Two groups have tightened the limits on the search for elusive dark matter and dark energy, the mysterious force accelerating the expansion of the Universe.
Physicists have proposed that dark energy could come from a 'chameleon' field: a force that would act in the low density of space but would not be felt in the relatively dense environment of the lab. Holger Müller at the University of California, Berkeley, and his team used a laser to measure the forces between caesium atoms and a sphere of aluminium in an ultrahigh vacuum — a set-up designed to mimic outer space. They found no evidence of new forces, ruling out many chameleon fields that would explain the Universe's acceleration.
A second group, working on the Xenon100 experiment at the Gran Sasso National Laboratory, Italy, found no evidence for dark matter interacting with atoms inside its underground tank of liquid xenon. The group's findings rule out three kinds of dark matter as the source of a signal seen previously in another experiment at the same lab.