Dark Matter and Dark Energy Explained What We Still Don’t Know Dark matter and dark energy sound like we know what they are… but we don’t. Dark matter accounts for about 85% of the universe’s gravity, yet we cannot see its source. Dark energy is an even stranger idea: a mysterious pressure in empty space that makes the universe expand faster and faster. If that acceleration continues, distant galaxies will eventually slip beyond our cosmic horizon, taking huge parts of the universe’s story with