Wave vs. Particle-Like Behavior

[peter0302]

So it's been said that the wavefunction has no physical meaning except to predict the presence of a particle at a particular space and time. Yet quanta seem to exhibit wave-like properties even in isolation (single-electron interference, for example). Further, quanta _NEVER_ exhibit particle-like behavior in the absence of an interaction (i.e. you can't see which slit the electron came through unless you interact with it while it's still close to the slit).

Doesn't the wave-particle duality mean simply that "particles" are nothing more than the result of two quanta (waves) interacting? And if so, is it really so peculiar? Isn't it possible that there is no such thing as a single free particle at all?

 

[monish]

Doesn't the wave-particle duality mean simply that "particles" are nothing more than the result of two quanta (waves) interacting? And if so, is it really so peculiar? Isn't it possible that there is no such thing as a single free particle at all?

Yes, I agree that that's what the "wave-particle duality" would mean if there was such a thing. It doesn't seem to be a very popular concept among physicists, where the particle is king. And yet over the course of time, many phenomena which were once held forth as the prime examples of things you couldn't explain without particles (light particles in particular), such as the stability of the hydrogen atom, the photo-electric effect, and the Compton effect, were easily explained as wave interactions, just as you suggested. All that was needed was for a correct wave equation of matter to be developed. The absorption and emission of radiation in specific quanta could then be understood as following from the properties of atoms.

The more difficult question is whether we can understand the charge of an electron as arising from a wave function. I don't think anybody has an idea of how to do this. Matter absorbs and emits light energy in specific quantities, and that follows purely from wave interactions. But matter also absorbs and emits CHARGE ("electrons") in specific quantities. If you could show that this somehow followed from a wave equation interacting with continuously distrubuted charge density, then you wouldn't need particles at all.

Of course, no one has any idea how to do this kind of thing. But that doesn't mean they never will.

Marty

 

[ZapperZ]

So it's been said that the wavefunction has no physical meaning except to predict the presence of a particle at a particular space and time. Yet quanta seem to exhibit wave-like properties even in isolation (single-electron interference, for example). Further, quanta _NEVER_ exhibit particle-like behavior in the absence of an interaction (i.e. you can't see which slit the electron came through unless you interact with it while it's still close to the slit).

Doesn't the wave-particle duality mean simply that "particles" are nothing more than the result of two quanta (waves) interacting? And if so, is it really so peculiar? Isn't it possible that there is no such thing as a single free particle at all?

You might want to start with reading the FAQ in the General Physics forum and see if you still think there is such a thing as a 'duality'.

Zz.

 

[peter0302]

You might want to start with reading the FAQ in the General Physics forum and see if you still think there is such a thing as a 'duality'.

I was referring more to massive particles and not necessarily photons.

 

[ZapperZ]

I was referring more to massive particles and not necessarily photons.

It really doesn't matter, because there aren't any "duality" in the description of any quantum particles, massive or not.

It is extremely important to see how things are done in practice. You'll never find such "duality"in QM where we have to switch formulation from a 'wave' to a 'particle', and vice versa, simply because one picture no longer works.

Zz.

 

[peter0302]

Well, the "duality" comes into play only when one of the following happens:
- Two quanta interact
- A quanta is observed
- A wavefunction "collapses"

IMO those are all the same thing. Until then, sure, the Schroedinger equation adequately and accurately predicts the location of the quanta. But when an interaction occurs, there's suddenly particle-like behavior such as -
- Cannot be in two places at once
- Cannot share space with another particle
- Conservation of momentum, etc.

The question I pose is whether the latter properties ever appear in the absence of an interaction, and, if not, then if we can really say there is such a thing as a free particle at all, or if everything is waves, and the particle-like behavior can be described by the interaction of two waves, as Monish discussed.

 

[ZapperZ]

Well, the "duality" comes into play only when one of the following happens:
- Two quanta interact
- A quanta is observed
- A wavefunction "collapses"

IMO those are all the same thing. Until then, sure, the Schroedinger equation adequately and accurately predicts the location of the quanta. But when an interaction occurs, there's suddenly particle-like behavior such as -
- Cannot be in two places at once
- Cannot share space with another particle
- Conservation of momentum, etc.

The question I pose is whether the latter properties ever appear in the absence of an interaction, and, if not, then if we can really say there is such a thing as a free particle at all, or if everything is waves, and the particle-like behavior can be described by the interaction of two waves, as Monish discussed.

You are forgetting that ALL of these are described by the SAME thing - the Schrodinger equation.

You should think of what we mean by "duality". Classical mechanics has different, completely different, way of describing "particles" and "waves". So if you have a system, and in one phenomena you had to use the wave description, and for other phenomena, you have to switch gears and use the particle description, then yes, that system has a 'duality', because no one description can account for all behavior.

