[JP]

I don't think anyone was trying to say photons were a misconception.  Certainly what I meant, and what I think the the other posters meant, was that photons aren't as simple as many lay-explanations make them out to be.  They aren't, for example, little bullets zipping around. The QM description of them is a lot more complex than that.

However, they do certainly exist and are probably best thought of in terms of the photoelectric effect: as the smallest packets of energy of light available.

[yor_on]

Well, if you go by both waves and photons interactions you have one, as I see it, clear difference. Photons do their work 'instantly' (less than 10-9 s) as far as I now, waves don't. When it comes to how we model them outside a interaction we can't say we observe them.
=

Ah, this might sound like I don't have any use for waves. Well, if so, neither do I have it for photons
My personal favorite for the moment is the idea of a universe where we have pointlike insertions made into causality chains by our arrow, following a thin line. Not that I understands how it does it? But i think it allows for both phenomena to exist, and I don't have to care that much about what happens where we don't observe, as that doesn't need to exist. To me the interactions will be defined by the need for them, you could say that the relations crave them, or that our arrow creates them through the shape it has. Feynman used many paths and probability to explain it, but in my universe that becomes too many paths simultaneously, so I'll stick to those 'points made' that we 'observe', sort of

And if the arrow act this way macroscopically, giving us one timely procession, could I look at what happens in a QM perspective as something (time) 'widening' becoming 'whole processes'. Doesn't make much sense, does it? It's more of a feeling I have than anything touchable, but to me time is a very weird thing and the arrow even worse. It sort of would make time into a cone where we always are at its 'tip' with its base being somewhere at string theory or loop quantum theory where all shapes becomes the same, as observed from us. I know, that's pretty weird.

[JP]

Well, if you go by both waves and photons interactions you have one, as I see it, clear difference. Photons do their work 'instantly' (less than 10-9 s) as far as I now, waves don't. When it comes to how we model them outside a interaction we can't say we observe them.

Maybe it's the same kind if language issue at work here that I talked about in the "aether" thread.  Photons have a QM wave function and by the rules of QM, that wave can interact instantly and at a point.  Classical EM waves don't have these properties, since they have to play by classical rules.  Maybe it's unfortunate that the term "wave function" brings to mind classical waves, since they don't mean the same thing or play by the same rules. 

The full quantum theory, when applied, also explains why classical waves work so well for so many things.  It also explains why they don't work well for quantum effects, such as the photoelectric effect.

[Geezer (OP)]

What what it's worth, it strikes me that a nanosecond is a really long time. The semiconductor guys have been counting in picoseconds for a long time.

[yor_on]

This sums it up nicely

"The mechanism whereby the Maxwellian fields (which are continuous in space and time) interact with electric charge is via the Lorentz force law. In brief, the Maxwell/Lorentz force on charged particles occurs continuously in space and time. In Einstein's explanation of the photoelectric effect, the interaction between the field and a charged particle occurs impulsively, essentially at a given point in space/time."

As for how long 'instant' is? I used the links definition in my post. But I don't know how long it takes in 'reality'. If you look you will see that it states 'less than'? But as we are talking freeing 'electrons' that are particles of matter from a metal it needs to take some measurable time I think, as we will have an acceleration.

[lightarrow]

Although. Thinking of it Are you saying that you can explain the the photoelectric effect by waves now?

Certainly.
The "photon" concept is not required at all. How many people (including me) deceived for so many years  [] []

People much more prepared than me says the prove it's in Mandel and Wolf "Optical Coherence and Quantum Optics" (section 9.3):
http://www.amazon.com/Optical-Coherence-Quantum-Optics-Leonard/dp/0521417112#reader_0521417112

Unfortunately I don't have that book, but I don't have reasons not to believe it.

[lightarrow]

Well, if you go by both waves and photons interactions you have one, as I see it, clear difference. Photons do their work 'instantly' (less than 10-9 s) as far as I now, waves don't. When it comes to how we model them outside a interaction we can't say we observe them.

As yor_on wrote, how long 'instantly' is? It seems it's not exactly zero seconds.

The full quantum theory, when applied, also explains why classical waves work so well for so many things.  It also explains why they don't work well for quantum effects, such as the photoelectric effect.

But a "semiclassical" approach, where a classical EM field and a detector treated quantistically, really seems to work (see my previous post).

[JP]

Part of it's available on google books.

The semiclassical treatment works to an extent, but it has some issues, as they note in that chapter.  I haven't gone through the details, though.

