Month-long calculation resolves 82-year-old quantum paradox
Now, Klaus Hornberger of Ludwig-Maximilians University in Munich and his postdoc Johannes Trost have resolved Hund’s venerable paradox.1 The two theoreticians analyzed the case of one of the smallest chiral molecules, dideuterium disulfide (D2S2; see figure 1), tumbling in and buffeted by a monatomic gas, helium. The calculation uncovered a surprisingly large phase dependence in the scattering amplitude that distinguishes the two isomers. Thanks to the phase dependence, the ambient gas atoms can pick out the molecule’s left-handed and right-handed isomers far more readily than the molecule’s other states. Even at low temperature and pressure, the effect of the He atoms colliding again and again with D2S2 is to knock the molecule into a chiral state and keep it there before it has a chance to tunnel out to its mirror image.
In one sense, Hornberger and Trost’s result is rather mundane: If you take proper, quantum account of how atoms collide with molecules, you derive the expected result, a mix of left-handed and right-handed isomers. But that mundanity is profound. The transition from a quantum superposition to a classical state arises not when some mysterious size threshold is breached but when the system’s interaction with its environment exceeds a calculable level of intensity. Decoherence theory, as that envirocentric view is known, is vindicated.
The decoherence theory of macroscopic and microscopic divide always appealed to me as an explanation of the quantum measurement problem (it boils down to saying that there is no fundamental problem), but … is this it?
Because of my damnable habit of falling asleep in lectures I couldn’t catch it all, but if I remember Prof. Commins’ description of the quantum measurement problem and its proposed solutions correctly, he had deep reservations about the decoherence theory (and he had a few examples to support his reservation which, again because of my habit of falling asleep in lectures, I didn’t catch).
Maybe I should drop by some time and ask him.