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Making Sure Our Lab Equipment Isn't Tricking Us
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)."
Don't anthropomorphize the machines. They hate that, and will go back into their past to get you!
This issue is a bit more complicated than you think.
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.
While interesting, it doesn't solve the most glaring assumption of Bell's inequality which is that the Universe is non-deterministic.
It's perfectly plausible that the Universe is deterministic, and hence the behaviour of the particles *and the experimenters* is pre-determined, ie. there is no choice in which measurement to take. Taking the determinism of the observers into account tends to be called "superdeterminism", and is necessarily a global property: either the whole Universe is superdeterministic, or nothing is deterministic. Bell's inequalities demonstrate this, since they cannot be explained by a *local* deterministic model, ie. a model which only involves properties of the particles (known as 'local hidden variables').
Note that superdeterminism doesn't necessarily rule out 'free will'. Personally I find the most elegant explanation of free will to be irreducibility: an irreducible process has no 'shortcuts'; the only way to predict its result is to run the process from start to finish. If, say, my mind is a deterministic but irreducible process, then a powerful-enough computer could predict my decisions exactly. However, I can still be said to have 'free will' because the computer can't take any shortcuts in its calculations: the only way it can predict my decisions is to run a perfect simulation of me and see what decisions that simulation makes, but in that case it's still (a perfect simulation of) 'me' making the decisions.
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.
Genocide Man -- Life is funny. Death is funnier. Mass murder can be hilarious.
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.
if this is supposed to be a new economy, how come they still want my old fashioned money?
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.
--- Most topics have many sides worth arguing, allow me to take one opposite you.