cover image of Black Holes and Baby Universes And Other Essays Thirteen extraordinary essays shed new light on the mystery of the universe—and on. NEW YORK TIMES BESTSELLER • Thirteen extraordinary essays shed new light on the mystery of the universe—and on one of the most brilliant thinkers. Black Holes and Baby Universes and Other Essays (eBook): Hawking, Stephen: "In his phenomenal bestseller A Brief History of Time, Stephen Hawking.
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humour, 4s when he Stemif the theory &*t on* might be able to dive into i blade hole im quickly from one cosmos to another *jjfif variety of material gives a roil. Black holes and baby universes and other essays by Stephen W. Hawking, , Bantam Books edition, Hardcover in English. Editorial Reviews. From Publishers Weekly. In 14 pieces, the author of A Brief History of Time examines astrophysics, current events and his own life. Copyright .
In his phenomenal bestseller A Brief History of Time, Stephen Hawking literally transformed the way we think about physics, the universe, reality itself. In these thirteen essays and one remarkable extended interview, the man widely regarded as the most brilliant theoretical physicist since Einstein returns to reveal an amazing array of possibilities for understanding our universe. Building on his earlier work, Hawking discusses imaginary time, how black holes can give birth to baby universes, and scientists' efforts to find a complete unified theory that would predict everything in the universe. With his characteristic mastery of language, his sense of humor and commitment to plain speaking, Stephen Hawking invites us to know him better--and to share his passion for the voyage of intellect and imagination that has opened new ways to understanding the very nature of the cosmos. From the Trade Paperback edition.
I therefore contacted a literary agent, A1 Zuckerman, who had been introduced to me as the brother-in-law of a colleague. I gave him a draft of the first chapter and explained that I wanted it to be the sort of book that would sell in airport book stalls.
He told me there was no chance of that. It might sell well to academics and students, but a book like that couldn't break into Jeffrey Archer territory. I gave Zuckerman a first draft of the book-in He sent it to several publishers and recommended that I accept an offer from Norton, a fairly up-market American book firm. But I decided instead to take an offer from Bantam Books, a publisher more oriented towards the popular market.
Though Bantam had not specialized in publishing science books, their books were widely available in airport book stalls. That they accepted my book was probably because of the interest in it taken by one of their editors, Peter Guzzardi. He took his job very seriously and made me rewrite the book to make it understandable to nonscientists like himself. Each time I sent him a rewritten chapter, he sent back a long list of objections and questions he wanted me to clarify. At times I thought the process would never, end.
But he was right: it is a much better book as a result.
Shortly after I accepted Bantam's offer, I got pneumonia. I had to have a tracheotomy operation that removed my voice. For a time I could communicate only by raising my eyebrows when someone pointed to letters on a card. It would have been quite impossible to finish the book but for the computer program I had been given.
It was a bit slow, but then I think slowly, so it suited me quite well. I was helped in this revision by one of my students, Brian Whitt. I had been very impressed by Jacob Bronowski's television series, Such a sexist title would not be allowed today. It gave a feeling for the achievement of the human race in developing from primitive savages only fifteen thousand years ago to our present state.
I wanted to convey a similar feeling for our progress towards a complete understanding of the laws that govern the universe. I was sure that nearly everyone was interested in how the universe operates, but most people cannot follow mathematical equations - I don't care much for equations myself.
This is partly because it is difficult for me to write them down but mainly because I don't have an intuitive feeling for equations. Instead, I think in pictorial terms, and my aim in the book was to describe these mental images in words, with the help of familiar analogies and a few diagrams. In this way, I hoped that most people would be able to share in the excitement and feeling of achievement in the remarkable progress that has been made in physics in the last twenty-five years.
The Ascent of Man. Still, even if one avoids mathematics, some of the ideas are unfamiliar and difficult to explain. This posed a problem: should I try to explain them and risk people being confused, or should I gloss over the difficulties? Some unfamiliar concepts, such as the fact that observers moving at different velocities measure different time intervals between the same pair of events, were not essential to the picture I wanted to draw.
