Foucault’s Swinging Experiment

We interrupt my ranting for one of those fun little historical items:

If you’ve heard of Foucault’s  Pendulum, you probably know it as that ball on the end of a long wire thing people set up in museums and observatories. Once in a great while, it knocks over a peg, proving that the earth does, indeed, rotate on its axis.

How? Pendulums, following Newton’s laws, will swing in the same plane, unless some force acts upon them to cause them do otherwise. But the plane of  Foucault’s pendulum slowly changes (in fact, it doesn’t seem to swing in a plane at all, but is observed to swing through a series of slightly curved surfaces.) By a fairly long series of logical steps, it is concluded that the only reasonable way to explain the motion of the pendulum is by the movement of the earth beneath it – it is considered too shocking of a coincidence for the movement to be exactly what would be expected if the earth rotated exactly once a day, yet to have some other cause. In fact, the pendulum also moves differently depending on the latitude in exactly the way it should, if the motion were caused by the earth’s rotation. There’s no other reasonable explanation

Big Whup? What makes this all very interesting is that Foucault demonstrated his pendulum – it was a sensation – in February, 1851.

Galileo died in 1642.

So, while scientists were all pretty well convinced that the earth rotated on its axis by 1851 – it explained a lot of otherwise baffling things in a nice tidy mathematical way – Foucault provided a clean, easy-to-understand demonstration. Less obvious, perhaps, is that Foucault also demonstrated the current state of scientific reasoning: As a scientist, you didn’t necessarily  have to come up with inescapable iron-clad reasoning, but only had to muster the preponderance of evidence to support your thesis, to the point where other arguments start tripping over their own feet, so to speak. (This is an echo of Aristotle, of course, who always insisted that different subject matter requires different standards of proof and provides different levels of knowledge – things you determine by looking at the material world were always going to be conditional to Aristotle.)

Anyway, two things happened in the 200+ years between Galileo and Foucault: The rotation of the earth went from an intriguing theory lacking any proof to an established scientific fact (or, to be precise, a well-established theory in the scientific sense that no other theory seriously contends with it), and the scientific method evolved from expecting scholastic-level logical certainty to recognizing that, more often than not, a good theory supported by the evidence and subject to change upon further evidence is the best we can do.

Of course, nowadays, and for the last couple hundred years, people have argued that scientific-style conditional knowledge is the ONLY kind of knowledge, making, in effect, a metaphysical argument that there are no metaphysics.  But enough for now.

Author: Joseph Moore

Enough with the smarty-pants Dante quote. Just some opinionated blogger dude.