07 October 2020 22:31

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- Coronation Street Eileen Grimshaw Sue Cleaver

Turning the gaze skyward, there are such celestial objects, which were a matter of speculation, by the British polymath John Michell in 1784 and independently by the French savant Pierre Simon de Laplace in 1796. The latter furnished in 1799 – mercifully not in the margins – a proof that non-luminous objects could exist, using Isaac Newton's theory of gravitation. Stars with a powerful gravitational force could prevent anything, even light, from escaping from its maws. What was regarded as a mere mathematical curiosity turned into a key question in the 20th century with the advent of black holes in the framework of Albert Einstein's general theory of relativity, which supplanted Newtonian theory. Einstein's special theory of relativity was concerned with overhauling Newtonian mechanics to produce a mechanics which applied uniformly to inertial frames that are either at rest or in uniform motion. This was needed because the first discovery of the phenomenon of electromagnetism by Hans-Christian Oersted whose bicentennial falls this year and Maxwell's unified theory of electromagnetism in 1865, showed that the laws of physics transformed in a different way than Galilean-Newtonian mechanics envisaged. The Lorentz transformations as these were called, were applied to mechanics, producing altogether different results. The constancy of the speed of travelling electromagnetic field, represented by light was an essential ingredient. The general theory of relativity went a lot further, seeking to represent the fundamental laws of physics so that they applied also to non-inertial ie accelerated frames. It suggested that the gravitational force was tantamount to the curvature of space-time. The prediction of the bending of light rays by intervening stars was verified in 1919 by Eddington's expedition, turning Albert Einstein into an iconic physicist worldwide. The possibility of black hole singularites following irreversible gravitational collapse, was present in the theory. As Einstein's equations were notoriously difficult to solve, the area went into a long period of somnolence until Roger Penrose emerged. Using global methods borrowed from topology, Roger Penrose was able to show that the black hole singularities were an inevitable consequence. Ironically enough, Penrose presented the path-breaking paper at a conference in Poland, which was attended by the physicist Richard Feynman who wrote to his wife to remind him not to go to conferences on general relativity. Strangely he failed to notice Penrose's work which opened the floodgates. A whole new field of inquiry had been opened up by Penrose. Acting on the advice of Dennis Sciama, Stephen Hawking began to collaborate with Penrose and to extend the technique to the universe as a whole, to show the existence of a singularity at the origin of the universe. This is the 'big bang' singularity, which replaced the earlier view of a steady state universe. Hawking was wont to say that he would get the Nobel Prize – and that would have included his mentor Roger Penrose – if black holes were actually observed. The supermassive black hole with the mass of a billion suns at the centre of the Milky Way, was discovered by astronomers. Roger Penrose's fascination with geometry began at an early age. Along with his father he was responsible for some of Escher's well-known paradoxical figures. Roger Penrose preferred an open universe, compared to Hawking's closed universe, as he found the former more interesting from a geometrical perspective. The discovery of universal acceleration makes it the inevitable choice. Lately, he has turned to a universe which is cyclic, each big bang leads to an open universe at the end of which there are just massless photons left. By an ingenious sleight of hand, he turns the scale invariance of a massless universe into a resource for a new universe which begins with another big bang. Our understanding of the universe has been transformed beyond measure and who knows what revolutions are likely to occur in the future. Roger Penrose has shown the way, which adventurous minds will follow.