[yor_on]

So we have a Quantum Mechanical approach to Waves explaining Photons? A contradiction in terms that one

QM = quanta, explaining Photons aka 'light quanta' as, ah, Waves?

Ahem?

[JP]

All the semiclassical model is explaining there is the photoelectric effect.  As you say, obviously photons themselves require the field to be quantized, since they're quanta.

But it's very interesting that the effect can be modeled without photons!  All my courses on QM used the photoelectric effect as a starting point for requiring quantized light.

[lightarrow]

So we have a Quantum Mechanical approach to Waves explaining Photons? A contradiction in terms that one

QM = quanta, explaining Photons aka 'light quanta' as, ah, Waves?

Ahem?

It doesn't explain photons, it explains the fact a detector "clicks" with discrete, definite energy and that the "clicks" are spatially localized. So the idea of a photon as a corpuscle travelling from source to detector is not necessary, in this case.

[yor_on]

I don't now Lightarrow, I've tried to localize any text on the Internet where Mandel state himself having explained the photo electrical effect as waves, but without success? If he had it should have been real big news as that should question the idea of everything being quanta (QM)? You can't have it both ways, not in QM, either it is quanta or it is not quanta, am I right?

So how about turning it around, can't you explain it as quanta too if so? All waves being quantified phenomena. Or strings Or loops Or quantum fuzziness. Awh..

Reading about solids and the way atoms lose their individuality, becoming 'whole entities' getting new unique properties, makes it even harder to see what photons /waves are in fact. How can a atom generate photons.  Have you seen this btw? Beautiful theory collides with smashing particle data
 
I think I'll stick to my own idea for the time being, naievly looking at it as being relations defining the interactions and outcome. Then I just need a explanation for where the 'light is' when not observed And that one I will solve by the metaphorical sword. They're not 'there', heh Anyway, my gut-feeling so far is still that photons are photons, waves are waves. They may have a common source, after all they're both 'light', but I suspect that source to be something different from what we envision today.

[JP]

I don't now Lightarrow, I've tried to localize any text on the Internet where Mandel state himself having explained the photo electrical effect as waves, but without success?

Try this:
http://tardis.ph.utexas.edu/~sudarshan/pub/1964_011.pdf

If he had it should have been real big news as that should question the idea of everything being quanta (QM)? You can't have it both ways, not in QM, either it is quanta or it is not quanta, am I right?

Well, we can describe the orbits of the planets really well with just Newtonian gravity.  Does that mean that General relativity is wrong?  Certainly not!  General relativity is of course the more accurate theory, but it's much more difficult to do the computations and it isn't needed to get good results in this case.

All Mandel et. al. did was to show that you can describe the photoelectric effect quite well with just classical light, assuming a quantized detector.  The photon model is still valid (and more accurate, though very complicated), but you don't need to use that model to get good results in this case.

[yor_on]

Thanks JP, I will look that up.

I read that USA had stopped teaching General relativity in their physics curriculum?
That's truly weird if true.

Found it.

"At the overwhelming majority of physics departments at American universities, even the most elite, key elements of basic physics are no longer taught. For example, I am aware of no American university that requires, for an undergraduate degree in physics, a course in general relativity, which is Albert Einstein’s theory of gravity. At the overwhelming majority of American universities, including Harvard, M.I.T. and Cal Tech, one is not even required to take a course in general relativity to get a Ph.D. in physics! As a consequence, most American Ph.D.’s in physics do not understand general relativity. If a problem arises that requires knowledge of Einstein’s theory of gravity, almost all American physicists can only look blank. This is in spite of the fact that general relativity has been known to be the correct theory of gravity for almost a century.

And it gets worse. The greatest achievement of physics since World War II has been the discovery of the Standard Model of particle physics, a unified theory of all forces and matter not including gravity. The electromagnetic force — light and radio waves — and the weak force responsible for radioactive decay, are shown to be two aspects of one force, the electroweak force, by the Standard Model. The Standard Model also explains how all fundamental particles obtain their mass and it predicts that matter can be directly converted into energy – which hints at a new energy source far more powerful than nuclear energy. The Standard Model has been experimentally confirmed, and some dozen and more Nobel Prizes in physics have been awarded for the discovery and experimental confirmation of the Standard Model. Yet I am aware of no physics department in the United States that requires a course in the Standard Model for an undergraduate degree in physics. Very few, if any, require a course in the Standard Model even for a Ph.D. in physics. It’s as if law schools stopped requiring students to take courses in crucial subjects like contracts and property law." Frank Tipler, professor of physics at Tulane University. .
==

