What happened before the big bang?.

For nearly a hundred years, scientists have believed that our universe was begun by a big bang some fourteen billion years ago. However, some scientists are now questioning that and this programme features some of their theories. For instance, Neil Turok, Director of Perimeter Institute for Theoretical Physics in Canada and Paul Steinhardt at Princeton, believe that the universe sprang into existence from a mysterious 'initial singularity' and that there were a series of big bangs or collisions with other parallel universes. Roger Penrose, on the other hand, imagines an eternal cycle of expanding universes where matter becomes energy and back again in the birth of new universes, ad infinitum. Other theories put forth include cosmic bounces, rips and multiple universes and attempts are made to explain what might have happened before the big bang.