Why do light particles behave like waves?

[ZapperZ]

Thanks again for the info. I guess I should explain my statement a little more. We have Chemistry in which we say there are electrons spinning around a nucleus and the nucleus has neutrons and protons and there are this many here and that many there. Yet when it comes to light, we just say its a photon. Its not an electron, but it can make electrons move the same way you plug a chord into a wall outlet. We say it is both a wave and a particle due to dual properties that it seems to have. We say that it progresses by switching from magnetism to energy and back again. We refer to it as a wavelength. Yet we don't know "What it is". So my statement that we don't know what it is, is just that. I never said that we didn't know certain properties about light. I just said we didn't know what it was exactly.

Sorry, but what you describe as light is of the same level of "knowledge" as what you describe as an atom! They are all properties of the entity that you are describing! Think about it. Your knowledge of an "atom" is no worse or better than your knowledge of light. In fact, dig deeper in PF and you'll find threads of people claiming that electrons or atoms don't exist!

And btw, if you have read our FAQ, you'd realize why the description of "electrons spinning around the nucleus" is not correct.

I can refer to a car and tell you its a car. I can tell you that my friend that had plastic surgery is my friend after I analyze other properties about him such as his build, his speach, his statements, personality and so forth.

In other words, you look at the various properties associated with the entity, and identify them as such.

Your argument is like me telling you to analyze an electron moving down a wire and telling me if it came from a magnet or a solar panel. To say that I know nothing of anything except by what I observer is absolutely true. It is also absolutely true of your argument of what we know about light.

Actually, and this is not to be picky, you actually cannot really tell if that same electron is the one that made it through various components. I hate to bring in indistinguishibility statistics here, but there's plenty of things not correct here.

Without observation we'd know nothing at all. So I really fail to see your point about how this ties into QM. Just because you look at a car from the moon and see that it seems to drive down lines doesn't mean you understand anything about a car. You can devise a mathmatical formula that determines whether a car will go left or right or continue straight ahead, but won't go at 45deg intervals when there is no path there, doesn't mean that we can now take your math that seems to work properly 70% of the time and start saying all sorts of strange things about life.

But at least you recognize the generic property of a car to say "Ah hah! That is a car!". We do that with photons, electrons, neutrons, muons, kaons, protons, neutrinos, etc...etc. In high energy physics experiments, we'd better have a set of defined properties for each of these elementary particles to be able to tag and identify them. The fact that we CAN recognize these things as well as you can recognize that something is a car (and you claim to know of a car), means that we DO know about photons.

Because of our predictions of the cars we can now say that its impossible to know anything about the cars. We've predicted the way they move, how fast they go, how they interact with each other so that's enough. Stop asking questions about things in reference to the moon as it doesn't have meaning.

I guess at this point we should just stop because you are getting way to tied up in this conversation. I'll keep reading and come back later if I have more questions. I really do appreciate the information and I"m sorry I made you so upset.

glenn

I am not upset, contrary to popular belief. I do get "animated", because this is something I've looked at very often - not the physics, but how people arrive at certain conclusions. I'm an experimentalist, and in many cases, I often have to sit down and examine what it is that I am actually measuring, and how I'm measuring it. In other words, in many instances, I have to really strip down all of the assumptions and "frames" that we all take for granted and figure out what exactly did Mother Nature gave me? Was it a "naked measurement", or did I inadvertently dressed that result inside of my equipment, my methodology, or even my bias! You end up examining what exact it is that you are asking, because the question often determines what kind of answers you can get.

So in this case, how do we determine if we "know" something. I have put it to you that you know something based on being able to get the relevant properties of it. There are still things that we don't know, but it certainly doesn't mean we know nothing of it, the same way that you certainly don't need to know every square inch of a car to know that that is a car and how to run it.

Zz.

 

[DrChinese]

...What I've learned however, (right or wrong), is that a lot of information is passed off as fact when in fact its an assumption and doesn't have a proven experiment to back it up.

...

Again, I'm really sorry that I am annoying you with my questions, but they are in ernest and not some guy trying to cause problems.

Thanks,

glenn

Your questions are not annoying.

But I would strongly disagree with your comment. There are 2 things you must separate: the physics and the interpretation of the physics. The physics is totally solid in books like Greene's. But from time to time, the author may switch into a mode in which the interpretation is being discussed. There is latitude in the interpretation of quantum physics, but none of it impacts (as far as we now know) the formulae or predictions.

It is a fact that the predictions of quantum theory have been very heavily tested to rigorous standards. Even the strangest predictions have been checked out and found to be spot on. Most scientists agree that quantum theory is extremely accurate.

