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PDF | We discuss the essential features of baby-universe production, starting from a description of black holes and wormholes, in terms of the. baby universes could be formed within our present universe – either in a the physics of black holes and wormholes, and their relationship to. NEW YORK TIMES BESTSELLER • Thirteen extraordinary essays shed new light on the mystery of the universe—and on one of the most brilliant thinkers.

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10 The Quantum Mechanics of Black Holes. 11 Black Holes and Baby Universes. 12 Is Everything Determined? 13 The Future of the Universe . Readers worldwide have come to know the work of Stephen Hawking through his phenomenal million-copy hardcover best-seller A Brief History of Time. Black holes and baby universes and other essays by Stephen W. Hawking, , Bantam Books edition, Hardcover in English.

He also sometimes has a tendency to mess up his pacing. And that baby universes might exist where particles go while inside a black hole, before they are emitted by the white hole that is born somewhere else. View all 4 comments. Romanian review: English review: I did not intend to read this book in until Stephen Hawking's death, but then I decided that's the least I could do in his honor. Until now, I only read by Stephen Hawking the first three books of the "George" series, written with his daughter Lucy, in other words, I did not read any of his science books in every sense of the word.

I'm glad I chose to read this one. I will not deny that I did not understand all the scientific parts, although Stephen Hawking has an accessible style, writing in order to popularize science, make it accessible to all, not to boast in academic circles. The book includes a biographical part, a science part and an interview from , every part being as interesting as the previous one.

Reading this volume I learned many new things and at the same time I realized that there are a lot of things that I do not understand yet, so I intend to inform myself as much as possible about quantum mechanics, general relativity and the cosmos, and that as soon as possible. One of the things that I can say has changed the way I see the world is the information that it is known how to determine whether the Universe will expand infinitely or collapse, I knew that so far it is not known whether the Universe and time will have an end, but I did not know anything about critical density, so about the fact the it is know how the future of the Universe will be determined, and that's just one of the interesting information I've learned from the book so I can say it was a valuable reading for me.

Interestingly, at one point in the book Stephen Hawking says he would not like a film to be made about his life, and yet in "The Theory of Everything" was made, with Eddie Redmayne who had a tremendous performance worthy of the Oscar he received playing Stephen, so it seems that in 21 years Stephen Hawking's opinion has changed. I'm sorry that Stephen Hawking died, and that the world remained poorer, deprived of another great genius, but I'm glad he lived about 50 years more than his doctors predicted and that he managed to discover amazing things, he certainly deserves more appreciation than he has received.

At the beginning of the book, Stephen Hawking spoke about how it is just a coincidence that he was born exactly years after Galileo Galilei's death January 8th , so I am curious what would have he said if he had known that Albert Einstein was born in the same day he died March 14th?

Jun 02, Natasha Off rated it liked it. I learned too much with this book, I don't like this type of books, but, its very helpful. Mar 26, Alan Johnson marked it as partially-read Shelves: Chapter 12 of this book of Stephen Hawking's occasional writings reproduces a lecture given at the University of Cambridge in April It is entitled "Is Everything Determined? Hawking concluded that science can neither prove nor disprove that free will is impossible in the face of scientific determinism and that, pending such proof, we "may as well adopt the effective theory that human Chapter 12 of this book of Stephen Hawking's occasional writings reproduces a lecture given at the University of Cambridge in April Hawking concluded that science can neither prove nor disprove that free will is impossible in the face of scientific determinism and that, pending such proof, we "may as well adopt the effective theory that humans are free agents who can choose what to do.

Maybe it's just that those who don't look don't survive to tell the tale. Instead, one has to adopt the effective theory that one has free will and that one is responsible for one's actions. This theory is not very good at predicting human behavior, but we adopt it because there is no chance of solving the equations arising from the fundamental laws. There is also a Darwinian reason that we believe in free will. A society in which the individual feels responsible for his or her actions is more likely to work together and survive to spread its values.

A collection of free individuals who share mutual aims. Thus, such a society is more likely to prosper and to spread its system of values. If one tries to deduce human behavior from the laws of science, one gets caught in the logical paradox of self-referencing systems.

Bantam Books, , , Considering my current interest in the issue of free will, I am not now reading the other essays in this book and accordingly am not rating the book as a whole. Alan E. Johnson revised June 2, View 1 comment. May 24, Bart Breen rated it really liked it. Fascinating and Stimulating Like others who have reviewed this work, I can endorse it as a stimulating and thoughtful book.

It is in essence however not a coherent book with a single theme. It is a compilation of articles and as such there is much in the book that is repetitive. Hawking acknowledges this and disclaims it at the outset. Even with the forewarning I found that element to be a tad annoying. I listened to the audio version of the book while commuting and I found it overall to be a fasc Fascinating and Stimulating Like others who have reviewed this work, I can endorse it as a stimulating and thoughtful book.

