Quantum Theory Fails Reality Checks: Scientific AmericanSo what is "realism"? Despite recently reading 1.5 modern books on QM, I don't know. I don't think the definition in the above article is complete, I suspect the study means that we can't dodge mind-boggling QM interpretations merely by surrendering to instantaneous correlation across the breadth of the universe. I didn't care for the flippant tone of the article, it's not just Einstein who was bugged by what QM means. Feynman, I think, once said something like "if it doesn't drive you batty you're not paying attention".
...Einstein was famously bugged by what are now well-established facts of quantum theory: the randomness of a particle's choices and the possibility of instantaneous linkages between far-flung light or matter. Experimenters now conclude that Einstein cannot even pick his poison, because allowing for instant links kills any simple notion of reality, too.
The team updated a classic 1982 experiment in which researchers measured the polarizations, or spatial orientations, of twin pairs of photons. In quantum theory, photons and other particles do not have definite values for properties such as location or polarization but rather acquire a specific property randomly when measured in an experiment.
... Researchers learned that they could test a related question using photons that are entangled, meaning they are instantaneously connected over any distance in such a way that the measured property of one depends on the other—like a pair of dice that always comes up doubles.
In the 1982 experiment, if the photons "rolled doubles" more than a certain fraction of the time, it meant that particles violated something called local realism: the idea that influences between particles ripple through spacetime like waves (locality) and that particles have hidden nonrandom properties (realism).
But which assumption might be wrong? "It could still be possible," Aspelmeyer says, "that you maintain realism … and that you just relax this locality condition." So he, along with team leader Anton Zeilinger and colleagues, tested a proposed antiquantum model in which influences travel instantaneously but particles have real properties (no locality but realism).
They split red laser photons into entangled pairs and sent the twinned light particles along separate paths. They then measured the polarizations of the photon at different angles to see how often they scored "doubles," called correlations.
Aspelmeyer says the group's hunch was that "if you allow for nonlocal interactions, anything goes, [so] you can recover quantum physics completely" without losing a grip on reality. But, as in the older experiment, they once again saw more correlations than nonlocal realism allowed.
In other words, Aspelmeyer says, nonlocality is not enough to save realism from quantum theory...
Thursday, April 19, 2007
It was thought, indeed hoped, that if we narrowed special relativity to 'meaning cannot travel faster than light', and allowed for instantaneous communication that did not allow meaning to be communicated, that we could preserve something called "realism". Not so.