Particle

Harvey had a tattoo of Schrödinger equation for the wave function of the particle. (AUDIO: The Big Blue Book)

The Higgs particle was, according to Jack Harkness, the "fundamental particle of existence". It was the particle that protons and other subatomic matter were made out of. After years of research, in 2009, scientists at CERN discovered the particle as a side effect of colliding neutron eaters' gateway with protons and antiprotons. (AUDIO: Lost Souls)