Forewords

Writing a review on this book has a special purpose behind it. It was when I joined IIT Delhi, that somebody important to me introduced a word Stephen Hawking to me. I read this book and later on I built up with my knowledge about him. Surprisingly, I learned that unlike other books, this book deals about God, from Whom most of the science books just try to escape away. As one of the Scientists, Carl Sagan of Cornell University, puts it this is book about absence of God. When I read it first time, although I came across Stephen Hawking questioning the existence of a Creator of this Universe, I could not really understand the logic behind them. This was might be much high theoretical physics or metaphysics or whatever. As myself I strongly believe in the existence of God. This book review is an attempt to understand one of the finest brains of twentieth century, Stephen Hawking, as some people call him. The objective of this book review is not to bias any personal judgement or prejudice, but to find out is it really justified to question the Supreme Authority, as I think God to be, by the one who attends church every week, not necessarily due to his belief in God, but for something else I do not know. Also as Stephen Hawking puts it himself that being unlucky enough to get Motor Neuron disease, he is still fortunate enough in almost every other respect. This book review will try to understand him through his book A Brief History of Time. In the last the reader should evaluate how much successful I am in achieving my goal.

About this book, being bestseller, I can't really have much to say, as Stephen Hawking has tried really his best to make it interesting and simple. Its being interesting is relevant from the first page of Acknowledgments in his book where he says that someone told him that each equation he would put in this book will halve the sales, and he resolve not to put any equation except one that is mass energy equivalence relation by Einstein. Then he hopes this will not scare off half of his potential readers.

For those who don't know Stephen Hawking, this book introduces him to be Lucasian Professor of Mathematics at Cambridge University, a post once held by Newton and later by P.A.M. Dirac, two celebrated explorers of the very large and the very small. He is now confined to wheelchair due to ALS or motor neuron disease. He has his wife Jane and three children Robert, Lucy and Timmy in his family.

Chapter 1: Our Picture of Universe

The people have been having different world view of how the universe should be. For some people it is infinite tower of tortoises. For others this model might be rather ridicules but the author questions, why do we think we know better? In fact, what do we really know about the universe and how do we know it? Where did universe come from, and where is it going? Did the universe have a beginning, and if so, what happened before then? What is the nature of time? Will it ever come to an end? These are questions being tried to answered in this book.

The author tries to establish that earth is spherical in shape by using Aristotle's arguments. The beauty of Aristotle's argument is that they are still used in present day science to some extent. Aristotle's estimate of earth diameter was twice the current accepted figure. But Aristotle's universe was geo-centric. He believed this because he felt, for mystical reasons, that the earth was center of universe, and that circular motion was the most perfect. Then comes Ptolemy's model, which was widely accepted, also by Christian church, because it was according to Scripture and left lots of room outside the spheres of fixed stars for heaven and hell. Then comes Copernicus' model, which is helio-centric. Later on this model was also supported by Galileo and Kepler. Galileo, from his observations of moons of Jupiter, insisted that everything did not have to orbit directly around the earth, opposite to what Aristotle and Ptolemy had earlier thought. Kepler modified the Copernicus model by making the circular orbits to be elliptical, which was rather ad-hoc hypothesis. Later on, final model in this course was given by Newton in his book Philosophiae Naturalis Principia Mathematica, including involved Mathematics. Here Stephen Hawking makes clear the well known story about Newton that apple fell on his head is certainly apocryphal, and what all Newton himself ever said was that idea of gravity came to his mind when he sat in a contemplative mood and was occasioned by the fall of an apple. By Newton's gravity, stars would all attract each other, so it seemed that they could not remain essentially motionless. But Newton argued to Richard Bentley that his universe was infinite and there was no central point where all stars would collapse to. But according to Stephen Hawking, this was an instance of pitfall and correct approach should have been as follows. Let consider the finite situation when the stars all fall in on each other and , what happens when we add one more star? According to latest theory, it is impossible to have static universe in which gravity is always attractive.

At this point, Stephen Hawking brings in the idea of origin of universe when he says that it was generally accepted that universe had existed forever in an unchanging state, and is largely due to people's tendency to believe in eternal truths, as well as comfort they found in the thought that even though they may grow old and die, the universe is eternal and unchanging.

Scientists in earlier days could not suggest that universe might be expanding and rather suggested that gravity might be repulsive at larger distance, which by present analysis leads to unstable equilibrium.

