The late Professor Stephen Hawking. Photo: Flickr

Stephen Hawking: Even briefer history of time

In 1998, Stephen Hawking wrote for Prospect, reflecting on A Brief History of Time and what had changed since the book's publication
August 19, 1998

This year is the tenth anniversary of my book, A Brief History of Time. Appropriately enough, it was first published on April Fool's Day, 1988. The idea of the book developed from lectures I gave at Harvard in 1982. By 1984, I had a first draft and began to consider whom I should get to publish it. My previous academic books had been published by Cambridge University Press. They had done a very good job, but I didn't feel they had the right approach for the mass market.

I told my literary agent that I wanted my book on airport bookstalls. The agent made polite noises, but clearly didn't think this was possible. Nevertheless, he got me several offers. I picked Bantam because of their strength in the mass market; I have never regretted my choice. They assigned me a fine editor, Peter Guzzardi, who made me rewrite my first draft in terms that he could understand. He also had the bright idea of changing the title. My original idea had been, From The Big Bang To Black Holes, A Short History Of Time. But Peter changed it to A Brief History Of Time. I am sure this title has helped.

Shortly after I met Peter Guzzardi I caught pneumonia while at the European Center for Nuclear Research in Geneva. For a time my life was despaired of. In the end, they had to perform a tracheostomy operation, which removed my power of speech altogether. Before that, I had been able to dictate to a secretary who could understand me, but for a time, I could communicate only by raising my eyebrows when someone pointed to letters on a card. At that rate, it would have taken until the next millennium to finish my book.

However, a software developer called Walt Waltosz heard of my plight, and provided me with a computer and a programme which allowed me to scan the screen and select words, which are printed on the bottom half of the screen. Over the years, the system has developed. My present version was made for me by Intel. It has a mobile telephone, with access to the internet. I can claim to be the most connected person in the world. I have kept my original speech synthesiser, however, partly because I haven't heard one with better phrasing, and partly because I now identify with this voice, despite its American accent. But the speech synthesiser uses chips which are now obsolete, so I will have to change eventually. That will bring a real identity crisis, especially for my wife, who won't recognise me.

With the computer system, I was able to finish A Brief History and it was duly published. Despite wanting it sold on airport bookstalls, I had expected it to be only modestly successful. So I was surprised by its reception. It was in the Sunday Times bestseller list for 237 weeks, longer than any other book in history. (Apparently, the Bible and Shakespeare don't count). And it has been translated into more than 30 languages. This means I am recognised wherever I go, though sometimes I try to disguise myself by saying that I am often mistaken for Hawking.

*** Why was A Brief History such a success? A contributing element must be the fact that I am disabled, or should I say, physically challenged, to be politically correct. But the main reason was that the public was hungry for a book of this type. There were already many books about the early universe and black holes on the market, ranging from the very good to the very bad. However, I felt that none of these really addressed the big questions which had led me to do research in cosmology and quantum theory. People have always wanted answers to the big questions. Where did we come from? How did the world begin? What is the meaning and design behind it all? The creation accounts of the past now seem less credible. They have been replaced by a variety of superstitions, ranging from New Age to Star Trek. But real science can be far stranger than science fiction, and much more satisfying. The problem is that most people believe that real science is too difficult for them. But I don't think this is the case. Not everyone can be or wants to be a theoretical physicist, but most people can understand the basic ideas, if they are presented clearly without equations.

Humanity is making great advances in science and technology, and the pace of change is quickening. I recently gave a lecture at the White House to an audience that included the Clintons. I argued that we will never reach a state of advanced, but essentially static science and technology, like that shown in Star Trek. Instead, progress will continue at an ever increasing rate. In this situation, it is vital that we all take part in the debate about where we are going. We don't want the knowledge and the decisions to be left to a few experts.

It has been said that people buy my book to leave on their coffee tables. I am sure this does happen, but it is not the reason for most of my sales. Hundreds of people write to me or stop me in the street, to tell me how they have enjoyed it. They ask detailed questions, or point out what they think are errors, so they must have read at least part of it. I can't answer all the letters, but I try to correct genuine errors. By now, most of them have been fixed, although I recently got a long letter from a lady in Toronto complaining about something I said about Aristotle.

I know the book is difficult. If you can understand everything in it, you would be ready to start a PhD in theoretical physics. It does not matter too much if people can't follow all the arguments. They can still get the flavour of the intellectual quest: to understand the universe on the basis of rational laws.

So what has happened in the ten years since A Brief History was first published? Should I write a sequel, and if so, what would I call it? A Brief History of Time, Part 2. Or maybe, A Slightly Less Brief History. However, I decided against both these possibilities. Everything I wrote in the original book is still valid. It just required extending, to include the exciting observational and theoretical developments over the last ten years.

On the observational side, there has not been much progress in conventional particle physics. The US was building a new particle accelerator, the SSC, which would have reached the energies where crucial evidence for our theories was expected. But in 1994, the US went through a fit of feeling poor and cancelled the project. I told President Clinton that this was a very short sighted decision. His defence was that he had been in favour of the SSC, but that it was cut by Congress. This is true, but I think he could have fought harder. As it is, we will have to wait until 2001 for a new particle accelerator in Geneva.

