The mid to late 1970s were a period of growing popularity and success for Stephen. His work was now much talked about; he was appearing in television documentaries, and in 1979 he became the Lucasian Professor of Mathematics at the University of Cambridge, a position he held for 30 years until his retirement in 2009. Hawking's inaugural lecture as Lucasian Professor of Mathematics was titled: "Is the end in sight for Theoretical Physics" and promoted the idea that super gravity would help solve many of the outstanding problems physicists were studying. In collaboration with Jim Hartle, Hawking developed a model in which the universe had no boundary in space-time, replacing the initial singularity of the classical Big Bang models with a region akin to the North Pole. One cannot travel north of the North Pole, but there is no boundary there – it is simply the point where all north-running lines meet and end. While initially the no-boundary proposal predicted a closed universe, discussions with Neil Turok led to the realization that it is also compatible with an open universe. Later work by Hawking appeared to show that, if this no-boundary proposition were correct, then when the universe stopped expanding and eventually collapsed, time would run backwards (Hawking famously used the example of broken teacups reassembling). However, work by Don Page, a former student of Hawking, led to Hawking withdrawing this concept.Along with Thomas Hertog at CERN, in 2006 Hawking proposed a theory of "top-down cosmology", which says that the universe had no unique initial state and therefore that it is inappropriate to formulate a theory that predicts the universe's current configuration from one particular initial state. Top-down cosmology posits that in some sense, the present "selects" the past from a superposition of many possible histories. In doing so, the theory suggests a possible resolution of the fine-tuning question