Understanding Single Particle Interference in Quantum Physics

[Smiley10]

Believe it or not I'm having trouble understanding quantum physics. If we take the double slit experiment and one photon is sent through the slits at a time an interference pattern is formed. From what I've read the particle goes through both slits and interferes with itself. Now when it says interfere is it taking in a general sense or does it mean that the particle will hit itself to interfere with itself?

I also don't understand why we just assume that the particle is going through both slits and then interferes with itself. It's just as crazy to say that the particle is only going through one slit and then takes two directions at the same time hitting different positions on the screen which just so happen to cause an interference pattern. I think the attitude quantum physics takes that it can't be proved wrong so it must be right type of attitude is very poor. If we can't measure the state that the particle is in then we should only conclude that it makes an interference pattern but we shouldn't start pretending that we know what is happening to the particle before it hits the screen.

I hope you can at least clear a little bit of my confusion. Thanks in advance.

 

[Repetit]

You have to stop thinking about the electrons and photons as particles. They are quantum particles, and exhibit both wave like and particle like properties, and this enables them to interfere with each other like in the double slit exp.

Quantum physics does not try to say anything about what happens to the particles before they hit the screen, because this is what quantum physics is all about! In the double slit experiment we cannot say anything about which slit the particle went through, and still have an interference pattern on the screen. If we make a measurement and determine which slit the particle went through, the wave-particle duality is determined (to be a particle, because we know it's position at some instance) and an interference pattern will no longer form.

 

[zbyszek]

Believe it or not I'm having trouble understanding quantum physics. If we take the double slit experiment and one photon is sent through the slits at a time an interference pattern is formed. From what I've read the particle goes through both slits and interferes with itself. Now when it says interfere is it taking in a general sense or does it mean that the particle will hit itself to interfere with itself?

I also don't understand why we just assume that the particle is going through both slits and then interferes with itself. It's just as crazy to say that the particle is only going through one slit and then takes two directions at the same time hitting different positions on the screen which just so happen to cause an interference pattern. I think the attitude quantum physics takes that it can't be proved wrong so it must be right type of attitude is very poor. If we can't measure the state that the particle is in then we should only conclude that it makes an interference pattern but we shouldn't start pretending that we know what is happening to the particle before it hits the screen.

I hope you can at least clear a little bit of my confusion. Thanks in advance.

The way out might be to step back and drop the assumption that QM applies to any single
particle. QM certainly applies to an ensemble of identically prepared particles for it gives
excellent predictions for probabilities (many repetitions of the same experiment). At the same time QM cannot predict where exactly a single photon in the double slit experiment will hit the screen.
This attitude is called the statistical interpretation of Quantum Mechanics. The wave
function there describes ensembles of identically prepared quantum objects and not
an individual quantum object.

The theory of single quantum objects is still to be discovered.

Good question, anyway!

Cheers!

 

[marlon]

The way out might be to step back and drop the assumption that QM applies to any single
particle.

Ofcourse QM applies to any single particle at the atomic scale. What are you saying ?

At the same time QM cannot predict where exactly a single photon in the double slit experiment will hit the screen.

So ? What is that supposed to mean ?

This attitude is called the statistical interpretation of Quantum Mechanics. The wave
function there describes ensembles of identically prepared quantum objects and not
an individual quantum object.

ANY "attidude" of QM should NOT contradict with it's basic fundaments.

The theory of single quantum objects is still to be discovered.

Good question, anyway!

Cheers!

Oooh, no, is this the single particle stuff again ? I already explained you why you were WRONG making such claims.

http://www.cs.caltech.edu/~westside/quantum-intro.html . Read the second and third paragraph on the Quantum Computer. You might actually read the very opposite of what you have been saying in this and the other thread with respect to a particle's self interference/interaction.

Greets
marlon

 

[zbyszek]

Oooh, no, is this the single particle stuff again ? I already explained you why you were WRONG making such claims.

You are barking on the wrong tree. I am not interested in your opinion anymore.

Good luck!

 

[marlon]

You are barking on the wrong tree. I am not interested in your opinion anymore.

Good luck!

Thanks for the mature answer but we have an obligation to correct mistakes. Otherwise this forum is not what it should be. Both Reilly and myself have asked you specific questions and clarifications in the "Statistical interpretation" thread to which you never answered. Both of us have explained you where you are making mistakes. Again, i have given you a CalTech reference where you can read the exact opposite of what you are claiming.

To be clear, you need to stop selling stuff that violates the very fundaments of physics. Such behaviour will not remain unnoticed, i assure you.

regards
marlon

 

[Anonym]

Smiley10:” Believe it or not I'm having trouble understanding quantum physics.”

Read R. Feynman Lectures. If you still do not understand, leave quantum physics.There are plenty interesting problems in other areas.

 

[marlon]

Read R. Feynman Lectures. If you still do not understand, leave quantum physics.There are plenty interesting problems in other areas.

LOL

Err, there is one problem though...Most of the physics area's that have direct applications to today's industry are based upon QM (semiconductors, electronics in general, spintronics, photonics, etc etc). So the OP really needs to understand what is going on.

TO THE OP : http://www.cs.caltech.edu/~westside/quantum-intro.html

Greets

marlon

 

[vanesch]

Smiley10:” Believe it or not I'm having trouble understanding quantum physics.”

Read R. Feynman Lectures. If you still do not understand, leave quantum physics.There are plenty interesting problems in other areas.

Or, to quote the same Feynman: "nobody understands quantum mechanics"

 

[zbyszek]

Smiley10:” Believe it or not I'm having trouble understanding quantum physics.”

Read R. Feynman Lectures. If you still do not understand, leave quantum physics.There are plenty interesting problems in other areas.

What kind of advice is that? Did you hear it from some one yourself?

If you think you understand QM then this place is just made for you to share this blessing.

Cheers!

 

[Smiley10]

Thanks for the replies everyone.