On the interpretation side, it is a different matter. There is currently a debate as to whether or not effects can travel faster than the speed of light; or alternately that particles do not take on some attributes until an observation is performed. Regardless of your opinion on the matter: it is still only an opinion as the physics does not support a conclusion to the matter at this time.

 

[Anonym]

I am not upset, contrary to popular belief. I do get "animated", because this is something I've looked at very often - not the physics, but how people arrive at certain conclusions. I'm an experimentalist, and in many cases, I often have to sit down and examine what it is that I am actually measuring, and how I'm measuring it. In other words, in many instances, I have to really strip down all of the assumptions and "frames" that we all take for granted and figure out what exactly did Mother Nature gave me? Was it a "naked measurement", or did I inadvertently dressed that result inside of my equipment, my methodology, or even my bias! You end up examining what exact it is that you are asking, because the question often determines what kind of answers you can get.

Your description is not complete. In addition, you ask your friends, experimentalists, whether they get the same answer with their equipment, their methodology (best case with the different setup), their bias and whether your answer is consistent with the other measurements. As an exception, you sometimes even ask a theoretician whether your result is consistent with the mathematical formalism of the theory.

Regards, Dany.

 

[cybercrypt13]

Ok guys, thanks for all the pointers. I'll keep studying and get back with you when I have more questions...

Thanks,

glenn

 

[Anonym]

If you think very carefully and examined your world, you will notice that everything that you think you can "explain" is really, at the very fundamental level, a "description". Every single "explanation" becomes a description at the very end of that line of explanations. For many people, science's role is simply to describe things at the most fundamental level. This is true even for classical physics, which, presumably, you have no problem with. Don't think that's true?

I am not sure that I understand you. Let consider CED as a model. It (dynamics) starts with M. Faraday. He demonstrated experimentally that something outside the classical analysis should be present in the mathematical formalism (vector derivative-curl). The work was done by Maxwell. It was clear that the obtained solution of the problem was adequate and complete (perfect). It satisfies all expectations: unification, predictive power, unexpected connections, etc. Hertz started the engineering applications. And then came on A. Einstein with his 1905 paper. Did it add anything to the Maxwell ED? No. Then what it is? It presents the physical content of Maxwell work on the deepest possible level. Is it a “description” or the “explanation” of what exactly did Mother Nature gave us?

By the way, I like real things (with the necessary and sufficient amount of the imaginary units), therefore, in relation to all that, I am very curious to know what do you see (“describe” or “explain”) in the results presented by A. Tonomura et al. “Double-biprism electron interferometry”, App. Phys. Lett., 84(17), 3229 (2004). The paper by K.Harada et al. “Triple-biprism electron interferometry”, JAP, 99, 113502 (2006) is also relevant, but I prefer double-biprism before.

Regards, Dany.

 

[Mentz114]

The whole idea that a photon can be deflected by a force, such as the sun, is of course a contradiction to the constant speed of light rule. For any force, hence acceleration, implies a velocity that is greater than the speed of light. Therefore, in a sense, the one particle, two slit phenomenon is a constradiction of this law.

Utter rubbish. OP don't pay attention to this.

 

[muppet]

ZapperZ... I don't think I've ever heard the word description sound so pejorative
No-one can seriously dispute that we have an excellent operational understanding of the physical laws governing the behaviour of what we understand to be light. But do you think it's fair to say that we have quite a limited understanding of the physical meaning of a wavefunction? My perspective from both reading and my lectures is that we have a fantastic mathematical model, without much idea of what underlying physical phenomena lead to the results observed in experiment to conform to our formulation, in much the same way that Newton's formula of gravity was limited to describing the results of his observations well, wheras Einstein's offered a rough mechanism by which those phenomena occurred (the bending of spacetime). In that respect, I'd find myself in some disagreement with you: we have an incredible description of how the systems behave (in the language of maths); but quite poor knowledge of the nature of the objects that comprise the system!

 

[ZapperZ]

ZapperZ... I don't think I've ever heard the word description sound so pejorative
No-one can seriously dispute that we have an excellent operational understanding of the physical laws governing the behaviour of what we understand to be light. But do you think it's fair to say that we have quite a limited understanding of the physical meaning of a wavefunction? My perspective from both reading and my lectures is that we have a fantastic mathematical model, without much idea of what underlying physical phenomena lead to the results observed in experiment to conform to our formulation, in much the same way that Newton's formula of gravity was limited to describing the results of his observations well, wheras Einstein's offered a rough mechanism by which those phenomena occurred (the bending of spacetime). In that respect, I'd find myself in some disagreement with you: we have an incredible description of how the systems behave (in the language of maths); but quite poor knowledge of the nature of the objects that comprise the system!

