Discovery of the Planet Vulcan

I took a class in college called Philosophy of Science. One of the things we studied was how scientific hypotheses can be based on foundations that may turn out to be flawed. Over time, even the simplest things we think we know from our observations of the world can be called into question as we discover new complexities. The story of the planets Neptune and Vulcan illustrate this beautifully.

The planet Neptune was officially discovered in 1846 by Johann Gottfried Galle, but its existence had already been proven by Urbain Le Verrier. Scientists had noticed irregularities in the orbit of Uranus. Using their knowledge of physics, they were able to deduce that the planet’s orbit was been affected by the gravity of another object in the sky, which turned out to be Neptune. The math told them that the planet had to be there. All that was left was for someone to look for it.

Having predicted Neptune, Le Verrier then went on to examine the orbit of Mercury. Using the same calculations, he predicted the existence of another yet undiscovered planet which he named Vulcan. Vulcan, according to the calculations, was about one-seventh the size of Mercury and orbited between it and the Sun. Its existence would make Earth the fourth rock from the sun, not the third. Except that it doesn’t exist. The math all worked out, just as it had for Neptune, yet no planet was ever observed. Decades later, Albert Einstein’s theories demonstrated that our understanding of physics had been too simple. Relativity could describe the orbit of Mercury where the sciences of Newton and Kepler could not. The numbers had all added up, but the mathematical systems themselves turned out to be inadequate. Extrapolating on this idea, one comes to the humble conclusion that any idea whatsoever can be called into question if one can poke holes in the underlying assumptions on which the idea depends. No matter how solid you think your ground may be, some jerk like Einstein can always come along and pull the rug out from under you.