You have to stop thinking about the electrons and photons as particles. They are quantum particles, and exhibit both wave like and particle like properties, and this enables them to interfere with each other like in the double slit exp.

Quantum physics does not try to say anything about what happens to the particles before they hit the screen, because this is what quantum physics is all about! In the double slit experiment we cannot say anything about which slit the particle went through, and still have an interference pattern on the screen. If we make a measurement and determine which slit the particle went through, the wave-particle duality is determined (to be a particle, because we know it's position at some instance) and an interference pattern will no longer form.

This does make a lot of sense and if I didn't have the answers to my questions I'd be satisfied with that. But I still can't help being curious about how the particle side of light could work (or even if it's possible to work).

From the link that Marlon gave it's reasonable from the experiment to assume that the particle can in fact be in two different places at the same time, at least as long as the detectors are in fact detecting a single photon since I don't think this is mentioned. The photon does seem to take a random path but where the photon hits the screen isn't completely random. We know that a photon will never hit the dark spots. But still the photons appear to take a random path so at some point the photon must be heading at this direction of the dark spot so the photon must somehow be interferred. Now at this point I haven't got a clue what the hell interferes with the particle. I've read that the photon interferes with itself but this sounds pretty crazy. What appears to be two photons in fact isn't they're the same matter so it just doesn't seem right that when the same matter hits together that momentum will be transferred (or will it?).

I'm not entirely sure on the photon taking a completely random path and I'll have a read up on hidden variables, bell's theorem etc.

I haven't read the lectures but I'll have a look at them and I'm glad that someone caught onto my very subtle joke in the first sentance of my first post.

Thanks again, at this point I'm just making discussions and I believe I have a good enough understanding to write about it in my coursework . Feel free to keep the thread going.

 

[reilly]

Given more opportunities like this thread, Marlon and I might write identical posts, or, more likely, ones that say much the same thing.

Now, one of the reasons that QM is difficult to grasp -- weird, contradictory, "shut up and compute", "but we really don't understand it" -- is that the phenomena that led to QM are strange, weird -- blackbody radiation, photoelectric effect, atomic spectra, electron and neutron diffraction, pair production, spin, and on and on.

For the double slit business, first review basic probability, preferably discussed in terms of events. That will cure you of any concerns about predictions of single events. For all practical purposes, the theory of electromagnetic wave diffraction and electron diffraction are very similar -- the diffraction occurs primarily from restriction of the impinging wavefront, just like Huygens told us a few years back.

Interfere with itself? In my view, that's a personal choice. In fact, given the broader behavior of waves governed by Maxwell or Schrodinger, I see no good reason to formulate such a controversial notion. It only serves to muddy and confuse something that is basically straightforward, provided you accept that the phenomena of particle diffraction does occur . Then the point is to accept reality and figure out a theory that can explain how such diffraction occurs. QM does just that, and has done so for almost a century. Also, contrary to some contentions that have appeared in this forum, the vast majority of physicists accept QM -- albeit sometimes in different flavors.

As Dorothy said, "Toto, we're not in Kansas anymore."

Regards,
Reilly Atkinson

 

[Anonym]

Vanesch:” Or, to quote the same Feynman: "nobody understands quantum mechanics".

You are right. But I don’t know what he meant: everything in QM or QED only.

Marlon:” Most of the physics area's that have direct applications to today's industry are based upon QM (semiconductors, electronics in general, spintronics, photonics, etc etc).”

If he going to be engineer, why he need understanding?

Zbyszek:” What kind of advice is that? Did you hear it from some one yourself?”
Smiley10:” I haven't read the lectures but I'll have a look at them and I'm glad that someone caught onto my very subtle joke in the first sentance of my first post.”

What is the matter with you? Jokes are forbidden?
You react with anger on my criticism of L.E. Ballentine. Is he your close relative? Before you wildly attack S.L.Adler (without justification).
You like Ballentine version of statistical interpretation? I never said that it is not legitimate (as well as other interpretations).

 

[vanesch]

Vanesch:” Or, to quote the same Feynman: "nobody understands quantum mechanics".

You are right. But I don’t know what he meant: everything in QM or QED only.

The situation is the following: in "ordinary" QM, the formalism is entirely understood ; in quantum field theories (such as QED), even the formalism is not entirely understood, but well enough to do some calculations. In other words, we know that the calculations that are done, are mathematically somehow unsound, but this can be explained away by saying that it must be an approximation to something else (effective field theories).

But Feynman wasn't talking about the formalism, he was talking about the "physical meaning". This is what is not understood, although several attempts with varying degrees of success have been invented. Nobody really knows what the mathematical objects in a quantum theory actually represent.

Some claim that it is just a mathematical tool which gives you statistical outcomes of experiments (in other words, that one shouldn't look for any physical meaning) - fine, but they can't come up with an explicit underlying physical mechanism ! Some (Bohr, with Copenhagen) claim that there IS no explicit physical mechanism, that all there is, is "statistics". This is essentially the "standard" Copenhagen interpretation: the quantum-mechanical formalism links statistically setups and outcomes of a "classical" macroscopic world, and there is no underlying explanation for this link. The formalism of quantum mechanics simply allows you to calculate the probabilities, but doesn't represent anything physical, because there IS nothing physical at that scale.

Others (such as me) claim that the formalism of quantum theory is to be taken seriously, and that it represents genuine physical quantities. These views are "many worlds" views, because you cannot avoid that way, to make a distinction between "the physical state" and "observed reality by an observer", which is so terribly weird.

Others think that the quantum formalism has something real to it, but that there is also an explicit "projection" mechanism. However, this usually introduces some clashes with relativity.

Still others think that there's something fundamentally wrong with the quantum formalism, although it makes correct predictions in many cases, for an ununderstood reason.

This is a discussion that goes on now for almost 80 years, and is usually referred to as the "measurement problem" of quantum theory. However, and that is the nice part: you don't need to think about all this to get the formalism working in practical cases, and in any case, it is a good idea to learn very well the formalism before delving into these issues.