Now, did you have to switch the QM formulation when describing ALL of the phenomena of a quantum system, before and after measurement? Can you point to me where you have to do this?

Zz.

 

[peter0302]

How do you explain any delayed choice two-slit experiment, then, if not by switching the formalism depending on the choice of measurement? Why is it that the emergence of an interference pattern depends on whether which-path information is obtainable?

[Edit] Also, how does the Schroedinger equation predict that the particle cannot be in two places at once? As Einstein once said, how do the atoms in the detector that did not get hit by the electron "know" that they didn't get hit if, at an infinitessimally small period of time before the detection, the electron's probability density was distributed across the entire detector? Either an FTL action propoagated across the entire universe promulgating the collapse of the wavefunction, or the formalism must change for the act of collision. No?

 

[ZapperZ]

How do you explain any delayed choice two-slit experiment, then, if not by switching the formalism depending on the choice of measurement? Why is it that the emergence of an interference pattern depends on whether which-path information is obtainable?

You should look at the formalism used to describe such an experiment. Did they have to "switch" from a "particle" to a "wave" formalism, or is the same general starting point remain the same?

Look at this paper on single-photon sources:

B. Lounis and M. Orrit, Rep. Prog. Phys. v. 68, p.1129 (2005)

Can you tell me where they had to change gears in the formulation of all the observed phenomena, including your which-way experiment?

Zz.

 

[peter0302]

Perhaps what I should be talking about is _interpreting_ the results rather than describing the experimental predictions. Granted the QM equations accurately predict all the results. But I don't see how you can interpret the results' physical meaning without the duality concept. You have to admit that it's the different interpretations of QM that leave the most to be desired at this point.

 

[ZapperZ]

Perhaps what I should be talking about is _interpreting_ the results rather than describing the experimental predictions. Granted the QM equations accurately predict all the results. But I don't see how you can interpret the results' physical meaning without the duality concept. You have to admit that it's the different interpretations of QM that leave the most to be desired at this point.

Interpretation is a matter of tastes. Nowhere in physics does interpretation dictates the formulation. It is always the other way around first.

Still, if only ONE formulation can describe ALL of the observed phenomena, what possible reason do you have to still want to insist that there is "duality". I mean, do you still insist on the electric and magnetic fields to be "different" even after it has been unified by Maxwell Equations? After all, before that, people thought they were of different beasts. Rational people would conclude that after a single set of formulations unify those two, all talk about them being different from each other would stop. It is the same thing here. Look at QM, and there's one single, consistent formulation for "wavelike" and "particlelike" behavior. Yet, you still want to insist that there are still "duality".

This "duality" only exists when we try to force our classical picture onto a quantum system, or when physicists talk to a general audience. We seldom even consider such a thing among ourselves.

Zz.

 

[peter0302]

Still, if only ONE formulation can describe ALL of the observed phenomena, what possible reason do you have to still want to insist that there is "duality".

How does the Schroedinger equation, or any mathematical formalism (other than, perhaps, MWI) describe the collapse of the wavefunction?

 

[ZapperZ]

How does the Schroedinger equation, or any mathematical formalism (other than, perhaps, MWI) describe the collapse of the wavefunction?

Look at the postulates of QM!

Besides, what does a "collapse" have anything to do with being a "particle" or a "wave"? If the system is a sum of its eigenstates, all you get after a measurement is still one of its eigenstate, which can still be a "wavefunction". What does this have anything to do with "particle" or "wave"?

I think you have missed or didn't understand what I meant by the "formulation". It isn't just ONE equation. It is the whole theoretical concept behind the description. You can set up the Schrodinger equation, or you can set up the Hamiltonian, typically via 2nd Quantization. It doesn't matter. You still get only one consistent formulation.

I don't particular care about "interpretation", and if we go by Feynman, neither did he. Unless you first understand the exact formulation, then it is useless to argue about interpretation, because what exactly is it that you're trying to interpret? That's like a blind man trying to interpret a painting.

Zz.

 

[peter0302]

Ok, I'm probably not using the terms right but what you said about eigenstates helps me formulate the argument (hopefully) slightly better.

What I mean by "particle-like" behavior is precisely the removal of eigenstates of the particle (and its entangled cousins) after a measurement. So, for the photon in a double slit before measurement, the wavefunction is .5|slitA>+.5|slitB>. Once you see it at slitA, the wavefunction is just 1*|slitA>, or vice-versa. (I could be using the wrong notation; I'm just an admitted hack). The former I'd call "wave-like", the latter I'd call "particle-like." Does that help frame the discussion better?

then it is useless to argue about interpretation, because what exactly is it that you're trying to interpret? That's like a blind man trying to interpret a painting.

Well, I'm not going to be able to get a physics PhD anytime soon. :) I still hope I'll be able to comprehend this a little better though!