Eh, I have this one if anyone is interested in the history of wave/particle duality,. Elements of the wave-particle duality of light. It's a master thesis from 2009. You don't need it JP, but I do

"In the first part we consider historical, theoretical and experimental aspects of the duality problem. We explain how the notion of duality has developed through the last 400 years. We discuss theoretical underpinnings of the duality emodied by Maxwell’s electromagnetic theory, quantization of electromagnetic modes, Fock’s states and coherent states. We critically review several experiments which serve to demonstrate the corpuscular or undulatory behaviour of light and matter; in particular we present how the photoelectric effect and the Compton effect can be explained using the undulatory model, and we critically review Grangier, Roger and Aspect correlation experiment.

In the second part we describe two illustrative experiments on the duality of light conducted at Quantum Optics Laboratory at University of Oslo. The results of the experiment allow us to discuss how coincidence measurements can be used to exhibit the corpuscular behaviour of light, and how Mach-Zender interferometry performed at very low intensity can be used to exhibit the undulatory behaviour at the (assumed) single-photon level. In addition, in the second part we review elements of theories closely associated with the experiment and the experimental setup: optical coherence, photocount and photon statistics, beam splitter models and Gaussian beams. A proposition for extending the semiclassical model is given, and shortcomings of the present beam splitter models are discussed.

In the third part of the thesis we consider first Afshar’s experiment and some of the critical response that it has been met with. Then we discuss how the wave-particle duality is to be understood in the standard interpretation of quantum mechanics, and how it could possibly be explained using either an alternative model for light or an alternative interpretation of quantum mechanics, and what difficulties such explanations present."

[Geezer (OP)]

Thanks JP, I will look that up.

I read that USA had stopped teaching General relativity in their physics curriculum?
That's truly weird if true.

Yes. George W. Bush thought it was better to teach the science of Creationism instead.

[lightarrow]

If he had it should have been real big news as that should question the idea of everything being quanta (QM)?

Not at all. JP answered you in the best way. However I'd like to add a bit: It's not easy, actually, to demonstrate the presence of the photon object in light. It requires experiments of coincidence counting on detectors at very low intensity and a statistical analysis of the results.

You can't have it both ways, not in QM, either it is quanta or it is not quanta, am I right?

It's both, you can't separate the concept of field from the concept of particles.

Reading about solids and the way atoms lose their individuality, becoming 'whole entities' getting new unique properties, makes it even harder to see what photons /waves are in fact. How can a atom generate photons.  Have you seen this btw?

It doesn't tell me much more than what is already clear to me. But if you read physics forums, you can be interested in this:
http://www.physicsforums.com/showthread.php?t=474537
Read what Arnold Neumaier says answering the various poster.

[yor_on]

I thought QM built on using a canvas whereupon your forces and quanta danced Lightarrow? That is, that it presumes a background. That is actually a different concept compared to Einsteins SpaceTime. Also I was under the distinct impression that all will be quanta in it.

Including waves?

You have a clear, no BS introduction to how you see it?
I would really like something unambiguous for this.

==

That link is talking about QED right? Well QED is neither one if you listen to Feynman. He also said that he didn't believe in any of the explanations made yet, including his own, if I remember right. So maybe, but then we're not talking quanta anymore. We're instead talking, depending on your interpretation 'waves' 'fields' or as Feynman most probably thought Approximations. And to me a 'field' may be the closest if you accept that SpaceTime, all included is one whole 'field' to me.

QFT has this to say "(It is important to note, at this point, that this article does not use the word "particle" in the context of wave–particle duality. In quantum field theory, "particle" is a generic term for any discrete quantum mechanical entity, such as an electron or photon, which can behave like classical particles or classical waves under different experimental conditions, such that one could say 'this "particle" can behave like a wave or a particle'.)"
==

Looking it up some more, QTF is not compatible with General relativity, and so QED fail too? It really gives me a headache reading theories that think they come from a SpaceTime approach, still not able to support a almost 100 year old theory that is the best approximation we have so far to gravity. Talking about string theory being 'before its time' while being totally theoretical at the same time as schools stop teaching General relativity? It's not strange that so many gloss it over, they can't even do the theory any more. I'm getting grumpy here

"Although Quantum Field Theory is fully compatible with, and in fact requires Special Relativity, the most naive application of field theory to General Relativity is known to be unworkable. This is generally considered to be the most difficult outstanding problem in Physics.

