An event horizon is the boundary of a black hole, defined by the light that can reach out that far and no further. Hawking himself sometimes uses pictorial metaphors to illustrate abstruse mathematical concepts, and this one occurred to me by way of an analogy of the brilliant illumination that I am trying to persuade to shine out far enough to reach my own dim wits hovering hopefully in the outer darkness.
The whole `feel' of Hawking's discourses reminds me of the stories I have read about Einstein at work - placid, orderly and without excitement (or should I say `perturbation'?). Genius of this kind seems to be a kind of glorified knack - such minds just operate naturally with concepts of this kind, and there is no sense of effort or struggle. Sandwiched between some biographical material and a radio interview, the main material in this book is a collection of essays and lectures. They include Hawking's inaugural lecture at Cambridge where he occupies the chair of mathematics once held by Newton, and all are intended in the first place for an audience of his peers. On the other hand, where Newton and Einstein did not try to address the general public, Hawking, like Russell, seeks to do just that, and he does it superbly. The style of writing is both literate and unpretentious, and the occasional jokes are very good. Readers who, like myself, are intensely interested in the subject-matter but entirely lacking in natural aptitude for it, ought to find this book enormously helpful. There is a certain amount of repetition inevitably, but the more of that the better so far as I'm concerned. Any amateur trying to get a handle on mathematical concepts like these has to get into a mathematician's way of thinking as best he can and stop thinking as a layman. We can all understand the basics of gravitation without being Newton, but if we are still struggling with the general idea of the General Theory of Relativity in 2006 it's worth remembering that it was propounded in 1915 and that physics and astronomy have came on a long way since then, so we had better get our minds round it at last.
At least as astounding to me as Hawking's triumph over his physical paralysis is the fact that this professor of mathematics at Cambridge never graduated in that subject. His degree subject was physics, allegedly on the grounds that the Oxford physics course was easy. Not easy enough to tempt me away from Latin and Greek, I must say, but doubtless for him. Mathematics is just a technique that Hawking invokes as a tool in his quest for a grand unified theory of the entire cosmos. This, said he 20 or 30 years ago, is something he hoped and largely expected could be achieved in 20 or 30 years. I'm sure we would have heard if he thought by now that he had got there, but he honours us with his ideas at the time of writing on the origin and future of the universe. The main obstacle to the final resolution of the issue is apparently that no one has yet successfully integrated old Newton's gravitation with the rest of it. However he also helps us with some more `back-at-the-office' theory concerning black holes, on which topic he appears to be the leading thinker, and that gives him the opportunity to remind us of the outlines of the most important advances since Einstein, namely quantum mechanics and Heisenberg's uncertainty principle.
The latter principle enunciates that the better the position of a particle can be predicted the less well its velocity can be predicted, and conversely. Since it is necessary to predict both, all we can do is predict the combination on a `smeared' statistical basis. It seems to come into everything, and Hawking invokes it to try to comfort us with the belief that although everything (and everyone) actually is determined by particle physics, the extent of the unpredictability is such that we might as well consider ourselves to be free agents. For once, I would dare question him. In the first place such a view doesn't seem to require Heisenberg - simply viewing the story of the cosmos as a chain of events constituting causes and effects would surely get us that far, as the permutation of these is incalculably large and therefore only to some extent predictable. Secondly, when we talk about `free will' and `determinism' what are we even talking about? I'm often told in arguments that I can think what I like. On the contrary, I wish I could, but my own observation and reason, such as they are, leave me unable to. When I exercise `free choice', e.g. in choosing from a menu, I can quite understand that my choice might be determined by physical causes (whether that is the truth of it or not). However when I change my mind about something factual or theoretical, which is taken as a sign of free intelligence, I do so because I feel that the evidence leaves me no choice, and evidence is not an `event' or a `cause' or any matter of particles or physics. Where does all this leave `free will'?
Those seeking God or a Creator will find that Hawking hedges his bets, so that any capable by nature of thinking what they would prefer to think remain, I suppose, `free' to do so. The issue is beyond me, and my own quest is for a better understanding of the cosmos I have been born into and will have to leave before too long. May I wish Professor Hawking a long and productive further career. We are much the same age, and his 20-30-year estimate for solving the riddle of the cosmos is up around now. If he finds it, I hope I can recognise it when I see it.