About three years ago, I was sailing on a 30-foot sloop in the British Virgin Islands with an odd assortment of fellow students from an American sailing school. Impressed by the brilliance of the shimmering greens and deep sea blues, I asked no one in particular, "Where do the colors come from?" My sailing mates clearly considered this a stupid question -- especially following the fact that I had just mentioned writing a rather extensive book on light and optics. Each of them had a quick and unambiguous answer to my query. The colors depend on the angle of the sun, on the shade of the sky, on the contour of the shore. Ashamed and embarrassed, I crawled back into the cabin, vowing never to let my stupidity out in public again.

Two weeks later, back in the more friendly waters of the science museum where I work, I asked three physicist friends why the water in Tortola was so blue, so green. To my surprise and delight, they argued about the issue for days -- and no one pretended to have a single right answer. Stupid questions had proven their proper place in science again.

My friend the physicist says that a stupid question is usually one "for which no one in the room has a ready answer." That makes almost any question you can ask about nature stupid. I remember a student who made many apologies to me before asking what he insisted would be a really stupid question. Then he asked, "What's gravity?"

I suppose there are a lot of science teachers who would say that is a stupid question because there are, after all, well-known laws that explain how gravity works. But no one has been able to explain why it works. That makes an inquiry into the nature of gravity a very good question, much more intriguing and difficult than, say, "How does a computer work?" Because for that there is an answer.

Many people shy away from science because they are afraid to ask stupid questions. Somewhere along the line they have been led to believe that all scientific questions have clear, unambiguous answers. They have been taught that science is all work and no play, all logic and no guesswork, all knowledge and no wonder. The truth is that the more complete the answer in science, the juicier the next question. Since Newton first formulated the laws of gravity, we have come to understand gravity as a curvature in the warp of space and/or a force carried by particles called gravitons. But why should space be cured? And what on earth is a graviton? Mark Twain used to say that the best thing about science was the enormous amount of conjecture one earned for such a trifling investment of fact.

In school, we often learn that stupid questions are those that the teacher didn't intend, questions that are out of place or off the wall, questions that make people uncomfortable -- like children who ask, "Why do people kill each other?" How many of us have the courage to tell even a 5-year-old, "I don't know?" Stupid questions are often just smart questions phrased in stark, simple terms.

It is certainly possible to ask, "What is gravity?" in such a way that one appears bright and profound. It is easy to learn long and impressive new words. But as MIT physicist Victor Weisskopf likes to say, "A new term is like an empty suitcase. It won't take you on a very long trip."

Science certainly isn't the only area in which people are put down for asking "stupid" questions -- questions that are couched in the wrong words or that have no obvious answers. I know people concerned about peace who dismiss as "stupid" questions about our ability to defend ourselves in times of war. I know people who think we should rearm America and think it's "stupid" to question how -- so armed -- we will protect the peace. People who are "pro-choice" are not supposed to question the ethics of mass abortions, and people who are "pro-life" are not supposed to ask what happens to the abused and unwanted babies of teen-age girls. Stupid questions are almost inevitably hard questions.

I asked a friend who is an entertainment writer what she considers a stupid question. She reminded me of the time about five years ago when I asked her, "Who is Linda Ronstadt?" It may seem trivial, but to me the world of popular music is every bit as mysterious as the world of atoms and stars is to others. My question was stupid only because the answer was something everybody (but me) knew. But if I hadn't asked who Linda Ronstadt was, I never would have found out. Which proves, I think, that asking stupid questions is usually well worth the price in humility or embarrassment; because asking stupid questions is often a very good way to get smart.