Kepler showed ellipses explain planetary motion well. Newton's theory of gravity subsumed Kepler's. Who first proved this, that is, that an inverse square law of gravity yields Kepler's elliptical orbits? Probably Newton: it's likely that Newton started with Kepler's laws and worked backward. (Try replicating this as an exercise.)
Newton theory of universal gravitation predicts more than Kepler's regarding planetary motion: Netwon's theory predicts that planets should affect each other, causing them to deviate slightly from their elliptical orbits. Was this observed or explicitly predicted first? There does not seem to be any landmark event marking Newton being proved right, or more precisely, Kepler being proved wrong.
Planets affecting each other, deviating from ellipses, seems a very important departure from a model with planets locked in unchanging crystal spheres. Even Kepler's model could have been imagined as planets sliding along crystal elliptical tracks as if in a giant clock.
Obviously planets affect their moons (e.g., Galilean moons around Jupiter, Earth's Moon), so maybe going from that to planets affecting each other was not a great leap. When did we discover that Jupiter's moons affect each other in a way consistent with Newton's theory?
When did we discover that Jupiter is extremely massive relative to the other planets?
The anomalous precession of the perihelion of Mercury (more than the amount explainable by planets affecting each other!) was observed first, then explained by Einstein in 1915 with general relativity, disproving Newton.
The solar eclipse experiment then happened in 1919, which conclusively disproved Newton, and was a highly celebrated event. Was the solar eclipse experiment more conclusive than observations of Mercury? I guess it has less complexity: how much did (say) Jupiter affect that beam of starlight just grazing the surface of the sun? Probably very little. Which planet had the greatest effect? Probably earth, possibly Moon.
No comments :
Post a Comment