Does a controversy still exist ?

[McQueen]

Three hundred years after the controversy had started , the question of whether light is wave like or particle like in nature is still raging. Modern theories of light tend more to the particulate view of light , in spite of the wave like properties associated with light and the generally accepted view of the wave-particle duality of light , wherein light possesses both wave like and particle like properties but can never possesses both properties simultaneously. One instance of the general dissatisfaction with the theory of wave-particle duality is that explanations of how light undergoes reflection , refraction , and transmittance through substances is today explained almost entirely in terms of the particle nature of light , while even ten years ago , explanations for the manner in which light underwent , reflection , refraction and transmittance were almost wholly wave based. The fact is that the overwhelming evidence tends towards the view that light , in the form of photons , does interact with matter ( electrons) in a very definable particulate manner. In order to support this view , the conjecture has been put forward that light might be composed of particles but that the particles themselves travel like a wave , this is analogous to the way in which water , which is made up of molecules , assumes a wave like form. The draw back with this point of view is that a wave never interacts with matter in the manner of a particle , while light does. This leads to the saying that light travels like a wave but arrives at its destination as a particle. Thus the debate still rages. Today the widely prevalent view is that Reflection is due to the rapid absorption and re-emission of photons , while refraction is also thought to be due to the result of the slowing down of light as it travels through a medium due to its absorption and emission as it travels through the medium. This raises the extremely interesting question of why , if light can travel through a medium such as glass by being rapidly absorbed and emitted by the electrons in the atoms of the glass , cannot it be transmitted through a metal in a similar manner. The rapid absorption and emission of photons through a glass pane implies that this kind of interaction is due to the conduction band properties of the glass. This being so , why cannot light travel through a metal , a metal has wide open conduction bands , it should theoretically be possible to replicate in a metal the phenomenon which is known to exist in glass , namely the transmittance of light . Why doesn’t it happen ?

 

[tbone]

For one thing, light can be reflected off of a metal pain. Secondly, metal is made up of more mass. With this light is is obsorbed but you also have to remember that, when the photons hit the tightly packed electrons, they lose some of their energy. Well with the thickness and tightly packed electrons in a metal you could imagine how many atoms they would hit before they made it through.

 

[Hurkyl]

Three hundred years after the controversy had started , the question of whether light is wave like or particle like in nature is still raging. Modern theories of light tend more to the particulate view of light

FYI, I stopped seriously reading your article after this introduction. The question has been answered for quite a while now: light is neither a (classical) particle nor a (classical) wave. Light is some quantum mechanical thing to which the classical notions of particles and waves are good approximations under various circumstances.

 

[tbone]

You know I think that is the best explanation of light I've heard yet. I'll have to remember that one

 

[Careful]

FYI, I stopped seriously reading your article after this introduction. The question has been answered for quite a while now: light is neither a (classical) particle nor a (classical) wave. Light is some quantum mechanical thing to which the classical notions of particles and waves are good approximations under various circumstances.

Very amusing No, no, light is just a good old fashioned EM wave, no fuzzy QM stuff involved.

 

[vanesch]

Very amusing No, no, light is just a good old fashioned EM wave, no fuzzy QM stuff involved.

Aren't you taking a bit your dreams for reality here ? I know that your programme is to show ONE DAY that SOME classical field theory might EVENTUALLY reproduce observed quantum effects, but for sure it will not be good old Maxwell with no additional stuff, right ? Try to explain anti-correlations such as the famous paper by Thorn et al (Am. J. Phys. 72) sept 2004 with *pure classical optics*.

So I'd say that *at least for the moment* the best description of light we have is the quantum-mechanical one and then Hurkyl's statement is very accurate.

 

[marlon]

McQueen,

I assure you, there is no problem with QM, what so ever. I think Hurkyl gave you a nice explanation concerning your question. I would like to add that al these "measurement problems" are all just coming from people who are interpreting the result and formalism of QM in the WRONG way.

QM works, Einstein was wrong, "point final"

regards
marlon

 

[Careful]

Aren't you taking a bit your dreams for reality here ? I know that your programme is to show ONE DAY that SOME classical field theory might EVENTUALLY reproduce observed quantum effects, but for sure it will not be good old Maxwell with no additional stuff, right ? Try to explain anti-correlations such as the famous paper by Thorn et al (Am. J. Phys. 72) sept 2004 with *pure classical optics*.
So I'd say that *at least for the moment* the best description of light we have is the quantum-mechanical one and then Hurkyl's statement is very accurate.

Sorry, don't have immediate acces to library. Can you explain me what the measurement setup is and what the results are?

Cheers,

Careful

 

[Careful]

McQueen,
I assure you, there is no problem with QM, what so ever. I think Hurkyl gave you a nice explanation concerning your question. I would like to add that al these "measurement problems" are all just coming from people who are interpreting the result and formalism of QM in the WRONG way.
QM works, Einstein was wrong, "point final"
regards
marlon

Really, and on what basis do you claim that ?!

 

[vanesch]

Sorry, don't have immediate acces to library. Can you explain me what the measurement setup is and what the results are?
Cheers,
Careful

It is also available freely here:

http://marcus.whitman.edu/~beckmk/papers/Thorn_g2_ajp.pdf

cheers,
Patrick.

