Hailing Frequency Open

John Stewart Bell, born in Belfast, was one of the giants of modern physics. His 1964 publication of what became known as Bell’s Theorem showed that it was possible to prove that Einstein was wrong in his rejection of the weird nature of quantum mechanics.

Quantum theory has passed every test of accuracy to an infinitesmal degree, but Bell demonstrated that if quantum theory is a correct description of reality, then one of the following has to be false:
1. Reality – that things have a consistent existence and have properties that can be measured.
2. Locality – that events separated in time and space do not influence each other, except by signals at light speed or slower.
3. Free will – that experimenters’ choice in setting up and running an experiment really is a choice.

Star Trek's Lt. Uhuru

What do you mean “wrong number”?

Subsequent experiments testing Bell’s Theorem have given results that only quantum mechanics and the theorem can explain, (although a few critics still have some niggles with the fine detail). Most physicists, uncomfortable with rejecting free will or the existence of reality, choose to interpret the results as proof that Number 2, Locality, is wrong.

A recent experiment, with entangled photons shot in opposite directions to detectors 18km apart, showed that the “influence” between them had to be travelling at least ten thousand times the speed of light. (It’s generally assumed that the speed is actually infinite, or to put it another way, that in some sense there is “no distance” between entangled particles, no matter where they are.)

Unfortunately, the very unpredictability of quantum mechanics, which is what Einstein didn’t like, probably rules out communication systems that run faster than light. I say “probably”, because some physicists think the door isn’t totally closed yet. Faster-than-light communication is a common idea in science fiction, with real-time conversations over interstellar distances taken for granted in the Star Trek universe and others.

But if Einstein’s other bright idea, Special Relativity, is correct (and much modern technology is based on it, so it must be at least kind of correct), then communication faster than light would mean that a further “obvious” property of the universe is false. Call it Number 4, Causality – that cause and effect have to be in that order, not effect happening before cause. If causality is actually untrue, then all bets are off and we don’t undertsand anything. I fear that may be the truth of it.


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