 

[ZapperZ]

Ok, I'm probably not using the terms right but what you said about eigenstates helps me formulate the argument (hopefully) slightly better.

What I mean by "particle-like" behavior is precisely the removal of eigenstates of the particle (and its entangled cousins) after a measurement. So, for the photon in a double slit before measurement, the wavefunction is .5|slitA>+.5|slitB>. Once you see it at slitA, the wavefunction is just 1*|slitA>, or vice-versa. (I could be using the wrong notation; I'm just an admitted hack). The former I'd call "wave-like", the latter I'd call "particle-like." Does that help frame the discussion better?

No, it doesn't.

The fact that one can actually write such a wavefunction and describe ALL observed phenomena is my argument that it is just ONE single description. It is the observable (or the operators) that determine what you get upon measurement. If you put a detector at one of the slit, then you've removed the superposition of path that the system have and the problem setup now gives you one or the other eigenstate. This came from the same, consistent premise. The fact that you are still using the eigenstates means that the mathematics is the same.

Now compare that to the drastic change you have to make in classical physics when you go from "particle" description to "wave" description. It is not even close. Do you get a particle if you simply select one harmonic out of the superposition of many within the classical wave description?

Zz.

 

[monish]

How does the Schroedinger equation, or any mathematical formalism (other than, perhaps, MWI) describe the collapse of the wavefunction?

You're right. The collapse of the wave function is a direct result of interpreting physics in terms of particles. I would say that particle descriptions are the basic source of all the paradoxes and strange things that baffle people about quantum mechanics.

I wouldn't worry too much about what ZapperZ is saying. He's misinterpreting the whole concept of duality. Duality doesn't mean you use waves to explain some things and switch to particles to explain other things. It means there are two entire, consistent ways of describing the universe: either you do it with particles or with waves. The mathematical results come out the same in either case. It's just the interpretations that are different.

People have done a lot of work on building up the particle interpretation and have basically got it working. The cost, which they're willing to pay, is that you get all these philosophical issues of causality and probability. Along the way, they've come up with quite a few half-baked "proofs" to the effect that it's impossible to explain such-and-such using waves. The most famous of these so-called proofs have been effectively rebutted over the course of time, but people keep repeating them and coming up with new ones.

It's an open question as to whether duality, in the sense I've explained it, actually describes the universe. As I said before, it's not a popular concept among physicists.
What some of them seem to forget is that there's a difference between the following statements:

1. "I don't know how to explain such-and-such using waves".

2. "It's impossible to expalin such-and-such using waves".

People often say #2 when they're only entitled to say #1.

Marty

 

[ZapperZ]

Fine. Look at a 2-spin system.

|\Psi> = a_1|up> + a_2|down>

Can you tell me where is this "wave"? If I make a measurement of the spin state, and get, say |down>, can you explain where in here is there a "particle"? Was this particle there before? Why?

In the Delft/Stony Brook experiment where there is a superposition of the supercurrent that has been equated to the Schrodinger Cat-state, they make a measurement of the coherence energy gap. Can you please show me where the "wave" and/or "particle" in those systems before and after such measurement?

At some point, you have to consider that you are getting stuck and paying way too much emphasis on words without understanding the formulation, which should have been the other way around. I also haven't seen anyone disputing the fact that in most physics papers, the issue of "wave" or "particle" have very seldom cropped up. It is obvious that this is a non-issue for most physicists. Why is it such a big deal here? Have you run out of things to puzzle on? I can give you plenty if you need some.

Zz.

 

[peter0302]

The cost, which they're willing to pay, is that you get all these philosophical issues of causality and probability.

Oh, it's more than that. It seems QM transcends spacetime all together. How about Wheeler's example where the paths of two entangled photons bent around a black hole that eventually arrive on Earth are determined by how they're measured on Earth light years away and years after they're sent? Only way that works is if the "collapse" is non-local, non-deterministic, and non-temporal. And no formalism I'm aware of can reconcile that with relativity.

You either have to believe in time travel (Cramer), stick your head in the sand (Copenhagen), or smoke something (MWI) to explain it. ;) (no offense to MWI believers - I just tend to be flippant now and then).

 

[peter0302]

I also haven't seen anyone disputing the fact that in most physics papers, the issue of "wave" or "particle" have very seldom cropped up. It is obvious that this is a non-issue for most physicists. Why is it such a big deal here? Have you run out of things to puzzle on? I can give you plenty if you need some.

You're not seriously telling us that you think the non-local collapse of the wavefunction is not a big deal are you? I think that's the $64,000 question of the 21st century, personally. Wave models can explain it, but as monish said, fail for other reasons. And particle models cannot. I think that's a big deal.

That said, I do not deny that I have much too much time on my hands.

