Scientists ask people to believe the strangest things. They say that the universe exploded out of nothing, and that 99% of the matter in it may be missing. They tell us that life forms bloom out of a simple solution of carbon and water; that the self-same carbon atoms, subtly rearranged, can sparkle as diamond, or dull the chimney as soot.
And then they look down their noses at people who believe in palm reading and astrology. Somehow, it's OK to believe in light-devouring black holes but not past lives; DNA but not ESP; 10-dimensional space, but not visits from aliens.
But how does one tell the difference between off-the-wall ideas accepted as "science" and off-the-wall beliefs that are just off the wall? What is the difference between science and pseudoscience anyway?
Ideas that can be tested by experiment or careful observation do not present much of a problem. Sooner or later, truth will tell. But some truths are more elusive.
Haim Harari, a physicist who is president of the Weizmann Institute of Science in Israel, likes to tell the story of a recent UFO sighting in his native land.
The bright light was seen by hundreds of people and soon after, almost as many explanations filled the radio waves as people called in with their theories--which ranged from stray bits of a satellite setting the sky on fire as they plunged into the atmosphere to aliens paying a call from a distant galaxy.
All sides agreed, said Harari, that "there is no solid proof that could rule out any of the possibilities."
But it didn't follow, said Harari, that all explanations were equally plausible. "Satellites exist, and little people coming from other galaxies are not known to exist."
Even though the satellite explanation could not be proved, it could be closely related to something known to be true. It is a small leap from real satellites orbiting the Earth to a possible fragment of satellite burning up in our atmosphere.
And so it is with even the most far-out ideas that scientists cook up. Ten-dimensional space may sound weird, but it's an extension of ideas that are tried and true. From the flat Earth idea of several hundred years ago to Einstein's four-dimensional space-time, to 10-dimensional string theory is but a hop, skip and a jump (albeit a rather large one).
Compare that series of links to the idea that the positions of the stars or planets at birth can influence one's love life or financial future. It is not just that experimental tests have failed to confirm the reliability of these predictions; there is no sensible way for planets or stars to exert that kind of influence on Earth. The gravitational pull of Venus or Mars on someone at birth would be overpowered even by the gravitational pull of the obstetrician walking around the delivery table.
Astrology, in other words, is not connected to anything known, while even black holes follow directly from what is known about gravity.
Of course, scientists themselves do not always agree on which wild ideas are worth pursuing. They do not entirely agree on the existence of black holes, the details of the Big Bang, or the plausibility of alien life in other solar systems.
"There obviously is no simple answer to the question [of which wild ideas are worth pursuing]," said Caltech Vice Provost David Goodstein.
Far-flung flights of fancy called "thought experiments" are sometimes scientists' best friends. But at some point, even experiments carried out in the laboratory of the mind need to be tested by others.
And as Goodstein points out, even the most abstract notions can be tested. Anyone with the requisite talents can do the calculations that revealed the link between gravity and black holes.
Making connections, after all, is what science is all about. The deep connections between electricity and magnetism remained unrecognized for many centuries, as did those between space and time, the fall of the apple and the orbit of the Earth, inheritance and DNA, disease and microbes.
Science gains strength from these tangled roots. The scientist is like a gardener planting bulbs, then finding the thick network of underground tentacles of all the bushes and trees and flowers that seem so solitary on the surface.
Following the roots is one of the best ways to tell which wacky ideas are worth pursuing. The path isn't always straight or solid, but there is always a path--even if it takes you out on a limb.