Engines of Our Ingenuity

No. 155:
EXPERIMENTAL PROOF

by John H. Lienhard

Click here for audio of Episode 155.

Today, we wonder why people run experiments. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

I visited the beautiful, baroque St. Isaac's Cathedral in Leningrad. The Russians called it a museum. They'd hung a huge Foucault pendulum from the dome -- right in the center -- cutting through the delicate architectural lines. A lady in a blue suit lectured squadrons of little children. She explained that the pendulum holds its path while the world turns under it -- that the pendulum itself seems to change direction as the day wears on.

The Foucault pendulum is a dramatic enough demonstration of Newtonian mechanics. But this wasn't science. It was a not-so-subtle propaganda lesson for kids -- a sidewise way to tell them that their lives were under the control of science and the state.

A lot of fancy experiments do little more than confirm what we already know. For instance: a Stanford group has made a perfectly round sphere of metal-coated quartz. It's about an inch in diameter. An electrostatic field will hold it -- without letting it touch anything -- in a satellite. It'll be set to spinning with its axis pointing toward the star Rigel, in Orion. As it moves through the earth's gravitational field, its axis will shift -- just a little bit. The reason is that our gravity field bends space. It'll bend the line pointing to Rigel. The experiment will prove Einstein's theory; but most people who understand Einstein's theory believe it already.

Experiments sometimes do reveal things, dramatically. The French physicist Poisson, for example, attacked Fresnel's theory of light. If Fresnel were right, he said, you'd see a spot of light in the middle of the shadow cast by a disc -- under the right conditions. That didn't make sense. But when Fresnel did the experiment, the white spot appeared. It surprised him as much as it did Poisson.

Experiments serve many purposes. After all, we have to look at nature before we can form a theory to describe it. And no theory will stand up to even one counterexample. The famous Michelson-Morely experiment was meant to show how fast light traveled in a hypothetical ether that was supposed to fill space. The experiment actually demolished the ether theory when it gave the wrong kind of result.

Once we're confident about a theory, experiments do start looking like propaganda. We do many experiments to sell our ideas to other people. That's an important part of the business of science. But the experiment that's really worth doing is the one that can give us results we don't want to hear.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)


The Fresnel/Poisson argument is described in some detail by Kuhn, T. S., The Structure of Scientific Revolutions (second ed.). Chicago, IL: University of Chicago Press, 1970.

This episode has been greatly revised asEpisode 1610.


The Engines of Our Ingenuity is Copyright © 1988-1997 by John H. Lienhard.

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