The idea the universe has a beginning is very old. According to certain cosmologies and religious faiths, universe was started at a finite time and not very distant time in the past. According to one argument, it was necessary to have a "First Cause" to explain the existence of the universe. This is brilliant argument as within the universe we always explained one event being caused by earlier event, but the existence of universe itself can be explained in this way only if it had some beginning. Another argument was put forward by St. Augustine in his book The City of God. According to him the beginning date was about 5000 BC which Stephen Hawking points out (perhaps sarcastically) is not far from last Ice Age, about 10000 BC, which is when archaeologists tell us that civilization really began.

Now comes the very interesting question, as discussed by Philosopher Immanuel Kant in his monumental (and very obscure, as put forward by Stephen Hawking) work Critique of Pure Reason (1781) that whether the universe has beginning in time and whether it is limited in space. The best argument he gave was that the time was property of universe that God created, and that time did not exist before the beginning of the universe. Now with the present scenario of expanding universe and big bang, time before the big bang is not defined. Also if the universe is expanding, then there may be physical reasons why there had to be a beginning. One could still imagine that God created the universe at the

instant of big bang, but it would become meaningless if one says it was created before big bang. An expanding universe doesn't preclude a Creator, but it does place a limit when He might have carried out His job! Not to forget here is the fact that for this statement Stephen Hawking assumes that existence of any events earlier than big bang can be ignored because it would not have any observational consequences!

Now a days, we have two predominant theories, Einstein's general theory of relativity and Quantum mechanics. Although both have established themselves, they are according to Stephen Hawking, inconsistent with each other. Now the search is for a new theory - a quantum theory of gravity. The last interesting thing Stephen Hawking says about this new Unified theory is that the theory itself would determine the outcome of our search for it. And why it should determine that we might come to the right conclusions from the evidences? Might it not equally well determine that we draw the wrong conclusion? Or no conclusion at all? Stephen Hawking tries to give his only answer regarding this based on Darwin's Principle of Natural Selection.

Stephen Hawking concludes this chapter with following words:

" Today we still yearn to know why we are here and where we come from. Humanity's deepest desire for knowledge is justification enough for our continuing quest. And our goal is nothing less than a complete description of the universe we live in."

Chapter 2: Space and Time

Stephen Hawking in the beginning discusses the development in theory of motion. With the advent of newer ideas, we could not give an event a absolute position in the space, contrary to what Aristotle had believed. Newton was very much upset about this idea as it infringed with his idea of an absolute God. He in fact refused to accept this lack of absolute space, although it was implied by his theory of motion. Also the remarkable achievement was proving that light travels at a finite speed and also a rough estimate of this speed by Roemer.

Stephen Hawking insists that we have had to change our ideas about space and time. This is because our apparently commonsense notion works well when dealing with things like apples, or planets that travel comparatively slowly, but it fails at all when dealing with speed comparable to light. Later developments in optics suggested that speed of light was same for any one observing it, regardless of what one would predict based on Doppler's effect. It was mainly confirmed by Michelson-Morley experiment (1887), and several ideas were put forward to account for this, including the ether theory, in terms of object contracting and clock slowing down when they move through aether. It was Einstein, and also Henry Poincare, who put forward the idea that the whole idea of ether was unnecessary if one was willing to abandon the idea of Absolute Time!

For Einstein it was physical necessity but for Poincare it was mathematical problem. By relativity, the idea of absolute time has been put to an end.

This is because the speed of light is same for all observers ( whether moving or stationary ) and nothing can travel more than the speed of light.

The theory of relativity does force us to change fundamentally our ideas of space and time. We must accept that time is not completely separate from and independent of space, but is combined with it to form an object called space-time. This is slightly forcing argument and a lay person or even scientist not comfortable with General Relativity will find it difficult to assimilate. Stephen Hawking should have given more insight at this point regarding space-time. Now the interesting thing to reader will be the notion that in general relativity there is no real distinction between space an time coordinates, just as there is no real distinction between any two space coordinate. Interestingly, in relativity, one can use a new time coordinate that was the old time (in seconds) plus the distance (in light seconds) in some particular direction of a place. Stephen Hawking puts it clear that it is impossible to visualize a four dimensional space. So people who are convinced by concreteness aspects of a theory will find it difficult to get convinced (like me). Anyhow, Stephen Hawking continues with his book.