So, the practical attitude to adopt when learning the formalism of quantum theory, is simply this: "quantum theory is a mathematical model which allows you to generate statistical predictions for outcomes of experiment, but for which no evident physical interpretation is known." From the moment that you try to do so, you delve into the problems of the measurement problem, which haven't really been resolved since about 80 years. This is what Feynman meant.

 

[zbyszek]

You react with anger on my criticism of L.E. Ballentine. Is he your close relative? Before you wildly attack S.L.Adler (without justification).

Is this another joke of yours? I have hard time telling whether you are joking or lying.

For those who would like to check on the moral integrity or the sense of humor (pick one)
of Anonym please read post #111 under the wave packet description thread
https://www.physicsforums.com/showthread.php?t=142399&page=8"

I believe I have provided quite detailed justification.

 

[vanesch]

Is this another joke of yours? I have hard time telling whether you are joking or lying.

If this is going to turn into a flame war, then this thread will be locked and warning points issued.

 

[zbyszek]

If this is going to turn into a flame war, then this thread will be locked and warning points issued.

Do I have a right to defend my reputation on this forum? You see, attacking somebody's
work without justification is one of the lowest things a scientist can do. I am being accussed
of doing just that.
Is it a flame war for you, vanesch? In this world, I mean.

Cheers!

 

[vanesch]

Do I have a right to defend my reputation on this forum?

The informal warning was not only directed at you, be reassured. Try to argument your position in a neutral way, or just don't argue, but try to avoid remarks of a personal nature which might trigger other remarks of the same kind and result in a silly flame war which is interesting for nobody to read. This counts for all of the antagonists. Let's keep it level-headed here...

 

[Anonym]

Reilly:” Marlon and I might write identical posts, or, more likely, ones that say much the same thing.”
“Interfere with itself? In my view, that's a personal choice. In fact, given the broader behavior of waves governed by Maxwell or Schrodinger, I see no good reason to formulate such a controversial notion.”

Marlon:”Particles, in QM, ALWAYS exhibit wavelike properties : THAT IS THE ENTIRE POINT OF THE DUALITY. This duality does NOT give us an "either wave or either particle like" picture.’
“Self interaction IS an essential part of QM.”
“But i just want to be clear here : the particle/wave duality does NOT say that particles are waves or something like that. this duality just states that at the atomic scale, particles exhibit wavelike behaviour like in the double slit experiment. This ALWAYS happens for each kind of particle like electrons photons, etc etc. Wavelike behaviour is a general term that denotes all the types of interference, diffraction, etc etc...
We need this duality because we look at QM through "classical eyes".”

I identify the opposite points of view.

Smiley10:” I've read that the photon interferes with itself but this sounds pretty crazy.”

Otherwise you should to accept that a single particle may do statistic with itself.
Make your choice what is more crazy.

In the double slit the photon/electron wavefront hit the lossless beamsplitter simultaneously. The lossless beamsplitter is the macroscopic device which do not perform the measurement. No violation of the special relativity take place. Each slit may be considered as Huygens secondary source as usual. The measurement performed at the detector screen (the macroscopic device) cannot produce two outcomes simultaneously. It require the collapse of the wave packet in time, otherwise the requirements of special relativity will be violated (A. Einstein,1928).
In addition, the macroscopic physics is the theory of certain events. Translation into the language of the functional analysis say: the classical physics is a dispersion free physical theory (J. von Neumann in Foundations for example). It require the collapse of the wave packet in space.
You may see more detailed discussion in the wave packet description session with Ueit,Reilly and Zbyszek. But you should read Feynman (at least double slit and Stern-Gerlach) before.

 

[kesh]

strangely aggresive thread over something fundamental to understanding QM. haven't these issues been thrashed out already?

maybe we should all "shut up and calculate", which i take to mean try and understand better the mathematical models

 

[Anonym]

Vanesch:” But Feynman wasn't talking… This is what Feynman meant.”

I agree with everything you wrote.

Vanesch:” The situation is the following: in "ordinary" QM, the formalism is entirely understood ; in quantum field theories (such as QED), even the formalism is not entirely understood, but well enough to do some calculations. In other words, we know that the calculations that are done, are mathematically somehow unsound, but this can be explained away by saying that it must be an approximation to something else (effective field theories).”

But let me joke. R.P. Feynman received nobel prize in physics for QED.

 

[marlon]

Reilly:” Marlon and I might write identical posts, or, more likely, ones that say much the same thing.”
“Interfere with itself? In my view, that's a personal choice. In fact, given the broader behavior of waves governed by Maxwell or Schrodinger, I see no good reason to formulate such a controversial notion.”

Marlon:”Particles, in QM, ALWAYS exhibit wavelike properties : THAT IS THE ENTIRE POINT OF THE DUALITY. This duality does NOT give us an "either wave or either particle like" picture.’
“Self interaction IS an essential part of QM.”
“But i just want to be clear here : the particle/wave duality does NOT say that particles are waves or something like that. this duality just states that at the atomic scale, particles exhibit wavelike behaviour like in the double slit experiment. This ALWAYS happens for each kind of particle like electrons photons, etc etc. Wavelike behaviour is a general term that denotes all the types of interference, diffraction, etc etc...
We need this duality because we look at QM through "classical eyes".”

I identify the opposite points of view.

I don't exactly know what you mean but if you are implying that Reilly and myself are saying the opposite, you are wrong. You can clearly read that we are saying the same story. Indeed one can debate the concept of "self interference" but that does NOT imply this behaviour is NOT exhibited by particles. IT DOES EXIST and if you read the CalTech link i provided in this thread, you will see that this concept is directly related to (ie the same as) "superposition". For example, the qubit being a superposition of "on" and "off" states. The first and primarily second photon experiment in the link shows just THAT (ie quantum interference).

Also, keep in mind that noth of us were debating the content of zbyszek's posts (like the stuff on preparing the electron ensemble for the double slit experiment).

