THE adage “what you see is what you get” could be thought to ring true for a group of people who dedicate their lives to collecting tiny flickers of light from very distant objects. But astronomers and cosmologists, who do exactly that, have long held that the universe is pervaded by far more than that which can be seen. Since the 1930s, they have postulated the existence of “dark matter”, an ethereal and, as yet, undetected form of matter.
Physicists claim to need dark matter to explain why the stars in the outermost reaches of rotating galaxies are moving at such great speeds. If these galaxies consisted only of the stars that can been seen, their gravity would be insufficient to hold on to the outermost stars. The individual stars would simply fly out of the galaxy, like a doll thrown from a rapidly spinning merry-go-round. Thus, the galaxy must contain some mysterious matter that makes it massive enough to keep hold of these stars. . .
Now, in a controversial paper that has recently appeared on arXiv, an online collection of physics papers, Fred Cooperstock and Steven Tieu of the University of Victoria in Canada claim that one of the key pieces of evidence for the existence of dark matter is not really there.
more from The Economist here.