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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: 2, Informative) by Anonymous Coward on Tuesday February 14 2017, @02:56PM
that is not true. literally not true.
"time" does not exist for photons, since they move at lightspeed.
For a photon, their creation may "last", their destruction may "last", but the duration of the "inbetween" is 0 (quotation marks because there are exactly zero seconds between creation and destruction).
So no, it makes no sense to say that the photons were created hundreds of years ago, unless you are talking about things outside the light cone, which the laws of physics (INCLUDING THOSE OF QUANTUM MECHANICS) forbid you to do. if you want to talk sense that is.
This whole thing made me angry enough to no longer care whether or not their experiment is useful for the general public.
If you rely on a fake storyline ("photons left hundrdds of years ago, so they can't know about what we're doing now") to push the truth ("quantum weirdness" is real) on people, then you're kind of missing the point.
(Score: 2) by sjames on Tuesday February 14 2017, @03:23PM
So you're saying that no time has passed FOR US since those photons were created?
Otherwise, you're just looking at more weirdness from a different angle.
(Score: 3, Informative) by Anonymous Coward on Tuesday February 14 2017, @03:24PM
It is true.
Time exists for us, since we move at earth speed. And therefore we can meaningfully ask about the time, in our frame of reference, between the two events (1) sending out that photon at the respective star, and (2) receiving the photon on earth.
Of course, it doesn't actually matter for the experiment; for that experiment it only matters that (a) neither of the photon emissions could possibly have been influenced by the experimental setup (that is, the emission events are not in the absolute future of any event of the experimental procedure), and (b) those two photon emission events were spacelike to each other (so there is no way the emission of one of them could possibly have influenced the emission of the other).
(Score: 0) by Anonymous Coward on Tuesday February 14 2017, @03:27PM
I forgot to add: Of course the fact that it was emitted 100 years ago in our frame of reference already implies that the emission event was not in the absolute future of any part of the experiment, as the experiment was started less than 100 years ago, and the absolute future of an event has the property to be in the future of that event in every frame of reference, including in ours.
(Score: 3, Informative) by wonkey_monkey on Tuesday February 14 2017, @05:49PM
This whole thing made me angry enough
I think you have issues. You're also wrong.
It makes perfect sense to say these photons were emitted hundreds of years ago, because they were, for any reference frame that has any relevance to this experiment (or, indeed, to us living on this planet).
So no, it makes no sense to say that the photons were created hundreds of years ago, unless you are talking about things outside the light cone
The emission of these photons was outside Earth's lightcone when (yes, when, hundreds of years ago) it happened. That's rather the point of the experiment.
which the laws of physics (INCLUDING THOSE OF QUANTUM MECHANICS) forbid you to do
No they don't. If that was true we wouldn't be "allowed" to talk about supernovae we see in the sky, or the apparent positions of the planets, or what's on your TV, since all of the events which emitted these photons are outside of our light cones.
systemd is Roko's Basilisk
(Score: 2) by JoeMerchant on Tuesday February 14 2017, @08:06PM
I agree, AC has issues, but he's right, from the perspective of the photons. All in all, though, I don't think photons really care about this experiment or what it is showing - though their violation of Bell's upper limit does seem to show that they are far from indifferent.
I think what the astronomers were hoping for was to establish independence in the photon sources, so whether they were emitted hundreds of years ago in our reference frame, or "just emitted" as the photon sees things, the relevant point is that they're coming from separate, uncorrelated sources.
Too lazy to read the article, I wonder if/how they compensated for backscatter light and other non-star origin photons - some of that would be using the two separate windows as receiver points, but there would still be some commonality in the incoming light, small, but not zero.
🌻🌻 [google.com]
(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.