Therefore I felt I could just mention them but not go into depth. But other difficult ideas were basic to what I wanted to get across. There were ypo such concepts in particular that I felt I had to include.
One was the so-called sum over histories. This is the idea that there is not just a single history for the universe. The other idea, which is necessary to make mathematical sense of the sum over histories, is 'imaginary time'. With hindsight, I now feel that I should have put more effort into explaining these two very difficult concepts, particularly imaginary time, which seems to be the thing in the book with which people have the most trouble.
However, it is not really necessary to understand exactly what imaginary time is - just that it is different from what we call real time. When die book was nearing publication, a scientist who was sent an advance copy to review for magazine was appalled to find it full of errors, with misplaced and erroneously labelled photographs and diagrams. He called Bantam, who were equally appalled and decided that same day to recall and scrap the entire printing. They spent three intense weeks correcting and rechecking the entire book, and it was ready in time to be in the bookshops by the April publication date.
By then, magazine had published a profile of me. Even so, the editors were taken by surprise by the demand. The book is in its seventeenth printing in America and its tenth in Britain.
It is difficult for me to be sure that I'm objective, so I think I will go by w4 fct other people said. I found most of the reviews, although favourable, rather uniliuminating. They tended to follow the formula: Stephen Hawking has Lou Gehrig's disease in American reviews , or motor neurone disease in British reviews. Yet he has written this book about the biggest question of all: where did we come from and where are we going?
The answer that Hawking proposes is that the universe is neither created nor destroyed: it just is. In order to formulate this idea, Hawking introduces the concept of imaginary time, which I the reviewer find a little hard to follow.
Still, if Hawking is right and we do find a complete unified theory, we shall really know the mind of God. In the proof stage I nearly cut the last sentence in the book, which was that we would know the mind of God. Had I done so, the sales might have been halved. Rather more perceptive I felt was an article in The which said that even a serious scientific book like could become a cult book. My wife was horrified, but I was rather flattered to have my book compared to Zen I hope, like Zen, that it gives people the feeling that they need not be cut off from the great intellectual and philosophical questions.
Undoubtedly, the human interest story of how I have managed to be a theoretical physicist despite my disability has helped. But those who bought the book from the human interest angle may have been disappointed because it contains only a couple of references to my condition. The hook was intended as a history of the universe, not of me.
This has not prevented accusations that Bantam shamefully exploited my illness and that I co-operated with this by allowing my picture to appear on the cover.
In fact, under niy contract I had no control over the cover. I did, however, manage to persuade Bantam to use a better photograph on the British edition than the miserable and out-ofdate photo used on the American edition. It has also been suggested that people download die book because they have read reviews of it or because it is on the bestseller list, but they don't read it; they just have it in the bookcase or on the coffee table, thereby getting credit for having it without taking die effort of having to understand it.
I am sure this happens, but I don't know that it is any more so than for most other serious books, including the Bible and Shakespeare. On the other hand, I know that at least some people must have read it because each day I get a pile of letters about my book, many asking questions or making detailed comments that indicate that they have read it, even if they do not understand all of it. I also get stopped by strangers on the street who tell me how much they enjoyed it.
Of course, I am more easily identified and more distinctive, if not distinguished, than most authors. But the frequency with which I receive such public congratulations to the great embarrassment of my nine-year-old son seems to indicate that at least a proportion of those who download the book actually do read it. People now ask me what I am going to do next. I feel I can hardly write a sequel to What would I call it?
A Time? My agent has suggested that I allow a film to be made about my life. But neither I nor my family would have any self-respect left if we let ourselves be portrayed by actors.
Hie same would be true to a lesser extent if I allowed and helped someone to write my life. Of course, I cannot stop someone from writing my life independently, as long as it is not libellous, but I try to put them off by saying I'm considering writing my autobiography. Maybe I will. But I'm in no hurry. I have a lot of science that I want to do first. A Brief History of Time. Instead, I will diacuss my approach to how one can understand the universe: what is the status and meaning of a grand unified theory, a 'theory of everything'.