I listened to the audio version of the book while commuting and I found it overall to be a fascinating read. The biographical material about Hawking helped to put a "person" to the personality.

Hawking is, without doubt, brilliant.

His ability to reduce difficult concepts to listener sound bites speaks to that brilliance. I came away with an appreciation for his brilliance and abilities as well as the field of cosmological science that I did not have before. Of particular note, I found Hawking's treatment of metaphysics to be interesting but ultimately no more valuable than anyone else's opinions in that area. Physics will never answer the question of why the universe exists or whether God in fact exists and created this universe.

Science can only answer how the universe works and what laws govern its behavior. Hawkings admits this himself so I took no offense to his words, I just found it interesting that his position did not make his insights in that regard any more valuable. The final segment of transcript from a radio show read by the narrator struck me a an opportunity missed to allow Hawking to finish with his own voice and presence.

I was disappointed they did not use the original sound feed and chose to read the transcript. Well worth the read or the listen. Already dated though and perhaps his more recent works would be of more value to most listeners. Mar 14, Mohamed al-Jamri rated it it was ok. Wonderful book for theoretical astrophysics neophytes such as me! The book is written in the same clear and simple style as 'A Brief History of Time'.

Hawking dumbs down his work enough to make it accessible to the masses without compromising on its intrigue or wonder. I was particularly impressed by his explanation for imaginary time, a concept I have been struggling to understand for some time.

More importantly, it is the kind of book that turns people on to science. Well done, Mr. My favorite aspect of this collection of essays is that Hawking reveals himself as well as his science. The book includes two autobiographical essays and an interview in which Hawking tells the reader about his early history and his contraction of motor neuron disease, as well as his transformation from a bored young adult to a well-established and cutting-edge theoretical physicist.

I like Hawking and his style as much as I enjoy learning about and reviewing key tenets of astrophysics. I also My favorite aspect of this collection of essays is that Hawking reveals himself as well as his science. I also like the fact that Hawking doesn't shy away from giving other people credit for their discoveries. It's endearing. Each of the essays in this collection was easy to follow and held my attention for different reasons. I like that Hawking is positive and life affirming.

I like that he doesn't ever deny the existence of God. I like his obvious admiration of Einstein. I like that Hawking is always conscious of his reader and clearly wants his reader to understand and appreciate the value of physics and the reasons that it matters for everyday life. I highly recommend this book to people interested in astrophysics, Stephen Hawking, and how things work and why they work the way they do after all, that's what got Hawking started with science: View 2 comments.

Apr 16, Lupita rated it it was amazing. Not as complex as I thought. Its very descriptive and give to the reader a lot of examples to understand the theories and the concepts. Pubblicato 5 anni dopo il suo primo libro e bestseller Dal big bang ai buchi neri - Breve storia del tempo , Buchi neri e universi neonati sceglie un'altra strada per il processo divulgativo.

In questo libro vengono proposte, in linea generale, le teo Pubblicato 5 anni dopo il suo primo libro e bestseller Dal big bang ai buchi neri - Breve storia del tempo , Buchi neri e universi neonati sceglie un'altra strada per il processo divulgativo.

Chiude poi il libro una trascrizione della storica trasmissione radiofonica inglese BBC Desert Island Discs andata in onda il giorno di Natale del , in cui durante una normale intervista all'ospite viene anche chiesto quali 8 dischi porterebbe su un'isola deserta, quale oggetto di lusso e quale libro. Per chi fosse curioso, view spoiler [i dischi scelti da Hawking sono Gloria di Poulenc, Concerto per violino di Brahms, Quartetto per archi op.

You read this collection of essays and get what you can from them. Hawking himself knows see the last essay, actually interview, at the end of the book that there is much the reader will not understand.

Hawking says that a universe that collapses onto itself is a "singularity of infinite density," but it's not clear what about it is "infinite. We understand that point as a circle and Hawking uses the earth as an example one can travel around t You read this collection of essays and get what you can from them.

We understand that point as a circle and Hawking uses the earth as an example one can travel around the earth and back to a starting point. But that stimulates the next question, which is what is beyond the circle? While we know some sort of space lies beyond the earth, is there nothing beyond space and time and, if so, what or how does one understand "nothing"?

Hawking summarizes nicely the four forces in the order of strength, but it's hard not to wonder whether the gravitational force, the weakest of the four, actually is the primary one.

Hawking says that matter in the beginning was created out of energy by borrowing from the gravitational energy of the universe and that this energy was necessary to counter the effects of gravity, the matter tucked tightly in a pre-Big Bang scenario. Even with a glimmer of understanding, that's heady stuff. Hawking says that a collapsed star that forms a black hole is a reverse version of the Big Bang process. Matter attracts to a singularity, which seems to be some sort of ultimate gravity, not because some mysterious center point pulls matter to itself, but because matter attracts matter and the only result is a pull to some center point.

