thread. I'll try to answer your questions but you should think about starting a new thread with your own questions.

What happens to the photons/electrons that do not go through the slits initially? They certainly “refract” around their area, right?

In the context of the two-slit experiment, we can ignore them. I don't know what happens to them.

but I am still blurry on exactly how the particles that enter the two slits can converge into an area of greater probability than directly in front of the slits. With the waves, it seems intuitive, but I have not seen any mathematical formulas describing the particle interaction yet. It seems to me that those particle interactions with two open slits are not actually possible - but I obviously don’t know.

This is discussed in earlier in this thread. If the wave-function for the particle and slits is solved, the probabilities show interference bands. This happens if we send one particle at a time, or lots at once. This really happens in experiments so it is possible.

Quantum tunnelling certainly happens and can easily be observed in semi-conductors, but it is irrelevant to to the two-slit experiment, where we use almost impenetrable barriers to eliminate the effect.

I was confused at this point as I've read that an electron in a bubble chamber was hit with UV light and underwent some type (I'm new at this) of quantum fractional division where the electron divided its charge into three separate packets that were allowed to move through the discrete paths in the a bubble chamber. I do not at all understand the implications of that, and have not been able to find much more data on it.

We can't answers questions if you can't give a reference to this stuff. I know nothing about it.

I've also read that at SLAC in around... 1997-- ?? they forced two photons to collide to create an electron-positron pair that annihilated into a photon again. I am still not sure if this constitutes a virtual particle, virtual photon, or just a superposition of a photon. Can you please explain this to me?

This is a standard experiment in colliders. The photon can decay into various particle/anti-particle pairs. Again, it's too big a topic to deal with here.

M

 

[bill cosby]

Hi Bill,
the problem with this is that you've hi-jacked the original posters (OP) thread. I'll try to answer your questions but you should think about starting a new thread with your own questions.

Point taken. I'll just do some additional reading before posing a question in my own thread. Thanks for the answers.

By the way, the experiment was done by Humphrey Maris, professor of physics at Brown University. Published Aug. 1, 2000 in the Journal of Low Temperature Physics.

 

[Mentz114]

Bill,
I looked up prof. H. Maris. He has investigated multi-electron bubbles (MEB) in liquid He. These are probably what is splitting, not individual electrons. There's a recent publication in the arXiv.

M

 

[reilly]

bill cosby -- First, the two slit experiment is just one of many that produce diffraction -- of electrons, and photons and ...Diffraction is a basic phenomena of any waves, and comes from interference of one or more waves (particles(i.e photons, electrons,,,, ) You can find very good explanations of single slit and multiple slit diffraction even in freshman physics books Halliday and Resnick do a good job -- it's all about phases, and can be nicely understood from Huyghen's Principle. Note that electron diffraction (Davisson and Germer expt 192?) was one of the key phenomena that resulted in QM, as we know it today. Plenty of books that deal with this issue -- QM and E&M

The particles that hit the screen with the slits count for absolutely nothing as far as the diffraction pattern is concerned.

Regards,
Reilly Atkinson