 

[marlon]

Marlon:” Most of the physics area's that have direct applications to today's industry are based upon QM (semiconductors, electronics in general, spintronics, photonics, etc etc).”

If he going to be engineer, why he need understanding?

Do you actually know what electronic engineers have to study ? How on Earth could you explain the band diagram of a MOSFET if one does not have some basic knowledge of QM (like the concept of superposition that we are talking about here).


marlon

 

[Anonym]

Marlon:” I don't exactly know what you mean but if you are implying that Reilly and myself are saying the opposite, you are wrong.”

Sorry for misinterpretation. I took your words literally.

Marlon:” Do you actually know what electronic engineers have to study ?”

No. I spent several years working with electronic engineers which produce amazingly complicated and amazingly successful projects using pretty funny understanding of basic physics. In addition, guys, what do you have against jokes?

 

[marlon]

Sorry for misinterpretation. I took your words literally.

But that is my point. Ofcourse you should take my words literally and i still don't get where you see a contradiction. Reilly is NOT saying that the behaviour of particles denoted by self interference does NOT exist.

Marlon:” Do you actually know what electronic engineers have to study ?”

No. I spent several years working with electronic engineers which produce amazingly complicated and amazingly successful projects using pretty funny understanding of basic physics.

Indeed, in college these guys are always introduced to the basics of QM to say the least.

In addition, guys, what do you have against jokes?

LOL

Nothing, but we just need to be certain we are not talking "next to each other", that's all.

Greets marlon

 

[Anonym]

Zbyszek:” You see, attacking somebody's work without justification is one of the lowest things a scientist can do. I am being accussed of doing just that.”

I did not accussed you in any crime. I consider your post #111 under the wave packet description only misreading and misiterpretation:

Zbyszek:”You list the postulates of QM. All of them, but last, after Ballentine. The last one is the "measurement" postulate Eq.(14). Right after that you claim that everybody agrees with the list.”
“If you read Ballentains work more cerfully you would see that your last postulate is certainly not a part of the statistical approach to QM.”

S.L. Adler wrote:”Let us begin with a review of the postulates of QM, in the arena of a complex Hilbert space, following for the larger part the presentation of Ballentine.”
S.L. Adler wrote:”While everyone agrees that the above postulates provide a practical set of rules for making predictions in quantum mechanics, and that these predictions to date have always agreed with experiment…”

Zbyszek:”In your work, you give wrong description of Ballentine's paper (section 1.2), you logic is questionable in the Recapitulation (section 1.6) when it comes to the two alternatives A and B (you conveniently forget that neither A or B captures the results from Ballentine's work). Namely, there is also C: QM is exact, no need for any reinterpretation, remove the postulate you have added to the Ballentine's list.”

S.L. Adler wrote:”According to this interpretation (Ballentine), (14) corresponds to the preparation of a new ensemble by the measurement. There may be, or there may not be , hidden variables that specify a complete, nonstatistical interpretation of individual systems: the statistical interpretation is agnostic with respect to this issue.”

In addition, Adler’s work devoted to the completely different issue.
S.L. Adler wrote:”This survey focuses particularly on the issue of whether probabilities in quantum mechanics are postulated or emergent.”

Compare with E. Schrödinger, Ann. Physik,82,186 (1927).

 

[Dense]

Believe it or not I'm having trouble understanding quantum physics. If we take the double slit experiment and one photon is sent through the slits at a time an interference pattern is formed. From what I've read the particle goes through both slits and interferes with itself. Now when it says interfere is it taking in a general sense or does it mean that the particle will hit itself to interfere with itself?

I also don't understand why we just assume that the particle is going through both slits and then interferes with itself. It's just as crazy to say that the particle is only going through one slit and then takes two directions at the same time hitting different positions on the screen which just so happen to cause an interference pattern. I think the attitude quantum physics takes that it can't be proved wrong so it must be right type of attitude is very poor. If we can't measure the state that the particle is in then we should only conclude that it makes an interference pattern but we shouldn't start pretending that we know what is happening to the particle before it hits the screen.

I hope you can at least clear a little bit of my confusion. Thanks in advance.

I find it helps to think of it this way:

Imagine lightning. You know how, before the visible lighting bolt strikes, the phenomenon first finds the path of least resistance; and once that path has been carved out in the atmosphere between the two charges, the bolt slams down that path.

So now imagine that a photon has been created, and before it starts to travel you stop time. With time stopped, all of the photon's possible paths are carved out in front of it. Imagine each of these paths as if they were independent photons. Now some of these paths are going to interfere with each other.

Now start up time again. The photon is going to travel down one of these paths. If it's one of the paths that interfered with another potential path, it's going to look as if the photon interfered with itself. Not because it actually did, but because the potential path it followed had already interfered with another potential path.

I'm not saying this is really what happens, I'm just saying it's an analogy that helps me understand the outcome.

 

[vanesch]

I find it helps to think of it this way:

Imagine lightning. You know how, before the visible lighting bolt strikes, the phenomenon first finds the path of least resistance; and once that path has been carved out in the atmosphere between the two charges, the bolt slams down that path.

So now imagine that a photon has been created, and before it starts to travel you stop time. With time stopped, all of the photon's possible paths are carved out in front of it. Imagine each of these paths as if they were independent photons. Now some of these paths are going to interfere with each other.

Now start up time again. The photon is going to travel down one of these paths. If it's one of the paths that interfered with another potential path, it's going to look as if the photon interfered with itself. Not because it actually did, but because the potential path it followed had already interfered with another potential path.

I'm not saying this is really what happens, I'm just saying it's an analogy that helps me understand the outcome.

This is pretty close to Bohmian Mechanics (maybe you didn't realize this...)

 

[marlon]

I find it helps to think of it this way:

Imagine lightning. You know how, before the visible lighting bolt strikes, the phenomenon first finds the path of least resistance; and once that path has been carved out in the atmosphere between the two charges, the bolt slams down that path.