There is a real problem here. The people who ought to study and argue such questions, the philosophers, have mostly not had enough mathematical background to keep up with modem developments in theoretical physics. There is a subspecies called philosophers of science who ought to be better equipped. But many of them are failed physicists who found it too hard to invent new theories and so took to writing about the philosophy of physics instead.
They are still arguing about die scientific theories of the early years of this century, like relativity and quantum mechanics. They are not in touch with die present frontier of physics. Maybe Tm being a bit harsh on philosophers, but they have not been very kind to me. My approach has been described as naive and simple-minded. I have been variously called a nominalist, an instrumentalist, a positivist, a realist, and several other ists.
The technique seems 'Originally given as a talk to a Caius College audience in May Surely everyone knows the fatal errors of all those isms. The people who actually make the advances in theoretical physics don't think in the categories that the philosophers and historians of science subsequendy invent for them.
I am sure that Einstein, Heisenberg and Dirac didn't worry about whether they were realists or instrumentalists. They were simply-concerned that the existing theories didn't fit together.
In theoretical physics, the search for logical self-consistency has always been more important in making advances than experimental results. Otherwise elegant and beautiful theories have been rejected because they don't agree with observation, but I don't know of any major theory that has been advanced just on the basis of experiment. The theory always came first, put forward from the desire to have an elegant and consistent mathematical model.
The theory then makes predictions, which can then be tested by observation. If the observations agree with the predictions, that doesn't prove the theory; but the theory survives to make further predictions, which again are tested against observation If the observations don't agree with the predictions, one abandons die theory.
Or rather, that is what is supposed to happen. In practice, people are very reluctant to give up a theory in which they have invested a lot of time and effort. They usually start by questioning the accuracy of the observations.
If that fails, they try to modify the theory in an ad hoc manner. Eventually the theory becomes a creaking and ugly edifice. Then someone suggests a new theory, in which all the awkward observations are explained in an elegant and natural manner. An example of this was the Michelson-Morley experiment, performed in , which 36 showed that the speed of light was always the same, no matter how the source or the observer was moving.
This seemed ridiculous. Surely someone moving towards the light ought to measure it travelling at a higher speed than someone moving in the same direction as the light; yet the experiment showed that both observers would measure exacdy the same speed. For the next eighteen years people like Hendrik Lorentz and George Fitzgerald tried to accommodate this observation within accepted ideas of space and time. They introduced ad hoc postulates, such as proposing that objects got shorter when they moved at high speeds.
The entire framework of physics became clumsy and ugly. Then in Einstein suggested a much more attractive viewpoint, in which time was not regarded as completely separate and on its own. Instead it was combined with space in a four-dimensional object called space-time. Einstein was driven to this idea not so much by the experimental results as by the desire to make two parts of the theory fit together in a consistent whole.
The two parts were the laws that govern the electric and magnetic fields, and the laws that govern the motion of bodies. I don't thiiik Einstein, or anyone else in , realized how simple and. It completely revolutionized our notions of space and time. This example illustrates well the difficulty of being a realist in the philosophy of science, for what we regard as reality is conditioned by the theory to which we subscribe. I am certain Lorentz and Fitzgerald regarded themselves as realists, interpreting the experiment on the speed of light in terms of Newtonian ideas of absolute space and absolute time.
These notions of space and time seemed to correspond to common sense and reality. Yet nowadays those who are familiar with the theory of relativity, still a disturbingly small minority, have a rather different view. We ought to 37 be telling people about die modern understanding of such basic concepts as space and time. If what we regard as real depends on our theory, h o w can we make reality the basis of our philosophy? I say that I am a realist in the sense that I think there is a universe out there waiting to be investigated and understood.
I regard the solipsist position that everything is the creation of our imaginations as a waste of time. No-one acts on that basis. But we cannot distinguish what is real about the universe without a theory. I therefore take the view, which has been described as simple-minded or naive, that a theory of physics is just a mathematical model that we use to describe the results of observations. A theory is a good theory if it is an elegant model, if it describes a wide class of observations, and if it predicts the results of new observations.
