Our understanding of gravity has gone through a few permutations, from Newton’s equations through to Einstein’s general relativity. With today’s discovery of gravitational waves, we look back on how our grasp of gravity has evolved over the centuries.
1687: Newtonian gravity
Isaac Newton publishes Philosophiae Naturalis Principia Mathematica, giving a comprehensive account of gravity. This gave astronomers an accurate toolbox for predicting the motions of planets. But it was not without its problems, such as calculating the precise orbit of the planet Mercury.
All planets' orbits precess – with the closest point of their orbit moving slightly with each revolution – due to the gravitational tugs from other planets.
The issue with Mercury’s orbit was that the amount of precession did not match what Newton’s theory predicted. It was only a small discrepancy, but big enough for astronomers to know it was there!
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