For some reason, despite the predictions of our current theories, the universe is expanding faster and faster in all directions. This strange fact has been attributed to dark energy, an elusive substance currently at the cutting edge of physics research.
Physicists have measured unmistakable gravitational effects in the universe where there isn’t any matter to cause it. This invisible substance, called dark matter, can be found in galaxies in large quantities, and has an unknown constitution. One theory proposes that dark matter is composed of weakly interacting massive particles (WIMPs).