"The universe is not only expanding, but it is expanding in an accelerated way," Robbert Dijkgraaf, Dutch mathematical physicist and string theorist, explained to an audience at Gresham College in London. "A force called 'dark energy' is pushing the universe apart," he said. Dark energy had been identified by Albert Einstein, who thought that it was holding the universe together. Physicists have since learned that dark energy acts completely opposite from Einstein's speculation.
The expansive qualities of the dark energy, Dijkgraaf says, has dramatic consequences. "In the end, the universe will be expanding so fast that most of the galaxies that we see now will actually be far, far away and we will, in some sense, be looking at really a dark void."
Dark energy is the greatest "known unknown" of the universe. Dark matter and energy comprise approximately 96 percent of the universe, but physicists know little about the physical phenomena. Only 4 percent of the universe is described in our textbooks and science.