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In 1845, Faraday noted that the plane of polarization of light is rotated when a light beam travels through a material in a magnetic field. Now, Faraday rotation due to one single electron spin has been observed.
Evidence for the superradiant behaviour of quantum dots — behaviour first described in the context of atoms in a gas over 50 years ago — suggests they can radiatively interact over distances of at least 150 nm.
Spacetime might seem smooth, but it could, at very short length scales, be quantized. Energetic neutrinos from gamma-ray bursts could provide a useful means to investigate further, and probe the nature of quantum gravity.