On 14 March 1879, Albert Einstein was born in the city of Ulm in the
southwest of Germany. On 11 August 1999, the skies above his birthplace will
darken as the Moon eclipses the Sun. It鈥檚 a fitting鈥攅ven
spooky鈥攖ribute to the man who transformed our picture of the natural
world. And an unlikely one too.
Although a total eclipse occurs roughly every 18 months somewhere in the
world, at a given location the gap between successive eclipses is about 350
years. So what chance then that the greatest scientist of the 20th century
should be commemorated by the very last total eclipse of the millennium? But
perhaps we shouldn鈥檛 be too surprised about the coincidence. After all, for
Einstein, eclipses have always been lucky.
Take the pivotal role played by a similar total eclipse 80 years ago in
establishing Einstein鈥檚 tour de force鈥攖he general theory of relativity.
One of the soaring achievements of Western civilisation, it was completed at the
very nadir of that civilisation: the second year of the First World War. But
even in that darkness there shone the faint light of international scientific
cooperation. Einstein鈥檚 paper, smuggled out of Germany, reached the British
physicist Arthur Eddington at Cambridge. And it was Eddington who realised that
the total eclipse of 29 May 1919 offered a golden opportunity to test one of
general relativity鈥檚 central predictions鈥攖hat the Sun鈥檚 gravity would bend
light from distant stars twice as much as Newton predicted.
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A total eclipse is vital here because the light-bending is measurable only
for stars whose light passes close to the Sun on its way to Earth and such stars
are visible only in the darkened sky at the time of a total eclipse. Eddington鈥檚
team travelled to the island of Principe off the coast of West Africa and duly
photographed their quarry. It took a long time to be sure鈥攖he shift in the
position of the stars was so small鈥攂ut in September 1919, Eddington
finally announced that Einstein was right.
Enter another piece of luck for Einstein. We now know that the light-bending
effect was actually too small for Eddington to have discerned at that time. Had
Eddington not been so receptive to Einstein鈥檚 theory, he might not have reached
such strong conclusions so soon, and the world would have had to wait for more
accurate eclipse measurements to confirm general relativity.
Then there is the sheer unlikeliness of total eclipses themselves. Requiring
the Sun and Moon to appear the same size in the sky鈥攄espite the fact that
the Sun is 400 times bigger than the Moon鈥攖otal eclipses have only been
visible for 3 per cent of Earth鈥檚 history. Without this piece of celestial luck,
scientists would have had to wait years to test general relativity by searching
by other means.
And let鈥檚 be clear about the importance of Eddington鈥檚 total eclipse
measurements. More than anything, it was the swiftness of the test of his theory
that turned Einstein not just into a well-known scientist, or even a celebrity,
but one of the century鈥檚 cultural icons. By the 1920s, Einstein was better known
than Charlie Chaplin: politicians and film stars were queuing up to be
photographed with him. And all thanks to a total eclipse.
So if you are a physicist, there is only one place to see next month鈥檚
spectacle: Ulm. Be there for what should surely be christened the 鈥淓instein
别肠濒颈辫蝉别鈥�.