Beyond that, it makes no sense to ask if it corresponds to reality, because we do not know what reality is independent of a theory. This view of scientific theories may make me an instrumentalist or a positivist as I have said above, I have been called both. The person who called me a positivist went on to add that everyone knew that positivism was out of date - another case of refutation by denigration.
It may indeed be out of date in' that it was yesterday's intellectual fad, but the positivist position I have outlined seems the only possible one for someone who is seeking new laws, and new ways, to describe the universe. It is no good appealing to reality because we don't have a model independent concept of reality.
In my opinion, the unspoken belief in a model independent reality is the underlying reason for die difficulties philosophers of science have with quantum mechanics and the uncertainty principle. There is a famous thought experiment called Schrodinger's cat.
A cat is placed in a sealed box. The prabtbitity of this happening is 50 per cent. Today ao-ooe would due propose such a thing, even purely as a thought experiment, but in Schrtkbnger's time they had not heard of animal liberation. If one opens the box, one willfindthe cat either dead if or alive. But before the box is opened, the quantum state of the cat will be a mixture of the dead cat state with a state in which the cat is alive. This some philosophers of sciencefindvery hard to accept.
The cat can't be half shot and half not-shot, they claim, any more than one can be half pregnant. Their difficulty arises because they are implicidy using a classical concept of reality in which an object has a definite single history. The whole point of quantum mechanics is that it has a different view of reality. In this view, an object has not just a single history but all possible histories.
In most cases, the probability of having a particular history will cancel out with die probability of having a very slightly different history; but in certain cases, the probabilities of neighbouring histories reinforce each other.
It is one of these reinforced histories that we observe as the history of the object. In the case of Schrddinger's cat, there are two histories that are reinforced. In one the cat is shot, while in the other it remains alive. In quantum theory both possibilities can exist together. But some philosophers get themselves tied in knots because they implicitly assume that the cat can have only one history. The nature of time is another example of an area in which our theories of physics determine our concept of reality.
It used to be considered obvious that time flowed on for ever, regardless of what was happening; but the theory of relativity combined time with space and said that both could be warped, or distorted, by the matter and energy in the universe. So our perception of the nature of 39 time changed from being independent of the universe to being shaped by it.
It then became conceivable that time might simply not be defined before a certain point; as one goes back in time, one might come to an insurmountable barrier, a singularity, beyond which one could not go.
If that were jthe case, it wouldn't make sense to ask who, or what, caused or created the big bang. To talk about causation or creation implicidy assumes there was a time before the big bang singularity. We have known for twenty-five years that Einstein's general theory of relativity predicts that time must have had a beginning in a singularity fifteen billion years ago. But die phi'osophers have not yet caught up with die idea. They are still worrying about the foundations of quantum mechanics that were laid down sixty-five years ago.
They don't realize that die frontier of physics has moved on. Even worse is the mathematical concept of imaginary time, in which Jim Hartle and I suggested the universe may not have any beginning or end. I was savagely attacked by a philosopher of science for talking about imaginary time. He said: 'How can a mathematical trick like imaginary time have anything to do with the real universe? This just illustrates my point: how can we know what is real, independent of a theory or model with which to interpret it?
I have used examples from relativity and quantum mechanics to show the problems one faces when one tries to make sense of the universe. It doesn't really matter if you don't understand relativity and quantum mechanics, or even if these theories are incorrect.
What I hope I have demonstrated is that some sort of positivist approach, in which one regards a theory as a model, is the only way to 40 understand the universe, at least fqr a theoretical physicist.
I am hopeful that we will find a consistent model that describes everything in die universe.
If we do that, it will be a real triumph for die human race. By this I mean that we might have a complete, consistent and unified theory of the physical interactions that would describe all possible observations.
