Is Classical EM Field the Same as Photon Wave Function?

[Blue Scallop]

Quantum mechanics is non-local
EM or electromagnetism obeys QM.
But why is EM not non-local?
How to make EM non-local?

 

[bhobba]

QM is not non local - that's a misconception but requires its own thread - start one if you like - note standard QM being based on the Galilean Transformations is explicitly not local but the explanation of what's going on, while not hard, is a bit wordy so really another thread is required.

EM is not non local because it in fact is derivable from SR, assuming simply Coulomb's law, which is from its foundations local:
http://www.cse.secs.oakland.edu/haskell/Special Relativity and Maxwells Equations.pdf

QED, being a quantum field theory (QFD), obeys what's called the cluster decomposition property which is the version of locality used in QFT, and in fact since standard QM is explicitly not local is really what locality is in QM:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

Once you understand the above the issue of locality is seen as nothing like what popularization's make it out to be - a big deal - it isn't. But again that's for the separate thread where all these issues can be discussed. Basically though the question comes about because of Bells theorem, but that involves correlation which is specifically not part of cluster decomposition so even the whole thing is rather moot.

Thanks
Bill

 

[Swamp Thing]

the question comes about because of Bells theorem, but that involves correlation which is specifically not part of cluster decomposition so even the whole thing is rather moot.

Is it the case that theories like QFT, which are based on cluster decomposition, are silent about the outcome of correlation type measurements?

 

[bhobba]

Is it the case that theories like QFT, which are based on cluster decomposition, are silent about the outcome of correlation type measurements?

Of course not.

Its simply in the definition of locality used in QM correlations are specifically excluded so the question of locality in Bell type experiments depends on what you mean by locality. If its just in the Cluster Decomposition sense then its not even a question that comes up. Correlated systems have correlated results - big deal. But if you ask about the nature of those correlations then its different to classical correlations - that's Bells theorem. Want it to be the same - you can have that - but you have to extend your view of locality beyond The Cluster Decomposition property ie what QM demands. You don't have to do that if you don't want to - you can just say the question of locality doesn't apply to correlated systems so forget about the issue - its not relevant. Its what I do. You may do it because certain interpretations are specifically non local eg BM - or you have some other reason - but if you don't want to go down that path you don't have to - its entirely up to you.

Thanks
Bill

 

[Blue Scallop]

Of course not.

Its simply in the definition of locality used in QM correlations are specifically excluded so the question of locality in Bell type experiments depends on what you mean by locality. If its just in the Cluster Decomposition sense then its not even a question that comes up. Correlated systems have correlated results - big deal. But if you ask about the nature of those correlations then its different to classical correlations - that's Bells theorem. Want it to be the same - you can have that - but you have to extend your view of locality beyond The Cluster Decomposition property ie what QM demands. You don't have to do that if you don't want to - you can just say the question of locality doesn't apply to correlated systems so forget about the issue - its not relevant. Its what I do. You may do it because certain interpretations are specifically non local eg BM - or you have some other reason - but if you don't want to go down that path you don't have to - its entirely up to you.

Thanks
Bill

So non-locality can be done away if one says locality doesn't even exist. So it's "non-blank" since there is no locality.. or since it's double none.. then its nothing. I went to that Cluster Decomposition thread. In a nutshell, is Cluster Decompoistion about correlations that don't involve locality?

 

[Demystifier]

Quantum mechanics is non-local
EM or electromagnetism obeys QM.
But why is EM not non-local?
How to make EM non-local?

There are different types of locality (or non-locality), like signal locality or Bell locality. QM obeys signal locality but Bell non-locality. Quantum electromagnetism, just like QM, also obeys signal locality and Bell non-locality.

 

[Blue Scallop]

There are different types of locality (or non-locality), like signal locality or Bell locality. QM obeys signal locality but Bell non-locality. Quantum electromagnetism, just like QM, also obeys signal locality and Bell non-locality.

please briefly define

signal locality
Bell non-locality

thanks.

