Double slit experiment wave interference?

[Mario Rossi]

Hi, my answer is about the double slit experiment: the interference is observable with the water waves, them are particle in movment, but when we observe it with the electrons, what is the medium for those waves? Are the particles made of matter between the gun and the slits? Or is it something other? The medium should be the particles made of matter because the interference is produced when a wave which the medium is matter hurts with two slits made of matter too, right?

Sorry for my bed... ehm, bad english :)

 

[hilbert2]

They don't need a material medium, just like light doesn't need a "luminiferous ether" to move in, as the Michelson-Morley experiment proved. The electrons, and their antiparticles positrons, are excitations of the Dirac fermion field, just as light quanta (photons) are excitations of the electromagnetic field. Both fields permeate all space and are not made of any material, but they differ in the sense that electrons are fermions (particles of half-integer spin) and photons are bosons (particles of integer spin).

 

[Mario Rossi]

They don't need a material medium, just like light doesn't need a "luminiferous ether" to move in, as the Michelson-Morley experiment proved. The electrons, and their antiparticles positrons, are excitations of the Dirac fermion field, just as light quanta (photons) are excitations of the electromagnetic field. Both fields permeate all space and are not made of any material, but they differ in the sense that electrons are fermions (particles of half-integer spin) and photons are bosons (particles of integer spin).

Thank you very much for your answer. Now the situation is more clear for me. If I understood what you said, there is a field of energy made by waves and there isn't matter and the particles are just a sort of concentration of energy (or excitations) of that field, right? Thank you another time. You solved my great mistery :)

 

[hilbert2]

Yes, if you have a wave that moves in some material, like a sound wave through a solid, you can also treat that kind of waves quantum mechanically and the excitations are then called phonons. But phonons are only "quasi-particles", not real particles like electrons which can exist in vacuum.

 

[Mario Rossi]

Yes, if you have a wave that moves in some material, like a sound wave through a solid, you can also treat that kind of waves quantum mechanically and the excitations are then called phonons. But phonons are only "quasi-particles", not real particles like electrons which can exist in vacuum.

Thank you very very much! So the phonons aren't real particles but just a way to consider the sounds in a field of waves. Do you know all this by a university book?

 

[entropy1]

Do you know all this by a university book?

They know stuff here. You may study, and you don't have to pay! But they require you do your homework!

 

[Mario Rossi]

They know stuff here. You may study, and you don't have to pay! But they require you do your homework!

Sorry I don't understand what you are saying. To pay what? Isn't this a free forum? Which homework? Am I considered inopportune for something? I am just a curios man who wanted to understand the two slits experiment. Sorry if I didn't understand the situation.

 

[PeroK]

Sorry I don't understand what you are saying. To pay what? Isn't this a free forum? Which homework? Am I considered inopportune for something? I am just a curios man who wanted to understand the two slits experiment. Sorry if I didn't understand the situation.

I'm not sure anyone knows what was meant by post #6.

 

[bhobba]

I'm not sure anyone knows what was meant by post #6.

I thought it was obvious.

We as a group know the answer to quite a lot of questions that get posted here. But, often, at least for me, don't spell it out. You must do some work yourself. What you discover yourself not only do you get a great feeling of accomplishment but for true understanding its the best way.

At a minimum you must study the background to understand the answer. For example we often get questions here about superposition. If you know linear algebra the answer is trivial, if you don't - well I have never been able to explain it - and boy have I tried. The same with the difference between pure and mixed states - that one I have not just tried, but pulled my hair out to get those that don't know Linear Algebra to understand - a total waste of time.

Thanks
Bill

 

[bhobba]

Sorry if I didn't understand the situation.

He means pay in terms of studying stuff to understand the answer. You also need to pay in further researching the outline of the answer many like me tend to give.

It varies with the level of the thread. This is an advanced thread. I expect participants to know certain things and/or have enough background to find them out. So I will use advanced concepts that quite possibly will require further work to understand. An example would be a Von Neumann Measurement vs a POVM - in an advanced thread I would use terms like that freely even though the person may not have come across them before.

