Wave vs. Particle-Like Behavior

[CaptainQuasar]

Another abstract ontological problem that comes into this is that some hoity-toity philosophical academic types insist that the conclusion is equivalent to the sum of the dialectic, rather than the dialectic being something that may or may not provide perspective on and texture to the conclusion. So they really, really believe in teaching the dialectic, the entire history of physics at once, even at the cost of in some cases making the student unable to understand what science's best guess is now in the 21st century.

 

[Gordon Watson]

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.

How about:

WAVICLE? Google count = 25,300
PARTAVE? Google count = 147.

 

[Xeinstein]

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?

I think in modern view of quantum field theory, every particle has its associated fields.
Particles are just excitation of quantized field, like SHO is quantized

 

[CaptainQuasar]

How about:

WAVICLE? Google count = 25,300
PARTAVE? Google count = 147.

Heh heh, good one JenniT. But I think that those might not be so good either because they still allude to "particle" and "wave" and my impression is that these QM entities we're talking about aren't either, really - my point is that they're something different entirely than the things in classical physics they're analogized to.

Someone up above pointed out that electrons very rarely behave as particles but do they actually behave like waves in a medium that frequently, either? Sure they submit to analysis with trigonometric functions ("wave mechanics", the mathematics of how waves in a medium behave and its outgrowth) but so does everything, even heartbeats as I mentioned. But sine doesn't appear in the Schrödinger equation so frequently referred to as the "wave function" during the last eighty years. (Does it? Definitely not in the basic formulas but I haven't done a lot with the Schrödinger equation in a while, physics is not my profession.) (Mathematics and software engineering are, BTW.)

It seems as though it's probably terminology issues like this that prompted Gell-Mann to pull "quark" out of James Joyce for a name, specifically seeking out a nonsense word rather than even remotely attempt to be descriptive.

 

[peter0302]

Something is still bothering me about this discussion. Could someone explain _how_ the Schroedinger equation predicts the result of the Wheeler experiment? Specifically, how does the equation take into account the presence or absence of the second beam splitter?

The way I understand it, this is taken into account through the wave-function itself, into which the behavior of the photon in the presence or absence of the second beamsplitter is imported. But this is merely based on our experimental observations, is it not? So the logic seems rather circular. The reason the formalism predicts what we see is because we constructed the formalism based on what we saw.

But if I'm misunderstanding please let me know. Thanks!

 

[CaptainQuasar]

So the logic seems rather circular. The reason the formalism predicts what we see is because we constructed the formalism based on what we saw.

But isn't this true of any science, including classical wave mechanics and particle ballistics?

The formalism is a mathematical model we created that emulates and predicts the behavior observed in experiments. So yeah, for an experiment that was either used to construct the formalism or which confirms the formalism you've got that kind of circular relationship. It's when you come up with a new experiment that doesn't agree with the formalism that we say we're going to need a new formalism. The formalism isn't any more fundamentally connected to some underlying "reality" than is the raw experimental data or anything else in science.

 

[peter0302]

Well, one of the goals is to boil down all the observations into a small number of postulates or axioms, and then build a logical formalism on top of those that predicts everything else that is observed and hopefully more. That's how Newton and Einstein did it. But I don't see that with QM. Instead I see a lot of observations that are to this day not fully understood, and virtually no success in boiling them down to more fundamental axioms, so instead we have a formalism that is essentially drawing a circle around all of the experimental data and calling it a theory.

At the very least, it is rather surprising to me that as the subject matter becomes smaller, the "axioms" become much more complex and high in number. If we were to translate the laws of physics into a computer program, we'd see an inordinate amount of complexity at the quantum level. I'd have expected God to write more elegant code.

 

[CaptainQuasar]

Well, one of the goals is to boil down all the observations into a small number of postulates or axioms,

I know that's what Newton and Einstein did but I don't think that there's any assumption or goal like that in science. It's nice when it works out that way but it's not wrong or assumed to be out of touch with reality when it doesn't. I would like it if it worked out that way too but it hasn't so far.

I'd have expected God to write more elegant code.

You're God's quality assurance tester?

Actually, I'm a software engineer and you're reminding me here of managers who insist that there just has to be a really simple way to solve what's actually a very complicated problem. It's not to say that there aren't sometimes simple solutions to complicated problems but to just insist that there has to be a simple, elegant solution is often erroneous in my experience.