So now imagine that a photon has been created, and before it starts to travel you stop time. With time stopped, all of the photon's possible paths are carved out in front of it. Imagine each of these paths as if they were independent photons. Now some of these paths are going to interfere with each other.

Now start up time again. The photon is going to travel down one of these paths. If it's one of the paths that interfered with another potential path, it's going to look as if the photon interfered with itself. Not because it actually did, but because the potential path it followed had already interfered with another potential path.

I'm not saying this is really what happens, I'm just saying it's an analogy that helps me understand the outcome.

Great post; I have read a seminar of Anthony zee once where he uses almost the very same formulation.

Again, here it is very clear that the interference (between paths) is a property inherent to one single particle, giving rise to the superposition of paths or even the entire path integral basis (ie summation over all possible paths to acquire the action etc etc).

greets
marlon

 

[eep]

I've seen this question come up a lot, and I think the problem is that people still want to stick to their classical pictures of "waves and particles" that we can understand from our personal experiences. "Quantum particles" have properties of both classical waves and classical particles, but don't they also have properties which neither have (the statistical interperation, uncertainy principle, etc)? I tend to not try and think about "quantum particles" with classical ideas, and simply call them "wavicles" that have their own properties, some of which classical waves and particles have. I feel like people just really need to stop thinking of "wave-particle duality" with a classical viewpoint, since quantum particles have properties which neither common to classical waves or particles. Is there anything wrong with what I'm saying?

 

[Anonym]

Marlon:” But that is my point. Of course you should take my words literally and i still don't get where you see a contradiction.”

Compare with Reilly under the wave packet description:
“Here's a simple fact: in this real world of ours we can't predict anything with certainty. Measurement error is a fact of Nature. Thus everything is uncertain, to a greater or lesser degree. Brownian motion occurs in 'classical systems'. That means, of course, that there is no theory of certain events.

That's why we use in experiments the largest sample possible so as to get info about the distribution of measurements with as much accuracy as possible”.

“So, if that's so, why do you single out QM for having a problem that is virtually a universal one?”

“After spending time moving lead bricks around for shielding for electron scattering experiments, and working extensively with data from such experiments, I'll claim that the measurements don't know from quantum or classical. It's all in the eye of the beholder. Perhaps it's not quite a mantra, but "experiments are experiments", and "propagation of errors is propagation of errors." There's nothing quite like computing or measuring the 5th decimal place; tends to make one practical.”

Here Reilly discuss three unrelated problems:
1.Whether statistics in quantum mechanics are emergent and how.
2.What is the purpose of the theoretical description ( For me if I know experimental result and perform computing to obtain it without additional information (understanding=modulation) , the information rate=0 and there is nothing to communicate).
3.Whether the classical physics is “theory of certain events”.
“I'll claim that the measurements don't know from quantum or classical. It's all in the eye of the beholder”.
Compare:” we look at QM through "classical eyes".
The macroscopic physics are the theory of certain events. Translation into the language of the functional analysis say: the classical physics are a dispersion free physical theory. W. Heisenberg UR demonstrate that QM is essentially not (field theory). You stated:” We need this duality because we look at QM through "classical eyes".” Here I see a contradiction between you and Reilly.

 

[Careful]

I feel like people just really need to stop thinking of "wave-particle duality" with a classical viewpoint, since quantum particles have properties which neither common to classical waves or particles. Is there anything wrong with what I'm saying?

Of course there is ! You may call it whatever you want it to, but if you say that electrons are wavicles, you still need to explain why we see them only as particles. Just as too many others who do not wish to bother themselves, you are doing nothing else but rephrasing the same question in a different way : QM splits the world in two, and the question is why we observe only one part of it given that we ourselves belong to both worlds. The only ``answers'' so far are simply declarations that it *is* so, that this leads to absurdities is then sold as a necessary consequence.

I agree that there is a single particle self interference, but that this needs to imply wave particle *duality* (as it stands now) is jumping to unnecessary conclusions (and actually there exist other models - which were mentioned already - which do accomplish this self interference).

 

[marlon]

Marlon:” But that is my point. Of course you should take my words literally and i still don't get where you see a contradiction.”

Compare with Reilly under the wave packet description:
“Here's a simple fact: in this real world of ours we can't predict anything with certainty. Measurement error is a fact of Nature. Thus everything is uncertain, to a greater or lesser degree. Brownian motion occurs in 'classical systems'. That means, of course, that there is no theory of certain events.

That's why we use in experiments the largest sample possible so as to get info about the distribution of measurements with as much accuracy as possible”.

But where is the contradiction ? When did i say something that would imply that the content of these quotes is wrong ?

REILLY : “I'll claim that the measurements don't know from quantum or classical. It's all in the eye of the beholder”.

Compare:” we look at QM through "classical eyes".

The macroscopic physics is the theory of certain events. Translation into the language of the functional analysis say: the classical physics is a dispersion free physical theory. W. Heisenberg UR demonstrate that QM is essentially not (field theory). You stated:” We need this duality because we look at QM through "classical eyes".” Here I see a contradiction between you and Reilly.

Again, what contradiction ? Do you think i mean that QM is also "a dispersion free theory" (whatever that may be ?). NOT AT ALL.

There is no contradiction because i am not talking about QM nor its formalism. I think you did not get my point. All i wanted to say is that we, as human beings are more familiar with the concepts of classical physics. For us, it is easy to distinguish between a particle and a wave. Ofcourse, QM does not care about that distinction, that's what the QM formalism proves us in the doubble slit experiment. Now, this "strange" behaviour of particles behaving like waves and the other way around is something we cannot understand easily. THAT is why we call this behaviour wave/particle duality.

Again, there is no contradiction between reilly and myself and there never has been. Even Reilly stated several times that we are saying THE SAME THINGS HERE. You claim to see two contradictions, the first one i still don't get and the second one is incorrect because what i mean with "looking at QM through classical eyes" is just the same as Reilly saying "it is in the eyes of the beholder". Again, if we would look at QM through QM glasses, we would not be spending so much time discussing about the strangeness of this socalled "duality between particles and waves".