Of course, one has to be very cautious about making such predictions. We have thought that we were on the brink of the final synthesis at least twice before. At the beginning of the century it was believed that everything could be understood in terms of continuum mechanics.
All that was needed was to measure a certain number of coefficients of elasticity, viscosity, conductivity, etc. This hope was shattered by the discovery of atomic structure and quantum mechanics. Again, in the late s Max Born told a group of scientists visiting Gottingen that 'physics, as we know it, will be over in six months'.
This was shortly after the discovery by Paul Dirac, a previous holder of the Lucasian Chair, of the Dirac equation, which governs the behaviour of the electron. This essay, my Inaugural Lecture, was read for me by one of my students. However, the discovery of die neutron and of nuclear forces disappointed those hopes. We now know in fact that neither the proton nor the neutron is elementary hut that they are made up of smaller particles. Nevertheless, we have made a lot of progress in recent years, and as I shall describe, there are some grounds for cautious optimism that we may see a complete theory within the lifetime of some of those reading these pages.
Even if we do achieve a complete unified theory, we shall not be able to ir ake detailed predictions in any but die simplest situations. For example, we already know the physical laws that govern everything that we experience in everyday life.
As Dirac pointed out, his equation was the basis of 'most of physics and all of chemistry'. However, we have been able to solve the equation only for the very simplest system, the hydrogen atom, consisting of one proton and one electron.
For more complicated atoms with more electrons, let alone for molecules with more than one nucleus, we have to resort to approximations and intuitive guesses of doubtful validity.
For macroscopic systems consisting-of 10 23 particles or so, we have to use statistical methods and abandon any pretence of solving the equations exactly. Although in principle we know the equations that govern the whole of biology, we have not been able to reduce the study of human behaviour to a branch of applied mathematics.
What would we mean by a complete and unified theory of physics? Our attempts at modelling physical reality normally consist of two parts: 1. A set of local laws that are obeyed by the various physical quantities. These are usually formulated in terms of differential equations.
Sets of boundary conditions that tell us the state of 43 some regions of the universe at a certain time and what effects propagate into it subsequently from the rest of the universe.
Many people would claim that the role of science is confined to the first of these and that theoretical physics will have achieved its goal when we have obtained a complete set of local physical laws.
They would regard the question of the initial conditions for the universe as belonging to the realm of metaphysics or religion. In a way, this attitude is similar to that of those who in earlier centuries discouraged scientific investigation by saying that all natural phenomena were the work of God and should not be enquired into.
I think that the initial conditions of the universe are as suitable a subject for scientific study and theory as are the local physical laws. We shall not have a complete theory until we can do more than merely say that 'things are as they are because they were as they were'.
The question of the uniqueness of the initial conditions is closely related to that of the arbitrariness of the local physical laws: one would not regard a theory as complete if it contained a number of adjustable parameters such as masses or coupling constants that could be given any values one liked. In fact, it seems that neither the initial conditions nor the values of the parameters in the theory are arbitrary but that they are somehow chosen or picked out very carefully.
For example, if the proton-neutron mass difference were not about twice the mass of the electron, one would not obtain the couple of hundred or so stable nucleides that make up the elements and are the basis of chemistry and biology. Similarly, if the gravitational mass of the proton were significantly different, one would not have had stars in which these nucleides could have been built up, and if the initial expansion of the universe had 44 been slightly smaller or slightly greater, the universe would either have collapsed before such stars could have evolved or would have expanded so rapidly that stars would never have been formed by gravitational condensation.
Indeed, some people have gone so far as to elevate these restrictions on the initial conditions and the parameters to the status of a principle, the anthropic principle, which can be paraphrased as, 'Things are as they are because we are. Most of these universes will not provide the right conditions for the development of the complicated' structures needed for intelligent life.
Only in a small number, with conditions and parameters like our own universe, will it be possible for intelligent life to develop and to ask the question, 'Why is the universe as we observe it? The anthropic principle does provide some sort of explanation of many of the remarkable numerical relations that are observed between the values of different physical parameters.
