At a family party some years ago, one of my uncles remarked on how little science really knows. For example, we still have no idea how gravity works - why things fall down.

"Actually, we do know how gravity works," I said. (My father, a Ph.D. physicist, was also present; but he wasn't even touching this one.)

"We do?" said my uncle.

"Yes," I said, "Gravity is the curvature of spacetime." At this point I had still swallowed Feynman's line about being able to explain physics to one's grandmother, so I continued: "You could say that the Earth goes around the Sun in a straight line. Imagine a graph that shows both space and time, so that a straight line shows steady movement and a curved line shows acceleration. Then curve the graph paper itself. When you try to draw a straight line on the curved paper, you'll get what looks like acceleration -"

"I never heard about anything like that," said my uncle.

When was the last time, in history, when it was possible for a single human to know the knowledge of the most advanced civilization? I've seen various estimates for this - usually in the form of polymaths nominated for the position of "last person to know everything". One plausible candidate is Leonardo da Vinci, who died in 1519 - shortly after the printing press began to become popular, and shortly before Copernicus inaugurated the scientific revolution.

In the ancestral environment it was possible to know everything, and nearly everyone did. In hunter-gatherer bands of less than 200 people, with no written literature, all background knowledge was universal knowledge. If one person, in a world containing 200 people total, discovered how gravity worked, you could certainly expect to hear about it.

In a world of 6 billion people, there is not one person alive who can say with certainty that science does not know a thing. There is too much science. Our current lifetimes are too short to learn more than a tiny fraction of it, and more is being produced all the time.

Even if last week's technical journal doesn't contain the answer to a mystery, that doesn't mean that no one knows it. Maybe someone out there is typing up the paper at this very moment. You can't generalize over all 6 billion people in the world because ...

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