"Dear Mother, -- Good news today.
H.A. Lorentz has wired me that the British expeditions have actually proved the
light deflection near the sun."
Einstein's new general theory of relativity predicted a remarkable effect: when
a ray of light passes near a massive body, the ray should be bent. For example,
starlight passing near the sun should be slightly deflected by gravity. This
deflection could be measured when the sun's own light was blocked during an
eclipse. Einstein predicted a specific amount of deflection, and the prediction
spurred British astronomers to try to observe a total eclipse in May 1919. Feverish
preparations began as the war ended. Two expeditions, one to an island off West
Africa and the other to Brazil, succeeded in photographing stars near the eclipsed
sun. The starlight had been deflected just as Einstein had predicted.
In a letter to an astronomer in 1913, Einstein predicted how gravity should
deflect rays of light that passed near the sun, making stars appear to shift
their positions. In photographs taken by expeditions to an eclipse of the sun,
the apparent positions of stars near the sun deviated from the positions of
stars photographed when the sun was elsewhere in the sky. A ripple in a pane
of glass can be detected when objects seen through the glass appear distorted.
So scientists detected a warping of space itself.