 

[bhobba]

please briefly define signal locality Bell non-locality

Signal locality does not include correlations because they can't be used to signal anything. Signal locality is what's required for SR - you need to sync clocks which needs a signal to pass between them - the same for QFT which is built on SR. Bell non-locality is one way to escape the non classical correlations QM has - you can have classical correlations if non locality is broken between correlated objects.

But one has to ask - why bother? There is no correct answer of course - I chose to not bother - things IMHO are much easier that way - but opinions vary.

Thanks
Bill

 

[Demystifier]

please briefly define

signal locality
Bell non-locality

Signal locality - inability of humans to send signals faster than light.
Bell non-locality - violation of Bell inequalities.
For more details see
http://www.scholarpedia.org/article/Bell's_theorem#Bell.27s_definition_of_locality
http://www.scholarpedia.org/article...derstandings_regarding_the_locality_condition

 

[martinbn]

If Bell had used a better term instead of local/non-local, for example a term that was not already in use, then most of the discussions about Bell's theorem would not exist. What's wrong with terms like non-separable or non-factorizable?

 

[Blue Scallop]

Signal locality does not include correlations because they can't be used to signal anything. Signal locality is what's required for SR - you need to sync clocks which needs a signal to pass between them - the same for QFT which is built on SR. Bell non-locality is one way to escape the non classical correlations QM has - you can have classical correlations if non locality is broken between correlated objects.

But one has to ask - why bother? There is no correct answer of course - I chose to not bother - things IMHO are much easier that way - but opinions vary.

Thanks
Bill

QFT and QED obey signal locality.. so we send radio waves over the atmosphere but it can't pass thru the Earth core because of the core and mantle density. Why is there no signal that still obey SR but doesn't use EM.. so we can make receiver in one side of the Earth and another side and it can appear without traveling but obey SR.. like using some king of higgs field but with vectorial component to communicate.. why doesn't such exist? what symmetry or laws of nature is violated by this (yet still obey SR)?

 

[stevendaryl]

Signal locality - inability of humans to send signals faster than light.
Bell non-locality - violation of Bell inequalities.

I wouldn't say that Bell non-locality means violation of Bell's inequalities. Rather it's an implication: Violation of Bell's inequalities implies Bell non-locality.

 

[Demystifier]

I wouldn't say that Bell non-locality means violation of Bell's inequalities. Rather it's an implication: Violation of Bell's inequalities implies Bell non-locality.

Conceptually, I perfectly agree. But then it's not so easy to give a precise short definition of Bell non-locality without dwelling into vague philosophy.

 

[Demystifier]

If Bell had used a better term instead of local/non-local, for example a term that was not already in use, then most of the discussions about Bell's theorem would not exist. What's wrong with terms like non-separable or non-factorizable?

There are several reasons for that. "Non-factorizable" sounds like a purely mathematical property without a direct physical content. "Non-separable" sounds mysterious, perhaps even more than "non-local". But probably the main reason was the fact that Bell wanted to justify his favored interpretation of QM, which was the non-local Bohmian interpretation.

 

[mfb]

Why is there no signal that still obey SR but doesn't use EM

Neutrinos? It is not practical, but in principle you can transmit information via neutrino beams. They can easily pass through the Earth.

 

[Demystifier]

Why is there no signal that still obey SR but doesn't use EM.

It must use one of the four fundamental forces. The so called strong and weak forces act only on small distances. Gravity is too weak. What remains is the EM force.

 

[vanhees71]

If Bell had used a better term instead of local/non-local, for example a term that was not already in use, then most of the discussions about Bell's theorem would not exist. What's wrong with terms like non-separable or non-factorizable?

Einstein used them, but nobody followed him, because everybody thought, he'd just not understood QT. I think the opposite is true, although I don't follow his argument that you can conclude that QT is "incomplete" in some way. As it looks today (much more than in 1948 when Einstein clarified his view which he felt not having been adequately represented by the famous EPR article; it's in German however: A. Einstein, Quanten-Mechanik und Wirklichkeit, Dialectica 2, 320 (1948)) QT seems to be rather complete as far as it is formulated and applicable (the great exception is the absence of a consistent QT of gravitation) is accurately describing the behavior of observable nature, including the irreducible probabilistic elements it includes.

