Originally published 6 December 1999
There is a week in late November when my walk across the meadows to work in the morning takes me directly into the rising sun. Ahead of me along the double track, as if in a gun sight, the sun lifts its fiery globe above the horizon.
It seems huge as it rises, twice the size it will appear later in the day when it hangs high in the sky. This is an illusion; 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 rises with a stately languor — a hot air balloon clearing the distant trees, 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 it takes me to walk the mile-and-a-half to the college, the spinning Earth whisks me 400 miles eastward. I’m traveling towards the sun faster than the speed of sound.
On the face of it, that sounds absurd. Moving at the speed of sound? Why don’t I feel the wind rushing past 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 flitter unperturbed in still trees.”
Galileo’s opponents were adamant that the Earth did not move. 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 escaped 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 invariably 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 not we 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, 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 moving at a walker’s pace is an illusion. In fact, 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; our senses are easily deluded; common sense is not always a reliable guide to an uncommon universe.
“The universe is not only queerer than we suppose, but queerer than we can suppose,” said geneticist J . B. S. Haldane. Common sense will only take us 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 classes a young person who was raised on fairy tales, Dr. Seuss, and Harry Potter, than a person who spent elementary school science classes measuring the growth of bean sprouts in styrofoam cups on the classroom windowsill. We all know that bean sprouts need sunlight and water; that’s common sense. But it requires a practiced imagination to appreciate the Big Bang or drifting continents or the spinning loom of the DNA…
…Or my whirling journey across the meadow towards the sun, my even more precipitous translation with the orbiting Earth towards the constellation Leo, 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 the other bold thinkers who refused to let common sense limit the dimensions of their universe.
