Friday, November 11


Mind The Planet

Glenn Reynolds links to an article at Tech Central Station by Uriah Kriegel that explains why ID is non-science rather than just bad science.

It's a good discussion of the notion of falsifiability, and how we distinguish scientific theories from other ideas. Unfortunately, he trips up when discussing Einstein's Theory of Relativity:

When Einstein came up with the theory of relativity, the first thing he did was to make a concrete prediction: he predicted that a certain planet must exist in such-and-such a place even though it had never been observed before. If it turned out that the planet did not exist, his theory would be refuted. In 1919, 14 years after the advent of Special Relativity, the planet was discovered exactly where he said. The theory survived the test. But the possibility of failing a test -- the willingness to put the theory up for refutation -- was what made it a scientific theory in the first place.
It sounds like Einstein predicted the existence of Pluto - but Pluto wasn't discovered until 1930. What Kriegel is actually referring to is the orbit of Mercury.

Astronomers had known since the 18th century that Mercury didn't behave as it ought. Its orbit could be calculated quite precisely using Newton's Law of Gravity, but it stubbornly refused to follow that orbit. It wasn't out by much, but it was enough. Some astronomers suggested that the difference might be due to the gravitational effects of another planet orbiting closer to the Sun (they even tentatively assigned it the name "Vulcan"), but no such body was ever observed.

Einstein's General Theory of Relativity had nothing specifically to do with Mercury, but it did provide a prediction of Mercury's orbit which was slightly, but still significantly, different from that produced from Newton's Law. The calculations based on Relativity happened to fit Mercury's observed orbit as precisely as we could measure it - strong support for Relativity, but not a decisive test as Mercury's odd orbit was something we'd known about all along.

What happened in 1919, though, really was something new. One of the predictions of Relativity is that gravity not only affects the path of matter travelling through space, it actually bends light. Nothing in Newton's Law of Gravity suggested any such thing. In 1919, just after the end of World War I, a British Navy exepedition set out to observe a total solar eclipse off the coast of Africa. You see, during a total eclipse the light of the Sun is hidden and stars that are near the Sun (as observed in the sky, that is, nothing to do with their true locations) are visible.

Astronomers could measure very precisely the positions of these stars relative to one another. And then they could do the same thing again during the eclipse. Einstein predicted that because the light of these stars would be bent by the gravitational field of the Sun, that they would appear in different positions when observed during an eclipse. What's more, he was able to calculate just how great the difference would be.

The expedition, led by Sir Arthur Eddington, made the observations required, and Einstein was proved correct. He become a household name almost overnight.

More details here, courtesy of Penn State.

Posted by: Pixy Misa at 08:53 AM | Comments (1) | Add Comment | Trackbacks (Suck)
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1 Nice catch. It's too bad Riemann never gets any credit, as Einstein himself said he never would have developed relativity without Riemann's previous work. It's interesting too how many times Einstein, like most great thereoticians, was wrong after his initial spectacular success: refusal to accept quantum mechanics, the cosmological constant debacle, missing the expanding universe that his theories should have predicted...

Posted by: TallDave at Friday, November 11 2005 10:46 AM (giBEj)

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