It works in reverse as well - I often have to research and learn new stuff. That's one reason I like this forum - I get pointed to so many interesting things. The misconceptions I now don't have are so many I have lost count - just a few - particles are not in some sense in two or more places at once, virtual particles do not exist, and exactly what decoherence explains and does not.

Thanks
Bill

 

[Mario Rossi]

He means pay in terms of studying stuff to understand the answer. You also need to pay in further researching the outline of the answer many like me tend to give.

It varies with the level of the thread. This is an advanced thread. I expect participants to know certain things and/or have enough background to find them out. So I will use advanced concepts that quite possibly will require further work to understand. An example would be a Von Neumann Measurement vs a POVM - in an advanced thread I would use terms like that freely even though the person may not have come across them before.

It works in reverse as well - I often have to research and learn new stuff. That's one reason I like this forum - I get pointed to so many interesting things. The misconceptions I now don't have are so many I have lost count - just a few - particles are not in some sense in two or more places at once, virtual particles do not exist, and exactly what decoherence explains and does not.

Thanks
Bill

Ok ok now i understand. Ok for this time I understood the answer but next time I will ask "which books will I read to come here and post my question" XD. The science is so difficult that you need to study from the base and then you can reach the high answers.

 

[bhobba]

Ok ok now i understand. Ok for this time I understood the answer but next time I will ask "which books will I read to come here and post my question" XD. The science is so difficult that you need to study from the base and then you can reach the high answers.

Not necessarily - it depends on the question. Ask away just like you normally would. The people here will guide you on the right path. So basically change nothing - just expect you may have to do some work yourself.

In this case read the following paper:
https://arxiv.org/abs/quant-ph/0703126

But since this is an advanced thread be aware the above is not the final answer either:
https://arxiv.org/abs/1009.2408

But either way it's not waves of anything that's at work in this classic experiment.

Beginner texts will tell you its wave particle duality - it's actually not. Its a demonstration of two principles:

1. The uncertainty principle
2. The principle of superposition.

Notice I gave you two papers to read. That's your 'payment' - I will not spell out the answer - you have to discover it for yourself.

Thanks
Bill

 

[bhobba]

Do you know all this by a university book?

Sometimes even they deceive.

I have learned my stuff from:

1. Books - but actually thinking about what they say.
2. Reading papers like the following about things not in textbooks:
https://arxiv.org/pdf/quant-ph/0101012.pdf
3. Discussing things here
3. Nutting stuff out for myself. That's the best way for true understanding

Thanks
Bill

 

[Mario Rossi]

Sometimes even they deceive.

I have learned my stuff from:

1. Books - but actually thinking about what they say.
2. Reading papers like the following about things not in textbooks:
https://arxiv.org/pdf/quant-ph/0101012.pdf
3. Discussing things here
3. Nutting stuff out for myself. That's the best way for true understanding

Thanks
Bill

Yes, I'm glad to study and understand the things. Thank you for those links, but aren't those links of the Cornell University Library? Aren't those abstract from their books? Anyway, I haven't experience in this field so thank you for this. Another thing: what means "Nutting stuff out for myself"? Sorry I'm not englis motherlanguage, I searched nutting and I found this: http://www.urbandictionary.com/define.php?term=Nutting ?

Oh another important thought... aren't books the best way to understand? What?? And how do the "normal people" like me undestand these things? University and labs secrets?

 

[Mario Rossi]

Ah and I know what is the superposition thanks to this: http://toutestquantique.fr/en/superposition/

Update: ok, I read those pages. So the Dirac field is considered a probability field. I also found this https://arxiv.org/abs/1703.04674 article talking about the difference between the electromagnetic field and the Dirac field. And I suppose it is right. I really can't associate nothing to the "probability wave". I think it like a graphical representation. But it must be made of something, maybe energy and also this word is associated with a representation: the energy is associated to the effects of the energy and not to the real energy, like this waves are associated to their effects (the probability to find a particle) and not to them. Maybe there is a very simple answer and I'm not understanding it... or maybe there is no answer because it is something of imperceptible both in reality as an object and in mind as a thought and we can just understand its effects.