EDIT: FYI, this is not an EPR style experiment. It would be very simple to explain the experiment with bullets, for instance. But with *classical optics* I think it is impossible (unless you modify about all we know about optical devices such as beam splitters in classical optics).
Although this is not demonstrated in the paper, similar setups can show *interference* after recombination of the split beams, so the argument that the beamsplitter sends little packets "left" and then "right" randomly would not do.

 

[marlon]

Really, and on what basis do you claim that ?!

err, really easy, how about the fact that we have transistors, semiconductors, diodes, ...

How about the fact there is not a single experiment that contradicts with QM ?


marlon

 

[ahrkron]

Really, and on what basis do you claim that ?!

QM is extremely well established now. For sure, there is no controversy among physicists about that.

Actually, the title of the paper quoted by vanesh is
"Observing the quantum behavior of light in an undergraduate laboratory".

Here's a bit of the abstract, in which I color-emphasize some parts:

"While the classical, wavelike behavior of light (interference and diffraction) has been easily observed in undergraduate laboratories for many years[/color], explicit observation of the quantum nature of light (i.e., photons) is much more difficult. For example, while well-known phenomena such as the photoelectric effect and Compton scattering strongly suggest the existence of photons, they are not definitive proof of their existence. Here we present an experiment, suitable for an undergraduate laboratory, that unequivocally demonstrates the quantum nature of light[/color]."

i.e., the article is not about a high end, controversial, multimillion dollar experiment, but about how to confirm in school a well established, well known result: that QM is a better description of nature than classical physics.

 

[vanesch]

QM is extremely well established now. For sure, there is no controversy among physicists about that.

That said, QM faces serious problems too on a more foundational level of which the measurement problem and the incompatibility with GR are the two principal ones. Another difficulty is of course the mathematical inconsistency of QFT - no matter how well it works to crank out numbers that compare to scattering experiments. But that doesn't do away the tremendeous experimental success it has seen in vastly different areas.
As such, I cannot say anything about how 'fundamentally true' QM is, but at least how successful it is as a current description of the workings of nature.

 

[Careful]

i.e., the article is not about a high end, controversial, multimillion dollar experiment, but about how to confirm in school a well established, well known result: that QM is a better description of nature than classical physics.

How, how, I was not aware of this result and I shall study it in detail; I thought people would come up with compton scattering again But I doubt it will be that unambiguous ... as the authors claim it is.

Will come back to this, thanks for the reference anyway Vanesch

 

[marlon]

That said, QM faces serious problems too on a more foundational level of which the measurement problem and the incompatibility with GR are the two principal ones.

Sorry, but on this one i disagree. Concerning the incompatibility with GR, i do not see how that is an issue for QM ? I mean we do not say this about Newtonian physics and QM, right ? QM is not built to explain the GR-phenomena, so why is this incompatibility an issue then ? This is just a matter of physical regimes. I know, in the past, i have stated this before but i really feel that we need to look at it like that ? We should not "create" problems based upon interpretations of the underlying mathematical formalism.

Same goes for this mysterious measurement "problem".

If it ain't broken, do not fix it.

Another difficulty is of course the mathematical inconsistency of QFT

ok, you may find this question to be very stupid, but...what mathematical inconsistency ?

Even if there is one, how is this correlated to QM ?

regards
marlon

 

[ahrkron]

That said, QM faces serious problems too on a more foundational level of which the measurement problem and the incompatibility with GR are the two principal ones.

Agreed. However, one has to be careful (which you have been) when discussing these, since people sometimes get the wrong impression that QM is not well tested.

Another difficulty is of course the mathematical inconsistency of QFT

What are you referring to in here? renormalization?
I've often heard good theorists say that this is now understood, in a tone of "we now have it solved"...

 

[vanesch]

What are you referring to in here? renormalization?
I've often heard good theorists say that this is now understood, in a tone of "we now have it solved"...

Renormalization is not the problem as such. The trouble starts with Haag's theorem which invalidates in fact the canonical approach to QFT, and which states that the "interaction picture" must always be equivalent with a free field theory if the creation and annihilation operators are to be what we think they are.
Now, you can leave the canonical approach for what it's worth, and switch to the Feynman path integral. But here the trouble is the measure. Nobody has ever been able to define a measure on the space of paths - as far as I understand, there are reasons to think that this is impossible. As such the path integral is an undefined quantity.
Next, you can STILL do a step backward, and consider QFT to be defined as the set of Feynman diagrams. Apart from difficulties of convergence (even after renormalization: in QED, it is now I think established that at best the perturbative series are only asymptotically meaningful, which means that they will start diverging again after a certain order - and as such that the "true" value is never reached) this would put aside a lot of non-perturbative results which clearly play a role.
As far as I know, there is no known axiomatic structure of QFT - this in sharp contrast to non-relativistic QM which was axiomatized by von Neumann.

That said, QFT as practiced DOES have a huge number of empirical successes on its record. But as far as I understand, it does not make mathematical sense. It is just a bag of phenomenological techniques which, when applied with care and fingerspitsengefuhl, cranks out good numbers which compare to experiment.

