In 1868, Hippolyte Fizeau realized that the lenses and mirrors in a telescope perform a physical approximation of a Fourier transform. He noted that by using an array of small instruments it would be possible to measure the diameter of a star with the same precision as a single telescope which was as large as the whole array — a technique which later became known as astronomical interferometry.
In a 2008 paper, Tegmark and Zaldarriaga proposed a telescope design that dispenses altogether with the lenses and mirrors, relying instead on computers fast enough to perform all the necessary transforms. His concept is an all-digital telescope with an antenna consisting of a rectangular grid. Building radio telescopes this way should become feasible within a few years if Moore's law continues to hold. Eventually optical telescopes could also be built this way. This technique is already being used in radar applications.
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