Astronomy Fundamentals

Time, Waves, and Particles

How do we know that the general theory of relativity is true?

To test this prediction, British astrophysicist Arthur Eddington (1882–1944) organized a major scientific expedition in 1919 to observe the sky during a solar eclipse. With the Moon shading the Sun’s bright light, astronomers measured the relative positions of distant stars near the Sun’s position at that time. Then they compared them to those positions measured at night, when the Sun was not in the field of view. The apparent positions were indeed different, and the discrepancies were consistent with the results predicted by Einstein’s theory. This observational confirmation of the general theory of relativity changed the field of physics forever. The discovery made news headlines, and Albert Einstein became an international celebrity.


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