 

[vanesch]

Sorry, but on this one i disagree. Concerning the incompatibility with GR, i do not see how that is an issue for QM ? I mean we do not say this about Newtonian physics and QM, right ? QM is not built to explain the GR-phenomena, so why is this incompatibility an issue then ? This is just a matter of physical regimes. I know, in the past, i have stated this before but i really feel that we need to look at it like that ? We should not "create" problems based upon interpretations of the underlying mathematical formalism.
Same goes for this mysterious measurement "problem".
If it ain't broken, do not fix it.
ok, you may find this question to be very stupid, but...what mathematical inconsistency ?
Even if there is one, how is this correlated to QM ?
regards
marlon

If you take QM to be a phenomenological theory, I agree with all this of course. However, if you consider QM to be a *fundamental* theory (or better, if you take the founding principle of QM, namely the superposition principle, to be a fundamental principle), then you ARE in trouble. And there are people (like Careful) who come from a quantum gravity background who have seen the problems that arise when you are combining both the principle of superposition and the principle of general covariance, and who prefer to stick to the latter. That said, they shouldn't close their eyes to those parts of QM which bother them if they are supported by experiment ; however QM proponents shouldn't be blind either to the difficulties.

 

[ahrkron]

The trouble starts with Haag's theorem which invalidates in fact the canonical approach to QFT, and which states that the "interaction picture" must always be equivalent with a free field theory if the creation and annihilation operators are to be what we think they are.

I don't understand the problem here. Why is that equivalence a problem?

they will start diverging again after a certain order - and as such that the "true" value is never reached

That's quite scary. Can you expand on that? or maybe give a reference? If things are expected to diverge again after some order, when can we trust any numbers obtained from it?

That said, QFT as practiced DOES have a huge number of empirical successes on its record.

Which, in light of what you mentioned, is quite puzzling.

[edit: fixed a quote]

 

[marlon]

I think established that at best the perturbative series are only asymptotically meaningful, which means that they will start diverging again after a certain order - and as such that the "true" value is never reached) this would put aside a lot of non-perturbative results which clearly play a role.

How is that ?

Besides, one can always chose to do a duality transform in order to go from high coupling constant to low coupling constant, like in the case of QCD. Either way, perturbation theory still holds.


marlon

 

[vanesch]

I don't understand the problem here. Why is that equivalence a problem?

the raw stuff:

http://en.wikipedia.org/wiki/Haag's_theorem

and a more poetic version:
http://www.cgoakley.demon.co.uk/qft/renorm.html

 

[vanesch]

That's quite scary. Can you expand on that? or maybe give a reference?

Just a random search on an article related to it which is freely available:

http://ej.iop.org/links/q55/xJRM4SDjMgSOxercMujz7g/jgv7i10pL221.pdf

 

[vanesch]

How is that ?
Besides, one can always chose to do a duality transform in order to go from high coupling constant to low coupling constant, like in the case of QCD. Either way, perturbation theory still holds.
marlon

Isn't that only possible in supersymmetric models ? And even then, you can transform high coupling constants in low ones, but for medium values you're screwed, no ? Because if it were so easy, I'd guess that hadron masses would easily be obtained and that one wouldn't have to go on the lattice!

Now, I have to say that I'm not up to level in all this, so you can easily hit me around the ears with lots of technical stuff I'm not aware of. But I don't think that that changes the content of my statement that there is no axiomatic basis for QFT as of today, and that it is a lot of phenomenology which works very well and where one invents more and more useful techniques, but not a crystal clear theory.

 

[George Jones]

or maybe give a reference?

Although this was demonstrated by Dyson [1] (but not proved) more than 50 years ago, it is not well known.

From [2], page 451: "Thus, QED may have a zero radius of convergence in \alpha space."

From [3], page 259: "The belief is that the perturbation series is an asymptotic series for real e at e = 0." Despite its title [3] is NOT a book about rigorous mathematics - it is a book that covers much the same topics as Peskin and Schroeder and at about the same level, and, in my opinion, is one of the best grad-level expositions of quantum field theory.

[1] QED and the Men Who Made It, S. Schweber, 9.17 Divergence of the Perturbation Series

[2] Quantum Field Theory, M. Kaku, 13.5 Does Quantum Field Theory Really Exist

[3] Quantum Field Theory for Mathematicians, R.Ticciati, Remark 9.4.12

Regards,
George

 

[ahrkron]

Thanks for the references!

50 years ago! Boy, do I feel ignorant! : S

 

[McQueen]

For one thing, light can be reflected off of a metal pain. Secondly, metal is made up of more mass. With this light is is obsorbed but you also have to remember that, when the photons hit the tightly packed electrons, they lose some of their energy. Well with the thickness and tightly packed electrons in a metal you could imagine how many atoms they would hit before they made it through.

