Today astronomers have come down on the side of believing that galaxies and galaxy clusters are pregnant with some sort of exotic material that is invisible to us—they are calling it dark matter. They haven't yet identified what it is exactly—or even established that it truly exists—but it is not for lack of trying. Despite decades of using every imaginable means of detection—from gamma-ray telescopes in outer space to cryogenic subatomic particle monitors buried deep inside a northern Minnesota mine—their occasional, tantalizing reports of success remain as unreliable as Elvis sightings.

And dark matter isn't even the most astonishing thing modem astrophysicists have discovered about gravity. Astrophysicists have discovered another mystifying reality—they call it dark energy. All told, astronomers have concluded that dark energy comprises some 68 percent of the total universe and dark matter, about 27 percent. That means only 5 percent of the entire universe is visible to us! In other words, everything we call scientific knowledge is based on but a pittance of what there is to know about our world. Ninety- five percent of it is hidden from us. Even with all of our advances our science is 95 percent in the dark about the universe it seeks and claims to understand; about what is real or not, what is possible or not—even about a prosaic force that exists literally right under our noses.