While the scientists are still not sure exactly what dark matter is, since they have yet to identify it in a laboratory, they said that the workings of the universe cannot be explained without it.
The finding will have potentially great impact on an active debate among physicists and cosmologists about not only dark matter but also the workings of gravity that it helps explain. Indeed, the theory of dark matter evolved largely to explain the finding several decades ago that there was not enough visible matter in the universe to produce and account for the gravity needed to keep galaxies from flying apart.
"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona in Tucson, leader of the NASA-Harvard University study. "These results are direct proof that dark matter exists."
I won't pretend to have any profound understanding of dark matter or the scientific theories and principles associated with its study, but since I first heard of dark matter some years ago, the concept has been a strangely compelling one for me. Science has a tendency to lack the exuberance of religious faith simply because it's based as much on destroying false positions as validating true ones; that rationalism is absolutely essential to human progress, but it can leave one feeling discomforted and a bit empty emotionally.
Concepts like dark matter give me a sense of what true religious faith must feel like -- a charge of excitement that comes from knowing that a powerful thing exists without knowing its appearance or nature. Unlike religious faith, however, science must be tested and many remain unconvinced:
While the theoretical existence of dark matter has been broadly embraced for years -- and has now been further endorsed by some of the most prominent researchers and institutions in the field -- a strong countertheory has also grown, contending that the laws of gravity established by Newton and Einstein need modification. The group supporting this theory believes that a relatively limited tweaking of those laws, especially as they pertain to the massive nature of faraway galaxies, could explain the missing gravity better than could undetectable dark matter.
Stacy McGaugh, an astrophysicist at the University of Maryland, has been one of the dark-matter skeptics, and he said yesterday that he remained unconvinced.
"I've been aware of this result some time, and I agree that it is interesting and may make more sense in terms of dark matter than alternative gravity," he said. "However, it is premature to say so."
He said that a definitive detection of dark-matter particles would mean "grabbing them in the laboratory, not just inferring that their effects can be the only possible explanation for an observation before the alternatives have actually been checked."