Tbone , yours is the only post that immediately addresses the direct question I had posed , which is why , if light can propagate through glass through the process of the rapid absorption and emission of photons by the electrons of the atoms which make up the glass , can’t light propagate in a similar way through metals ? Unfortunately your explanation does not hold water. For one thing. Most matter , even metals , are mostly made up of empty space , for instance electrons are separated by approximately 10 ^^ 5 times their own diameters ( classically is taken to be about 10 ^^ -13 m.) so the chances of one electron hitting another are small. The transmittance of light through a material has to do with conductance bands or the ability of the material in question to absorb and emit electrons within a certain range of energies. The energy range for visible light is from 1.8 to 3.1 eV. Materials with band gap energies in this range will absorb those corresponding colors (energies) higher and lower than the band –gap and transmit the others. Since ordinary glass has a band gap corresponding to the energies 1.8 to 3.1 eV , it appears transparent and colorless. When light is absorbed and re-emitted from the surface at the same wavelength, it is called reflection . Metals, are highly reflective, and those with a silvery appearance reflect the whole range of visible light. The energy levels of electrons are quantized, i.e., each electron transition between levels requires a certain specific amount of energy. The absorption of energy results in the shifting of electrons from the ground state to a higher, excited state. The electrons then fall back to the ground state, accompanied by the reemission of electromagnetic radiation. The energized electrons vibrate between the two levels and send the energy back out of the object as light with the same frequency as the incoming light.

This is not an EPR style experiment. It would be very simple to explain the experiment with bullets, for instance. But with *classical optics* I think it is impossible (unless you modify about all we know about optical devices such as beam splitters in classical optics).
Although this is not demonstrated in the paper, similar setups can show *interference* after recombination of the split beams, so the argument that the beamsplitter sends little packets "left" and then "right" randomly would not do.

This lifts the argument out of the mundane , or more succinctly , vitiates the whole argument. The second experiment referred to on interference can be found at [PLAIN]http://www.people.virginia.edu/~xy9z/qubit/qubit.php[/PLAIN] . If this is true it implies that non-locality exists , yet despite numerous practical applications being carried out in quantum encryption , wherein the polarization of one of two spatially separated photons is detected thereby automatically assigning a polarization value to the other photon , a variation of the experiment to prove non-locality has been ignored . Using the same equipment and altering the polarity of the first spatially separated photon should always result in an opposite polarization of the other photon. Thus if the detector at A clicks the detector at B should never click and vice versa. The infrastructure is in place , yet the experiment , which would be conclusive has never been performed. Why? The proof of non-locality , if it exists , would be conclusive with regard to many issues vital to QM , including FTL interactions , the Wave function etc., Can , the experiment quoted in this post , with its statistical approach , be given due credence in the face of this huge lacuna ?

 

[George Jones]

In grad school. I learned about this neither in the QFT courses that I took nor in informal discussion. Later, I just happen to stumble upon it during random page flipping - needle in a haystack type of thing.

A friend of mine had a worse experience. She attended a seminar by a guy who works in QED, and, because of comments that I had made to her earlier, she brought up the issue of series divergence. The guy's response was to ridicule her publicly, and to say that of course everything converged.

The topic divergences of QFT (after regularization and renormalization) is one of a number of topics to which with hindsight I think that I should have been exposed as a ungrad or grad student. I would rate Godel's theorems, a topic I know interests you, as the most important thing that I had to "discover" on my own.

Regards,
George

 

[ZapperZ]

Tbone , yours is the only post that immediately addresses the direct question I had posed , which is why , if light can propagate through glass through the process of the rapid absorption and emission of photons by the electrons of the atoms which make up the glass , can’t light propagate in a similar way through metals ?

For some odd reason, I seem to have to re-explain this over and over again. (See, for example https://www.physicsforums.com/showpost.php?p=795179&postcount=22)

When atoms form into solids, a lot of their individuality disappears as far as the bulk properties of the material is concerned. You do not get a "conduction band" from single atoms. You get it when a conglomerate of atoms get together, their valence bands overlap and hybridize, and voila! You get these continuous bands! The same can be said with insulator and glass. When they form a solid, you now have to consider one very important factor that has a lot to do with the material's property - the PHONON structure!

The tranparency of many dielectric is dictated by the phonon structure. If that phonon mode is available, then chances are, the material will absorb a photon with that particular energy. The lattice vibration that can either convert this into heat, or cause another transition. If the vibrational mode is not available, the ions will simply get displaced and retransmit the same energy since it cannot sustain that mode!

I will repeat this one more time. There is a HUGE field of study in condensed matter physics that deals with optical conductivity through matter. Techniques such as FTIR, Raman scattering, etc. are examples of the application of the knowledge of how "light" interacts with materials. So I would strongly disagree with the idea that we don't really know how these things work. If we can actually use it to study other things, this is the clearest indication that I know of that the principle behind it is very secure.

Zz.

 

[vanesch]

In grad school. I learned about this neither in the QFT courses that I took nor in informal discussion. Later, I just happen to stumble upon it during random page flipping - needle in a haystack type of thing.

Same happened to me, in fact. I learned about the existence of Haag's theorem on s.p.r. What's funny is that if you look up "Haag" in Weinberg's account on QFT, it isn't even mentioned!

 

[McQueen]

So I would strongly disagree with the idea that we don't really know how these things work. If we can actually use it to study other things, this is the clearest indication that I know of that the principle behind it is very secure.