In cosmology, on the other hand, there has been spectacular progress on the observational front. The Hubble space telescope, and new large land-based telescopes such as the Keck telescope in Hawaii, have enabled us to see galaxies and supernova near to the limiting distance we can observe. But even more important, we have detected faint ripples in the background of microwaves that fills the universe. These ripples are tiny-one part in 100,000-but are evidence that the early universe was not homogeneous. These small variations in the make up of the early universe are big enough to have grown into the structures we observe in the universe, like galaxies, stars and even ourselves. So we are seeing in these ripples the finger prints of creation.

The form of the ripples is consistent with the theory of inflation-the idea that the universe had a period of accelerating expansion, in the very early stages. And it agrees with the proposal that Jim Hartle and I made, that the universe has no boundaries, in space and imaginary time. But it is inconsistent with most alternative theories of the origins of the ripples. Observations of the microwave background by new satellites should settle the issue and tell us if we indeed live in a universe that has no boundaries.

The ripples in the microwave background had been predicted. It was gratifying to have our theories confirmed, but it was not a great surprise. The really exciting moments in science are when we discover something unexpected. Although it is not definite yet, there are suggestions in some recent observations of supernova that there may be a repulsive gravitational force called the cosmological constant. Einstein originally introduced the constant into his equations, when he still believed that the universe was static. If the galaxies started off at rest relative to each other, the gravitational attraction between them would cause them to fall towards each other, unless it was balanced by a repulsive force.

However, Hubble later discovered that the universe is expanding, and so removed the need for a cosmological constant to hold the universe in a static equilibrium. After that, Einstein called the cosmological constant "my greatest mistake." A cosmological constant would still have been possible, but observations indicated that it had to be very small, less than one over one, with 120 zeroes after it. People thought that no theory would predict a number that small. But we may have to think again; Einstein may not have made a mistake after all. This would mean that the universe would continue to expand forever, at an ever increasing rate. Inflation might be a law of nature, to the discomforture of monetarist economics. But the inflation of the universe is less than a millionth of a per cent per century.

*** On the theoretical side, there has also been spectacular progress, although we still seem to be some way from a Theory of Everything. When I wrote the first edition of A Brief History in 1988, most physicists believed that the ultimate theory was Super Strings. As its name suggests, this was a theory in which the fundamental entities were not point particles, but objects which had a length but no other dimension, like a piece of string.

What we think of as particles, were pictured as waves on the string, like waves on a violin string. The word "super" means that the theory has a new kind of symmetry, called super symmetry. This means that the universe has some extra dimensions, as well as the ordinary dimensions of space and time. Science fiction has been telling us for years that the universe has other dimensions, but even science fiction never thought of anything as odd as the extra dimensions of superspace.

The strings in string theory would have vibrations of all wave lengths and frequencies in this superspace. If the strings were moving only in the ordinary dimensions of space and time, the energies in the waves would all add up, and would curl the universe up into a tiny ball. But the vibrations in these other dimensions have negative energies. Thus they can cancel the positive energies of the vibrations in the ordinary directions. It is a bit like the national budget. Both government spending, and its tax income, are large amounts. It requires delicate adjustment to get them to balance.

The situation in physics is similar. It requires careful balancing to get the infinite positive and negative energies to cancel, and leave a universe that is nearly flat. To get such a cancellation, this idea of super symmetry with extra dimensions seems essential. However, so far, we have no experimental confirmation of super symmetry. This would have come from the SSC, but as it is, we will have to wait for results from the particle accelerator in Geneva. If it finds evidence for super symmetry, it will be a great boost for our efforts to unify the laws of physics into a Theory of Everything.

In fact, people haven't waited for experimental confirmation of super symmetry, but have continued to develop the theory. It seems that string theory is not the whole answer, as was thought ten years ago. An early indication of this was the fact that there appeared to be five different super string theories. Which of these described our universe? Shouldn't the ultimate Theory of Everything be unique? But starting in 1994, it was discovered that these apparently different theories were related by what were called dualities. This increased our confidence that we were on the right track, because it meant that all five super string theories could be regarded as different aspects of the same underlying theory. But it also meant that none of the five super string theories were themselves the fundamental theory.

Super string theories were further demoted when it was discovered that there are whole families of extended objects called p-branes. A particle is just a point, with no dimensions. So it is called a zero-brane. A string has length, but no other dimension. So it is called a one-brane. But there are other fundamental objects, with higher dimensions. All these p-branes seem to be on the same footing. So one is led to the idea of p-brane democracy: "All p-branes are created equal."

We still have some way to go to understand p-branes and how they interact. However, we are making progress, helped by the fact that all theoretical physics papers are now on the internet. It has made physicists the world over into a global village. If someone has a new idea, they send it to a computer in Los Alamos. Within a week, there will be several developments to the idea.

Twenty years ago, I said I thought there was a 50 per cent chance that we would find a complete unified theory in the next 20 years. I would have lost that bet, but I think I am on stronger ground for finding it in the next 20 years.