George and the Unbreakable Code

by Stephen Hawking

  “Maybe,” Annie replied.

  They drew up to George’s front door, which still lay on the ground, ripped off its hinges by the furious mob. But the street itself was quiet and empty: no cars, no airplanes overhead, no phones ringing, no televisions blaring; none of the usual hustle and bustle of a small city waking up to greet another day.

  “Wow, this is so strange!” remarked Annie. “Do you think this is what life was like before computers were invented?”

  “Suppose so,” said George. “But it won’t stay like this for long—not if your dad and all the other scientists are working to get everything started up again. In a few hours it could all be back to normal.”

  They went into George’s house. “Talking of peace and quiet … ,” he said as they stood in his kitchen looking down at the trapdoor. They could hear the twins singing away merrily and someone saying groggily, “Girls! It’s really early!”

  Annie laughed and shot back the bolts that were keeping the trapdoor closed. She and George lifted one flap each, opening the basement below to the light of the beautiful Foxbridge morning. As they did so, Hera and Juno scrambled quickly toward the stairs, eager to leave their underground shelter.

  “Let there be life!’ said Annie as they burst into the kitchen once more.

  LIFE IN THE UNIVERSE

  Professor Stephen Hawking

  In this chapter, I would like to talk to you about the development of life in the universe, and in particular, the development of intelligent life. I shall take this to include the human race, even though much of its behavior throughout history has been pretty stupid!

  We all know that things get more disordered and chaotic with time. This observation even has its own law, the so-called Second Law of Thermodynamics. This law says that the total amount of disorder, or entropy, in the universe always increases with time. However, the law refers only to the total amount of disorder. The order in one body can increase, provided that the amount of disorder in its surroundings increases by a greater amount.

  This is what happens in a living being. We can define life to be an ordered system that can keep itself going against the tendency to disorder, and can reproduce itself. That is, it can make similar, but independent, ordered systems. To do these things, the system must convert energy in some ordered form—like food, sunlight, or electric power—into disordered energy, in the form of heat. In this way, the system can satisfy the requirement that the total amount of disorder increases while, at the same time, increasing the order in itself and its offspring. This sounds like parents living in a house that gets messier and messier each time they have a new baby!

  A living being like you or me usually has two elements: a set of instructions that tell the system how to keep going and how to reproduce itself, and a mechanism to carry out the instructions. In biology, these two parts are called genes and metabolism.

  What we normally think of as “life” is based on chains of carbon atoms, with a few other atoms such as nitrogen or phosphorous. There was no carbon when the universe began in the Big Bang, about 13.8 billion years ago. It was so hot that all the matter would have been in the form of particles, called protons and neutrons. There would initially have been equal numbers of protons and neutrons. However, as the universe expanded, it cooled. About a minute after the Big Bang, the temperature would have fallen to about a billion degrees, about a hundred times the temperature in the Sun. At this temperature, neutrons start to decay into more protons.

  If this had been all that had happened, all the matter in the universe would have ended up as the simplest element, hydrogen, whose nucleus consists of a single proton. However, some of the neutrons collided with protons and stuck together to form the next simplest element, helium, whose nucleus consists of two protons and two neutrons. But no heavier elements, like carbon or oxygen, would have been formed in the early universe. It is difficult to imagine that one could build a living system out of just hydrogen and helium—and anyway the early universe was still far too hot for atoms to combine into molecules.

  The universe continued to expand, and cool. But some regions had slightly higher densities than others, and the gravitational attraction of the extra matter in those regions slowed down their expansion, and eventually stopped it. Instead, they collapsed to form galaxies and stars, starting from about two billion years after the Big Bang. Some of the early stars would have been more massive than our Sun; they would have been hotter than the Sun and would have burnt the original hydrogen and helium into heavier elements, such as carbon, oxygen, and iron. This could have taken only a few hundred million years. After that, some of the stars exploded as supernovas, and scattered the heavy elements back into space, to form the raw material for later generations of stars.

  Our own solar system was formed about four and a half billion years ago, or about ten billion years after the Big Bang, from gas contaminated with the remains of earlier stars. The Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, some of these atoms came to be arranged in the form of molecules of DNA. This has the famous double helix form, discovered in the 1950s by Crick and Watson in a hut on the New Museum site in Cambridge.

  We do not know how DNA molecules first appeared. As the chances of a DNA molecule arising by random fluctuations are very small, some people have suggested that life came to Earth from elsewhere—for instance, brought here on rocks breaking off from Mars while the planets were still unstable—and that there are seeds of life floating round in the galaxy. However, it seems unlikely that DNA could survive for long in the radiation in space. There is fossil evidence that there was some form of life on Earth about three and a half billion years ago. This may have been only 500 million years after the Earth became stable and cool enough for life to develop. The early appearance of life on Earth suggests that there is a good chance of the spontaneous generation of life in suitable conditions.

