There is an unwritten precept in modern physics, often facetiously referred to as Gell-Mann's totalitarian principle, which states that in physics "anything which is not prohibited is compulsory." Guided by this sort of argument we have made a number of remarkable discoveries, from neutrinos to radio galaxies.
Particles Beyond the Light Barrier, Physics Today, Volume 22, Number 5, May 1969 (p. 44)