There, does matter become so dense infinite? Do black holes explode in the same way, thereby helping to perpetuate the cyclic nature of the universe? If matter and energy are equivalent Hawking doesn't describe how speed of light fits into Einstein's formula and if gravity is matter attracted to itself, what creates the attraction and how does this relate to energy?

Understandably, these speculative questions, more fun than frustrating, may make a professional physicist wince. In one essay Hawking attempts to bridge physical laws and human behavior. He says the fundamental laws of science cannot be used to deduce human behavior. Yet, it's fair to wonder. Are not the four forces termed "interaction" which includes gravity that, while often talked about as an attractive force, involves a critical distance where another mass resists being attracted.

Are not humans matter and are not human relationships with each other and the world characterized by attraction and resistance? In the free will arena, Hawking seems to say that while physical laws predetermine, it is too complex to deduce whether and how humans are predetermined and, therefore, he seems to conclude that humans have some sort of free will.

We know humans have a degree of choice, save for situations like genetic disease and death that make choices for us though we try with religion and medicine. Hawking is silent on why we choose the way we do. On what basis is choice made? Does survival and well-being have a lot to do with such choices and isn't this science based? In Epicurean fashion, we seek whatever we are attracted to need and we resist what we are not attracted to don't need. Is this similarity with the physical laws of the universe a coincidence?

Hawking makes a revealing, throw away, comment about Feynman resigning from the Academy of Sciences because "he hated pomp and humbug" and the Academy scientists were too preoccupied with who should be admitted to the Academy. Maybe that aside reveals that the best minds rest on animal-biological needs survival and rank behavior related to survival which, it is interesting to speculate, may tie into how matter relates to matter we seek objects from the world to live; we resist threats to our life.

On the whole, this is a terrific book. Me ha gustado bastante, principalmente por tres razones: Sep 07, Michael rated it really liked it Shelves: Apr 18, Kathryn rated it it was ok. Even though it is a collection of speeches and essays, Hawkings writing is not to my liking. It is too plain and not detailed enough in topics of actual interest. I'm glad this book was short but even so it was a struggle to complete. Mar 25, Joshua rated it it was amazing.

A Brief History of Time, both the book as well as the documentary about the life of Stephen Hawking, completely altered my perception of reality, the foundation of it, the origin of absolutely everything, and my conception of what existence actually is. For whatever reason, I followed up this masterpiece by disappearing into James Joyce's Ulysses and I left Hawking to his work. It's fair to say I picked up this collection for the fifth time because of the man's death.

We had a display set up for A Brief History of Time, both the book as well as the documentary about the life of Stephen Hawking, completely altered my perception of reality, the foundation of it, the origin of absolutely everything, and my conception of what existence actually is. They have been well received. I think that is in a large part due to the quality of the speech synthesizer, which is made by Speech Plus.

One's voice is very important.

If you have a slurred voice, people are likely to treat you as mentally deficient. This synthesizer is by far die best I have heard because it varies the intonation and doesn't speak like a Dalek. The only trouble is that it gives me an American accent. However, by now I identify with its voice. I would not want to change even if I were offered a British-sounding voice. I would feel I had become a different person.

I have had motor neurone disease for practically all my adult life. Yet it has not prevented me from having a very attractive family and being successful in my work. This is thanks to the help I have received from my wife, my children, and a large number of other people and organizations.

I have been lucky that my condition has progressed more slowly than is often the case. It shows that one need not lose hope. Some people would like to stop these changes and go back to what they see as a purer and simpler age.

But as history shows, die past was not that wonderful. It was not so bad for a privileged minority, though even they had to do without modern medicine, and childbirth was highly risky for women. But for the vast majority of the population, life was nasty, brutish, and short. Anyway, even if one wanted to, one couldn't put the clock back to an earlier age.

Knowledge and techniques can't just be forgotten. Nor can one prevent further advances in the future. Even if all government money for research were cut off and the present government is doing its best , the force of competition would still bring about advances in technology.

Moreover, one cannot stop enquiring minds from thinking about basic science, whether or not they are paid for it. It has been updated. All it would do is slow down the rate of change.

If we accept that we cannot prevent science and technology from changing our world, we can at least try to ensure that the changes they make are in the right directions. In a democratic society, this means that the public needs to have a basic understanding of science, so that it can make informed decisions and not leave them in the hands of experts. At the moment, the public has a rather ambivalent attitude towards science. It has come to expect the steady increase in the standard of living that new developments in science and technology have brought to continue, but it also distrusts science because it doesn't understand it.