  As DNA reproduced itself, there would have been random errors, many of which would have been harmful and would have died out. Some would have been neutral—they would not have affected the function of the gene. And a few errors would have been favorable to the survival of the species—these would have been chosen by Darwinian natural selection.

  The process of biological evolution was very slow at first. It took two and a half billion years to evolve from the earliest cells to multi-cell animals, and another billion years to evolve through fish and reptiles to mammals. But then evolution seemed to have sped up. It only took about a hundred million years to develop from the early mammals to us. The reason is that fish contain most of the important human organs and mammals—essentially, all of them. All that was required to evolve from early mammals, like lemurs, to humans was a bit of fine-tuning.

  But with the human race, evolution reached a critical stage, comparable in importance with the development of DNA. This was the development of language, and particularly written language. It meant that information can be passed on from generation to generation, other than genetically through DNA. There has been some detectable change in human DNA, brought about by biological evolution, in the ten thousand years of recorded history, but the amount of knowledge handed on from generation to generation has grown enormously. I have written books to tell you something of what I have learned about the universe in my long career as a scientist, and in doing so I am transferring knowledge from my brain to the page so you can read it.

  The DNA in human beings contains about three billion nucleotides. However, much of the information coded in this sequence is redundant, or is inactive. So the total amount of useful information in our genes is probably something like a hundred million bits. One bit of information is the answer to a yes/no question. By contrast, a paperback novel might contain two million bits of information. So a human is equivalent to about 50 Harry Potter books, and a major national library can contain about five million books—or about ten trillion bits. So the amount of information handed down in books or via the Intern
et is a hundred thousand times as much as in DNA!

  This means that we have entered a new phase of evolution. At first, evolution proceeded by natural selection—from random mutations. This Darwinian phase lasted about three and a half billion years and produced us, beings who developed language to exchange information. But in the last ten thousand years or so, we have been in what might be called an external transmission phase. In this, the internal record of information, handed down to succeeding generations in DNA, has changed somewhat. But the external record—in books, and other long-lasting forms of storage—has grown enormously.

  Some people would use the term “evolution” only for the internally transmitted genetic material, and would object to it being applied to information handed down externally. But I think that is too narrow a view. We are more than just our genes. We may be no stronger or inherently more intelligent than our caveman ancestors. But what distinguishes us from them is the knowledge that we have accumulated over the last ten thousand years, and particularly over the last three hundred. I think it is legitimate to take a broader view, and include externally transmitted information, as well as DNA, in the evolution of the human race.

  But we still have the instincts, and in particular, the aggressive impulses, that we had in caveman days. Aggression, in the form of subjugating or killing others and taking their food, has had definite survival advantage, up to the present time. But now it could destroy the entire human race, and much of the rest of life on Earth. A nuclear war is still the most immediate danger, but there are others, such as the release of a genetically engineered virus. Or the greenhouse effect becoming unstable.

  There is no time to wait for Darwinian evolution to make us more intelligent and better-natured! But we are now entering a new phase of what might be called self-designed evolution, in which we will be able to change and improve our DNA. We have now mapped DNA, which means we have read “the book of life.” So we can start writing in corrections. At first, these changes will be confined to the repair of genetic defects—like cystic fibrosis and muscular dystrophy, which are controlled by single genes and so are fairly easy to identify and correct. Other qualities, such as intelligence, are probably controlled by a large number of genes, and it will be much more difficult to find them and work out the relations between them. Nevertheless, I am sure that during the next century, people will discover how to modify both intelligence and instincts like aggression.

  If the human race manages to redesign itself, to reduce or eliminate the risk of self-destruction, it will probably spread out and colonize other planets and stars. However, long-distance space travel will be difficult for chemically based life-forms—like us—based on DNA. The natural lifetime for such beings is short, compared to the travel time. According to the theory of relativity, nothing can travel faster than light, so a round trip to the nearest star would take at least eight years, and to the center of the galaxy about a hundred thousand years. In science fiction, they overcome this difficulty by space warps, or travel through extra dimensions. But I don’t think these will ever be possible, no matter how intelligent life becomes. In the theory of relativity, if one can travel faster than light, one can also travel back in time, and this would lead to problems with people going back and changing the past. One would also expect to have already seen large numbers of tourists from the future, curious to look at our quaint, old-fashioned ways!

  It might be possible to use genetic engineering to make DNA-based life survive indefinitely, or at least for a hundred thousand years. But an easier way, which is almost within our capabilities already, would be to send machines. These could be designed to last long enough for interstellar travel. When they arrived at a new star, they could land on a suitable planet and mine material to produce more machines, which could be sent on to yet more stars. These machines would be a new form of life, based on mechanical and electronic components rather than macromolecules. They could eventually replace DNA-based life, just as DNA may have replaced an earlier form of life.