 

[peter0302]

Hah. Well I was a CS major in college, so I got indoctrinated with the "elegance" requirement pretty completely. I won't deny that it guides some of my biases about physics. But I cannot deny the elegance of the Theory of Relativity compared to Quantum Mechanics, and I cannot help but prefer the former approach.

Ultimately, any theory of everything that cannot be completely described in one sentence and is not understandable to a 10th grader is probably too complicated to be correct.

 

[CaptainQuasar]

Ultimately, any theory of everything that cannot be completely described in one sentence and is not understandable to a 10th grader is probably too complicated to be correct.

Well, I'm glad that you know so much about the way universes have to be made. I've got some Creationist friends you might get along with.

 

[peter0302]

On the contrary, that thought is anti-creationist. Only an intelligent being could design rules so complex and disjointed. The laws of a universe without a creator should flow as inevitably as 2 + 2 = 4. Otherwise, how can you not see a designer behind them?

 

[monish]

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. "

I'm going to make an observation about the experiment quoted above. Bascially, it splits a beam into two separate paths, then recombines them and looks for interference. If you look for which path was followed, the interference goes away.

Up to this point the experiment would be consistent with a wave description. But then they do two things:

1. They contrive to operate the apparatus "one photon at a time".

2. They make the choice of whether to observe the path AFTER the photon beam has already been split.

It's a very impressive experiment but I have to point out one peculiar aspect which leaves room for a shadow of doubt about the intended conclusion: the interference pattern is NOT based on the path length difference. It's created AFTER the "beams" are recombined using something called a "KDP electro-optic modulator".

(edit:) My mistake: the EOM activates the second beam-splitter. Tilting the beam splitter varies the relative phase. Which takes place at the point of recombination.)

The whole point of the experiment is to show that the beams take one definite path if observed, and both paths simulataneously if not observed: "quantum wierdness". But wouldn't it be more convincing if the observed interference was caused by the path length difference? Yet that's not how they chose to do it.

 

[peter0302]

Isn't it because the beams always take both paths simultaneously until detection? Thus, the interference wouldn't be due to the path-length differene, but rather just due to the beamsplitters.

 

[monish]

Isn't it because the beams always take both paths simultaneously until detection? Thus, the interference wouldn't be due to the path-length differene, but rather just due to the beamsplitters.

Well, I think that's my point. Since the interference is due to something that happens at the beamsplitters, I don't think you can conclude that the photon took both paths simultaneously.

What I mean is that there is still a viable wave interpretation. Case 1, no recombination, the wave was split into path A or path B at the first beamsplitter. So there's no interference at the detectors. Case 2, with "recombination", you now have a device which sets up standing waves of multiple reflection between the second beamsplitter and the two detectors with the net effect that all the wave energy ends up in one of the detectors. I know that sounds farfetched, but it would seemingly have been easy to rule out such a scenario by letting the interference be governed by the path length difference. That's why I say it was peculiar that they didn't set up the experiment in this way. Because it leaves a loophole for the wave theory to survive.

That's what I mean by the wave-particle duality. For every particle explanation, there is a corresponding wave-based explanation which also works. The advantage of the wave-based explanations, where they exist, is that they provide a realistic mechanism for understanding what happens. It doesn't seem like the particle theories can ever do that.

 

[peter0302]

No, they can't, and if you read my other thread about the Afshar experiment, assuming I'm correct that the grid will never alter the detection rate, it literally means that the photons pass through the grid as though it wasn't there. That another area where the particle model breaks down completely. That's why I asked at the beginning of this thread whether we can consider particle "collision" as simply the interaction of two waves at a randomly chosen point in space.

 

[colorSpace]

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.

I guess this is a typo and what you meant is that in addition to (all) local realistic theories, now also large classes of non-local realistic theories have been disproven.

 

[peter0302]

Maybe. I don't think FTL theories have been disproven, especially not if one allows backwards-in-time signaling. That would be non-local, non-temporal realism.

 

[colorSpace]

AFAIK, Bohmian Mechanics isn't in those classes which have been disproven, even though it is non-local realistic.

