Copenhagen & Many Worlds Falsified?

[ZapperZ]

Then, hold it one itty-bitty second! Where in the galaxy! did you get the impression that in the Afshar experiment a measurement of any kind is performed at the site of the slits?

(... or was it Skippy who answered question (i)?)

He somehow knew which pinhole the photon passed though. [I used the double slit as a generic example]

This is why I emphasized that I need to actually read the paper since by making such a statement, I immediately assume that there was some kind of measurement, rather than an inference. If it is the latter, than there's more than enough ammo to go around at arguing against the results and conclusion. So I automatically guessed the former since it has to be on a stronger ground.

So, did I interpret the experiment incorrectly?

Zz.

 

[Eye_in_the_Sky]

I immediately assume that there was some kind of measurement, rather than an inference.

I have a little picture for (!)you(!) (... Skippy already knows about it.).

... If it is the latter, than there's more than enough ammo to go around at arguing against the results and conclusion.

... "results"? ... "conclusion"?

If by "results" you mean (note: WG = wire grid):

(from post #11 of this thread, "Afshar Setup")

Summary of reported results:

a) No WG + both slits open --> no loss;

b) WG + only one slit open --> 6% loss;

c) WG + both slits open --> < 0.1% loss.

... and if by "conclusion" you mean:

(from post #11 of this thread, "Afshar Setup")

Conclusion:

Since the results of c) are very nearly the same as those of a) and, on the other hand, appreciably different from those of b), the situation in c) must be that of "wave-like" behavior (i.e. the quantum system interacts with both slits, and not just one slit). That is to say, two waves are propagating, one from each slit, and in the vicinity of WG these waves overlap and interfere to produce minima at the locations of the wires in WG. For this reason, WG is essentially transparent to the incident beam.

... then there is zero "ammo". These are merely confirmations of what QM predicts.

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(ii) Are you the same ZapperZ who wrote (in post #2 of this thread):

"... So how he [Cramer] came up with the conclusion that they [CI and MW] offer a result that differ from the QM formalism itself is puzzling. This is because if that is true, then one can LOGICALLY falsify both interpretations without having to do any experiment."

(ii) yes (unless my evil twin Skippy has been up to no good again).

... so ... it was Skippy.

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So, did I interpret the experiment incorrectly?

You gave Afshar and Cramer the benefit of the doubt - that was quite noble of you ... yet, quite incorrect.

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I offer my criticism to this Afshar/Cramer's point not based on an inherent philosophy, but rather on the experiment itself.

If Afshar's results are experimentally valid, then we obtain a confirmation of a QM prediction; if Afshar's results are not valid, then we obtain no new information.

... The only real "debate" is one over the question of whether or not CI (MWI, or whatever else) "permits" or "forbids" the inference.

 

[SimonA]

Well I do appreciate what you're both saying and I've never (nor have Afshar or Cramer to my knowledge) said that this experiment contradicts "QM". The issue is with Bohrs interpretation.

Bohr writes (1939):

...the very fact that in quantum phenomena no sharp separation can be made between an independent behavior of the objects and their interaction with the measurement instruments, lends indeed to any such phenomena a novel feature of individuality which evades all attempts at analysis on classical lines, because every imaginable experimental arrangement aiming at a subdivision of the phenomena will be incompatible with its appearance and give rise, within the latitude indicated by the uncertainty relations, to other phenomena of similar individual character.

I got that quote from this page --> this page which summarises the hub of why Afshar is saying "Einstein was right" (but not why he says "for the wrong reason" which is due to the claim that quantisation is a property of the emmiter and the detector along the lines quoted by Cramer in his 1986 paper on the Hanbury-Brown-Twiss effect)

From Einstein's point of view, it seemed the "free choice" we have of which of the two possible measurements to make involves one and the same system. But from Bohr's point of view, in order to give terms like "position" and "momentum" empirical significance, "system" must be interpreted in the sense of that which is observed. And since the experimental arrangement necessary for alternative observations of position and momentum are mutually exclusive, he concluded that the two observations refer to the properties of two distinct phenomenal objects. There was simply no "same system" in a sense that both position and momentum could be observed.

Simon

 

[Eye_in_the_Sky]

I feel compelled to qualify a statement I made in post #52 of this thread. That statement appears to suggest a point of view which I neither intended to convey nor accept as valid. The statement was:

... The only real "debate" is one over the question of whether or not CI (MWI, or whatever else) "permits" or "forbids" the inference.

These words appear to suggest that there can be no "real" debate over the experimental validity of the Afshar results. This is something which I did not wish to convey. On the contrary, issues of this kind (i.e. questions concerning the validity of experimental results) are at the very heart of what makes physics what it is really about - namely, about what happens in the "world". Moreover, not only are such issues essential, but they can also involve highly nontrivial, subtle, complex, and intricate matters.

Therefore, to qualify what I meant in making the above quoted statement, my intention was to say no more than:

With regard to the question of the validity of CI (MWI, or whatever else) as an interpretation of QM, the only real "debate" is over whether or not it "permits" or "forbids" the inference.

 

[slyboy]

There was an article on the Ashfar experiment in the New Scientist a couple of weeks ago. This made what was going on in it much clearer to me than it was from Cramer's powerpoint presentation. I think that the experiment only violates Copenhagen if you take a VERY VERY VERY (+ many more VERY's) naive version of Copenhagen. The experiment does no more than show that it is possible to measure much more sophisticated things than straightforward observables in QM. This is already well-known, and you might as well say that any measurement of a POVM that has ever been made violates Copenhagen, which is clearly ridiculous.

These people clearly do not understand quantum measurement theory, which is inexcusable for anyone making such claims about the foundations of quantum mechanics. They also do not understand what complementarity is, which is much more excusable because it is a very vague and imprecise notion. However, it is clear from Bohr's writings that he meant something more sophisticated than wave-particle duality.