The Big Bang event itself is a singularity, where (and when) the currently understood laws of physics cannot describe what is going on. This means that the behavior of the universe can only be traced back to a time after the Big Bang, when the laws of physics first begin to apply. By combining the minimum size and time scales that are described by the two major theories that describe the universe—general relativity and quantum mechanics—scientists have deduced that the earliest time to which the behavior of the universe can be traced is about 10–43 second after the Big Bang. That is a ten-millionth of a trillionth of a trillionth of a trillionth of a second! This earliest, all-but-unknowable period of cosmic history is called the Planck time, after the German physicist, and pioneer of quantum theory, Max Planck.