  We speculate that the early Universe was inside a primordial black hole. The
interior of the the black hole is a dS background and the two spacetimes are
separated on the surface of black hole's event horizon. We argue that this
picture provides a natural realization of inflation without invoking the
inflaton field. The black hole evaporation by Hawking radiation provides a
natural mechanism for terminating inflation so reheating and the hot big bang
cosmology starts from the evaporation of black hole to relativistic particles.
The quantum gravitational fluctuations at the boundary of black hole generate
the nearly scale invariant scalar and tensor perturbations with the ratio of
tensor to scalar power spectra at the order of $10^{-3}$. As the black hole
evaporates, the radius of its event horizon shrinks and the Hubble expansion
rate during inflation increases slowly so the quantum Hawking radiation
provides a novel mechanism for the violation of null energy condition in
cosmology.