The incompatibility is due both to the complications of curved space-time required by GR, as well as from presumed properties of gravitons. Gravitons are hypothetical bosons which, in the most naive application of Field Theory to GR, would mediate the gravitational force between particles. Unlike the bosons mediating the other forces of nature, which are spin 1, gravitons in the simplest case would be bosons of spin 2, coupled to the Einstein mass-energy tensor. This difference in spin greatly complicates the renormalization of quantum gravity.

Consequently, alternative theories of quantum gravity are an active area of research among physicists, including popular theoretical attempts such as string theory and loop quantum gravity. None of these alternative approaches yet has experimental confirmation. "

And renormalization really make me suspicious. Using those any theory will work it seems, you just set in parameters you find 'working' in reality and voila, your 'theory works'. I mean, most theorys have to accept some parts of reality to be accepted, don't they? It would be interesting to se an study in how far you can go from what we know to work (like 'laws' we already use) and still make the theory seem reasonable. That should be a good field of study. Yep, I'm definitely getting grumpy here

[yor_on]

But maybe? I always liked Feynman, he seemed a very cool cucumber And Dirac sounds quite sharp too.

"Dirac's quantum electrodynamics made predictions that were - more often than not - infinite and therefore unacceptable. A workaround known as renormalization was developed, but Dirac never accepted this.

"I must say that I am very dissatisfied with the situation," he said in 1975, "because this so-called 'good theory' does involve neglecting infinities which appear in its equations, neglecting them in an arbitrary way. This is just not sensible mathematics. Sensible mathematics involves neglecting a quantity when it is small — not neglecting it just because it is infinitely great and you do not want it!"

His refusal to accept renormalization, resulted in his work on the subject moving increasingly out of the mainstream. However, from his once rejected notes he managed to work on putting QED on "logical foundations" based on Hamiltonian formalism that he formulated. He found a rather novel way of deriving the anomalous magnetic moment "Schwinger term" and also the Lamb shift, afresh, using the Heisenberg picture and without using the joining method used by Weisskopf and French, the two pioneers of modern QED, Schwinger and Feynman, in 1963. That was two years before the Tomonaga-Schwinger-Feynman QED was given formal recognition by an award of the Nobel Prize for physics. Weisskopf and French (FW) were the first to obtain the correct result for the Lamb shift and the anomalous magnetic moment of the electron. At first FW results did not agree with the incorrect but independent results of Feynman and Schwinger (Schweber SS 1994 "QED and the men who made it: Dyson, Feynman, Schwinger and Tomonaga", Princeton :PUP). The 1963-1964 lectures Dirac gave on quantum field theory at Yeshiva University were published in 1966 as the Belfer Graduate School of Science, Monograph Series Number, 3. After having relocated to Florida in order to be near his elder daughter, Mary, Dirac spent his last fourteen years (of both life and physics research) at the University of Miami in Coral Gables, Florida and Florida State University in Tallahassee, Florida." from Paul Dirac

[JP]

It sounds like you're thinking of these theories as actually telling us what light is.  They don't.  They're just models of increasing accuracy telling us about how light behaves and allowing us to do accurate computations.  Until there's at theory of everything, we can't really say what something is.  This gets into a lot of philosophy of science, though, which is something I haven't looked into much. 

In this discussion, the model of light as photons is generally more accurate for small events than the model of light as waves, but the model of light as waves is good enough to account for the photoelectric effect.  If string theory ends up panning out, maybe there's a model of light as strings in the future, which is more accurate than the photon model.  (And if some string theorists are to be believed, it might be the theory of everything that tells us that light is strings.)

[burning]

I read that USA had stopped teaching General relativity in their physics curriculum?
That's truly weird if true.

Sadly, the only thing misleading about this remark and the supporting quote is that it implies that this is a recent development.  I got my PhD fourteen years ago at a school that has one of the top 20 graduate physics programs.  We were not required to take general relativity, and special relativity had maybe about a week each in the classical mechanics and electromagnetism classes.  The philosophy seemed to be that if you needed to know it, you could take the special seminar, and that you would only need it if you were a theoretician in certain areas (mostly astrophysics and cosmology).  My knowledge of GR is almost entirely self-taught and none too solid at that.  You are making want to pull out my copy of Misner, Thorne, and Wheeler and give it another go.  []