In inflationary models of cosmology, times before the end of inflation (roughly 10 seconds after the Big Bang) do not follow the same timeline as in traditional big bang cosmology. Models that aim to describe the universe and physics during the Planck epoch are generally speculative and fall under the umbrella of " New Physics ". Examples include the Hartle–Hawking initial state, string theory landscape, string gas cosmology, and the ekpyrotic universe.