 

[ZapperZ]

You're not seriously telling us that you think the non-local collapse of the wavefunction is not a big deal are you? I think that's the $64,000 question of the 21st century, personally. Wave models can explain it, but as monish said, fail for other reasons. And particle models cannot. I think that's a big deal.

That said, I do not deny that I have much too much time on my hands.

But your ability to actually say "non-local collapse" came out of current formulation of QM which didn't switch from one formulation to another! Don't you see that?

You are being mired by needing to "explain" why such-and-such occurs, and you're confusing that by thinking you can explain it by going back and forth between "particles" and "waves". And I haven't even started to question you on how you think "waves" would explain such "non-local collapse", considering that in QM, there's no physical anything that connects those remote properties. Your "wave" nor "particle" does nothing to explain such entanglement or have they been detected.

I still want you to explain how the collapse of the example of my spin states somehow implied something went from a wave to a particle. You are going off on using more complex example of quantum entanglement, yet ignoring a simple example that I've given. Unless you can illustrate it using something we know very, very well already and on a very simple scale, then what hope do you have that your "model" will work with something that has an added layer of complexity such as entanglement?

Zz.

 

[peter0302]

Fine. Look at a 2-spin system.

|\Psi> = a_1|up> + a_2|down>

Can you tell me where is this "wave"? If I make a measurement of the spin state, and get, say |down>, can you explain where in here is there a "particle"? Was this particle there before? Why?

Ok, to me, wave is the ability for there to be two different, superpositioned states which can interfere with one another (such as with the double slit). The wave can exist at multiple places in spacetime, and can share space with other waves (interference).

Particle is when something exists in one place in one time and nowhere else; obeys the Pauli exclusion principle; and does not interfere with itself.

So, in your example, any time there is a non-zero value for two mutually exclusive states, that's a wave. If we had:

|\Psi> = 1|up> + 0|down>

I'd call that a particle.

 

[ZapperZ]

Ok, to me, wave is the ability for there to be two different, superpositioned states which can interfere with one another (such as with the double slit). The wave can exist at multiple places in spacetime, and can share space with other waves (interference).

Particle is when something exists in one place in one time and nowhere else; obeys the Pauli exclusion principle; and does not interfere with itself.

So, in your example, any time there is a non-zero value for two mutually exclusive states, that's a wave. If we had:

|\Psi> = 1|up> + 0|down>

I'd call that a particle.

Why is that a particle? All I've given you is the spin state? I didn't say that it is at a particular location!

When you do a Fourier sum of a number of harmonics, each one of them can have their own frequency or wave number k. If I filter it out and select only ONE k, I've done the very same thing as in that wavefunction above. Yet, you are calling this harmonic, which really is a true wave, a "particle"? This makes no sense.

Zz.

 

[peter0302]

I'm just using that as an example. I should have said "particle-like" property or "Wave-like" property. And, yeah, a single harmonic of a standing wave looks a lot like a particle in my opinion. Which goes to my question of why not JUST waves?

 

[ZapperZ]

I'm just using that as an example. I should have said "particle-like" property or "Wave-like" property. And, yeah, a single harmonic of a standing wave looks a lot like a particle in my opinion. Which goes to my question of why not JUST waves?

And now you're changing position. So now how would you want to explain the distinct spot on a detector when a photon hits it? And how would you want to use a wave to explain the which-way experiment? You also want an electron to be nothing more than a "wave" under all circumstances?

How about "why not just use QM as it is?"

Zz.

 

[peter0302]

I don't have a position, but my question was what if the distinct spot on the detector was a result of the interaction of two waves - one, the "free" electron, the other, one of the electrons in the detector. I.E. the particle-like properties that are observed come merely from the interaction of two waves, and that the idea of a free particle has no physical meaning.

I always come back to the fact that the only reason we "observe" anything anywhere ever is because of interaction. We are _completely_ ignorant as to what is going on before and after the interaction. The free electron might as well be schroedinger's cat before it hits the detector. How do we know it's not a wave? How do we know that there is ANYTHING there other than a potential before and after the interaction?

How about "why not just use QM as it is?"

Soemtimes it's when no one even realizes anything is majorly wrong with the paradigm that a groundbreaking paradigm shift is needed. In 1905 no one was saying "Gee, Newtonian mechanics breaks down at speeds close to the speed of light. We need to fix this!" It was more like "Gee, it's pretty weird that light doesn't change speed with the Earth. Oh well, Newton works anyway so who cares." As a layperson, it discourages me to see some physicists (not saying you're doing this) express some of the same "we've discovered just about everything" sentiments that people had in 1900.

 

[ZapperZ]

I don't have a position, but my question was what if the distinct spot on the detector was a result of the interaction of two waves - one, the "free" electron, the other, one of the electrons in the detector. I.E. the particle-like properties that are observed come merely from the interaction of two waves, and that the idea of a free particle has no physical meaning.

