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)."

Comments

Please!

[NotQuiteReal]

Don't anthropomorphize the machines. They hate that, and will go back into their past to get you!

again with the assumptions.

[clovis]

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.

[MozeeToby]

You cannot have entanglement without interaction, you cannot have interaction between two things that lie outside of each other's light cones.

To be fair, you can't have interaction outside of your light cone without also having faster than light communication. But you can't have faster than light communication without also having the possibility of sending messages back in time. And you can't have the possibility of sending messages back in time without breaking causality. So, on the one side you have the assumption that causality doesn't exist and faster than light communication is possible (both of which are contradicted on scales from pico-meters to billions of lightyears), on the other side you have the assumption that information can't travel faster than light (which again, seems to be supported by every experiment and observation made in human history).

Superdeterminism

[Warbothong]

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.

Re:Superdeterminism

[jfengel]

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.

how about detector poisoning?

[swschrad]

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.