Is the Following How Most Students Think of Einstein's View Of QM

[bhobba]

I don't know, what precisely it is what Weinberg thinks is missing, because in his book he just says that which interpretation is "correct" is an open question,

He believes there is no interpretation that does not have serious flaws. But says 'this view is not universally shared'. I personally do not share it, but his arguments are coherent and clearly detailed. For example his objection to Consistent Histories is its use of the Born rule seems to bring people into the laws of nature. Indeed he thinks any instrumentalist approach has this problem. To me, like John Baez says, often it's the old disagreements about the meaning of probability bought into another area, and I think Weinberg's arguments are to some extent along those lines.

Thanks
Bill

 

[bhobba]

Here is another quote from Weinberg:

He tries very hard to be carefull, to his great credit, and in understanding his views for people like me that have thought long and hard about the issues. For example he points out when in a state that when measured will give a value close to a certain value, it is tempting to think it has a value close to that value. But that is not what it says - it says if you measure it that's what happens - when not measured it says nothing. From this he draws the conclusion that such instrumentalist approaches are human dependant, and this inclusion of the 'experimenter' into the theory is not compatible with an objective reality. That I do not agree with - I believe because the Von-Neumann cut can be placed anywhere, you can consider it as having that value by placing the cut there. But the view is coherent and obviously with a lot of thought behind it. I really would have liked to see a discussion between Gell-Mann and Wienberg on this point because he was a proponent of Consistent Histories that often looks at things this way.

Thanks
Bill

 

[Elias1960]

Why do you call it Einstein causality? Is this your terminology or not? Can you give a reference?

It is what is called Einstein causality or locality in the discussions about Bell's theorem. I prefer not to use to name it "locality" because this is misleading - a completely local theory with maximal speed of information transfer 100 c would have to be named "nonlocal" if one follows this convention. Therefore I name it either Einstein-local or Einstein-causal.

The terminology, however chosen, has to distinguish two notions of causality. There is a weak one which forbids only to send signals, and therefore usually named signal causality. It is a theorem in QFT, but also holds in dBB, despite the fact that in dBB causal influences happens faster than light. These FTL influences can nonetheless not be used to send signals, and therefore signal causality is not violated. And there is the strong one which is necessary to prove Bell's theorem. With signal causality alone you cannot prove it, as QFT and dBB show, where it cannot be proven.

 

[martinbn]

It is what is called Einstein causality or locality in the discussions about Bell's theorem. I prefer not to use to name it "locality" because this is misleading - a completely local theory with maximal speed of information transfer 100 c would have to be named "nonlocal" if one follows this convention. Therefore I name it either Einstein-local or Einstein-causal.

The terminology, however chosen, has to distinguish two notions of causality. There is a weak one which forbids only to send signals, and therefore usually named signal causality. It is a theorem in QFT, but also holds in dBB, despite the fact that in dBB causal influences happens faster than light. These FTL influences can nonetheless not be used to send signals, and therefore signal causality is not violated. And there is the strong one which is necessary to prove Bell's theorem. With signal causality alone you cannot prove it, as QFT and dBB show, where it cannot be proven.

OK, but my question was if this is your own terminology or is it used by other people. Any examples you can point out?

 

[bhobba]

OK, but my question was if this is your own terminology or is it used by other people. Any examples you can point out?

It is terminology sometimes found in foundational discussions of SR. Strictly speaking SR does not forbid speeds FTL - just the ability to sync clocks by signals FTL ie signals carrying information. I don't see too much about it these days because the geometric/group theory approach to SR, while not doing away with the issue, makes it not really needed in 'deriving' the Lorentz transformations eg:
http://www2.physics.umd.edu/~yakovenk/teaching/Lorentz.pdf

Because it's not germane to the main argument, the speed c that derivation requires the fixing of experimentally, is really the maximum speed information can be sent. It does not rule out faster speeds that can't be used to send information, but a full discussion of this fine point is best left for a thread in the relativity forum where other forms of clock syncing can be discussed such as slow clock transport. Although I can't recall specific examples, I seem to recall they sometimes give different synchronizations than using, say light signals - but that takes me way back to when I was interested in the foundations of relativity, which these days is more a vague memory. Ohanian, the author of the book - Einstein's Mistakes, and that 'different' book on GR (it its not derived by geometrical methods) was careful about it:
https://pdfs.semanticscholar.org/41f5/72b841a358998a0aaab03fed3561d80c5491.pdf

Note the above does not analyse the newer methods like the group theoretic argument I gave before which gives SR without any issues. The clock sync issue applies to Einstein's original papers so the conclusions the above paper reaches is very dubious , and while a peer reviewed Journal it would not pass my review without pointing out better ways of deriving/explaining SR now exists. Added later - but even aside from this, the postulate of relativity is that the laws of physics is the same in all inertial frames. Now whatever laws of physics determine the speed of light if you reverse the coordinate system it obviously is still an inertial frame - but the light travels in the opposite direction, but at the same speed. You are invoking the POR but by reversing the coordinate system it becomes very clear.

Thanks
Bill

 

[Pony]

It is terminology sometimes found in foundational discussions of SR. Strictly speaking SR does not forbid speeds FTL - just the ability to sync clocks by signals FTL ie signals carrying information.

What does this mean? How could SR forbid the ability to sync clocks by signals FTL?

Also, AFAIK aether theories or other preferred frame theories give the same predictions as SR, and are consistent with a restricted form of FTL communication, that is, we can allow FTL communication in a preferred frame, still no causal loop or causality paradox could occur.

 

[bhobba]

What does this mean? How could SR forbid the ability to sync clocks by signals FTL?

Please, as I mentioned, take this up on the relativity forum.

But just as an overview, SR says the fastest information can be sent is the speed of light. The reason is the c that appears in the equations must the unique speed the same in all frames. Let s be the fastest speed information can be sent - it could be infinity. Now to sync clocks by signals you can't do that with signals faster than s. But by the Principle Of Relativity that must be the same in all frames. However only one speed is the same in all frames - that is the c in the SR equations ie s=c. Now if you can't send information, then you can't use it to sync clocks - or anything really - so the argument breaks down.

Thanks
Bill