Quantum mechanics flummoxes physicists again

A fresh take on a classic experiment makes no progress in unifying quantum mechanics and relativity.

Jon Cartwright

If you ever want to get your head around the riddle that is quantum mechanics, look no further than the double-slit experiment. This shows, with perfect simplicity, how just watching a wave or a particle can change its behaviour. The idea is so unpalatable to physicists that they have spent decades trying to find new ways to test it. The latest such attempt, by physicists in Europe and Canada, used a three-slit version — but quantum mechanics won out again.

A 3-slit experiment has confirmed a basic rule of quantum mechanics but failed to help physicists to reconcile the theory with relativity.

Science/AAAS

In the standard double-slit experiment, a wide screen is shielded from an electron gun by a wall containing two separated slits. If the electron gun is fired with one slit closed, a mound of electrons forms on the screen beyond the open slit, trailing off to the left and right — the sort of behaviour expected for particles. If the gun is fired when both slits are open, however, electrons stack along the screen in comb-like divisions. This illustrates the electrons interfering with each other — the hallmark of wave behaviour.

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