Thanks for the link , it was useful. It was not my intention to imply that we did not know why light cannot propagate through metals , I just wanted to stimulate some thought on the subject. The structure of materials does have a lot to do with the different properties of materials. In the example you had pointed out , carbon with an identical atomic structure as Graphite is an insulator while graphite conducts , so it all comes down to structure. The same holds true for magnetic properties. Coming back to the second half of my post , is there any news yet on the experiment I had referred to viz-a-viz locality/non-locality.

 

[Sherlock]

i.e., the article is not about a high end, controversial, multimillion dollar experiment, but about how to confirm in school a well established, well known result: that QM is a better description of nature than classical physics.

I'd say it this way: qm is a better predictor of quantitative experimental results wrt certain setups than classical physics.

The word "description" implies a qualitative apprehension of the thing being described. Qm doesn't provide this.

The rigorous definition of photon that produces those better predictions doesn't give me any good idea of what sort of qualitative phenomenon (beyond the level of its mathematical and instrumental manifestations) a photon might correspond to in nature.

 

[Sherlock]

Using the same equipment and altering the polarity of the first spatially separated photon should always result in an opposite polarization of the other photon.
Thus if the detector at A clicks the detector at B should never click and vice versa. The infrastructure is in place , yet the experiment , which would be conclusive has never been performed. Why? The proof of non-locality , if it exists , would be conclusive with regard to many issues vital to QM , including FTL interactions , the Wave function etc., Can , the experiment quoted in this post , with its statistical approach , be given due credence in the face of this huge lacuna ?

I don't understand what you're getting at here? What do you mean by "altering the polarity of the first spatially separated photon"?

 

[Pythagorean]

statements:

quamtums awesome, quantums great;
quantum mechanics is incomplete.

If you're expecting it to be the Grand Theory of Unification, then you'll probably be disapointed, especially if you're one of those who compares physics logic to other things you may experience in life (which is easy to do if physics is your life).

question:

What ever came of Einstein's work on the GTU before he died? I watched a vague show by Brian Greene that (if I remember correctly) somehow associated string theory with Einstein's last work.

I've also heard of M-theory, which seems like a patchwork between the different accepted theories (qm, gr, string, etc).

 

[ahrkron]

The rigorous definition of photon that produces those better predictions doesn't give me any good idea of what sort of qualitative phenomenon (beyond the level of its mathematical and instrumental manifestations) a photon might correspond to in nature.

Unless you hold the position that the word "photon" refers precisely to this set of instrumental manifestations, in which case the phenomenon is fully described by the mathematical machinery of QM.

 

[Sherlock]

Unless you hold the position that the word "photon" refers precisely to this set of instrumental manifestations, in which case the phenomenon is fully described by the mathematical machinery of QM.

As fully as is currently possible anyway -- which, in my estimation, doesn't allow quantum theory to be called a description of nature. The 'nature' of quantum phenomena is still pretty much a mystery, wouldn't you agree?
We use analogies from our experience of macroscopic events to assign some physical meaning to, and give some description of, the nature of quantum phenomena. But this leaves us with complimentarity, wave-particle duality, wave function collapse, etc. -- and, for me at least, the feeling that what is happening *in nature* isn't really that well understood yet.

 

[George Jones]

Same happened to me, in fact. I learned about the existence of Haag's theorem on s.p.r. What's funny is that if you look up "Haag" in Weinberg's account on QFT, it isn't even mentioned!

"Haag's theorem" is in the index of Haag's booK! It was on s.p.r that I too first learned of its importance.

I just had a brief look through Weinberg for mention of asymptotic series - nothing caught my eye.

Regards,
George

 

[McQueen]

I don't understand what you're getting at here? What do you mean by "altering the polarity of the first spatially separated photon"?

Sorry it should have been polarization , not "polarity". Surely , performing an experiment which could prove conclusively that many basic precepts of QM such as the collapse of the wave function and FTL interactions is more important than sending a few thousand dollars by an encryption process.
http://www.newscientist.com/article.ns?id=dn4914 . Think of it using this analogy , I have two objects , one black and one white , which I put in two boxes. The boxes are mixed up so that no-one knows which is which and one is sent to a spatially separated location at A while the other is sent to B. If A gets the white object then B must get the black object and vice versa. Now introduce two more oppositely coloured objects say Red and blue. And while sending the object to A assume that it is intercepted and the whi8te object taken out and replaced with the Blue object , will the box at B now have a Red object ?

 

[vanesch]

"Haag's theorem" is in the index of Haag's booK! It was on s.p.r that I too first learned of its importance.

Yeah... I never managed to read it. Have it on my shelf allright, but never got down to reading it.

 

[George Jones]

Yeah... I never managed to read it. Have it on my shelf allright, but never got down to reading it.

I didn't claim that I'd read it, only that I'd read part of the index! :-)

Regards,
George

 

[selfAdjoint]

Haag actually is pretty light in his presentation of "Haag's Theorem" in his book. Kind of s**t kicking, if you catch my drift.

