Thoughts in a Haystack

The planet Vulcan has been discovered! In fact, it was discovered and rediscovered well over 100 years ago and it carries an important message about the nature of science.

The French astronomer Urbain Jean Joseph Le Verrier predicted, in 1859, the existence of a planet (or numerous small planets) inside Mercury's orbit. The proposed planet was quickly dubbed "Vulcan." Just in case anyone might think Verrier was just passing moonshine, he had experienced some success in that field before, having correctly predicted, in 1846, the existence of Neptune, based on the orbital anomalies of the then known planets.

The reason he predicted the existence of Vulcan was an anomaly in the orbit of Mercury known as the precession of the perihelion. In short, Mercury's orbit shifts slightly after each turn about the sun. This might not seem to be such a great problem ... except that Newtonian mechanics couldn't account for such behavior.

The issue is why, given such a clear problem with Newton's mechanics, did scientists go looking for planets in a place that they were unlikely to be able to hide all that well, instead of looking for errors in Newton's theories? Even more so, why did comments such as the following, based on the work of a German astronomer, show up in an engineering magazine of 1876:

Our text-books on astronomy will have to be revised again, as there is no longer any doubt about the existence of a planet between Mercury and the sun.

The fact is that science is both conservative and conservational. It is slow (for relative meanings of the word) to adopt a theory and, once one works well at explaining phenomena, it is slow to discard it. In a process known as the Duhem–Quine thesis, scientists will, when faced with anomalous results that challenge an otherwise successful theory, begin to test the bundle of background theories and assumptions that all theories rest on. In the case of Newton's mechanics, the anomalous behavior was ascribed to a highly elusive planet for some 50 years, until Einstein came along to explain that the problem lay with Newton.

And what is more ... that's the way it should be. In modern science, the flow of information often far exceeds the available time in which to incorporate it properly into theory. If each and every new bit of data was taken to upset the entire applecart, science would be constantly thrown from pillar to post. That is among the errors of those who point to the latest finds in humanoid fossils as being grounds for being "skeptical of a theory that seems to be in constant flux." In point of fact, it's not a sign of distress that discoveries are being constantly made and our understanding bettered, it's a sign of the robust health of evolutionary theory.
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