Then the author comes up with ideas of light cone, future light cone, past light cone etc. Interesting enough, the events outside the light cone of an event at point P cannot be influenced by what happens at P. Also, if one knows what is happening at some particular time everywhere in the region of space that lies within the past light cone of event at P, one can predict what will happen at P. Now the problem came up with special relativity (1905) that it was inconsistent with Newtonian theory which required instantaneous gravitational effects, i.e. speed greater than of light, which special theory of relativity doesn't permit. This problem finally led Einstein to propose General Theory of Relativity (1915). Einstein suggested that space-time is not flat, as earlier thought, but is curved or warped by the distribution of mass and energy in it. In general theory, body always follows straight line in four dimensional space-time, but it looks to us that follows curved path in three dimensions. Light rays in relativity follows what is called geodesics in space-time. One interesting thing author points out is about Twin Paradox, that it will be a paradox only if one has the idea of absolute time at the back of one's mind.

Stephen Hawking concludes the chapter by following words:
"Space and time are now two dynamic quantities: when a body moves, or a force acts, it affects the curvature of space and time - and in ten the structure of space-time affects the way in which bodies move and forces act."

Chapter 3: The Expanding Universe

Stephen Hawking begins with his discussion about star lit sky. As long ago as 1750, some astronomers were suggesting that the appearance of Milky Way (Akaash Ganga) can be explained if most of the visible stars lie in a single disc like configuration, one example of what we now call as spiral galaxy. He also points out that we can measure the distance of a star if we know its luminosity. The great blow will be his statement to devotee of god Sun, when he says that our sun is just an ordinary, average sized, yellow star near the inner edge of one of the spiral arms of this galaxy Milky way (and has nothing special with it, not even its position in the galaxy!). For every star there is one important property associated - the color of its light. We can observe the spectrum of a star by focussing a telescope on it. Also, we can tell stars temperature by observing its spectrum. The interesting this that came when most of the stars were observed was that most of the galaxies appeared red shifted: nearly all are moving away from us. Even the size of galaxy's red shift is not random but is directly proportional to its distance from us. The deductions like weightlessness, and also the idea that if universe is expanding at more than a certain critical rate then the gravity will never be strong enough to stop it, and the universe would continue to expand forever, didn't come to genius people's mind, may be largely due to the strong belief in the static universe. Even the Einstein was so sure of the static universe that he modified his general relativity, introducing a solaced cosmological constant into his equations. Einstein also introduced a new "antigravity" force, which unlike other forces did not come from particular source, but was built into very fabric of space-time. Although this approach was later on realized to be wrong, it really puts a question whether we should really rely on our genius people for something which we cannot understand. What would have happened if that fault were not realized and we would have been teaching our students about antigravity. If every idea is subjected to same judgement then I am not sure people will really find it convincing to believe whatever we today believe. But this is an important aspect of a reliability of a theory that it can be brought into falsifiability. Now come back to Stephen Hawking's expanding universe.
If everything is moving away from us then we must be at the center of universe (same as Aristotle had thought, although for different reasons). There is an alternative explanation not to think like this because universe might look the same in every direction from any other galaxy as well (although no one has yet observed this, and there is no chance for this in near future as well). Stephen Hawking puts three models of universe that obey two fundamental assumption Friedmann. First is expanding slowly and will cause expansion to slow down and eventually to stop. Second model is expanding forever and third model is expanding just sufficient to avoid recollapse. The remarkable feature of first model is that universe is not infinite in space, but neither does space has any boundary. An interesting comment given by author is that although theoretically it is possible by first model to go round the universe, but it can be shown that the universe would recollapse to zero size before one can get around ( a bad news for writers of science fictions ! ). The present evidence suggests that the universe would continue to expand forever, but all we can be sure of is this that even if it is going to recollapse, it will not do so atleast another ten thousand million years, since it has already been expanding for that long, and according to Stephen Hawking, this should not unduly worry us now, because if we have not colonized beyond solar system by then, we will naturally get into end with our beloved sun much before that time.

