Stephen Hawking's work on black holes and the possibility of parallel universes have depended on the theories of a mathematician who died 150 years ago, writes Leo Enright.
When Stephen Hawking came to Dublin last week and changed yet again the way we think about the universe he did so with the help of an Irishman who died almost 150 years ago.
The astonishing insights of Sir William Rowan Hamilton, probably the greatest of Irish mathematicians, provided the tools for many of the papers presented at GR17, the 17th International Conference on General Relativity and Gravitation, at the Royal Dublin Society, even though they were in branches of physics that were unknown when the Irishman was developing his theories at Dunsink Observatory in the mid-1800s.
The science of quantum mechanics is perhaps so baffling to most of us because it can appear to have more in common with the calculation of bookmakers' odds than with unravelling the secrets of the universe. It seems ludicrous that reality could be better described by a set of often-contradictory probabilities than by the certainties we have clung to since childhood.
Making some sense of these conundrums was the great achievement of the Austrian physicist Erwin Schröinger, who fled to Dublin from Nazi-occupied Europe with the help of Eamon de Valera's government. Schrödinger's use of Hamilton's equations showed that the Irishman's brilliant insights into the complexities of old-world physics could be applied to the new world of quantum theory.
Today Hamilton's methods - known as Hamiltonians - have a key function in describing the total energy of a system - and held one of the keys to Hawking's latest breakthrough. Hawking must have felt he was simply stating the obvious when he told delegates: "The time evolution, including gravity, will be generated by a Hamiltonian. This will give a unitary mapping from the initial surface to the final."
Hawking, who has held the Lucasian chair of mathematics at Cambridge since 1979, disappointed many people with his latest conclusions, among them science-fiction fans.
"It is great to solve a problem that has been troubling me for nearly 30 years, even though the answer is less exciting than the alternative I suggested," he said. "There is no possibility of using black holes to travel to other universes."
The idea that black holes could somehow connect with other universes has embroiled Hawking in controversy for almost 30 years, because his defining study of black holes shattered a cosy consensus among cosmologists. He suggested that they do not continue to grow omnipotently for ever but eventually lose energy - through "Hawking radiation" - and evaporate into nothingness.
The problem is, what happens to all the information the black hole had gobbled up over aeons? Even the laws of quantum mechanics do not allow information about past events to just disappear, willy-nilly.
One answer proposed by Hawking was that another universe, a "baby universe" as he called it, existed on the other side of the black hole, receiving the missing information. This problem became known to cosmologists as the information paradox.
Hawking did not say he was wrong 30 years ago to pronounce on the lonely death by evaporation of black holes. Where he did say he was wrong was in the complex physics of what happens to the matter swallowed by black holes. Even his trademark speech synthesiser managed to sound wistful as he declared: "There is no baby universe branching off, as I once thought. The information remains firmly in our universe."
Hawking now believes that the information leaks out of black holes, through a mechanism he will describe in more detail in an academic paper to be published next month.
To his audience, of more than 600 cosmologists, this was a profoundly exciting and emotionally charged announcement, but for the rest of us the revised theory does not fundamentally change what we need to know about black holes: they remain awesome vortexes of energy, sucking stars to destruction.
Throughout all of the deliberations at the conference, the work of several major figures in the history of Irish science was drawn on repeatedly. In addition to the work of Hamilton, speakers cited George Francis FitzGerald and John Lighton Synge - a nephew of the playwright, who was credited last week with inspiring some of the world's greatest living theorists in relativity to embark on their careers.
Next Wednesday, on the 199th anniversary of Sir William Rowan Hamilton's birth, the Tánaiste, Mary Harney, will declare that 2005, International Year of Physics, is to be called the Hamilton Year of Physics in Ireland.