Re: Look out Einstein, here come Weinstein
PS - "Planet X doesn't exist under Mercury? Newton loses."
Yes - as in, you don't invent arbitrary add-ons to save a theory proven false.
But by the same line of reasoning the theory was proven false earlier when the arbitrary add-on called "Neptune" had to be invented to hold it together. Except it turned out it actually existed. The thing that made the difference was the fact that Planet X did not exist whilst Neptune did, not whether it was "invented" or "arbitrary". Otherwise the situations were completely the same – observations don't conform to the theory, come up with a planet to fix it. These arbitrary add-ons as you call them happened to actually work from time to time, so we in fact have instances in which they were the right conclusion.
R.I.P. Admiral James T. Kirk (2233-2267, 1969, 2267, 1930, 2267-2268, 1968, 2268-2269, Serpeidon Middle Ages, 2269, 2237, 2269-2286, 1986, 2286-2293, 2371)