I'm speaking of quintessence. Here are some articles:
Many physicists are uncomfortable with this line of reasoning, and they are seeking the answer in different class of theories known as quintessence, after the Greek word for the fifth element. Modern physics, noted Dr. Paul Steinhardt, a theorist at Princeton, is replete with mysterious energy fields that would exhibit negative gravity. The trick, Dr. Steinhardt explained, is finding a field that would act like the dark energy without a lot of fudging on the part of theorists.
"The observations are forcing us to do this," he said. "Dark energy is an interesting problem. Any solution is quite interesting."
One theory that captured the fancy of the astronomers in Baltimore was a modification of gravity recently proposed by three string theorists at New York University: Dr. Gia Dvali, Dr. Gregory Gabadadze and Dr. Massimo Porrati. In string theory — so named because it describes elementary particles as tiny vibrating strings — the ordinary world is often envisioned as a three-dimensional island (a membrane, or "brane" in string jargon) floating in a 10- or 11- dimensional space. Ordinary particles like electrons and quarks and forces like electromagnetism are confined to three dimensions, to the brane, but gravity is not.
As a result, Dr. Dvali suggested that gravity could only travel so far through conventional space before it leaked off into the extra dimensions, thereby weakening itself. To an observer in the traditional three dimensions it looks as if the universe is accelerating. The cosmological constant, in effect, he said, is a kind of gravitational brane drain. "Gravity fools itself," he said. "It sees itself as a cosmological constant."
Dr. Dvali's theory was welcomed by the astronomers as a sign that string theory was beginning to come down from its ivory tower of abstraction and make useful, testable predictions about the real world. (In another string contribution, Dr. Steinhardt introduced a new theory of the early universe, in which the Big Bang is set off by a pair of branes clashing together like cymbals.)
Afterward Dr. Riess and Dr. Perlmutter pressed Dr. Dvali on what they would see when they looked out past the crossover point where gravity began falling out of the world; would the transition between a decelerating universe and an accelerating one happen more abruptly than in the case of the cosmological constant? Dr. Dvali said he hadn't done any calculations, but he said it was his "naïve guess" that the crossover would happen more smoothly than in a lambda world.