 

[Igor_S]

McQueen,
I assure you, there is no problem with QM, what so ever. I think Hurkyl gave you a nice explanation concerning your question. I would like to add that al these "measurement problems" are all just coming from people who are interpreting the result and formalism of QM in the WRONG way.
QM works, Einstein was wrong, "point final"
regards
marlon

There is a nice book by R. Feynman "QED: The strange theory of light and matter" where he explains things in his simple way (its a popular book). I read only a part of it and it seemed ok. He even pulls out some number, comparing theoretical and experimental results and they match up to something like 10 digits or so.

Maybe the person who wrote 1st post could learn more from this book then from other stuff mentioned here. :) I just got that impression.

 

[Sherlock]

Using the same equipment and altering the polarization of the first spatially separated photon should always result in an opposite polarization of the other photon.

It depends on how the entangled photons are produced. In most of the Bell tests for example, paired photons at A and B are identically polarized. That is, with the polarizers aligned, if A registers a detection, then so does B, and vice versa.

In the case of opposite polarization, then with polarizers aligned, if A registers a detection then B doesn't register a detection.

The test you're talking about has been done many times, and it doesn't reveal whether A and B are, or aren't, interacting FTL.

QM doesn't assign a definite polarization prior to measurement. It does assign a definite combined angular momentum prior to measurement.

Surely , performing an experiment which could prove conclusively that many basic precepts of QM such as the collapse of the wave function and FTL interactions is more important than sending a few thousand dollars by an encryption process.

"Collapse of the wave function" has to do with changes in the wave function due to the quantum object's interaction with a measuring apparatus. There's no 'test' required to prove this, it just has to do with the way qm works.

"Collapse of the wave function" doesn't imply FTL interactions. If it was possible with existing technology to prove conclusively that FTL interactions either do or don't exist, then it seems like a good bet that it would have been done.

Think of it using this analogy , I have two objects , one black and one white , which I put in two boxes. The boxes are mixed up so that no-one knows which is which and one is sent to a spatially separated location at A while the other is sent to B. If A gets the white object then B must get the black object and vice versa. Now introduce two more oppositely coloured objects say Red and blue. And while sending the object to A assume that it is intercepted and the whi8te object taken out and replaced with the Blue object , will the box at B now have a Red object ?

A probability function is meaningful only insofar as it refers to a set of identically prepared and executed experiments. The probability function that applies to quantum correlations between A and B is the mean value of psi*psi, averaged over many experiments. The mean value for B is the same after a measurement at A as it is before a measurement at A, and vice versa.

 

[McQueen]

"Collapse of the wave function" has to do with changes in the wave function due to the quantum object's interaction with a measuring apparatus. There's no 'test' required to prove this, it just has to do with the way qm works.

Right , but just to make sure that we don't lose sight of the original reason and meaning of the EPR experiment , here is a quote from Einstein. "One can escape from the conclusion [that QM is incomplete] only byt assuming that measuring S1 (telepathically) changes the real situation at S2 or by denying independent real situations as such to things which are spatially separated from each other. Both alternatives appear to me unacceptable." Again "...on one supposition we should , in my opinion , absolutely hold fast; the real factual situation of the system S2 ( the particle in Area B) is independent of what is done with the system S2 ( the particle in area A) which is spatially separated from the former. "

 

[McQueen]

A probability function is meaningful only insofar as it refers to a set of identically prepared and executed experiments. The probability function that applies to quantum correlations between A and B is the mean value of psi*psi, averaged over many experiments. The mean value for B is the same after a measurement at A as it is before a measurement at A, and vice versa.

Can a commercially marketed encryption system , which is used for the transfer of money be based on such a system of averages , I think not , at least not above that necessary for corrective purposes.For the same reason it should be easy to carry out and confirm , the experiment I had referred to earlier.

 

[McQueen]

...

"Consider the curious incident of the dog in the night-time," Sherlock Holmes said to Watson in "Silver Blaze"
"The dog did nothing in the night-time."
"That was the curious incident,"remarked Holmes.

 

[Sherlock]

... just to make sure that we don't lose sight of the original reason and meaning of the EPR experiment , here is a quote from Einstein. "One can escape from the conclusion [that QM is incomplete] only by assuming that measuring S1 (telepathically) changes the real situation at S2 or by denying independent real situations as such to things which are spatially separated from each other. Both alternatives appear to me unacceptable."

If we want to talk about the physical reality of quantum phenomena as being something other than instrumental phenomena, then the conclusion that qm is an incomplete description of physical reality is inescapable. But as far as quantum theory is concerned the physical reality is the instrumental phenomena. Whatever might be happening independent of that can't be described in realistic terms. That is, a one to one mapping between events in the microworld and the mathematical entities of qm is impossible according to the principles of the theory. A visualizable geometrical representation of the microworld that qm deals with had to be sacrificed in order for the theory to be consistent internally and wrt experimental results. That's the tradeoff. And there's no way around it as far as anybody knows.

Again "...on one supposition we should , in my opinion , absolutely hold fast; the real factual situation of the system S2 ( the particle in Area B) is independent of what is done with the system S1 ( the particle in area A) which is spatially separated from the former."

This supposition seems correct so far, because there's nothing in the qm formulation of the situations that Einstein is talking about which necessitates the conclusion that the "particle in area A" is affecting the "particle in area B" in any physical sense which would require a transmission between A and B during the joint measurement interval. A and B can be linearly combined in a wave function and are statistically related because of certain isomorphisms in the experimental situation.