Greets
marlon

 

[Careful]

Again, if we would look at QM through QM glasses, we would not be spending so much time discussing about the strangeness of this socalled "duality between particles and waves".


Greets
marlon

Sure, and if we would look at crimes through the glasses of a criminal, we might not need justice at all.

 

[marlon]

I've seen this question come up a lot, and I think the problem is that people still want to stick to their classical pictures of "waves and particles" that we can understand from our personal experiences.

Well that's true but that just normal human behaviour and we cannot do anything to change that. Even YOU wants to hold on to what you know about particles and waves and that fact that there is a distinction between the two. I just want to say that we can hold on to our classical principles and still cope with the strangeness of QM. But, THAT IS EXACTLY WHY THIS DUALITY EXISTS.

"Quantum particles" have properties of both classical waves and classical particles, but don't they also have properties which neither have (the statistical interperation, uncertainy principle, etc)?

It's like this : quantum particles have indeed properties of both classical waves and particles but the way they behave with each other (and themselves !) is totally different.

I tend to not try and think about "quantum particles" with classical ideas, and simply call them "wavicles" that have their own properties, some of which classical waves and particles have.

But didn't you just write that quantum particles have classical wave/particle properties ? Actually, the duality is a classical idea in itself.

I feel like people just really need to stop thinking of "wave-particle duality" with a classical viewpoint, since quantum particles have properties which neither common to classical waves or particles. Is there anything wrong with what I'm saying?

Again, think of WHY this duality exists and what kind of terms are used in it's definition. They are ALL classical. Two classical terms are a fundamental part of the definition of this duality. Besides, here's the 64.000 dollae question : why do you think we call it duality ?


marlon

 

[marlon]

Sure, and if we would look at crimes through the glasses of a criminal, we might not need justice at all.

LOL

Nope that is NOT what i said. You should have written that we would not see "a crime", allthough we are looking at the same action that we, in our world, would call a crime. Crime is defined in our world...

Do you see what i mean ?

Particles and waves are classical properties. The duality between the two is a QM property.

marlon

 

[Careful]

LOL

Nope that is NOT what i said. You should have written that we would not see "a crime", allthough we are looking at the same action that we, in our world, would call a crime. Crime is defined in our world...

Do you see what i mean ?

Particles and waves are classical properties. The duality between the two is a QM property.

marlon

Nope, you confirm again what I said. You watch trough the world in QM glasses, in either you accepted all the possible discomforts and assume QM to be the holy mother. The fact that you constantly say ``you should say like that'' given your bias which is exactly the thing the other party is questioning is irrational.

You said ``Again, if we would look at QM through QM glasses, we would not be spending so much time discussing about the strangeness of this socalled "duality between particles and waves"´´ which is correct. In the same way, if we would look at a crime in the way a criminal thinks about it, we cannot condemn him. This does not imply in any way that we would not see a crime, just that we would *treat* the criminal according to his own judgements (but possibly interpret it from a very different perspective). Perhaps I should have clarified this ``subtlety'' but I thought it was clear.

 

[Anonym]

Marlon:” what i mean with "looking at QM through classical eyes" is just the same as Reilly saying "it is in the eyes of the beholder".

That what I meant. I did not mention two contradictions, just one. I took Railly words also literally:” That means, of course, that there is no theory of certain events.” Correct, I do not know what you say about that.” All i wanted to say is that we, as human beings are more familiar with the concepts of classical physics.” No information added. To be concrete, please, go to Google, type a key words: Hilbert space, dispersion free, classical mechanics. You will find my recent paper together with other relevant contributions. I will appreciate obtaining your opinion on it.

 

[eep]

The only language we have to express ourselves comes from the "classical" eye. Human language wasn't developed to talk about strange quantum particles, and the reason why we call it "wave-particle" duality is because yes, quantum particles have both properties of classical particles and waves. The idea of something being a wave is complementary to something being a particle, so it seems obvious to me that the language we use to talk about quantum particles only hints at what is really going on, but there is no way around it. When one person talks to another, we always have to use "classical" language because that's the realm with language deals with.

 

[Careful]

The only language we have to express ourselves comes from the "classical" eye. Human language wasn't developed to talk about strange quantum particles, and the reason why we call it "wave-particle" duality is because yes, quantum particles have both properties of classical particles and waves.

No, that is not the reason why we call it wave particle duality.
Wave-particle duality means that those entities which manifest themselves as particles to us, also undergo wavelike phenomena. That is not the same as saying that quantum particles have properties of classical waves, a potentially important distinction it seems to me. This is all we can deduce from observations.

The idea of something being a wave is complementary to something being a particle, so it seems obvious to me that the language we use to talk about quantum particles only hints at what is really going on, but there is no way around it.

Sure, there is a way around it : we ``simply'' have to come up with something better.

When one person talks to another, we always have to use "classical" language because that's the realm with language deals with.

Correct, but the reason why we use classical language is because the latter is suggested by the world we live in. There is *in principle* no reason why we could not speak in quantum language by using quantum logic.

 

[eep]

No, that is not the reason why we call it wave particle duality.
Wave-particle duality means that those entities which manifest themselves as particles to us, also undergo wavelike phenomena. That is not the same as saying that quantum particles have properties of classical waves, a potentially important distinction it seems to me. This is all we can deduce from observations.

How is "undergo wavelike phenomena" any different than saying they have properties of classical waves??

Correct, but the reason why we use classical language is because the latter is suggested by the world we live in. There is *in principle* no reason why we could not speak in quantum language by using quantum logic.

The reason why we can't speak in quantum language using quantum logic is because our language has evolved in the macroscopic realm.

 

[Careful]

How is "undergo wavelike phenomena" any different than saying they have properties of classical waves??

Well, by saying that a wavicle has properties of a classical wave, you indicate that it is the wavicle itself which behaves as a classical wave under some circumstances; a conclusion which is by no means necessary.

The reason why we can't speak in quantum language using quantum logic is because our language has evolved in the macroscopic realm.