 

[PeterDonis]

aren't those links of the Cornell University Library?

No, they are links from the arxiv.org site, which happens to be managed by the Cornell University Library, but which contains preprints of papers written by researchers all over the world. The site is also funded by institutions all over the world; see here:

https://confluence.cornell.edu/pages/viewpage.action?pageId=340900096

 

[Mario Rossi]

No, they are links from the arxiv.org site, which happens to be managed by the Cornell University Library, but which contains preprints of papers written by researchers all over the world. The site is also funded by institutions all over the world; see here:

https://confluence.cornell.edu/pages/viewpage.action?pageId=340900096

Ok ok. Sorry but I didn't know it, and I read "Cornell University Library".

 

[Mario Rossi]

I found this: https://arxiv.org/ftp/arxiv/papers/0912/0912.2985.pdf about the mind-MIND theory and the wave function. Anyway I think the interpretetions of the waves of probability is just a "graphical representation", like diagrams. For me this mistery will make scientists busy for the next century too :D

 

[Mentz114]

I found this: https://arxiv.org/ftp/arxiv/papers/0912/0912.2985.pdf about the mind-MIND theory and the wave function. Anyway I think the interpretetions of the waves of probability is just a "graphical representation", like diagrams. For me this mistery will make scientists busy for the next century too :D

I got as far as this

The Schrödinger equation of quantum mechanics governs the motion of the wave functions, so it is
(on the least abstract level) the wave functions, rather than particles, which are the ‘physical objects’ in the mathematics of quantum mechanics. A useful visual picture of the wavefunction is that it is matter spread out in a mist or cloud of varying density.

This idea was dropped very soon after Schroedingers work. This paper is far from what is now acceptable theory and I caution you not to take anything it states seriously. It has got some good laughs, though.

 

[bhobba]

This idea was dropped very soon after Schroedingers work. This paper is far from what is now acceptable theory and I caution you not to take anything it states seriously. It has got some good laughs, though.

This can't be stressed often enough. Many books and even some articles written by 'knowledgeable' people do not understand that the modern conception of QM is vastly different from what they thought in the past, especially the early pioneers like Schrödinger, Bohr etc. The best was Dirac because he basically said shut up and calculate (he didn't really - Meriman said it, it was attributed to Feynman as well but that too is a myth). The next best believe it or not was the later Einstein who was the originator of the ensemble interpretation which is still one of the main interpretations (Copenhagen has to some extent been replaced by Consistent Histories but is still around, although I believe CH is the better interpretation - but that it's just a personal preference).

Even textbooks that I sometimes recommend make you wince like David McMahon's otherwise excellent book:
https://www.amazon.com/dp/0071765638/?tag=pfamazon01-20

His 'axioms' as Vanhees said obscure rather than illuminate. The best by far is IMHO Ballentine - but to be fair we all have to start somewhere and Ballentine is NOT a good place to start, even though his treatment from two axioms is by far the most illuminating.

I recommend these books in the following order:
https://www.amazon.com/dp/0465075681/?tag=pfamazon01-20
https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20
https://www.amazon.com/dp/0071765638/?tag=pfamazon01-20
https://www.amazon.com/dp/9332519005/?tag=pfamazon01-20
https://www.amazon.com/dp/9814578584/?tag=pfamazon01-20

But please, please understand that it builds up to full understanding - you have to 'unlearn' things as you go. But you will come out the other end knowing QM VERY well.

Thanks
Bill

 

[Mario Rossi]

This can't be stressed often enough. Many books and even some articles written by 'knowledgeable' people do not understand that the modern conception of QM is vastly different from what they thought in the past, especially the early pioneers like Schrödinger, Bohr etc. The best was Dirac because he basically said shut up and calculate (he didn't really - Meriman said it, it was attributed to Feynman as well but that too is a myth). The next best believe it or not was the later Einstein who was the originator of the ensemble interpretation which is still one of the main interpretations (Copenhagen has to some extent been replaced by Consistent Histories but is still around, although I believe CH is the better interpretation - but that it's just a personal preference).