This distrust is evident in the cartoon figure of the mad scientist working in his laboratory to produce a Frankenstein. It is also an important element behind support for the Green parties.

But the public also has a great interest in science, particularly astronomy, as is shown by the large audiences for television series such as and for science fiction. Cosmos What can be done to harness this interest and give the public the scientific background it needs to make informed decisions on subjects like acid rain, the greenhouse effect, nuclear weapons and genetic engineering?

Clearly, the basis must lie in what is taught in schools. But in schools science is often presented in a dry and uninteresting manner. Children learn it by rote to pass examinations, and they don't see its relevance to the world around them. Moreover, science is often taught in terms of equations. Although equations are a concise and accurate way of describing mathematical ideas, they frighten most people.

When I wrote a popular book recently, I was advised that each equation I included would halve the sales. Maybe I would have sold twice as many copies without it. But for the rest of us, a qualitative grasp of scientific concepts is sufficient, and this can be conveyed by words and diagrams, without the use of equations.

Stephen Hawking

The science people learn in school can provide the basic framework. But the rate of scientific progress is now so rapid that there are always new developments that have occurred since one was at school or university. I never learned about molecular biology or transistors at school, but genetic engineering and computers are two of the developments most likely to change the way we live in die future. Popular books and magazine articles about science can help to put across new developments, but even the most successful popular book is read by only a small proportion of the population.

Only television can reach a truly mass audience. There are some very good science programmes on TV, but others present scientific wonders simply as magic, without explaining them or showing how they fit into the framework of scientific ideas. Producers of television science programmes should realize that they have a responsibility to educate the public, not just entertain it.

What are the science-related issues that the public will have to make decisions on in the near future? By far the most urgent is that of nuclear weapons. Other global problems, such as food supply or the greenhouse effect, are relatively slow acting, but a nuclear war could mean the end of all human life on earth within days. The relaxation of east-west tensions brought about by the ending of the cold war has meant that the fear of nuclear war has receded from public consciousness.

But the danger is still there as long as there are enough weapons to kill the entire population of the world many times over. In former Soviet states and in America, nuclear weapons are still poised to 27 strike all the major cities in the Northern Hemisphere.

It would only take a computer error or a mutiny by some of those manning the weapons to trigger a global war. It is even more worrying that relatively minor powers are now acquiring nuclear weapons. The major powers have behaved in a reasonably responsible way, but one cannot have such confidence in minor powers like Libya or Iraq, Pakistan, or even Azerbaijan.

The danger is not so much in the actual nuclear weapons that such powers may soon possess, which would be fairly rudimentary, though they could still kill millions of people.

Rather, the danger is that a nuclear war between two minor powers could draw in the major powers with their enormous arsenals. It is very important that the public realize the danger and put pressure on all governments to agree to large arms cuts. It probably is not practical to remove nuclear weapons entirely, but we can lessen the danger by reducing the number of weapons.

If we manage to avoid a nuclear war, there are still other dangers that could destroy us all. There's a sick joke that the reason we have not been contacted by an alien civilization is that civilizations tend to destroy themselves when they reach our stage.

But I have sufficient faith in the good sense of the public to believe that we might prove this wrong. It was published later in Britain than in die United States.

It is being translated into twenty languages twenty-one if you count American as different from English. This was much more than I expected when I first had the idea in of writing a popular book about the universe. My intention was partly to earn money to pay my daughter's school fees. In fact, by the time the book actually appeared, she was in her last year of school.

But the main reason was that I wanted to explain how far I felt we had come in our understanding of die universe: how we might be near finding a complete theory that would describe the universe and everything in it. At week , it went into the Guinness Book of Records for achieving the most appearances on this list. The number of translated editions is now thirty-three.

My previous technical books hud been published by Cambridge University Press. That publisher had done a good job, but I didn't feel that it would really be geared to the sort of mass market that I wanted to reach. 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 buy 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 buy 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.

Black Holes And Baby Universes And Other Essays

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.

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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.Related Interests. His supervisor was Denis Sciama, although he had hoped to get Fred Hoyle who was working in Cambridge.

If that were jthe case, it wouldn't make sense to ask who, or what, caused or created the big bang. These are self-contained universes that branch off from our region of the universe. Therefore I felt I could just mention them but not go into depth. But in schools science is often presented in a dry and uninteresting manner. Well done, Mr. I also like the fact that Hawking doesn't shy away from giving other people credit for their discoveries.

Mar 26, Alan Johnson marked it as partially-read Shelves: Hawking's use of a particular, popular analogy and a light, sociable tone serve to keep his audience interested in his subject matter to express his feelings on the nature of his particular branch of science.

ALEX from Kentucky
Also read my other posts. I take pleasure in beatboxing. I do fancy sharing PDF docs seldom .