Principal of Locality - Einstein

[Q_Goest]

In physics, the principle of locality is that distant objects cannot have direct influence on one another: an object is influenced directly only by its immediate surroundings. This was stated as follows by Albert Einstein in his article "Quantum Mechanics and Reality" ("Quanten-Mechanik und Wirklichkeit", Dialectica 2:320-324, 1948):

The following idea characterises the relative independence of objects far apart in space (A and B): external influence on A has no direct influence on B; this is known as the Principle of Local Action, which is used consistently only in field theory. If this axiom were to be completely abolished, the idea of the existence of quasienclosed systems, and thereby the postulation of laws which can be checked empirically in the accepted sense, would become impossible.

Ref: http://en.wikipedia.org/wiki/Principle_of_locality"

I don't have this article, so my first request is that if anyone has it and can either post it or (if concerned about copyright issues) you could email it to me, that would be appreciated. I may need it as a reference for a paper I'm working on, and I can't seem to locate it on the net and don't have access to it.

This quote of Einstein seems to be bantered around quite a bit. A few questions:

1. Do you believe Einstein meant this principal to apply only at the quantum level, or do you think he wasn't differentiating between classical and quantum mechanics (ie: the principal of locality is a fundamental principal of nature)? It seems to me as if Einstein was simply applying the same philosophy used in classical mechanics to quantum mechanics. This would say that the principal of locality is applicable to classical mechanics regardless of whether it can be applied to quantum mechanics.

2. Would it be wrong to quote this principal with respect to classical mechanics only? When we consider the time evolution of a phenomenon such as the flight of an aircraft or rocket, or the response of a bridge to loads induced by vortex shedding (ie: Tacoma Narrows bridge), I would think this principal was applicable. But if the intent of this phrase is specifically to address quantum mechanical phenomena, then it's questionable if one could quote Einstein in this regard, saying something to the affect, "The principal of locality is applicable to the interaction of matter and energy at the classical level."

 

[Q_Goest]

I don't suppose I've missinterpreted Einstein, but it would be good to confirm this. Thoughts?

 

[Dbjergaard]

AHHH Wikipedia RUN!

Wikipedia should only be used for a launch pad to other credible websites... Unless you have checked the sources I would be skeptical as to the legitimacy of the research. (I read your post and obviously there's a journal article there) Anyway, that's my two cents on wikipedia, back on topic, I'm not sure at all... Unfortunatly I don't have a copy of this article.

 

[Marco_84]

You should read first the article of the 1935 by Einstein-Podolsky-Rosen on their "paradox" about locality. It's a discussion on the hiddens variables in QM. i suggest you to read something on the bell's inequalities about 1960 and Alain Aspect experiments 1980. i think the problem is insight the postulate of quantum Mechanichs but if we don't accept them we trash all we know from it. Spectral lines, superfluidty, superconductivity, quantum computation, SM... an so on. really big troubles i think... :-)

bye marco

 

[Q_Goest]

Hi Marco,

You should read first the article of the 1935 by Einstein-Podolsky-Rosen on their "paradox" about locality. It's a discussion on the hiddens variables in QM.

If you have the article, can you post it?

Are you suggesting that quantum mechanics disproves locality? Entanglement seems to be the best example where locality seems to fail. I wonder if physicists consider Einstein's "principal of locality" to be false or not.

But even so, even if we claim locality is invalid for quantum mechanical phenomena, what does this say for classical mechanics or phenomena at the classical level?

I can't see how one can avoid the principal of locality at the classical level. I can't think of a single classical level phenomenon that doesn't exhibit locality. Aircraft, bridges, and any classical level construct seem to depend only on classical level phenomena, and these phenomena require causal, local interactions between 'parts'.

The issue for me is whether or not the principal of locality is valid for classical mechanics, and whether or not it is a generally accepted principal.

 

[Marco_84]

Hi G_Oest,
i've read it, i can ask a friend for that article.
but if you go to university you can download it for free from a
university proxy..
If you don't find it give me few days... i'll send you also Aspec's experiment original papers.

I was telling you that the problem can be the interpretation of QM! we just know that |psi|^(2) make sense in this theory. We have only the limited, but really powerfull Born interpretation (probabilistic). Formally locality is a "classic" principal that seems to fail in QM and this is Einstein's argumentation on the "problems" of QM. He entroduced hidden variables to explain this, but bell's inequalities show that QM has no hidden variables. So or it is correct or not!

What i think it's that locality is a principal we cannot avoid! even in QM or any field theory. Maybe we have to reformulate this principal in a way that if we make a limit from QM--->ClassM we can refind the same defintion gived by Einstein.
Cuz if its not like this what about fields theories?
i KNOW IT IS A REALLY BIG TROUBLE that physicist, mathematician, phylosphers, you, me...all together have to figur out..

I'll talk to you later.
bye
Marco

 

[Q_Goest]

Thanks Marco. I'll have a look for the paper, but I don't attend college. I graduated long ago.

 

[Tomsk]

I read a fascinating article on a relatively new interpretation of QM called Relational Quantum Mechanics, which seems to solve the EPR problem (though I am by no means an expert): http://en.wikipedia.org/wiki/Relational_quantum_mechanics - or if Wiki can't be trusted, http://plato.stanford.edu/entries/qm-relational/ although I'm only half way through this one.

I didn't think locality was necessary in classical mechanics, doesn't Newtonian gravity have action at a distance?

 

[Q_Goest]

Hi Tomsk, Thanks for the links. I'll have a look at them when I get a moment.

I didn't think locality was necessary in classical mechanics, doesn't Newtonian gravity have action at a distance?

From what I've read, Einstein was troubled by the apparent problems QM created in regard to locality, and spent much time arguing (esp. w/ Niels Bohr) against any kind of non-local philosophy of nature. Relativity does not disobey locality because gravity is believed to propogate at the speed of light.

Is there any other reason classical mechanics wouldn't obey locality?

 

[nealh149]

Classical gravity, if I'm not mistaken, does actally disobey locality because Newton believed it to be an instantaneous reaction. GR cleared this up of course.