Sure, and in what does this differ from what I said before : I never said I met somebody who spoke it fluently.

 

[marlon]

Nope, you confirm again what I said.

How is that ? Besides, when did i confirm what you said the first time ? I am not following here, sorry.

You watch trough the world in QM glasses, in either you accepted all the possible discomforts and assume QM to be the holy mother.

Possible discomforts ? You mean all the "strangeness" of QM right ? If so, then what you say is NOT what i mean because through QM glasses, there would be no such strangeness.

The fact that you constantly say ``you should say like that'' given your bias which is exactly the thing the other party is questioning is irrational.

I don't get this. What do you mean here ?

You said ``Again, if we would look at QM through QM glasses, we would not be spending so much time discussing about the strangeness of this socalled "duality between particles and waves"´´ which is correct. In the same way, if we would look at a crime in the way a criminal thinks about it, we cannot condemn him. This does not imply in any way that we would not see a crime, just that we would *treat* the criminal according to his own judgements (but possibly interpret it from a very different perspective).

Not at all. If we are looking through the criminal's glasses we would not know what a crime is because a crime is something that has been defined using our "classical" (non criminal glasses) principles.

Again, i don't think you are getting the point or perhaps i am not making myself clear enough. What i mean is this : when looking through QM glasses you do not know what classical physics is. Looking through " the criminal's glasses" means that you do not know what "non criminal behaviour is" so judging is not even relevant here. In our "non criminal world" we don't put an innocent guy to trial right (or we would recognize there is something seriously wrong here).

But, coming back to the particle wave duality. The duality exists because we are familiar with waves and particles from classical physics. When we first found out about the strangeness of QM via the doubble slit experiment, we tried (succesfully) to explain what is going on using our classical concepts. This does NOT mean that QM behaves classically ofcourse. We said, hey we have got particles like electrons that exhibit interference, which we are used to be a wave like behaviour. So, particles and waves have a dual nature on the atomic scale. That is what happened and that is what i wanted to say. Even, concepts like superposition are explained using quantum interference, which has it's same basis in the doubble slit exp.

I hope you understand what I am saying here.

greets
marlon

 

[marlon]

Well, by saying that a wavicle has properties of a classical wave, you indicate that it is the wavicle itself which behaves as a classical wave under some circumstances; a conclusion which is by no means necessary.

No, there is a direct reference to classical wave behaviour in the double slit exp since that is the only wavelike behaviour that we know (at that stage in the development of the QM formalism).

But that is not the point, the point is that the concepts (eg interference, diffraction) of wavelike behaviour apply also to particles. That is all.

marlon

 

[marlon]

No, that is not the reason why we call it wave particle duality.
Wave-particle duality means that those entities which manifest themselves as particles to us, also undergo wavelike phenomena.

Look, what you write above is EXACTLY what i am talking about. You are using two concepts that you know from classical physics (that is what i mean by looking at QM through classical glasses) and you acknowledge that "particles" exhibit wavelike behaviour. You knew what a particle was and you excpected it to behave like one, but in QM it does NOT. That is why the duality is there and that is what i wanted to say.

That is not the same as saying that quantum particles have properties of classical waves, a potentially important distinction it seems to me.

I don't get the distinction here. Care to elaborate.

This is all we can deduce from observations.

So you can deduce that particles "also undergo wavelike phenomena" but they do not "have properties of classical waves" ? Again, i don't get what is so fundamentally different about the two expressions here.

I think this is a semantics thing we've got goin' on here...

greets
marlon

 

[eep]

Yeah, I think it is just semantics. This is what I mean when I say there's a problem expressing quantum ideas using our language, because our language doesn't have a good way to explain wave-particle duality, for example. saying a particle has properties of a wave makes no sense. waves and particles are complimentary ideas (classically), but we have to use both in order to try and express what's going on in the quantum mechanics. There's a good discussion about this throughout Heisenberg's "Physics and Beyond"

 

[Careful]

Possible discomforts ? You mean all the "strangeness" of QM right ? If so, then what you say is NOT what i mean because through QM glasses, there would be no such strangeness.

Even as someone who accepts QM, it is quite something to state that you are at least not slightly bothered by it . It means that you are in a complete denial of realism (or locality if you prefer copenhagen), probably you are willing to sacrify general relativity (without too much motivation) - although Rovelli wants to ``unify'' GR with MWI - too. I have never met someone who did not feel at least slightly uncomforatble with either the collaps postulate, or the consciousness crap.

Not at all. If we are looking through the criminal's glasses we would not know what a crime is because a crime is something that has been defined using our "classical" (non criminal glasses) principles.

I said to you that if a judge were to punish the criminal according to the latter's standards; the bandit would walk out free and hence, we would not need justice at all. Now, you interpret my first sentence ``if we would look through the glasses of a criminal, then we would not need justice at all'' as literally meaning that ``you think all the time like the criminal''. Then, I tried to explain you that ``to look through ones glasses'' had to be interpreted as ``to imagine her/his point of view'' and that does not imply at all that I have to share this person's opinions, neither that I am incapacitated to declare his act a crime even though he is not punished for it. The reason for not punishing the criminal, even though we know he/she commited a crime according to the letter of the law, is that it might make no sense to punish someone for something he/she considered to be morally acceptable given his/her circumstances. Similarly, the fact that by accepting the QM laws as the holy mother you are released of the wave/particle duality problem, does not mean at all this is the right way to proceed given the fact that QM has the dual nature embraced in it's axioms (wavefunction and reduction).

Even, concepts like superposition are explained using quantum interference, which has it's same basis in the doubble slit exp.

Superposition is not a logical consequence of (quantum) interference.

I hope you understand what I am saying here.

I got what you said the first time, but I doubt whether the reverse is also true.

 

[Careful]

Look, what you write above is EXACTLY what i am talking about. You are using two concepts that you know from classical physics (that is what i mean by looking at QM through classical glasses) and you acknowledge that "particles" exhibit wavelike behaviour. You knew what a particle was and you excpected it to behave like one, but in QM it does NOT.