I always come back to the fact that the only reason we "observe" anything anywhere ever is because of interaction. We are _completely_ ignorant as to what is going on before and after the interaction. The free electron might as well be schroedinger's cat before it hits the detector. How do we know it's not a wave? How do we know that there is ANYTHING there other than a potential before and after the interaction?


Soemtimes it's when no one even realizes anything is majorly wrong with the paradigm that a groundbreaking paradigm shift is needed. In 1905 no one was saying "Gee, Newtonian mechanics breaks down at speeds close to the speed of light. We need to fix this!" It was more like "Gee, it's pretty weird that light doesn't change speed with the Earth. Oh well, Newton works anyway so who cares." As a layperson, it discourages me to see some physicists (not saying you're doing this) express some of the same "we've discovered just about everything" sentiments that people had in 1900.

But the fact the Newton did NOT work under certain circumstances means that we have to formulate something new. Nowhere in what you have described here is there any indication of something that QM could not describe. All you have argued here is nothing more than simply a matter of TASTES. You are using that as justification to come up with something completely unverified with your "2-waves" scenario.

At least QM works, and it works empirically. That is more than what can be said about your speculation on how some of these things should be explained. I would think that if you question QM even with all it successes, you'd be even MORE uncomfortable with coming up something so speculative that it has no empirical support.

I think I am done with this thread. You have gone full circle and shifted position a few times. It is difficult to pin point the exact issue when things are being made up as one goes along. We are now back at the true "wave-like" and "particle-like" description that I started with way in the beginning, and not just "wave collapse" puzzle. The fact that a "quantum particle" unlike the classical description that we are so familiar with seems to be something that you have a difficulty of grasping. I've seen way too many system in which the so-called "wave-particle" duality is the LEAST of the weird and puzzling things that can happen. Try, for example, observing the "spin" and "charge" of a quasiparticle moving separately instead of sticking together with that quasiparticle, or having the smallest charged particle going through a constriction having only 1/3 of an electron's charge. There are tons of other astonishing observations and theoretical description that make that "wave-particle duality" mere child's play. Yet, QM's description has the ability to account for all that. This amazing theory is what you are so quick to dismiss.

Zz.

 

[peter0302]

Well, ok, but I'm not dismissing anything. I'm just asking questions because, really, I don't know, and was hoping to be educated by people who know more than me. Instead, what you're essentially saying is that my question is not worth asking, which, you'll forgive me, is not very helpful.

 

[CaptainQuasar]

Instead, what you're essentially saying is that my question is not worth asking, which, you'll forgive me, is not very helpful.

I think the problem is that the particle/wave duality is a concept that arose when science didn't have or didn't accept QM. ZapperZ is saying that if you accept QM the concept particle/wave duality isn't intelligible. It's like if you accepted relativity and then asked "but what if a massive particle did go faster than the speed of light?"

 

[ZapperZ]

I think the problem is that the particle/wave duality is a concept that arose when science didn't have or didn't accept QM. ZapperZ is saying that if you accept QM the concept particle/wave duality isn't intelligible. It's like if you accepted relativity and then asked "but what if a massive particle did go faster than the speed of light?"

I can't say it any better than what CaptainQuasar has mentioned.

In physics, sometime the nature of our question is almost as important as the answer that we seek. We are forced to reexamine just what exactly is it that we are asking, and the nature of the property that we are trying to determine. This is why you can't just toss around with little regard to what is meant by "wave" and "particle" and how we are encumbered by our familiarity of them in classical physics.

This is what we tried to do when we wrote the FAQ, to force someone to reexamine how we categorize something with some label that could, in fact, be quite meaningless when applied to the quantum realm. The question that we ask may not be meaningful. Do a search on the "size of a photon" on here. You'll find that I've echoed the same thing.

Zz.

 

[lightarrow]

At this point there is something I don't understand: if we only have one formalism to describe quantum objects (and not wave and particles), why there is a branch of physics called "particle physics"?

 

[ZapperZ]

At this point there is something I don't understand: if we only have one formalism to describe quantum objects (and not wave and particles), why there is a branch of physics called "particle physics"?

.. or condensed matter physics, or nuclear physics, or quantum optics, etc...

These fields apply quantum mechanics/QFT to specific areas of physics. "Particle physics" studies the so-called elementary particles typically at the high energy scale. That's why it is also called high energy physics. Condensed matter study particle interactions when there's a gazillion of them via many-body physics, etc.. etc.

But they all use the same "recipe".

Zz.

 

[peter0302]

I understand that the terminology I was using was perhaps not the best, but I have yet to hear anyone argue that the current QM formalisms are adequate at doing anything other than predicting the outcome of an observation - they seem to bear no resemblence to physical reality. Netwon's mechanics were once in the same position. The "wave-particle" duality, or whatever you want to call it, as exemplified in the recent entanglement experiments, show us that QM has a long way to go before it can be said to be an accurate description of reality at the subatomic level. I'm not rejecting it, but it's definitely not the whole picture.

