© NASA/WMAP Science Team.
The success of our standard model of cosmology in explaining phenomena observed in the universe today gives us confidence to extrapolate back in time to when the temperature of the universe was a few MeV. The Big Bang clearly happened before that, at TeV temperatures, but we do not know how it took place. Was there really an initial singularity, in which all the energy in the universe today was packed into a single point? How could the singularity itself have appeared? These remain open questions, at the forefront of modern gravitational research. (Unit: 4)