Sunday, August 12, 2007

Uncommon sense

On the hill above the house there is a megalithic tomb aligned with the rising of the equinoctial Sun. Many centuries ago, the tomb was covered with a mound of earth. Now there is only an empty chamber of massive flat stones. It is called locally The Giant's Bed.

I have gone up there on the equinox, stretched myself out on the the "bed," and watched the Sun rise between my toes. It seems huge as it bubbles up above the hills, twice the size it will appear later in the day when it hangs high in the sky. This is an illusion, of course. If I hold my hand out at arm's length, the Sun's rising disk is about half as wide as my little finger, the same as at any other time of the day. It climbs with a stately languor, like a hot air balloon clearing the distant horizon, beginning its long, slow drift across the sky.

Another illusion. The Sun does not rise. Rather, the spinning Earth carries me towards the Sun, over the curve of the horizon. In the thirty minutes I lay on the Giant's Bed, I am whisked 400 miles eastward. I'm traveling towards the Sun faster than the speed of sound.

On the face of it, it sounds absurd. Moving at the speed of sound? Why don't I feel the wind rushing against my face? Why aren't the birds in the sky left reeling behind?

Poor Galileo. Imagine him trying to convince his contemporaries that he and they were whizzing along at 800 miles per hour on a spinning Earth. And at 66,000 miles per hour on an Earth that orbits the sun. "Ridiculous!" they might have said. "We have no sense of motion. The air is still. The birds perch unperturbed in breathless trees."

Galileo's opponents were adamant that the Earth did not move, and common sense confirmed their view. They made the nearly blind old man kneel on the marble floor of a Vatican palace and deny what he knew to be true. The Earth is at rest, he swore, and thereby evaded possible torture and confinement in a Roman prison.

"And yet it moves," he is purported to have whispered under his breath at the end of his public recantation. The story of the whispered remark is probably apocryphal, but it certainly expresses what must have been in his mind.

Galileo taught us convincingly that common sense is an unreliable guide to truth. Consider the following argument against a spinning Earth, a version of which he gave in his book on the Copernican world system:

Place a small item, a coin say, at the edge of a turntable. Now set the turntable spinning. The coin flies off the edge. That is the evidence of the senses. That's common sense. Why, then, if the Earth is spinning briskly, as claimed by Copernicus, do we not fly off into space? Along with everything else that is not tied down?

Galileo answered the objection by articulating a new physics, involving an "impetus" or tendency of an object to maintain its motion, and a tendency of terrestrial objects to be drawn to the center of the Earth. Only with these new "laws of nature," which he painstakingly investigated by careful experiments (and which Newton would later elaborate), did Galileo remove the objections of common sense.

In Galileo's new physics, the air and birds share my vertiginous velocity through the universe, so that we are at rest with respect to each other. My perception of rest on the Giant's Bed is an illusion. I am careening along at a spectacular velocity.

Galileo's great lesson is one of the first we should teach our children: Everything is not as it seems. Common sense is not always a reliable guide to an uncommon universe. The ways of thinking we are born with, or are inculcated with early in life -- animism and artificialism, for example -- can lead us astray.

"The universe is not only stranger than we imagine, it is stranger than we can imagine," said the British geneticist J. B. S. Haldane. Common sense takes us only so far. It is the glory of the human imagination that we have been able -- collectively, as a species, through that wonderful instrument called science -- to transcend common experience and enter into the universe of the whirling galaxies, the winding DNA, and the eons of deep cosmological time.

I would rather have in my science class a young person who was raised on fairy tales and Harry Potter than a person who spent elementary school science classes measuring the growth of bean sprouts in styrofoam cups on the classroom window sill. We all know that bean sprouts need sunlight and water; that's common sense. But it requires a practiced imagination to appreciate the spinning loom of the DNA that makes the plants what they are...

...or my whirling journey towards the "rising" Sun, my even more precipitous translation with the Sun and orbiting Earth towards the star Vega, my flight at 600,000 miles per hour with the Sun about the galactic center, and my racing away with the expanding universe from the instant of creation -- a deliriously improbable adventure, for the knowledge of which I am indebted to Galileo, Einstein, and other bold thinkers who refused to let personal incredulity limit the dimensions of their universe.

Further Reading

I should add that every classroom should have bean sprouts growing on the window sill, and that close observation and measurement are skills to be cultivated in every child. Here's an book I read many years ago, now out of print, recounting the inspiring experiences of an elementary school teacher in New Zealand: In the Early World, by Elwyn S. Richardson. Art, language, math, science -- all working seamlessly together. Extraordinary.

Discuss this essay and more over on the Science Musings Blog.