The double slit experiment with electrons says that the entity which we observe to be the electron does not behave like a free particle, neither as a particle in a classical random noise field, but instead undergoes wavelike phenomena. QM says more than that, it says that those entities are represented by probability waves individually and that observation consists of applying a projector (or corresponding acts in other interpretations). Moreover, it also declares that the reality content behind the observed effects is entirely revealed through observation (even BM takes the schizoid attitude that the wave isn't real).

So, if you agree with what I say about wave particle duality, then you also acknowledge that QM draws possibly wrong conclusions, otherwise we disagree about it. QM is simply agnostic about wave particle duality, the latter merely serving as a guideline for its axiomatic system.

 

[Careful]

Yeah, I think it is just semantics.

To get the semantics right is usually the first step to progress.

This is what I mean when I say there's a problem expressing quantum ideas using our language, because our language doesn't have a good way to explain wave-particle duality, for example. saying a particle has properties of a wave makes no sense.

Right, therefore my protest. I believe my formulation is much better (since it does not suffer from any such problems) and if you think about it, you might see some other possibilities.

waves and particles are complimentary ideas (classically),

Yes, and that is why I said a week ago that it might be desirable to develop a particle theory of waves (albeit it is difficult) and as far as I am concerned, this does not need to have anything to do with the distinction quantum/classical (in either \hbar).

but we have to use both in order to try and express what's going on in the quantum mechanics. There's a good discussion about this throughout Heisenberg's "Physics and Beyond"

For quantum mechanics as it stands now yes, to describe what might be going on in the double slit experiment and other phenomena, no.

 

[marlon]

Even as someone who accepts QM, it is quite something to state that you are at least not slightly bothered by it .

Ofcourse you would not be bothered by it because it is "the only reality" you would know (if you look through the QM glasses). The reason we are bothered by QM (if we look at it through classical glasses) is because it is contra intuitive. Why is that so ? Well, because the contra intuitivity comes from the fact that our classical way of thinking does not apply to phenomena at the atomic scale. But if we were all born in a "QM world" the situation is a 180° different from the situation we are really in. In other words, we are used to look through classical glasses and that is why particles and waves do NOT seem strange to us.

It means that you are in a complete denial of realism (or locality if you prefer copenhagen),

Why ? I never spoke about the validity of QM what so ever and i never talked about the possible interpretations of it's formalism.

probably you are willing to sacrify general relativity (without too much motivation)

Why ? Care to motivate ?

Besides, i asked you another question in my previous post to you. Why did you not answer that ?

I have never met someone who did not feel at least slightly uncomforatble with either the collaps postulate, or the consciousness crap.

Ofcourse, that is perfectly normal because these concepts are contra intuitive to our classical world. This is excatly what i am saying. I still think you are not getting my point.

I said to you that if a judge were to punish the criminal according to the latter's standards; the bandit would walk out free and hence, we would not need justice at all.

But that is wrong because there would be no trial in the first place because no crime has been committed. Looking through the criminal's glasses implies that criminal behaviour is "normal". Just the same as normal behaviour is normal when we look through "normal" glasses. There would be a crime if one committed an act that is defined as normal behaviour, when looking through normal glasses.

Then, I tried to explain you that ``to look through ones glasses'' had to be interpreted as ``to imagine her/his point of view'' and that does not imply at all that I have to share this person's opinions, neither that I am incapacitated to declare his act a crime even though he is not punished for it.

BINGO : this is exactly why you are missing my point. You cannot judge his acts because they would seem normal to you. Again, you do not know the "abnormal criminal behaviour" (read : normal behaviour) or at least it would seem contra intuitive to you. This is, going back to QM <--> classical physics, is what i mean by : we only knew about particles and waves as they were defined in classical physics. Then, QM comes in, and we observe there is strangeness going on. We call that strange because we are NOT familiar with "objects" that exhibit borth particle and wavelike behaviour. Solution : duality. Looking through QM glasses means that we found out about QM first and this behaviour would seem normal to us. The duality is NOT a problem in that case.

Why is it so difficult to see that analogy ?

The reason for not punishing the criminal, even though we know he/she commited a crime according to the letter of the law, is that it might make no sense to punish someone for something he/she considered to be morally acceptable given his/her circumstances.

Wrong again, you are mixing the two perspectives here. Note that i never did that. I always start from one perspective and then we come to some strange behaviour that seems contra intuitive.

Also, you are talking about the perspective of different individuals. that is NOT something i have been doing. We all look at physics in the same way, the duality is the same for all of us. When i say "look through classical glasses", i mean we all have to do that.

Similarly, the fact that by accepting the QM laws as the holy mother you are released of the wave/particle duality problem, does not mean at all this is the right way to proceed given the fact that QM has the dual nature embraced in it's axioms (wavefunction and reduction).

Again you are mixing perspectives.
Ofcourse QM has a dual nature because it's very fundaments are defined by looking at them through classical glasses. Why ? Because there is no other way. Just look at how the concept of wavefunction is born. The introduction of probabilities (Born etc etc) was necessary because our classical principles didn't work anymore for certain phenomena. This is just the very same story.

Superposition is not a logical consequence of (quantum) interference.

?

I SAID : "Even, concepts like superposition are explained using quantum interference, which has it's same basis in the doubble slit exp."

Are you saying this is NOT correct ? Are you saying there are not related ?Because that is all they need to be to prove my original point.

http://www.cs.caltech.edu/~westside/quantum-intro.html


Really, you cannot just regurgitate these cheap "dogma's" because i cannot do anything with that. What is your point ? What do you want to say ?

I got what you said the first time.

I seriously doubt that. Actually, if you reread our lasts posts, you will notice that i am always saying the same stuff over and over again. Especially on the criminal glasses stuff you do not seem to be able to get my point. It is quite easy though because the analogy is the same as the stuff about the duality.

marlon