Through science, we discover not only what we didn’t know but what we thought we knew but didn’t. Something that for ages may have been taken as a self-evident truth ? the flatness of the Earth, for instance ? can be exposed as a myth. What is easy to overlook is that even science does not always know what it thinks it knows.

Myth, in the form of theoretical speculation, is the mortar in which many of the bricks of scientific discoveries are laid. Or you might say that it is the dark matter that holds the universe of scientific knowledge together.

And dark matter, of course, is itself an example of a scientific “myth.” Though its existence remains speculative, it is increasingly taken as factual. But another myth has for so long and so well masqueraded as fact that most of us would never even think to question it: gravity.

Who would think there was doubt in something that seems to be substantiated simply by picking up an apple and letting it drop? But, as The Times reported, a respected Dutch physicist has declared that gravity is an illusion. “Gravity doesn’t exist,” Erik Verlinde told The Times.

There is, of course, no doubt that objects on Earth do fall, and pick up speed on descent. But a force called gravity is not necessarily the best explanation for that. Dr. Verlinde’s own explanation is too complex even for fellow physicists. But he is not the first to attack Newton ‘s credibility. Stephen Hawking and, before him, Einstein both had cracks at it. Less surprising, perhaps, are attacks on the theory of evolution. Outside intelligent-design Tea Parties, though, Darwin’s brainchild is often assumed to be substantiated in all respects.

One of its most curious demonstrations: the way certain species uncannily mimic the shape and coloring of other species . The Times reported on a remarkable example of this among caterpillars and chrysalises in Costa Rica. But this magical-seeming mimicry sits uneasily with the idea that it was produced, as Darwin would have it, by an exhaustive, eon-consuming series of slight random mutations that just happened to help propagation.

The real triggering mechanism behind it, and how it adjusts and perfects the mimicry, remains something that science may seem to know, is assumed to know, but really does not know. That science doesn’t know a particular thing can even be confounding. Who would have thought that scientists did not really know how small birds migrate, how they travel such vast distances or how often they have to stop? According to The Times, researchers using new tracking technology were astounded to discover that many of the birds preferred, like most of us, nonstop flights.

Scientists are, of course, positivists. They do not like to draw attention to the “negative matter” that is the immensity of the gaps in their knowledge. And this allows us to live as if science were lighting our way more brightly than it is.

Perhaps it is time for some Carl Sagan of scientific ignorance to step forward with a book on the subject of the billions and billions of things that science surprisingly doesn’t yet know. It would be a project that could end with what even scientists agree they are unlikely ever to know: why there is something instead of nothing and, of course, the purpose or meaning of it all.

CARLOS CUNHA