Looking through Albert Einstein's eyes
On November 25th, 1915, Albert Einstein presented his general theory of relativity, which was published on December 2nd. To mark these dates, we are highlighting stories from The Economist's archive showing how the theory, and the man behind it, were received. Here, we consider one of its effects, gravitational lensing.
A STRAIGHT line is the shortest distance between two points. So light, which never travels farther than it must, moves in straight lines. On flat surfaces, this poses no difficulty: only one straight line runs From A to B. 0n curved surfaces, there may be many such lines—which would matter little to astronomers, were it not for Einstein. General relativity explains gravity in terms of curves in the multi-dimensional geometry of space and time. If an intervening mass bends space in the required manner, light setting out from A will move along many different "straight-line' paths to B. Observers at B see a distorted image of A or multiple images of it, because the mass in between acts as a lens.
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