Saturday, June 4, 2011

When is a Duck to be Found as to being a Duck?






Since yesterday’s release of a paper entitledObserving the Average Trajectories of Single Photons in a Two-Slit Interferometer”, authored by Aephraim Steinberg et al, in the journal Science, there has been quite a stir. However the stir was not the normal one, where the Web picks up on a science story to have it sensationalized and misinterpreted; which is normally the case. No this time it was the self appointed experts who rushed in to fend off the consequences of what they anticipated as such an occurrence.

The only problem being is that many such experts agreed in only one thing, and that’s what the experiment revealed simply could not be what it appeared to have revealed. For instance Prof. Chad Orzel at “Uncertain principles” remarked "This is an extremely cool example of the art of experimental physics, and a spectacular demonstration of the power of weak measurements, but it's not that revolutionary. Though, as I said above, I confidently predict that there will be no shortage of crazy people trying to claim this as conclusive proof for their particular favourite interpretation of quantum theory.”

In the journal Nature, Prof. David Deutsch echoed pretty much the same in saying "it's quite cool to see strange predictions verified", the results could have been obtained simply by "calculating them using a computer and the equations of quantum mechanics...Experiments are only relevant in science when they are crucial tests between at least two good explanatory theories, Here, there was only one, namely that the equations of quantum mechanics really do describe reality."

The most definitive and critical of these was published by Ars Technica, a technical news provider. where physicist Chis Lee remarks “It's important to realize that these are not the trajectories of individual photons—instead they are more like probability clouds that tell you where photons are most likely to be found. And what do you know? Half the photons appear to have gone through one slit and half go through the other. But, in fact, this is a lie. That photon still has to have gone through both slits. It is important to realize that a measurement has to produce a result. It is always going to find that the photon is somewhere, and that tells us very little about where it came from or where it is going to.” He finishes by saying “With that knowledge, it is hard to say what this experiment tells us that we didn't know before. The only difference is that now we have both data and theory saying the same thing, which is important.”

However to be fair, I did find among them all ‘Physics World’ a publication of the Institute of Physics to be a notable exception with at least quoting the principle physicist associated with the paper with the following:

“This weak momentum measurement does not appreciably disturb the system, and interference is still observed. Both measurements had to be repeated on a large ensemble of particles in order to gain enough information for the whole system, but we did not disturb the outcome at all.” explains Steinberg. "Our measured trajectories are consistent, as Wiseman had predicted, with the realistic but unconventional interpretation of quantum mechanics of such influential thinkers as David Bohm and Louis de Broglie,"

Now on the other hand , the great unwashed, known as the general press, didn’t come to such a conclusion, yet rather choose to report it factually even to the point of not expressing what the experimentalist’s views had been. One typical example being the BBC, who quoted Marlan Scully of Texas A&M University as saying, “This paper is probably the first that has really put this weak measurement idea into a real experimental realisation, and it also gave us the trajectories." He said that the work would - inevitably - raise philosophical issues as well. "The exact way to think about what they're doing will be researched for some time, and the weak measurement concept itself will be a matter of controversy - but now we have a very pretty experiment with these weak measurements."

For me this all serves to drive home a point first made by the late physicist John Stewart Bell, when he expressed similar misgivings as follows:

“But in 1952 I saw the impossible done. It was in a paper by David Bohm (5). ....... But why then had Born not told me of this ‘pilot wave’? If only to point out what was wrong with it? Why did von Neumann not consider it? More extraordinarily, why did people go on producing ‘‘impossibility’’ proofs, after 1952, and as recently as 1978? . When Pauli, Rosenberg and Heinsenberg, could produce no more devastating criticism of Bohm’s version than to brand it as “metaphysical” and “idealogical”. Why is the pilot wave picture ignored in text books? Should it not be taught, not as the only way, but as an antidote to the prevailing complacency? To show us that vagueness, subjectivity, and indeterminism, are not forced on us by experimental facts, but by deliberate theoretical choice?

-John Stewart Bell, “On The Impossibility of The Pilot Wave”, CERN, Geneva, Ref.Th.3315-CERN (1982)

So I will simply finish in asking the same as Bell, that is when are the majority of the physicists going to stop insisting that the vagueness, subjectivity, and indeterminism, are forced upon us by experimental facts, but rather by deliberate theoretical choice? Perhaps it is only when they themselves are taken through one of two definitive slits to then be carried along by an unseen yet irresistible potential to be slammed up against a screen. Then again perhaps David Deutsch may not, as in insisting that such an occurrence happened to only a particular version of himself among the infinite multitude of many worlds :-)

"when I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck.”

-James Whitcomb Riley

3 comments:

Plato said...

Hi Phil,

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck. Duck Test

There is no uncertainty when it comes to "irreducible elements?"

It's a duck.:)

Best,

Plato said...

This independence created by philosophical insight is—in my opinion—the mark of distinction between a mere artisan or specialist and a real seeker after truth. (Einstein to Thornton, 7 December 1944, EA 61-574)
See also: Entheorizing



Black Swan Theory

Phil Warnell said...

Hi Plato,

Perhaps I should have entitled this post “ Things are not so Ducky in Quantum Foundations” :-) However, as noted here this will do little to have many reconsider their positions. Strange though as they are quite prepared to having things in two places simultaneously;-)

Best,

Phil

P.S. I read your black swan piece and wondering what I might add; other then perhaps just to agree its something more which should consider.