The First Discovery of Gravity in History

Isaac Newton discovered it. If you don't like the word 'Newton', then let us say Isaac discovered it. 

Gravity is a unique insight in the history of human thought. Never before Isaac Newton, anybody in their wildest dreams thought that there could be a single mathematical law which would unite heavenly bodies and earth and it would quantitatively describe tides, seasonal changes, lunar size variations, motion of comets... list is endless.., all expressed in a simple mathematical package, which you can use to predict a HUGE class of phenomena up to incredible precision! Never before, anything remotely similar, had happened!

From almost a total nothing, Isaac Newton, single-handedly, changed the face of knowledge for ever and ever. This was totally new and there was no precedence whatsoever.

That material bodies can influence one another at a distance, is a much older thought. Even older than Bhaskara! These speculations had nothing to do with science or gravity. People, before the time of Newton or Galileo, had no/foggy understanding of causality. None of their ideas or thoughts were motivated by causal requirements. These were various random/astrological speculations without any empirical foundations.

For example, in the 6th century, a philosopher (probably 'Dionysius the Areopagite (pseuodo)') wrote something like this: 'All bodies should attract every other bodies since they are all filled with God's love'. Would you say, he discovered gravity? Even if you do, I ask you what value it added? Can you calculate the orbit of a comet? Does it predict seasonal changes? Can it explain why the orbits of heavenly bodies are conic sections? You can't. It is useless. It doesn't add any value to knowledge.

Newton's motivation came from a scientific requirement. It was to explain Kepler's laws of planetary motions. People, genuine experts, were struggling with the problem. Descartes proposed his vortex model. But it failed. Christiaan Huygens made some modifications. But again it failed.

Newton showed that the problem of solar system was a central force problem. Central force problems were known to the then specialists like Edmond Halley, Robert Hooke or Isaac Barrow. But since differential calculus was not discovered then, these problems were extremely difficult to solve. Isaac Newton invented this whole branch of calculus to sort out these central force problems (well, Leibniz also did independently)! He then discovered that if the force field is inverse square the orbit would be a conic section!

During a casual discussion with Halley, Newton informed him about all these. When Halley asked Newton, what would be the orbit of a particle under inverse square law of force, satisfying certain energy condition, Newton casually replied 'an ellipse'. A surprised Halley asked Newton, 'how do you know?' Again the casual reply came 'I have calculated it'!! No guessing, no conjecture! A super stunned Halley immediately asked Newton to show him the proof. Newton, for some time, searched his tables and drawers but didn't find. Halley, completely flabbergasted, wondered, 'here is a man, solved the age old mystery of solar system, lost his notebook!' Newton then promised Halley to send the proof by calculating again from scratch and he did.

Most importantly, Isaac Newton postulated the universality of gravity. This was perhaps the most crucial insight. The same force that makes solar system work, is responsible for apple falling. Laws of falling bodies were known from Galileo. But they were kinematic laws. Newton deduced them from gravitational dynamics with his laws of motion.

If we ignore the electromagnetic phenomena and if we are not concerned with systems having nearly the speed of light and not too massive and not too small then Newton's theory of gravity along with his laws of motion is 'the theory of everything'! A TOE so powerful that even today when we send a space shuttle into Mars we use virtually nothing more than Newton's TOE.

Isaac Newton did not discover gravity. Aristotle, Bhaskaracharya and many other mathematicians knew and wrote about gravity. Newton is credited with the discovery of the theory of universal gravitation which is not the same as discovering gravity itself.