  What are the chances that we will encounter some alien form of life as we explore the galaxy? If the argument about the timescale for the appearance of life on Earth is correct, there ought to be many other stars whose planets have life on them. Some of these stellar systems could have formed five billion years before the Earth—so why is the galaxy not crawling with self-designing mechanical or biological life-forms? Why hasn’t the Earth been visited, and even colonized? By the way, I discount suggestions that UFOs contain beings from outer space, as I think that any visits by aliens would be much more obvious—and probably also much more unpleasant.

  So why haven’t we been visited? Maybe the probability of life spontaneously appearing is so low that Earth is the only planet in the galaxy—or in the observable universe—on which it happened. Another possibility is that there was a reasonable probability of forming self-reproducing systems, like cells, but that most of these forms of life did not evolve intelligence. We are used to thinking of intelligent life as an inevitable consequence of evolution, but what if it isn’t? Is it more likely that evolution is a random process, with intelligence as only one of a large number of possible outcomes?

  It is not even clear that intelligence has any long-term survival value. Bacteria, and other single-cell organisms, may live on if all other life on Earth is wiped out by our actions. Perhaps intelligence was an unlikely development for life on Earth, from the chronology of evolution, as it took a very long time—two and a half billion years—to go from single cells to multi-cell beings, which are a necessary precursor to intelligence. This is a good fraction of the total time available before the Sun blows up. So it would be consistent with the hypothesis that the probability for life to develop intelligence is low. In this case, we might expect to find many other life-forms in the galaxy, but we are unlikely to find intelligent life.

  Another way in which life could fail to develop to an intelligent stage would be if an asteroid or comet were to collide with the planet. It is difficult to say how often such collisions occur, but a reasonable guess might be every twenty million years, on average. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last 67 million years. Other planets in the galaxy, on which life has developed, may not have had a long enough collision-free period to evolve intelligent beings.

  A third possibility is that there is a reasonable probability for life to form—and to evolve to intelligent beings—but the system becomes unstable, and the intelligent life destroys itself. This would be a very pessimistic conclusion, and I very much hope it isn’t true.

  I prefer a fourth possibility: that there are other forms of intelligent life out there, but we have not yet been able to make contact or pick up any signals. Now a new project called Breakthrough Listen hopes to change all that. The biggest ever search for signs of alien life, Breakthrough Listen will use powerful radio telescopes to search over one million stars for signals of alien communications. This project will run for ten years. I am part of this great new quest to search the universe for signs of life—and I hope you will be too! It’s your universe and it’s up to you to explore it!

  Acknowledgments

  Like the other books in the series, George and the Unbreakable Code is made possible by the willingness and great enthusiasm of scientists and technology experts to explain their research. I’d like to thank our distinguished contributors for their brilliant and entertaining work, taking the abstract, the cutting edge, or the simply baffling and making it accessible to readers young—and not so young. They are: Professor Michael Reiss, Professor Peter McOwan, Dr. Raymond Laflamme, Dr. Tim Prestidge, Dr. Stuart Rankin, Dr. Toby Blench, and, of course, Professor Stephen Hawking.

  In particular, I would like to thank Dr. Stuart Rankin for his long-term assistance and input into the George series, which includes writing the fantastically informative text boxes on computing, as well as h
is advice and his numerous contributions to the book as a whole. I would also like to thank Dr. Toby Blench for introducing a chemical element to the series and for his authorship of Annie’s half-term chemistry project, more of which can be read online. Alastair Leith of the Online Astronomy Society provided very helpful advice on the astronomical elements of the book and IT expert Dawn Mancer wrote the advice on how to keep safe online.

  I’d like to thank our young readers who read and helpfully commented on an early draft of George and the Unbreakable Code. They are: Marina McCready, Jamie Ross, Francesca Bern, and Lola and Amelie Mayer.

  Garry Parsons has given the characters and the storyline a visual life with charm and verve. I’m so grateful to Garry for taking on the challenge of drawing a quantum computer in space and doing such a fabulous job!

  The team at Random House Children’s Publishers have gone on a cosmic journey with George and his adventures—and produced a really beautiful book. Working with Ruth Knowles and Sue Cook as editors has been a joy, and Annie Eaton and the rest of her team have given us the chance to explore the universe in style.

  I’d like to thank my agents at Janklow and Nesbit, Claire Paterson and Rebecca Carter, for their unstinting hard work on the series, and Kirsty Gordon for managing such a complex project so very well.

  Most of all, I would like to thank all our readers for their interest and excitement at the prospect of a new George story! Originally, there were only going to be three—and now there are more. Thank you for traveling with us—the universe is a big place and there is still so much more to discover. In the words of my awesome coauthor and father, Stephen—Be Curious!

  Lucy Hawking

  STEPHEN HAWKING, a Lucasian Professor of Mathematics at Cambridge, is the preeminent theoretical physicist in the world. His book A Brief History of Time was a phenomenal worldwide bestseller. He has twelve honorary degrees and was awarded the Commander of the Order of the British Empire and was made a Companion of Honour. He has three children and one grandchild. Visit him at Hawking.org.uk.