Equations describing Grand Unification theories.
A Grand Unification theory was any idea proposed which offered hope of marrying general relativity and quantum mechanics.
In 2367, after having his intelligence drastically increased through an encounter with a Cytherian probe, USS Enterprise-D engineer Reginald Barclay spent an entire night debating the finer points of Grand Unification with a holographic Albert Einstein. (TNG: "The Nth Degree")
In the script for "Q Who", Sonya Gomez waxed philosophically, "And is it here because we believe in it and have therefore created it, or has it created us?" To which, Geordi La Forge said that both the Grand Unified Theory and Supersymmetry had not been seriously discussed for years. In response, Gomez replied that both theories had not been disproved and, although she did know not if the theories were true or not, she had to try and find out. These lines were later cut and did not appear in the episode.