It's like if you accepted relativity and then asked "but what if a massive particle did go faster than the speed of light?"

Tachyons?

 

[monish]

I think the problem is that the particle/wave duality is a concept that arose when science didn't have or didn't accept QM. ZapperZ is saying that if you accept QM the concept particle/wave duality isn't intelligible. It's like if you accepted relativity and then asked "but what if a massive particle did go faster than the speed of light?"

I can give a true example of particle-wave duality that everyone should agree with: the theory of phonons. No one argues that sound travels through a solid as waves, and that the vibrations of a solid can be analyzed in terms of the standing modes of these waves. It turns out that someone came up with a mathematically equivalent way of doing these problems where the vibrational energy is analyzed in terms of particles called "phonons". The "duality" is that everything you can calculate according to one picture, you can also calculate according to the other picture.

 

[ZapperZ]

I can give a true example of particle-wave duality that everyone should agree with: the theory of phonons. No one argues that sound travels through a solid as waves, and that the vibrations of a solid can be analyzed in terms of the standing modes of these waves. It turns out that someone came up with a mathematically equivalent way of doing these problems where the vibrational energy is analyzed in terms of particles called "phonons". The "duality" is that everything you can calculate according to one picture, you can also calculate according to the other picture.

As a condensed matter physicist, I work with phonons all the time. You never treat phonons as 'waves'. When you are using the phonon picture, you are already invoking QFT, which has no waves or fields!

There's a very good paper on the "visualization" of phonons that illustrates this very well.

S.C. Johnson and T.D. Gutierrez, Am. J. Phys. v.70, p.227 (2002).

Furthermore, I would like to see how one uses the 'wave' picture to derive at the coupling between electron and the lattice vibration to get the formation of Cooper Pairs in conventional superconductivity.

Zz.

 

[ZapperZ]

I understand that the terminology I was using was perhaps not the best, but I have yet to hear anyone argue that the current QM formalisms are adequate at doing anything other than predicting the outcome of an observation - they seem to bear no resemblence to physical reality.

What physical reality? How are you able to know that there is a physical reality that doesn't resemble what QM is describing? It appears here that you're making quite a lot of guess work.

Netwon's mechanics were once in the same position. The "wave-particle" duality, or whatever you want to call it, as exemplified in the recent entanglement experiments, show us that QM has a long way to go before it can be said to be an accurate description of reality at the subatomic level. I'm not rejecting it, but it's definitely not the whole picture.

What recent entanglement experiments? As far as I can tell, the experiments themselves are showing that large classes of local realistic theory have been disproven by the experiment, and that the results are consistent with QM. Read a thread in the General Physics forum on Recent Noteworthy Papers, especially on the most recent experiment testing the Leggett inequality.

So here, it appears that QM has a huge leg up on your speculation.

Zz.

 

[f95toli]

I understand that the terminology I was using was perhaps not the best, but I have yet to hear anyone argue that the current QM formalisms are adequate at doing anything other than predicting the outcome of an observation - they seem to bear no resemblence to physical reality. Netwon's mechanics were once in the same position.

But how do you even know that there is such a thing as a "reality"? We can of course assume that there is such as thin which then would beindependent of observations but that has nothing to do with physics. Physics is- by definition- a science where we try to predict the outcome of experiments and the only way to observe the an outcome is of course by observation. Everything else is is just metaphysics.

Edit: Also, you should take a look at Gröblacher et al, Nature 446, 871-875 (2007). Their experiment seems to indicate that non-local realisic theories do not work unless they are modified. Hence, one interpretation is that the usual concept of a "reality" might have to be abandoned.

 

[jtbell]

I have yet to hear anyone argue that the current QM formalisms are adequate at doing anything other than predicting the outcome of an observation - they seem to bear no resemblence to physical reality.

How can we possibly know what physical reality is, other than by comparing the predictions of our theories with experimental observations? We have a mathematical formalism (QM) that agrees with experiment, so far. People have come up with a variety of interpretations (ideas of physical reality) for this formalism. All of these interpretations have "strange" features, in different ways. Since they are constructed to fit the formalism, they are apparently incapable of being distinguished by experiment. How are we to choose among them in an objective way?

 

[peter0302]

What recent entanglement experiments? As far as I can tell, the experiments themselves are showing that large classes of local realistic theory have been disproven by the experiment, and that the results are consistent with QM.

I was referring to DCQE (which I know Copenhagenists think is no big deal), and one of the recent Wheeler-style exerpiments:

http://arxiv.org/pdf/quant-ph/0610241

which I quote:

The quantum “mystery which cannot go away” (in Feynman’s words) of wave-particle duality is illustrated in a striking way by Wheeler’s delayed-choice GedankenExperiment.