Now comes the important point that all theories have been formulated on the assumption that space-time is nearly flat and smooth, so that they break down at big bang singularity, including the theory of general relativity itself. At big bang curvature is infinite and any event before big bang and big bang itself can not be used for any prediction. Many oppositions rose up against big bang, and many theories were proposed including steady state theory, which was later on withdrawn. Later on big bang got hold on, and many advances were made. The author himself proved that there must have been big bang singularity provided only that general relativity is correct and universe contains as much matter as we observe. But the irony as author points out is that now he is convincing people that there should not have been a singularity at the beginning of the universe - as it can disappear once quantum effects are taken into account. We have two partial theories - general theory of relativity and quantum mechanics. At the beginning universe was so tiny that quantum effects cannot be neglected.

Stephen Hawking concludes with the words that now we are trying to search for what is called quantum theory of gravity.

Chapter 4: The Uncertainty Principle

It was Laplace who suggested that there should be a set of scientific laws that would allow us to predict everything that would happen in the universe. This doctrine of scientific determinism was strongly resisted by many people, who felt that it infringed God's freedom to intervene in the world. This idea although had to be abandoned later on. It was Max Planck who suggested that light can travel nothing lesser than a quantum. Later on, Heisenberg proposed his Uncertainty Principle which said that it is impossible to find out both velocity and position of an object with complete accuracy. Thus quantum mechanics therefore introduces an unavoidable element of unpredictability or randomness in science. Later in this chapter Stephen Hawking discusses interference, Bohr's model and other things which are not discussing.

Stephen Hawking concludes the chapter with with following word:
"Thus in the sense, classical general relativity, by predicting points of infinite density predicts its own downfall, just as classical (non quantum) mechanics predicted its own downfall by suggesting that atoms should collapse to infinite density. We do not yet have a complete consisted theory that unifies general relativity and quantum mechanics."

Chapter 5: Elementary Particles and the Forces of Nature

Aristotle believed that everything was made up of four basic elements, earth, water, air and fire. These elements were acted upon by two forces, gravity (earth and water) and levity (air and fire). After this author talk about atom, Dalton's theory, discovery of electron, proton and neutron. The notion of elementary particles being proton, electron and neutron was later changed with discovery of quarks which form these particles. The origin of this name quark, according to author is enigmatic quotation from James Joyce : "Three quarks for Muster Mark!" Also there are six flavours of quarks, described by author as up, down, strange, charmed, bottom and top. This would seem to be strange naming, but as pointed out by Stephen Hawking, this is more imaginative way of naming by present day scientists who do not restrict themselves to greeks. Each proton and neutron is formed of three quarks each (of different flavours of course).

Another important property of particles is spin. Here comes the genius of Stephen Hawking in describing what a spin of particle is. What the spin of particle really tell us is what the particle looks like from different directions. A particle with spin 0 is like a dot (looks same when rotated by 360 degrees). Spin 2 is like double headed arrow (needs rotation by 180 degrees to look the same). If intuition works, then what would be the interpretation for particles of spin half (1/2)? These are the particles who need two complete revolutions to look the same! Isn't it quite amazing?
Particles of spin 0,1 and 2 are force producing. While electrons have spin 1/2. These behavior of these particles are governed by Pauli's exclusion principle which says that two similar particles cannot exist in the exactly same state. The exclusion principle is crucial because it explains why matter particles do not collapse to a state of very high density under the influence of forces produced by 0,1 or 2 spin particles.

Also every elementary particle is supposed to have its antiparticle, with which it will annihilate. However we must be careful enough for Stephen Hawking warns us not shake hands with our antiselves when we meet them as they will both vanish in great flash of light.
Also one important point is that laws of physics are not quite the same for particles and antiparticles. This may explain why should there be more matter than antimatter.

After this author talks about C,P,T symmetries, about which, although interesting, we will not discuss now.

Stephen Hawking concludes the chapter by:
"Grand unified theories do not include the force of gravity.... So for a sufficiently large number of matter particles, the gravity adds up and dominates over all other forces. This is why it is gravity that determines the evolution of the universe."

Chapter 6: Black Holes

Although black holes were thought before 1783 itself, it was really S. Chandrashekhar who realized that there is a limit to the repulsion that exclusion principle can provide. Chandrashekhar calculate a limit, called Chandrashekhar limit, which decides the fate of a star. According to this a star with more more mass than Chandrashekhar limit may collapse to infinite density under certain conditions. Eddington, a scientist that time was shocked by Chandrashekhar's result and got a really hostile attitude that Chandrashekhar was really forced to give up his research.
Behavior of black holes as predicted are very strange. The event horizon is path of last ray of light which just managed to escape from black hole. One would say about event Horizon, what the poet Dante said of the entrance to Hell: "All hope abandon, ye who enter here." Anyone who enters here." There are so many interesting things we are just skipping, but reader must enjoy them while reading this book.

