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Einstein's insights come into focus

作者:郝海箴    发布时间:2019-02-27 09:17:04    

By Marcus Chown A NEW study of Albert Einstein’s notebooks reveals that the great physicist had realised the existence of an effect called gravitational lensing more than two decades before he shared his breakthrough with the rest of the world. Gravitational lensing can produce multiple images of a distant celestial object and is caused by the bending of light by the gravitational field of a massive object—usually a galaxy—lying in the same line of sight. Einstein described the effect in a paper published in 1936, and the first example was not seen by astronomers until 1979. But science historians have now found that Einstein described lensing in a notebook from 1912. “This provides an important window on Einstein’s thought processes as he struggled to develop his theory of gravity,” says Jürgen Renn of the Max Planck Institute for the History of Science in Berlin, who led the team which describes the notebook entries in last week’s issue of Science. This theory of gravity, known as general relativity, was not published until 1915. Renn and his colleagues have been examining Einstein’s notebooks to uncover the genesis of general relativity. The discussion of gravitational lensing was written in April 1912. “We know the date because Einstein was at Berlin’s Royal Observatory visiting the astronomer Erwin Freundlich between 15 and 22 April 1912 and his calculations are interspersed with Berlin appointments and addresses,” says Renn. Einstein imagined a situation in which a distant star was hidden behind a nearby star. If the stars were perfectly aligned, Einstein calculated, there would be a ring of light around the nearby star, nowadays called an “Einstein ring”. If the stars were not perfectly aligned, there would be no ring but a double image of the distant star. Einstein calculated both the separation of such images and their magnification. “However, he put the calculations aside because he thought the effect unobservable,” says Renn. “He only published in 1936 when urged to do so by a Czech amateur scientist.” What Renn finds most fascinating about Einstein’s work on gravitational lensing is that it shows how much intuition he had about general relativity before he was able to formulate the theory mathematically. Einstein had guessed that his eventual theory must predict light bending in 1907,

 

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