Can a commercially marketed encryption system , which is used for the transfer of money be based on such a system of averages , I think not , at least not above that necessary for corrective purposes. For the same reason it should be easy to carry out and confirm , the experiment I had referred to earlier.

The potential for greater security using quantum encryption, and also the main stumbling block to its practical implementation, is the sensitivity of quantum entangled systems to environmental (external) influences.
As for your experiment. Afaik, it's been done many times and there's no way to tell if A and B are physically affecting each other during the joint measurement interval. Non-locality (FTL transmission) remains a possibility, but isn't a necessary conclusion -- and it isn't what quantum encryption depends on, afaik.
Concerning the question posed in the title of this thread, a controversy still exists wrt the qualitative nature of light.
Because qm is a probabilistic accounting of quantitative experimental results, it can't, at least in its present form, resolve this controversy.

"Consider the curious incident of the dog in the night-time," Sherlock Holmes said to Watson in "Silver Blaze"
"The dog did nothing in the night-time."
"That was the curious incident,"remarked Holmes.

All I know about Sherlock Holmes is that he was a detective whose deductive analyses were often correct because he knew a lot of stuff. He knew lots of facts. I don't know lots of facts yet. I chose the nickname Sherlock because I aspire to the sort of investigative skills that his legacy represents.
Unfortunately, I don't know exactly what your citing above is supposed to be an analogy of.

 

[McQueen]

Sherlock while I appreciate that you have taken a lot of trouble to answer my questions and doubts and have furthermore done a good job of it , I also get the feeling that many of the pertinent points I had raised have been glossed over in your replies or simply ignored. I hope you don’t mind my making this criticism and will try to justify my statements during the course of this reply. Take first your statement that FTL is at the most a marginal issue viz-a-viz quantum mechanics.: In actual fact FTL turns out to be very much a central issue as far as QM is concerned. Take for example the phenomenon of Quantum Tunneling which is inevitably raised whenever QM is discussed. FTL is implicit in the QM explanation of quantum tunneling. I clearly remember a reference to a group of scientists who had claimed to have transmitted a Mozart composition using FTL at 4.7 c ! If I remember rightly the subject was discussed in Physics Forums and eventually these claims were proved wrong. (I am unable to find the exact post) . Nevertheless , the fact remains that FTL is central to Quantum tunneling. Again , take your insistence that EPR has nothing whatsoever to do with QM .

"Collapse of the wave function" doesn't imply FTL interactions. If it was possible with existing technology to prove conclusively that FTL interactions either do or don't exist, then it seems like a good bet that it would have been done.

Yet many people feel that the EPR is a decisive issue as to whether Quantum Mechanics , at least as regards the superposition of states , is viable or not. Which is precisely the point I had repeatedly made in this thread. Also your claim that the Quantum Encryption system used in the transfer of money , posted at New Scientist and to which I had given a link in one of my earlier replies , would result in an anomalous result , seems to me quite incredible

The potential for greater security using quantum encryption, and also the main stumbling block to its practical implementation, is the sensitivity of quantum entangled systems to environmental (external) influences. As for your experiment. Afaik, it's been done many times and there's no way to tell if A and B are physically affecting each other during the joint measurement interval.

Consider the fact that this is an encryption system , where even the slightest mistake made could result in catastrophic misunderstandings. For instance take a three letter word such as cat if any of the three letters are changed the whole meaning would be drastically changed. As for instance , hat , mat , fat , cot ,etc., etc., . Yet this is a system which is now being manufactured and sold commercially , you or I could just go to a shop and buy one. Given that this is so it should be possible to conduct the experiment by changing the polarization of one of the spatially separated photons and determining if the other photon also undergoes the relevant change. Lastly the quote from “Silver Blaze” referred to just this obtuseness which is demonstrated by (a) either not conducting the experiment or (b) obfuscating the results if the experiment has been conducted. Hence the question of why the dog did not bark. i.e., why hasn’t the experiment been carried out.

 

[McQueen]

Sherlock while I appreciate that you have taken a lot of trouble to answer my questions and doubts and have furthermore done a good job of it , I also get the feeling that many of the pertinent points I had raised have been glossed over in your replies or simply ignored. I hope you don’t mind my making this criticism and will try to justify my statements during the course of this reply. Take first your statement that FTL is at the most a marginal issue viz-a-viz quantum mechanics.:

"Collapse of the wave function" doesn't imply FTL interactions. If it was possible with existing technology to prove conclusively that FTL interactions either do or don't exist, then it seems like a good bet that it would have been done. "

In actual fact FTL turns out to be very much a central issue as far as QM is concerned. Take for example the phenomenon of Quantum Tunneling which is inevitably raised whenever QM is discussed. FTL is implicit in the QM explanation of quantum tunneling. I clearly remember a reference to a group of scientists who had claimed to have transmitted a Mozart composition using FTL at 4.7 c ! If I remember rightly the subject was discussed in Physics Forums and eventually these claims were proved wrong. (I am unable to find the exact post) . Nevertheless , the fact remains that FTL is central to Quantum tunneling. Again , take your insistence that EPR has nothing whatsoever to do with QM .