Since they are constructed to fit the formalism, they are apparently incapable of being distinguished by experiment. How are we to choose among them in an objective way?

As (I believe) Feynman said, you need a hypothesis that fits all of the existing data but makes different predictions about experiments that haven't yet been tried, but can be. That's when you potentially learn something new about the nature of reality.

Edit: Also, you should take a look at Gröblacher et al, Nature 446, 871-875 (2007).

I read the abstract online - sounds fascinating. Any idea where I can get a copy of the whole article? Thanks!

 

[ZapperZ]

I was referring to DCQE (which I know Copenhagenists think is no big deal), and one of the recent Wheeler-style exerpiments:

http://arxiv.org/pdf/quant-ph/0610241

Yeah? And?

I'm not sure why this would somehow support what you've been arguing considering that this which-way experiment is more in line with what *I* have been saying. If you know about this, and you STILL asked me why can't everything be just "waves", then either you somehow missed your own contradiction, or something isn't kosher here.

Zz.

 

[peter0302]

Yeah? And?

AND these experiments show that the wave-particle duality is still real. All I'm asking is whether particle-like behavior can be explained via the interaction of two waves. Monish kindly answered that some phenomena could be, while others could not be at present. You, in another thread, said essentially the same thing, though you clearly place more weight in the particle model than he does. That's all the answer I was looking for. Thus, I don't understand your reaction to my question or how we got on a tangent about the meaning or existence of the duality.

or something isn't kosher here.

I assure you if I were trying to cause trouble this would not be my first choice of methods.

 

[ZapperZ]

AND these experiments show that the wave-particle duality is still real. All I'm asking is whether particle-like behavior can be explained via the interaction of two waves. Monish kindly answered that some phenomena could be, while others could not be at present. You, in another thread, said essentially the same thing, though you clearly place more weight in the particle model than he does. That's all the answer I was looking for. Thus, I don't understand your reaction to my question or how we got on a tangent about the meaning or existence of the duality.

No it isn't! It appears as if all you read was the abstract! Read the paper carefully and tell me afterwards that this is still what you think. Hint: They used single-photon sources, which was a reference I gave you way back in this thread. And read the final line of that paper:

"Once more, we find that Nature behaves in agreement with the predictions of Quantum Mechanics even in surprising situations where a tension with Relativity seems to appear."

So who here suggested that QM can be superceded?

I assure you if I were trying to cause trouble this would not be my first choice of methods.

Then it baffles me how, when you're in possession of such a paper, that you STILL had no qualms in making that statement.

Zz.

 

[peter0302]

I *quoted* the abstract because it is the clearest statement they make on the topic. However I (re)read the body of the paper and I see nothing inconsistent with that statement, nor my assertion that the photon self-interferes (wave-like) sometimes, and does not (particle-like) other times. The part you quote about a tension with relativity doesn't go to that at all.

You seem to be taking issue with my assertion that while QM provides (so far) accurate predictions of observations, it doesn't give us the whole picture of reality, i.e. it doesn't explain _why_ we observe what we observe. Far greater minds than mine believe this. Instead, all I asked was if a wave-interaction model could work. Clearly it cannot, and the answer to my question is 'no.' As far as I'm concerned I've received a satisfactory answer.

 

[CaptainQuasar]

I understand that the terminology I was using was perhaps not the best, but I have yet to hear anyone argue that the current QM formalisms are adequate at doing anything other than predicting the outcome of an observation - they seem to bear no resemblence to physical reality.

No, it doesn't resemble a reality we could feel or touch, or any "sensible" reality that Einstein could imagine. That's why it really frustrated Einstein and has frustrated lots of other people during the last eighty-odd years. Supposedly some scientists in the late 1920s literally became suicidal as it became clear that QM was the only option that could carry physics forward.

The "wave-particle" duality, or whatever you want to call it, as exemplified in the recent entanglement experiments, show us that QM has a long way to go before it can be said to be an accurate description of reality at the subatomic level.

I think you're making a mistake in interchanging the concepts "accurate" and "realistic". It's possible to come up with mechanisms that might place more "realistic" mechanisms behind the mathematical behavior we see but doing that requires coming up with crazy, complex structures and explanations that we have absolutely no experimental evidence of. Any deeper mechanisms that underlie the current QM may not be things that seem "real" to the human mind that only experiences things on the macro scale.

 

[peter0302]

I think you're making a mistake in interchanging the concepts "accurate" and "realistic". It's possible to come up with mechanisms that might place more "realistic" mechanisms behind the mathematical behavior we see but doing that requires coming up with crazy, complex structures and explanations that we have absolutely no experimental evidence of. Any deeper mechanisms that underlie the current QM may not be things that seem "real" to the human mind that only experiences things on the macro scale.

