Nithyanandan Thyagarajan

A network of radio telescopes scattered across the planet catches the whisper of a distant black hole. Each antenna records a signal, but how do you combine these recordings if the clocks at the stations tick at different rates and the atmosphere distorts incoming waves?

A radio telescope with thousands of antennas is like a giant ear that hears the whole sky at once. But an ear cannot draw a picture: signals from every pair of antennas must be multiplied, and in an array of ten thousand elements there are already fifty million pairs. A classical correlator does exactly that, and its complexity grows as the square of the number of antennas.