This supposition seems correct so far, because there's nothing in the qm formulation of the situations that Einstein is talking about which necessitates the conclusion that the "particle in area A" is affecting the "particle in area B" in any physical sense which would require a transmission between A and B during the joint measurement interval. A and B can be linearly combined in a wave function and are statistically related because of certain isomorphisms in the experimental situation.

Yet many people feel that the EPR is a decisive issue as to whether Quantum Mechanics , at least as regards the superposition of states , is viable or not. Which is precisely the point I had repeatedly made in this thread. Also your claim that the Quantum Encryption system used in the transfer of money , posted at New Scientist and to which I had given a link in one of my earlier replies , would result in an anomalous result , seems to me quite incredible

The potential for greater security using quantum encryption, and also the main stumbling block to its practical implementation, is the sensitivity of quantum entangled systems to environmental (external) influences. As for your experiment. Afaik, it's been done many times and there's no way to tell if A and B are physically affecting each other during the joint measurement interval.

Consider the fact that this is an encryption system , where even the slightest mistake made could result in catastrophic misunderstandings. For instance take a three letter word such as cat if any of the three letters are changed the whole meaning would be drastically changed. As for instance , hat , mat , fat , cot ,etc., etc., . Yet this is a system which is now being manufactured and sold commercially , you or I could just go to a shop and buy one. Given that this is so it should be possible to conduct the experiment by changing the polarization of one of the spatially separated photons and determining if the other photon also undergoes the relevant change. Lastly the quote from “Silver Blaze” referred to just this obtuseness which is demonstrated by (a) either not conducting the experiment or (b) obfuscating the results if the experiment has been conducted. Hence the question of why the dog did not bark. i.e., why hasn’t the experiment been carried out and why is no reference made to it.

 

[Haelfix]

Yea I agree with Vanesch on this in general. You can take the phenomonological viewpoint (shut up and calculate) but even there there are mismatches in various regimes.

Anyway, I think there is still an open question on foundational interpretation issues in Quantum mechanics. Not so much in the wave/particle duality, but more so in the nonlinear nature of the collapse coupled with the quantum to classical limit (somewhat helped by decoherence). Every possible method tends to have various logical pitfalls at some point, and when you poll most theorists they are all over the place on exactly which formalism they prefer. I still consider it an unsolved and dare I say it, unsatisfactory *question* in physics and I also don't believe any of the current proposals is ultimately the *right* answer.

As far as QFT, the mathematical axiomatization thereof is very unsatisfying, tons of open issues and a very hard and unrewarding subject in general. Throw in curved backgrounds, and all hell breaks loose. This is not just an academic problem, there are plenty of experiments you could think off that could give quite different results depending on what you choose. Some very fundamental gap in our knowledge is clearly lurking in the midst in all of that.

Keep in mind, we are still very far from *perfect* theories, even in the standard model on flat space at a physicists lvl of rigor. For instance QED is plagued by the Landau pole, and more or less strongly suggests that it only effective and there is something more fundamental lurking in the UV.
For QCD we still have inabilities to show a correct mass gap.

 

[McQueen]

The tranparency of many dielectric is dictated by the phonon structure. If that phonon mode is available, then chances are, the material will absorb a photon with that particular energy. The lattice vibration that can either convert this into heat, or cause another transition. If the vibrational mode is not available, the ions will simply get displaced and retransmit the same energy since it cannot sustain that mode!

I agree with what you have stated . But this again leaves the question of how electrical energy is actually conveyed through a metal. QM regards electrons as the charge carriers , that is to say it is electrons that actually convey electrical energy ; loosely bound valence and free electrons are drawn to the positively charged ions. Unfortunately , this theory does not actually work. Take the circumstance where electrical energy flows over an open circuit without any electrons being observed. One could say , oh well ! that’s a simple one to deal with , Maxwell’s equations say it all. But the point is that Maxwell’s equations do not say it all , if they did we would once again be left with something like the Ultra violet catastrophe. If this question is raised , the answer that is usually given is that yes electrical energy is conveyed through electrons but that the energy passes from electron to electron via virtual photons . This is very confusing , is it admissible ? I was under the impression that virtual particles had to conform to Heisenberg’s Uncertainty principle , which in turn has to conform to the Conservation Laws , which means in effect that the interactions of virtual particles can not be real , except possibly in the sense of altering the direction of a real particle , they ( virtual particles ) cannot under any circumstances impart any extra momentum or energy to the real particle they are interacting with. At least this is my understanding. Thus although the concept of virtual particles might be acceptable from the QFT point of view viz-a-viz low frequency EM radiation , it cannot be applied to the conveying of electrical energy. My question is this : every interaction between electrons and other particles is mediated by real photons. This has been made especially clear in recent years , with the creation and observation , of low energy photons ( 1.4eV , 800 Nm. ) . Photons of this energy and slightly lower can only be absorbed by loosely bound valence electrons , which would make them the ideal candidate for the conveying of electrical energy. Note , that this would also escalate the wave OR particle question of light to a whole new level. It just doesn’t seem right that only in the phenomenon of electricity , exclusively , do we see electrons directly delivering energy. Isn’t it time that this was changed.