It's often a case of swings and roundabouts. If you save money by buying a house out of town, you spend more time and money commuting. If you really measure the momentum of an electron, you have no idea where the little guy is located. And now, according to a new analysis by a pair of University of Texas electrical engineers, the better an object is hidden by an invisibility cloak at a given wavelength of light, the easier it is to see at other wavelengths. Swings and roundabouts.
Quantum entanglement, one of the odder aspects of quantum theory, links the properties of particles even when they are separated by large distances. When a property of one of a pair of entangled particles is measured, the other "immediately" settles down into a state compatible with that measurement. So how fast is "immediately"? According to research by Prof. Juan Yin and colleagues at the University of Science and Technology of China in Shanghai, the lower limit to the speed associated with entanglement dynamics – or "spooky action at a distance" – is at least 10,000 times faster than light.