Making Sure Our Lab Equipment Isn't Tricking Us 108
An anonymous reader writes "In a newly published paper, MIT researchers propose an experiment that may close the last major loophole of Bell's inequality. The test is to see whether, as far-fetched as it sounds, a particle detector's settings conspire with events in the shared past to determine which properties of a particle to measure — a scenario that implies that a physicist running the experiment does not have complete free will in choosing each detector's setting. MIT’s David Kaiser says, 'It sounds creepy, but people realized that's a logical possibility that hasn't been closed yet. Before we make the leap to say the equations of quantum theory tell us the world is inescapably crazy and bizarre, have we closed every conceivable logical loophole, even if they may not seem plausible in the world we know today?' The test involves quasars, telescopes, and lots of deep, deep space. It was published this week in the journal Physical Review Letters (pre-print available at the arXiv)."
again with the assumptions. (Score:5, Interesting)
From the article:
The idea, essentially, is that if two quasars on opposite sides of the sky are sufficiently distant from each other, they would have been out of causal contact since the Big Bang some 14 billion years ago, with no possible means of any third party communicating with both of them since the beginning of the universe — an ideal scenario for determining each particle detector’s settings.
Why would you assume that if they're 14 billion years apart that it would be any different than 14 seconds apart in time, at least in regard to entanglement?
" with no possible means of any third party communicating" makes me think "we don't know of a means to communicate"
Could the outcome of the experiment could show either action at a distance, or some faster-than-light communication without excluding either possibility?
If it does happen that entanglement went away, it would be most interesting.
Re:again with the assumptions. (Score:4, Interesting)
Exactly right.
There are two possibilities:
1) The universe is infinite, and it would be possible to find two quasars which never shared a quantum state.
2) The universe is not infinite and it is not possible to find two of anything which have never shared a quantum state.
They've completely failed to close this loophole.
News will report it as proof of Free Will (Score:4, Interesting)
A year from now you should expect to hear about this research again, but it will be delivered as a dramatic result: "Scientists have proven Free Will exists!", or "Scientists have disproven Free Will!" The experiment won't actually do this, but that's how the press will report it.
The thought that some hidden variable may affect not only both sides of the universe but our own minds is frightening. It would really shake things up. So I expect that QM and 'free will' will come out triumphant in this test. Whether it's an actual assessment of Free Will or not will be the interesting argument afterward.
how about detector poisoning? (Score:5, Interesting)
a much simpler explaination... the detector material is still groaning from the last collision and doesn't have its calibrated act together for the next one. you detect subatomic particles, after all, by watching what happens when they distort a known material, and extrapolate from the distortion what whacked into it. whacking things causes them to go off kilter. from black bands and reduced light in fluorescent light tubes to bright-bloom in old TV cameras to getting wacky when you leave a dark room and are sun-blinded, this has been a known phenonema as long as we have been around.
Re:Superdeterminism (Score:5, Interesting)
Yeah, superdeterminism was my first thought in reading this. It sounds like they're pushing any superdeterminism all the way back to the time of inflation, but since that's exactly what superdeterminism would predict, I don't see that they've contradicted anything.
It's intellectually unsatisfying to think that superdeterminism could relate to something as supremely complicated as a scientific apparatus: the whole state two measuring apparatuses conspires to yield opposite results on particles that were, up to that instant, completely identical, without any communication. But I think it makes more sense than trying to impose some outside "free will" force that also makes itself visible only on the most carefully isolated particle experiments yet also just happens to manifest as something we see numerous orders of magnitude larger as "what we think", despite layers of purely chemical interactions in between.
We're still obligated to explain the larger-scale version of "free will", in that the phenomenon that we believe it exists is real, and I think your way of looking at it is good as any. And superdeterminism doesn't contradict that.
Superdeterminism still doesn't satisfy, but I suspect that "satisfaction" is a purely human property. The equations yield the right answers, and that's all you get. Like classical dynamics, free will is an idea that we're going to keep expecting to see, even though we'll always get out unsatisfying answers when we try to explain corner cases.
Re:How about not-quite-random numbers? (Score:4, Interesting)
AC has it right - *any* source of (psuedo)random numbers from causally connected sources is suspect, and no number of repetitions will rule out forces that retroactively ensure consistency. Frank and Bob could be simultaneously flipping coins on the opposite side of the planet, yet still be causally connected by the fact that their results will determine the settings for an experiment that the universe decrees must be consistent with certain principles. Even this experiment won't be able to close the loophole completely - it could be that the experiment and its settings were already fully defined in the first few instants of the universe while the not-matter that would eventually become the quasars was still causally connected. Basically this is a negative-evidence only experiment - it can't show that hidden variables aren't controlling QM, but it could potentially show that they are. Unless of course the hidden variables ensure that the choice of quasars will be such that the experiments yield consistent results. Though if they do it multiple times with different quasar pairs the odds of that being possible drop dramatically.