Einstein was wrong about at least one thing: There are, in fact, "spooky actions at a distance," as now proven by researchers at the National Institute of Standards and Technology (NIST).
Einstein used that term to refer to quantum mechanics, which describes the curious behavior of the smallest particles of matter and light. He was referring, specifically, to entanglement, the idea that two physically separated particles can have correlated properties, with values that are uncertain until they are measured. Einstein was dubious, and until now, researchers have been unable to support it with near-total confidence.
As described in a paper posted online and submitted to Physical Review Letters (PRL), researchers from NIST and several other institutions created pairs of identical light particles, or photons, and sent them to two different locations to be measured. Researchers showed the measured results not only were correlated, but also—by eliminating all other known options—that these correlations cannot be caused by the locally controlled, "realistic" universe Einstein thought we lived in. This implies a different explanation such as entanglement.
The NIST experiments are called Bell tests, so named because in 1964 Irish physicist John Bell showed there are limits to measurement correlations that can be ascribed to local, pre-existing (i.e. realistic) conditions. Additional correlations beyond those limits would require either sending signals faster than the speed of light, which scientists consider impossible, or another mechanism, such as quantum entanglement.
The research team achieved this feat by simultaneously closing all three major "loopholes" that have plagued previous Bell tests. Closing the loopholes was made possible by recent technical advances, including NIST's ultrafast single-photon detectors, which can accurately detect at least 90 percent of very weak signals, and new tools for randomly picking detector settings.
"You can't prove quantum mechanics, but local realism, or hidden local action, is incompatible with our experiment," NIST's Krister Shalm says. "Our results agree with what quantum mechanics predicts about the spooky actions shared by entangled particles."
The NIST paper was submitted to PRL with another paper by a team at the University of Vienna in Austria who used a similar high-efficiency single-photon detector provided by NIST to perform a Bell test that achieved similar results.
The NIST results are more definitive than those reported recently by researchers at Delft University of Technology in the Netherlands.
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