Sushil Sharma

A PET scanner catches flashes of light that occur when a radioactive tracer introduced into the body meets electrons in tissues. Usually, the device merely notes where a flash occurred. But between the birth of the tracer and the flash, there is a pause — tiny, in billionths of a second.

Each positron annihilation is like the birth of a pair of dancers, connected by an invisible thread of polarization. Two gamma quanta fly apart, but their states remain entangled: measuring one instantly determines the other — as if one partner senses every movement of the other, no matter the distance.