However, it is not completely satisfactory; one cannot help feeling that there is some deeper explanation. Also, it cannot account for all the regions of the universe.
For example, our solar system is certainly a prerequisite for our existence, as is an earlier generation of nearby stars in which heavy elements could have been formed by nuclear synthesis. It might even be that the whole of our galaxy was required. But there does not seem any necessity for other galaxies to exist, let alone the million million or so of them that we see distributed roughly uniformly throughout the observable universe. This large-scale homogeneity of the universe makes it very difficult to believe that the structure of the universe is determined by anything so 45 peripheral as some complicated molecular structures on a minor planet orbiting a very average star in the outer suburbs of a airly typical spiral galaxy.
If we are not going to appeal to the anthropic principle, we need some unifying theory to account for die initial conditions of die universe and the values of the various physical parameters.
However, it is too difficult to think up a complete theory of everything all at one go though this does not seem to stop some people; I get two or three unified theories in the mail each week. What we do instead is to look for partial theories that will describe situations in which certain interactions can be ignored or approximated in a simple manner.
We first divide the material content of the universe into two parts: matter particles such as quarks, electrons, muons, etc. The matter particles are described by fields of one-half-integer spin and obey the Pauli exclusion principle, which prevents more than one particle of a given kind from being in any state. This is the reason we can have solid bodies that do not collapse to a point or radiate away to infinity. The matter particles are divided into two groups: the hadrons, which are composed of quarks; and the leptons, which comprise the remainder.
The interactions are divided phenomenologically into four categories. In order of strength, they are: the strong nuclear forces, which interact only with hadrons; electromagnetism, which interacts with charged hadrons and leptons; the weak nuclear forces, which interact with all hadrons and leptons; and finally, the weakest by far, gravity, which interacts with everything. The interactions are represented by integer-spinfieldsthat do not obey the Pauli exclusion principle.
This means they can have many particles in the same state. In the case of electromagnetism and gravity, the interactions are also long-range, which means that thefieldsproduced by a large number of matter 46 particles tan all add up to give a field that can be detected on a macroscopic scale.
For these reasons, they were the first to have theories developed for than: gravity by Newton in die seventeenth century, and electromagnetism by Maxwell in the nineteenth century. However, these theories were basically incompatible because the Newtonian theory was invariant if die whole system was given any uniform velocity, whereas the Maxwell theory defined a preferred velocity - the speed of light.
In die end, it turned out to be the Newtonian theory of gravity that had to be modified to make it compatible with the invariance properties of the Maxwell theory. This was achieved by Einstein's general theory of relativity, which was formulated in The general relativity theory of gravity and the Maxwell theory of electrodynamics were what are called classical theories; that is, they involved quantities that were continuously variable and that could, in principle at least, be measured to arbitrary accuracy.
However, a problem arose when one tried to use such theories to construct a model of the atom. It had been discovered that the atom consisted of a small, positively charged nucleus surrounded by a cloud of negatively charged electrons.
The natural assumption was that the electrons were in orbit around the nucleus as the earth is in orbit around the sun. But the classical theory predicted that the electrons would radiate electromagnetic waves.
These waves would carry away energy and would cause the electrons to spiral into the nucleus, producing the collapse of the atom. This problem was overcome by what is undoubtedly the greatest achievement in theoretical physics in this century: the discovery of the quantum theory.
The basic postulate of this is the Heisenberg uncertainty principle, which states that certain pairs of quantities, such as the position and momentum of a particle, cannot be measured 47 simultaneously with arbitrary accuracy. In the case of the atom, this meant that in its lowest energy state the electron could not be at rest in the nucleus because, in that case, its position would be exactly defined at the nucleus and its velocity would also be exactly defined to be zero.
Instead, both position and velocity would have to be smeardi out with some probability distribution around the nucleus. In this state the electron could not radiate energy in the form of electromagnetic waves because there would be no lower energy state for it to go to. Can you add one? Download ebook for print-disabled. Check Other Editions. Prefer the physical book? Check nearby libraries with:.
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