Nature asks: Physicists bid farewell to reality? (abstract) (see also)
Nature’s Editor summarizes: Quantum physics gets unreal
Physics Web reports: Quantum physics says goodbye to reality (see also)
Scientific American mourns: Quantum Theory Fails Reality Checks (see also)
Here is the article that has caused the commotion — complete and for free:
An experimental test of non-local realism
(published in Nature 446, 871-875, 19. April 2007)
And here is how it begins:
Physical realism suggests that the results of observations are a consequence of properties carried by physical systems…
This defines the realism in question.
Quantum physics, however, questions this concept in a very deep way.
That’s what I’ve been been harping on in so many papers for so many years, under the motto “to be is to be measured“.
To maintain a realistic description of nature, non-local hidden-variable theories are being discussed as a possible completion of quantum theory.
Why would Nature use variables and then make sure that they cannot be measured? One might as well posit strictly unobservable elastic strings to explain Newton’s law of gravity. The only sensible reason why so-called “hidden variables” are hidden is that they do not exist. Physical variables have values only if, only when, and only to the extent that they are actually measured (that is, their values are indicated by some actual event or state of affairs).
We present an inequality… that allows us to test an important class of non-local hidden-variable theories against quantum theory.
Three cheers for Simon Gröblacher, Tomasz Paterek, Rainer Kaltenbaek, Časlav Brukner, Marek Żukowski, Markus Aspelmeyer, and Anton Zeilinger!
Finally, we perform an experiment that violates the new inequality and hence excludes for the first time a broad class of non-local hidden-variable theories.
Hooray!!! Now if you want to understand what’s going on, why don’t you google for the Pondicherry interpretation of quantum mechanics? Or visit This Quantum World?
This pivotal paper — in my opinion, the most important physics paper of the 21st Century thus far — ends with the words:
We have experimentally excluded a class of important non-local hidden-variable theories… We believe that the experimental exclusion of this particular class indicates that any non-local extension of quantum theory has to be highly counterintuitive. For example, the concept of ensembles of particles carrying definite polarization could fail…
Could??? Get real, boys!
We believe that our results lend strong support to the view that any future extension of quantum theory that is in agreement with experiments must abandon certain features of realistic descriptions.
Certain features? Why this extraordinary understatement? Did the editors of Nature make you do it?
Postscript: Quantum Quandaries points out that this experiment does not amount to a refutation of “nonlocal realism”, inasmuch as the class of “nonlocal realisms” refuted does not include Bohm’s theory. Indeed, no experiment that simply confirms the predictions of quantum theory can be said to rule out nonlocal realism. But this just means that nonlocal realism belongs into the same category as said elastic strings.
