| − | A '''tachyon''' is a hypothetical particle that travels only faster than the [[speed of light]], needed to satisfy the [[theory of relativity]] they have never been detected. Tachyons cause non-causalities <ref>Phys. Rev. D 1, 3224 - 3225 (1970)</ref>. | + | A '''tachyon''' is a hypothetical particle that travels only faster than the [[speed of light]], needed to satisfy the [[theory of relativity]] they have never been detected. Tachyons cause non-causalities.<ref>Phys. Rev. D 1, 3224 - 3225 (1970)</ref> |