 

[Blue Scallop]

It must use one of the four fundamental forces. The so called strong and weak forces act only on small distances. Gravity is too weak. What remains is the EM force.

why are there no non gauge forces? what exact stuff in physics is violated?

 

[Simon Phoenix]

signal locality
Bell non-locality

Personally, I don't find these terms to be too helpful and in some sense I think they're confusing. Intuitively the local/non-local thing is about whether things we do in our lab (local) can affect the results of experiments performed in some other lab (non-local) - and I suppose we also ought to add in the qualification that any such effect (if it exists) must not occur faster than the time it takes light to travel between the labs.

In this sense QM is a fully local theory - even in its standard (non-relativistic) formulation. Of course the fact that in QM things we do 'here' do not affect results 'there' implies that we can't send any information, so the signal locality is really a consequence in my view.

I personally don't really see much virtue in defining something called "Bell non-locality" since Bell's inequality is an entirely classical inequality that (loosely) says $if$ our system is described by variables that are (a) local and (b) have some meaning independent of measurement $then$ the correlations are constrained by the Bell inequality. It doesn't really say anything about QM, as such.

What we can say is that the predictions of QM cannot be fully reproduced by a theory constructed from variables that have the properties (a) and (b). So clearly QM is not this kind of theory - which doesn't really tell us what kind of theory QM actually $is$, it just says what kind of theory QM cannot be. To then say that QM is therefore "Bell non-local" seems a bit arse-about-face to me, to use a quaint English expression. I don't really get what describing QM as Bell non-local brings to the table, so to speak - it just seems to muddy the waters.

And I'll stop there before the mixed metaphor and idiom police arrest me.

 

[DrChinese]

Of course the fact that in QM things we do 'here' do not affect results 'there' implies ...

But that is precisely why we need a term like Bell non-local: your statement is not necessarily true, and Bell tests highlight this. It is absolutely the case that Alice's choice of measurement *appears* to change the nature of Bob's reality somewhere else faster than any light signal. (Of course, the reverse is equally true for Bob, and can even *appear* to be backwards in time.) You cannot rule that out - so whatever that is, it is Bell non-local and that is a perfectly reasonably description in my eyes. Or you can call it quantum non-locality, a term I also see used. But it is clearly different than signal non-locality.

 

[Simon Phoenix]

It is absolutely the case that Alice's choice of measurement *appears* to change the nature of Bob's reality

Yes - and the words "appears to" are, I think, critical here.

Alice's (local) measurement results are entirely described by the (local) reduced density operator and the (local) measurement operator - and similarly for Bob.

There's nothing in QM in which the results Alice observes are in any way affected by things Bob does (including measurements).

The notion that something Alice does in her lab affects something in Bob's lab is interpretation dependent I think.

 

[Blue Scallop]

Electromagnetic waves use spacetime to propagate. If you move the spacetime fabric. you also get gravitational wave. If spacetime has capability for both signal locality and Bell's non-locality, why isn't there any signal that doesn't violate SR but doesn't travel in the spacetime fabric.. yet it can appear and disappear anywhere at spacetime (just like Bell's non-locality) but without traveling in between (and yet whose correlation effect doesn't travel faster than light or limited by equivalent light speed). I mean if Spacetime is so versatile and Bell's non-locality works even millions of light years away why can't Spacetime have this mode where we have a radio on Earth and Neptune whose wave doesn't travel in space but appear there and here limited by lightspeed but doesn't travel in between?

 

[stevendaryl]

You can call things whatever you like, but I think there is a sense of the word "local" that is not captured by signal speed.

Suppose that there were a pair of correlated coins such that, no matter how far away the two coins are from each other, the nth flip of one coin always gives the opposite result from the nth flip of the other coin. Other than that correlation, the coin flips seem to be perfectly random--the nth flip of each coin considered separately has a 50/50 of resulting in "heads" or "tails".

I would call such a correlation "nonlocal"; it relates distant phenomena.

