Before the Big Bang
A new, mathematically solvable model of quantum cosmology by Penn State faculty Martin Bojowald provides detailed insights into how the universe could have emerged from a pre-existing one which was collapsing before the big bang. In this simplified model, the collapse of the precursor universe is halted when it reaches high energy densities by a repulsive force whose origin lies in quantum gravity. Afterwards, the universe expands and evolves through the standard phases of the big bang model. The solvable model allows one to compute the full quantum state before and after the big bang. One can thus address the question, in what quantum state the universe may have been before the big bang, based on assumptions on its present state. It turns out that a form of uncertainty relations limits what can be said about the early quantum state, since quantum fluctuations before and after the big bang appear complementary to each other. For more information, read "Physicist explores what happened before the Big Bang" on Penn State Live.