Since an earlier bigger bang
A BRIEF HISTORY OF TIME by Stephen Hawking
Bantam Press, f14.95, pp.
Does time have a beginning and an end? Or, to ask the question in another way, did the universe start in timelessness, and will it end in a similar patch of non-time? This is the major question that Stephen Hawking asks in this, his latest book, and to anticipate his final chapters, he is unhappy with the current idea that time does have a stop. The book is fascinating and absorbing. Hawking's own view is that without his complex mathema- tics, we can hope only for an overview of his subject — cosmology: but he was warned by his publisher that each mathe- matical equation would halve the number of readers. He included, therefore, only one (e=mc2) and, as a result, the book, though using the theories of relativity and quantum mechanics, is open to the non- scientific reader.
The nature of the history of time is (obviously) connected with the origin of the universe, and with its history. The idea that the universe had a history at all, in the sense that it changed with time, started in 1929, when the astronomer Edwin Hubble noticed a very surprising fact about the light from the stars. The light was redder than it should have been — the effect is known as the Red Shift — and this means that the stars are moving away from us. (The effect is the exact equivalent of the lowering in pitch of the sound of a police- car bell as it passes and starts to go away.) One possible explanation is that every star in the universe is receding from the Earth: a less egocentric view is that the universe is expanding, which has the same effect on the light. If the universe is expanding, it must once have been smaller and astro- nomers have plotted the expansion back- wards in time to give an instant when the entire universe was a dot of immense mass that exploded in the 'Big Bang'. On the `plotting back' basis, the origin of the universe was between 10 and 20 thousand million years ago. It is difficult to hold in our minds this idea: that the entire matter of the universe was present, though not as atoms and molecules, let alone as the elements we now have, in this compact dot.
The accepted idea is that this dot existed and then started to expand in the Big Bang, giving rise in the end to, among other wonders, theoretical physicists and Spectator readers and book reviewers. Hawking believes that science should be eventually able to explain everything in the world around us, even including these particulars: science is about understanding in that sense. But on present views, ex- plainability doesn't extend to the Big Bang: we cannot hope to understand why the original dot started to expand.
This is a consequence of one of the two great 20th-century scientific theories, re- lativity, which Einstein put forward in 1915. According to this, any event in the universe could be located by four measure- ments — three in space, one in time. Einstein said that space-time was curved by any solid object (he found that the details of the movements of the planets and of electrons could be better explained in this way than by conventional physics.) But space-time would be infinitely curved, wrapped in a tight ball, around the pri- maeval dot, and this meant that there could be no science, and no prediction about this state. It also means that time, in the sense that we know it, started with the Big Bang. This infinitely compact mass, existing outside science, is technically known as a singularity.
Hawking is at home with the idea of singularities. He proposed, with another theoretician, Roger Penrose, another ver- sion, the Black Hole. A Black Hole is the remnant of a massive star. Stars generate heat, and thus light, from radioactive burning of their elements. For a while, a very long while, the energy of the burning overcomes the star's own gravity, and the star expands. Eventually the radioactive fuel starts to run out and the star starts to collapse under the effects of gravity. In some stars, energy and gravity eventually come to a new balance in a smaller, dimmer star, but with some very massive stars the collapse is a runaway process. As the star collapses, the gravitational forces become stronger, and eventually the star becomes so small, with its mass so concen- trated, that the gravity holds even the light in. This star is called a Black Hole and is also a singularity. (Theoretical physicists consider that once a Black Hole is disco- vered, Hawking and Penrose will receive a Nobel Prize. There is a problem in that Black Holes are by definition invisible: so far, there are some strong candidates, but no secure discovery.) Hawking is, in this book, unhappy with the idea of singularities. We are close to understanding all the processes since the Big Bang (though not in the detail that would predict our individual histories) and to Hawking it is absurd that we should understand more than 99 per cent of the history of the universe and be forced to stop there. One way out comes from the second great scientific theory of our cen- tury, quantum mechanics, proposed by Werner Heisenberg, Erwin Schrodinger and Paul Dirac in the 1920s. As relativity is the science of fairly large objects, quantum mechanics is the science of the very small — particles smaller than an atom, such as the electron and the neutron. Quantum mechanics partly derives its name from the quantum, the unit of radiation discovered by Max Planck. But it derives its nature from the Uncertainty Principle that Wer- ner Heisenberg proposed in 1926. This said that we could never simultaneously know the exact position and velocity — speed of a sub-atomic particle. The reason was that to determine either of these, we would have to make a measurement, and the act of making a measurement would change the quantity we were trying to measure. (As a simple example, if we tried to use a beam of light to check the position and speed of a sub-atomic particle, the energy of the light would alter the speed, simply because the energy is of a scale comparable with that of the particle.) The result is that we cannot make exact predictions about sub-atomic particles as we can about, say, billiard balls. The physics of the sub-atomic is always statistical: it is very likely that this will happen: it is never certain. Many scientists are unhappy with the ideas of quantum mechanics : Einstein never accepted it, saying, famously, 'God does not throw dice'. But it works for sub- atomic physics as relativity works on the larger scale. But both are sciences talking about the same real world, and there should be a unified theory. Hawking considers that in this unified theory, quantum relativity, space-time will be finite yet unbounded. (To an amphibious pedestrian, our Earth is finite but unbounded. The pedestrian can walk indefinitely without falling off, but the Earth has a definite size.) Space-time, Hawking thinks, will in the unified theory turn out to be like a curved ribbon, joined at the ends, so that no event is beyond time and thus beyond science.
This is an absorbing book, brimming with rich ideas — a 20th-century master- piece of popularisation, written, as happens rarely, by the scientist himself. This particular scientist has a mere shell of a body. He has been crippled, confined to a wheelchair for the last 20 years, by motor neurone disease, a degenerative illness that rarely spares anyone for so long. It is to us a marvel that someone who can write only through a computer and speak only through a voice synthesiser can be one of the world's leading scientists and a fascinating, stimulating writer. Hawking sees it other- wise. 'I am lucky. As a theoretical physicist, I do all my research in my mind.'