True enough, but I think the value in looking for "realistic mechanisms," that is to say any deeper understanding than the ability to predict, is more than superficial. There is, after all, potentially the ability to _influence_ quantum outcomes. Even if that's a pie in the sky hope, at least it seems a good motivation to keep looking deeper.

Or I suppose I might simply be going nuts like the scientists of the 1920s you mentioned. :)

 

[ZapperZ]

I *quoted* the abstract because it is the clearest statement they make on the topic. However I (re)read the body of the paper and I see nothing inconsistent with that statement, nor my assertion that the photon self-interferes (wave-like) sometimes, and does not (particle-like) other times. The part you quote about a tension with relativity doesn't go to that at all.

But think about what I said WAY in the beginning of this, that there is ONE, and ONLY ONE, single formulation to explain BOTH the so-called wave-like and particle-like behavior. ONE! That paper clearly demonstrates this! We went through such painful argument back and forth, when what I've been trying to illustrate all along has been in your very possession! And you don't realize this?

You seem to be taking issue with my assertion that while QM provides (so far) accurate predictions of observations, it doesn't give us the whole picture of reality, i.e. it doesn't explain _why_ we observe what we observe. Far greater minds than mine believe this. Instead, all I asked was if a wave-interaction model could work. Clearly it cannot, and the answer to my question is 'no.' As far as I'm concerned I've received a satisfactory answer.

Show me what area of physics actually "explains" anything at the very fundamental level. Until you can do that, what you have asked for has never existed and you're picking on QM the same way you're picking on photons without realizing that the rule applies to all of them.

Zz.

 

[CaptainQuasar]

True enough, but I think the value in looking for "realistic mechanisms," that is to say any deeper understanding than the ability to predict, is more than superficial.

Oh, definitely there's value! Especially because the clever attempts to do so have to be met with a serious response from science and hopefully are testable for some kind of experimental confirmation or disproof. And that keeps giving us more shots from more angles of what's actually going on, decade after decade. And with stuff this hard to grok it doesn't hurt to keep hearing "yes, it really, really works that way" if each explanation can clear up the picture a little bit.

 

[CaptainQuasar]

Hey, maybe a useful perspective is to go back even further. The fact that photons emitted by matter must be released in quantized amounts of energy, how Planck had to solve the ultraviolet catastrophe problem at the end of the 18th century, is what led to all this. That doesn't make any sense either, right? It doesn't have what we'd call realism. But trying to explain that, trying to make it realistic, is why we ended up with quantum mechanics.

So I think in not trying to be too aggressive in fitting the square pegs of QM into the round holes of realism physicists are operating on the "be careful what you wish for" principle, it's not that they're trying to be obstructive of anyone understanding physics.

 

[monish]

...all I asked was if a wave-interaction model could work. Clearly it cannot, and the answer to my question is 'no.' As far as I'm concerned I've received a satisfactory answer.

I don't think anyone has put forth conclusive arguments throughout this discussion to rule out the possibility of a wave-based model which would provide all the same conclusions as standard qm with its particles and "collapse of the wave-function". The paper you quoted claims to have ruled out all possible "semi-classical descriptions" of light. This is based on supposedly being able to generate one photon at a time and send it through an apparatus at will. I don't think this is as easy as it's made out to be.

Just because someone doesn't know how to explain something with waves doesn't mean it can't be done.

 

[ZapperZ]

Just because someone doesn't know how to explain something with waves doesn't mean it can't be done.

Luckily, this is physics, and not philosophy. We demand to be shown that something can be done first before we adopt it as valid.

Maybe you might want to consider the Philosophy forum, which might be more suitable for such speculation devoid of evidence.

Zz.

 

[CaptainQuasar]

So after considering the https://www.physicsforums.com/showthread.php?t=200819" than "wave" is for these purposes but specifically using "particle" is only confusing people between ballistic Newtonian particles, which include tennis balls and planets as well as elementary particles, and the QM entity that is referred to as a particle. And it totally doesn't help that people will say things like "well theoretically there's a vanishingly small likelyhood that a tennis ball could quantum tunnel through your racket too!"

For example, consider someone who never learned any classical physics at all, who started off in QM and got to fully understand it before anything else (which doesn't actually happen of course, this is hypothetical). When confronted with the phenomenon of light bending in a prism and how similar that is to the propagation of sound in air or other mediums, I don't think such an individual would question the existence of photons or start looking for a wave medium underneath QM, they would simply say "Oh wow, you're right! Photons passing through a prism is mathematically just like a wave analysis of vibration!"

Remember that the wave-like similarity between light and sound isn't obvious or realistic either, it's just as much an artifact of scientific learning as QM is. Biorhythms are waves too but biologists don't get any "but what about the heartbeat / chambered pump duality?!?" Physics is carrying around a ton of linguistic and historical baggage.