When did Isaac Newton finally fail? (Synopsis)

"To explain all nature is too difficult a task for any one man or even for any one age. 'Tis much better to do a little with certainty & leave the rest for others that come after you." -Isaac Newton

Perhaps the greatest, most successful scientific theory of the past century is Einstein's General Relativity, our theory of gravitation that has answered every challenge to it for the past 101 years with resounding success. Yet before that, Newton's gravity did the same thing for more than twice as long! The culprit that finally brought the universal theory of ground was incredible in its simplicity: the orbit of the planet Mercury.

The orbits of the inner planets, along with a comet expected to have a near-Earth encounter in 2880. Image credit: NASA / JPL.

Observations dating from the late 1500s of the planet Mercury's position indicated a precession of its orbit of 5600" per century, while Newtonian gravity predicted 5557" per century. That less-than-1% difference proved significant, however, and it was Einstein's General Relativity that eventually made all the difference.

Images credit: New York Times, 10 November 1919 (L); Illustrated London News, 22 November 1919 (R).

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