By Geoffrey Koch, ScienceNOW

In 2008, the Italian satellite PAMELA picked up an unusual signal: a spike in antimatter particles whizzing through space. The discovery, controversial at the time, hinted that physicists might be coming close to detecting dark matter, an enigmatic substance thought to account for 85% of the matter in the universe. Now, new data from NASA’s Fermi Gamma-ray Space Telescope confirm the spike. Alas, they also undermine its interpretation as a sign of dark energy.

Theorists generally believe that when two dark matter particles collide, they should annihilate each...