 

[rubi]

Locality in physics refers to the principle that actions in one spacetime region can only affect tht events in the future lightcone of that region. We can prove that QM is compatible with this principle. Correlations over spacelike distances don't necessarily violate this principle and indeed, QM predicts such correlations. What Bell proved is that one possible explanation for these correlations (hidden variables) is incompatible with the principle of locality. This is one reason for why most people reject hidden variable theories.

Unfortunately, some people (mostly Bohmians) are very dishonest about this situation. They claim that hidden variables are the only possible way to explain the correlations and therefore QM must violate the principle of locality. Of course, this argument is invalid and the existence of perfectly local interpretations proves them wrong.

 

[atyy]

Locality in physics refers to the principle that actions in one spacetime region can only affect tht events in the future lightcone of that region. We can prove that QM is compatible with this principle. Correlations over spacelike distances don't necessarily violate this principle and indeed, QM predicts such correlations. What Bell proved is that one possible explanation for these correlations (hidden variables) is incompatible with the principle of locality. This is one reason for why most people reject hidden variable theories.

Unfortunately, some people (mostly Bohmians) are very dishonest about this situation. They claim that hidden variables are the only possible way to explain the correlations and therefore QM must violate the principle of locality. Of course, this argument is invalid and the existence of perfectly local interpretations proves them wrong.

That is untrue. There are simply different definitions of nonlocality, and reality is certainly nonlocal by one of these well motivated definitions

 

[bhobba]

QFT and QED obey signal locality.. so we send radio waves over the atmosphere but it can't pass thru the Earth core because of the core and mantle density. Why is there no signal that still obey SR but doesn't use EM.. so we can make receiver in one side of the Earth and another side and it can appear without traveling but obey SR.. like using some king of higgs field but with vectorial component to communicate.. why doesn't such exist? what symmetry or laws of nature is violated by this (yet still obey SR)?

Of course you can use something else than radio waves to send signals. But via SR that is limited to the speed of light. Correlations can't be used to send information. If you could SR is down the tibe and since its reallly based on just some symetry considerations we would be in VERY VERY deep do do:
http://www2.physics.umd.edu/~yakovenk/teaching/Lorentz.pdf

Thanks
Bill

 

[PeterDonis]

Electromagnetic waves use spacetime to propagate.

This is not a good description of the physics, and is bordering on personal speculation.

 

[Blue Scallop]

This is not a good description of the physics, and is bordering on personal speculation.

how does electromagnetism propagate then with respect to spacetime?

or do you mean since spacetime is just a graph.. electromagnetism doesn't "propagage" in spacetime at all? then what language to use to describe how electromagnetism behave in spacetime?

 

[PeterDonis]

how does electromagnetism propagate then with respect to spacetime?

Electromagnetism propagates in spacetime, because anything that propagates propagates in spacetime. But that doesn't mean electromagnetism "uses spacetime" to propagate.

what language to use to describe how electromagnetism behave in spacetime?

The issue isn't the language in itself, but the inferences you are drawing from it. Your post #22 is basically personal speculation based on the language you used. (You might notice that a subsequent post of yours got you a warning and has been deleted.) language is not physics; if you want to draw inferences from the physics, you should be looking at the actual mathematical models that describe the physics. What ordinary language you use to refer to those models is beside the point as far as physics is concerned, since you're not using the ordinary language to draw inferences anyway.

 

[Blue Scallop]

Electromagnetism propagates in spacetime, because anything that propagates propagates in spacetime. But that doesn't mean electromagnetism "uses spacetime" to propagate.

What? Mulling over it after reading some relativity threads, I thought nothing moved in spacetime because the worldline was the graph of it. So how can electromagnetism even propagates in spacetime (in the worldlines).. when spacetime is and ever will be same size... .. unless you mean electromagnetism propagate in space?

The issue isn't the language in itself, but the inferences you are drawing from it. Your post #22 is basically personal speculation based on the language you used. (You might notice that a subsequent post of yours got you a warning and has been deleted.) language is not physics; if you want to draw inferences from the physics, you should be looking at the actual mathematical models that describe the physics. What ordinary language you use to refer to those models is beside the point as far as physics is concerned, since you're not using the ordinary language to draw inferences anyway.