A time ram was what happened if two TARDISes attempted to occupy exactly the same time and space. The resulting paradox would destroy both TARDISes and cause extreme spacio-temporal destruction in its wake. The fate for those caught in a time ram was what the Third Doctor considered tantamount to "extinction" and "utter annihilation". (TV: The Time Monster) According to the Fifth Doctor, a time ram would cause a black hole large enough to destroy an entire universe. (TV: Time Crash)