Professor Stephen Hawking lectures on the origin of the universe

27 February 2006

'Cosmology is a very exciting and active subject. We are getting close to answering the age-old questions: Why are we here? Where did we come from?' said Professor Stephen Hawking, delivering the third Dennis Sciama Memorial Lecture on Friday 24 February.

He gave his lecture to a packed Martin Wood Lecture Theatre, joined by additional audiences in the neighbouring Lindemann Lecture Theatre and at SISSA in Trieste, Italy, through a live audio-visual link.

Professor Hawking reviewed some historical ideas about the origin of the universe - the debate as to whether there was a beginning at all or whether the universe had existed forever.

He described how the general theory of relativity and the discovery of the expansion of the universe provoked conceptual changes, which meant that the idea of an ever existing, ever lasting universe was no longer tenable. The theorem which he and Professor Roger Penrose developed in 1970 said that general relativity predicted that the universe and time itself would begin in the big bang and that time would come to an end in black holes.

He likened the question of what happened at the beginning of time to what happened at the edge of the world. By combining the theory of general relativity with quantum theory, Jim Hartle and Stephen Hawking realised that time could behave like another direction in space under extreme conditions.

Professor Hawking explained: 'This means one can get rid of the problem of time having a beginning in a similar way in which we got rid of the edge of the world. Suppose the beginning of the universe was like the South Pole of the earth, with degrees of latitude playing the role of time. The universe would start as a point at the South Pole. As one moves north, the circles of constant latitude, representing the size of the universe, would expand. To ask what happened before the beginning of the universe would become a meaningless question because there is nothing south of the South Pole.'

In this view, the beginning of the universe would be governed by the laws of science: the creation of the universe would be down to spontaneous quantum creation. The image which Professor Hawking drew of this process was that of bubbles appearing and bursting, corresponding to mini universes that expand and collapse. Only those which grew to a certain size would be safe from recollapse and would continue to expand at an ever increasing rate. This process is called inflation.

Professor Hawking explained that the process of inflation would not be completely uniform but there would be irregularities in the early universe, which meant that some regions would have slightly higher density than others. The gravitational attraction of the higher density would slow the expansion of the region and eventually cause it to collapse to form galaxies and stars.

He concluded: 'We are the product of quantum fluctuations in the very early universe. God really does play dice'.

The memorial lectures are an occasional series with each lecture being given by a leading world expert, focussing on topics which were of particular interest to Dennis Sciama (1926-1999), the eminent astrophysicist who worked at Cambridge, Oxford and Trieste. He played a pivotal role in the development of modern cosmology and relativistic astrophysics.

Stephen Hawking is Lucasian Professor of Mathematics at Cambridge University, a chair that was held in 1669 by Isaac Newton. Professor Hawking studied Physics at University College, Oxford, and was supervised by Dennis Sciama for his PhD at Cambridge.

Picture: Professor Stephen Hawking delivering the Dennis Sciama lecture at Oxford. Credit: Physics Photographic Unit.