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)."
Re:again with the assumptions. (Score:5, Insightful)
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 (Score:5, Insightful)
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.