But you are forgetting that Einstein presents no "explanation" on why spacetime HAS to be warped in the presence of a massive body. If you look closely, SR and GR are also "description", not "explanation". In fact, find everything that you think are "explanation", and I'll show you immediately that they are "description". This is because when you explain a higher level phenomenon, that explanation then becomes merely a description when a lower level explanation comes along. This process continues ad nauseum as far as we have seen so far.

For example, you discover that an object suddenly has a resistivity drop to zero below a certain temperature. You then later discover that the explanation for it is the ability for the charge carrier to move in the material with zero resistance. That's the explanation. But really, if you start asking what causes it to move with zero resistance, then the explanation becomes nothing more than a description because you are expecting a lower level explanation for it. You discover that you can in fact construct a coherent wavefunction called the order parameter, and by using several phenomenological parameters, you actually managed to "explain" why the charge carrier could actually propagate without any resistance. But then you start asking the origin of such wavefunction, and now your last explanation starts to become a description because you think you can find a lower-level explanation for it, and you do. You find that the formation of cooper pairs can produce a composite boson made up of electron pairs, and this can actually condensed into a coherent state that propagates without any resistance. So you have found an explanation on the origin of the wavefunction. Are you done? No! Someone can easily ask what is the mechanism that produce such cooper pairs, and why can't you come up with an explanation to include ALL of the conduction electrons in the material, not just 1 electron pair? Etc... etc... Do you see what I'm getting at?

The QM wavefunction (actually, it is the Hamiltonian, since in many real systems, you do NOT solve the wavefunction because it is unsolvable) is the "explanation" for many phenomena. But the wavefunction itself is nothing more than a description of the system, the same way that Maxwell equations are a description on EM phenomena. Each time you think you've come up with an "explanation", look at it carefully. What you got was a description.

Zz.

 

[muppet]

But you are forgetting that Einstein presents no "explanation" on why spacetime HAS to be warped in the presence of a massive body. If you look closely, SR and GR are also "description", not "explanation". In fact, find everything that you think are "explanation", and I'll show you immediately that they are "description". This is because when you explain a higher level phenomenon, that explanation then becomes merely a description when a lower level explanation comes along. This process continues ad nauseum as far as we have seen so far.

For example, you discover that an object suddenly has a resistivity drop to zero below a certain temperature. You then later discover that the explanation for it is the ability for the charge carrier to move in the material with zero resistance. That's the explanation. But really, if you start asking what causes it to move with zero resistance, then the explanation becomes nothing more than a description because you are expecting a lower level explanation for it. You discover that you can in fact construct a coherent wavefunction called the order parameter, and by using several phenomenological parameters, you actually managed to "explain" why the charge carrier could actually propagate without any resistance. But then you start asking the origin of such wavefunction, and now your last explanation starts to become a description because you think you can find a lower-level explanation for it, and you do. You find that the formation of cooper pairs can produce a composite boson made up of electron pairs, and this can actually condensed into a coherent state that propagates without any resistance. So you have found an explanation on the origin of the wavefunction. Are you done? No! Someone can easily ask what is the mechanism that produce such cooper pairs, and why can't you come up with an explanation to include ALL of the conduction electrons in the material, not just 1 electron pair? Etc... etc... Do you see what I'm getting at?

The QM wavefunction (actually, it is the Hamiltonian, since in many real systems, you do NOT solve the wavefunction because it is unsolvable) is the "explanation" for many phenomena. But the wavefunction itself is nothing more than a description of the system, the same way that Maxwell equations are a description on EM phenomena. Each time you think you've come up with an "explanation", look at it carefully. What you got was a description.

Zz.

Ok, I'm now out of my depth on the theory But I understand your point.
I think the OP, in these terms, really amounts to saying that we have no lower level explanation that the wavefunction describes.
Do you think such a level (e.g. the "pilot wave" proposal of De Broglie and later Bohm) exists?

 

[ZapperZ]

Ok, I'm now out of my depth on the theory But I understand your point.
I think the OP, in these terms, really amounts to saying that we have no lower level explanation that the wavefunction describes.
Do you think such a level (e.g. the "pilot wave" proposal of De Broglie and later Bohm) exists?

I don't know, and at this point, no one does. As an experimentalist, as long as none of these have any empirical and practical differences, I think it is a waste of time to argue which one exists and which doesn't.

Zz.