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There might be no getting around what Albert Einstein called "spooky action at a distance." With an experiment described [February 7th] in Physical Review Letters — a feat that involved harnessing starlight to control measurements of particles shot between buildings in Vienna — some of the world's leading cosmologists and quantum physicists are closing the door on an intriguing alternative to "quantum entanglement."
[...] In the first of a planned series of "cosmic Bell test" experiments, the team sent pairs of photons from the roof of [Anton] Zeilinger's lab in Vienna through the open windows of two other buildings and into optical modulators, tallying coincident detections as usual. But this time, they attempted to lower the chance that the modulator settings might somehow become correlated with the states of the photons in the moments before each measurement. They pointed a telescope out of each window, trained each telescope on a bright and conveniently located (but otherwise random) star, and, before each measurement, used the color of an incoming photon from each star to set the angle of the associated modulator. The colors of these photons were decided hundreds of years ago, when they left their stars, increasing the chance that they (and therefore the measurement settings) were independent of the states of the photons being measured.
And yet, the scientists found that the measurement outcomes still violated Bell's upper limit, boosting their confidence that the polarized photons in the experiment exhibit spooky action at a distance after all.
Source: https://www.quantamagazine.org/20170207-bell-test-quantum-loophole/
(Score: 0) by Anonymous Coward on Wednesday February 15 2017, @08:01AM
ok, maybe I'm wrong, but I don't understand how I'm wrong.
it's been more than ten years since I learned about special relativity, and I no longer remember how to define a reference system.
the relativistic distance between these two events: "star emits photon" and "observer sees photon".
Is it time-like in the reference frame of the observer? Or distance like? Or both?
I do agree that the setting up of the experiment is an event outside the light cone of the photon emission event, so there is no causal relation between them (but there is quantum entanglement present because the universe is described by a single quantum state).
(Score: 0) by Anonymous Coward on Wednesday February 15 2017, @10:29AM
The fourth alternative: It's neither. Rather, it's light-like. Note that this notion is independent of the frame of reference.
But terms like " a hundred years ago" don't make sense without specifying a frame of reference, and then it denotes not the spacetime distance, but the difference in coordinate time. For objects moving with constant slower-than-light speed, there exists a reference frame for which the elapsed time agrees with the spacetime distance; this is the reference frame in which the object rests. For light, there is no reference frame in which it rests (light moving at light speed in all frames of reference is, after all, one of the fundamental postulates the theory rests on). Indeed, for any nonzero value of elapsed time you can find a frame of reference where the time between emission of the photon and its detection is exactly that value.
However unless explicitly stated otherwise, when giving times or distances, the frame of reference those times and distances are relative to is the frame of the observer. If there are no observers, or if there is more than one (and those different observers have sufficiently high speeds relative to each other that the difference doesn't vanish in the rounding error), you have to explicitly state which frame of reference you are referring to.