 

[peter0302]

Bohmian mechanics is basically the same as pilot wave, right? I think the pilot wave idea is probably pretty close to what I've been suggesting in this thread.

 

[CaptainQuasar]

On the contrary, that thought is anti-creationist. Only an intelligent being could design rules so complex and disjointed. The laws of a universe without a creator should flow as inevitably as 2 + 2 = 4. Otherwise, how can you not see a designer behind them?

If you don't regard things like that as theological statements I don't think I can express to you what I'm talking about. If you're confident that you know what the nature of the universe is and therefore what its governing rules must be like go ahead and run with that but don't use it to critique science. (Using a priori beliefs about the universe to critique science is the way I'm saying that you're similar to a creationist, I'm not saying that your doctrine is similar to theirs.)

 

[peter0302]

I really don't want to give the moderators any more justification to lock this thread than they already have, but I disagree that my statement is theological. What I'm saying is that a simple theory is more likely to be correct, and therefore I personally favor theories involving small numbers of axioms to theories that just happen to fit the experimental data with no underlying understanding of why.

 

[CaptainQuasar]

... I disagree that my statement is theological. What I'm saying is that a simple theory is more likely to be correct...

You said "Only an intelligent being could design rules so complex and disjointed." I think you've made my point for me. But I don't think it's a reason to close the thread, I just think it's a reason to stop saying "QM cannot be true and accurate because it doesn't fit my aesthetics for what scientific theory should be like."

 

[peter0302]

"Only an intelligent being could design rules so complex and disjointed."

If the rules cannot be simplified to simpler, more fundamental postulates? Yes, I stand by that statement. If you look at the evolution of every physical system, be it cosmological, biological, or what have you, what we see again and again are very simple rules being applied across vast scales of space and/or time to create the complexity that exists today. The idea that there is extraordinary complexity at the most fundamental of levels runs counter to our experience in other areas of science.

And for the record, I never said QM cannot be true and accurate. I said QM doesn't tell us the whole story.

 

[CaptainQuasar]

Yes, I stand by that statement.

But do you stand by the assertion that it isn't theological?

And for the record, I never said QM cannot be true and accurate. I said QM doesn't tell us the whole story.

You're correct. I'm sorry, I mischaracterized what you were saying.

 

[peter0302]

You're right, I should stop at "simpler rules are more likely to be correct" and leave my subjective belief as to why out of it. :)

 

[Tanja]

I didn't follow the whole converstion and I'm pretty ill, right now. My conclusions could ground on a fever delusion.

Looking back to the equation of motion could help.

1.) Particles move according to the solutions of the Hamilton function H(p,q;t) = pv-L(q,v;t) with L the Lagrangian. The differential equations to be solved are dH/dq = dv/dt, -dH/dv = dq/dt and dH/dt =- dL/dt.
The equations are solved for space coordinates.
2.) Maxwell's equations are solved for the electric and magnetic field vector E and B. Because of the form (second derivative in space and in time) the solution consitst of sinand cosin (or written as an exponential).
3.) Schrödinger equation is solved for something with no physical meaning \Psi leading to a probability. (second derivative in space and one in time). Must also lead to a wavefunction but in the complex domain.

It depends on the potential and the specific equation of motion you have to use to describe potentials actions.

Probably it has been mentioned in a previous reply: de Broglie found out that each particle can be seen as a wave through the connection E = \hbar \omega and p = \hbar \k. That's like building a bridge between Lagrange and Maxwell. Another bridge between Schrödinger and Lagrange could be the density of states.

 

[colorSpace]

In quantum physics, the particle or wavicle, can be seen as a 'wavepacket' of waves that cancel each other out except where the particle is, AFAIK, probably what Tanja says above. The remaining wave segments which don't cancel each other out then explain how the wavicle is "smeared out" in probability over a range of positions or impulses. So these waves are not like classical waves, they do not reflect a certain classical state. In regards to a classical state, the uncertainty remains even when described as a wave.

(The interference pattern can be seen only with multiple photons, even though each photon's probabilities are determined by it.)

[Edit added:] Meaning, whether a photon behaves more like a particle or like a wave in a specific situation, it still won't have a certain position and impuls, not even in terms of a wave. It will be either here or there when measured, rather than distributed over the area like a classical wave.