Even textbooks that I sometimes recommend make you wince like David McMahon's otherwise excellent book:
https://www.amazon.com/dp/0071765638/?tag=pfamazon01-20

His 'axioms' as Vanhees said obscure rather than illuminate. The best by far is IMHO Ballentine - but to be fair we all have to start somewhere and Ballentine is NOT a good place to start, even though his treatment from two axioms is by far the most illuminating.

I recommend these books in the following order:
https://www.amazon.com/dp/0465075681/?tag=pfamazon01-20
https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20
https://www.amazon.com/dp/0071765638/?tag=pfamazon01-20
https://www.amazon.com/dp/9332519005/?tag=pfamazon01-20
https://www.amazon.com/dp/9814578584/?tag=pfamazon01-20

But please, please understand that it builds up to full understanding - you have to 'unlearn' things as you go. But you will come out the other end knowing QM VERY well.

Thanks
Bill

Sorry, I didn't understand: I need to read all those books, but when I read the last I will "unlearn" what I read in the first? So I will read just the last :) Sorry I have no time to read books, I will read it in some years and the QM will discover other things making the book I read useless. I am trying to search one of those pdf in arxiv.org

 

[bhobba]

Ah and I know what is the superposition thanks to this: http://toutestquantique.fr/en/superposition/

'Some quantum systems, such as atoms, photons, or spins, can be in two simultaneous different states. We call these “Schrödinger’s cats”.

Sigh. Its both right and wrong. That's why you need to build up and unlearn. Its impossible, utterly impossible, for cats to be in a superposition of alive and dead - that's just one way it's wrong. Where it's correct is generally given two different states we can find a combination of them that's also a state - but just like 2+3 = 5 does not mean 5 is simultaneously 2 and 3 that combination is not simultaneously the two states that came from it. Indeed just like 1+4 =5 many many states can form a superposition that gives that state.

The correct, but advanced answer is all a superposition is is that quantum states (specifically pure ones) form a vector space, To understand what that means means studying linear algebra and you will see the above is basically nonsense. You will not learn that in a beginning QM course because you probably have not studied Linear Algebra by that time - that is left to an intermediate course. But intermediate courses will likely not tell you things like a state is an operator not an element of a vector space. The full understanding only comes once you have all the background. Prior to that is - how to put it - half truths.

May I suggest you start a beginner level thread on the double slit? Others can maybe explain it better than me at that level.

Thanks
Bill

 

[Mario Rossi]

'Some quantum systems, such as atoms, photons, or spins, can be in two simultaneous different states. We call these “Schrödinger’s cats”.

Sigh. Its both right and wrong. That's why you need to build up and unlearn. Its impossible, utterly impossible, for cats to be in a superposition of alive and dead - that's just one way it's wrong. Where it's correct is generally given two different states we can find a combination of them that's also a state - but just like 2+3 = 5 does not mean 5 is simultaneously 2 and 3 that combination is not simultaneously the two states that can form it. Indeed just like 1+4 =5 many many states can form a superposition that gives that state.

The correct, but advanced answer is all a superposition is is that quantum states (specifically pure ones) form a vector space, To understand what that means means studying linear algebra and you will see the above is basically nonsense. You will not learn that in a beginning QM course because you probably have not studied Linear Algebra by that time - that is left to an intermediate course. But intermediate courses will likely not tell you things like a state is an operator not an element of a vector space. The full understanding only comes once you have all the background. Prior to that is - how to put it - half truths.

May I suggest you start a beginner level thread on the double slit? Others can maybe explain it better than me at that level.

Thanks
Bill

Ok ok I understand what you are saying, but for this moment I can continue with the hilbert2 answer. When I will have more time I will surely read those books. Thank you all guys for all this informations, before this I believed just Google and Nasa scientists know the modern QM.

 

[AlexCaledin]

Thank you all guys...

...especially the whole ensemble of Bhobbas

 

[Mario Rossi]

...especially the whole ensemble of Bhobbas

Yes! Escpecially thank you @bhobba ! :D The discover of arxiv.org is really great for me. Now I know how to find the modern science!