One of the strangest concepts in quantum mechanics is the notion of entanglement. This is the idea that two quantum particles can be so deeply linked that they share the same existence. When that happens, a measurement on one immediately influences the other, regardless of the distance between them.
This “spooky action at a distance”, as Einstein called it, has puzzled and fascinated physicists since it was first discussed in the 1930s. Einstein initially used it as evidence of the failure of quantum mechanics since this instantaneous action clearly seemed to violate relativity.
Later, physicists realised there was no conflict because the “spooky action” cannot be used to send information faster than the speed of light. However, important questions remain about the nature of entanglement and spooky action. “If the spooky action does exist, what is its speed?” ask Juan Yin and pals at the University of Science and Technology of China in Shanghai.
Today, they reveal the answer. They say spooky action travels at least four orders of magnitude faster than light.