Chapter 7: Black Holes Ain't So Black

Stephen Hawking considers the Second law of thermodynamics which states that entropy of an isolated system always increases, and when two systems are joined together, the combined entropy is greater than sum of individual entropies. The area of the event horizon was measure of entropy of black hole and hence when matter carrying entropy fell into a black hole then the area of event horizon must would go up if the Second law of thermodynamics is not to be violated. According to quantum mechanical uncertainty principle rotating black holes, and even non rotating must create and emit particles in a steady rate. The emission is of particles and radiation like that of a hot body with more mass the lower the temperature and vice versa. However to our great surprise these particles do not come out of black holes but are coming from the event horizon.
With this account we come closer to Aristotle that nothing is absolute empty, as this account also supposes that empty space cannot be completely empty!

We are not discussing much about black holes. But reader must enjoy reading every bit of it.

Chapter 8: The Origin and Fate of the Universe

This is rather a sarcastic chapter which fulfills the Carl Sagan's claim of this book being a book of absence of God. It was after a meeting organized by Catholic church to advice it upon the cosmology. At the end of talk, participants were granted an audience with the Pope who told that it was all right to study the evolution of the universe after the big bang, but we should not inquire into the big bang itself because that was the moment of Creation and therefore the work of God. Stephen Hawking says that he was glad that Pope did not know the subject of talk author had just given at the conference- the possibility that space-time was finite but had no boundary, which means it had no beginning, no moment of Creation. This is not a big deal as even some of the participating knowledgeables might not have been able to infer this out of the talk. Stephen Hawking puts forward some question regarding the initial configuration of universe, and says that one possible answer to them is that God chose the initial conditions of universe for reasons the we cannot hope to understand. After this author talks about anthropic principle which can be paraphrased as "We see the universe the way it is because we exist". Now, why is the universe the way we see it? The answer is simple: If it had been different, we would not be here.

We are skipping a much and we come to Stephen Hawking's concluding remarks for this chapter:
"So long the universe had a beginning, we could suppose it had a creator ( notice the small c of creator). But if the universe is "really" completely self contained, having no boundary or edge, it would have neither beginning nor end: it would simply be. What place, then, for a creator?"

This argument is nothing better than some arguments I have heard that it is "natural" for life to exist. But lets not go before this "natural" aspect
for the moment.

Chapter 9: The Arrow of Time

The laws of science do not distinguish between the past and the future. More precisely, the laws of science are unchanged under the combination of operations or symmetries known as C, P and T. The author has given so many nice examples and reader must enjoy reading them. We are not discussing this chapter in a detail. But the ideas like thermodynamic arrow of time etc. are really fascinating. The last example regarding increasing disorder of universe is really great.

Chapter 10: The Unification of Physics

We have progressed by finding the partial theories, and one would look forward for an ultimate theory that would include all partial theories.
Einstein spent most of his later years unsuccessfully searching for a unified theory, but the time was not ripe as very little was known about nuclear forces The uncertainty principle was tried to be incorporated into general relativity. Some theories like "supergravity" was proposed. The idea was to combine graviton (spin 2) with other particles of spin 3/2, 1, 1/2, 0. This would have caused many possible infinities to cancel out, but was suspected that some infinities might still remain. The author in this chapter discusses various aspects of this unified theory we are searching for. One question interesting enough regarding unified theories is possibility that there no theory of the universe; events cannot be predicted beyond a certain extent but occur in a random and arbitrary manner. Here Stephen Hawking points out that some people will try to give third argument a favour because if there would have been a complete set of laws, it would infringe God's freedom to change His mind and intervene in the world. Its bit like the old paradox: Can God make a stone so heavy that He can't lift it? But the idea that God might want to change His mind is fallacy, pointed out by St. Augustine, of imagining God as being existing in time: time is a property only of the universe God created.
Presumably, He knew what He intended when He set it up!

Stephen Hawking completes this chapter with:
"A complete, consistent , unified theory is only the first step: our goal is the complete understanding of the events around us, and of our own existence."

Chapter 11 : Conclusion

Regarding Laplace's Determinism, author points out that in nineteenth's century, God was confined to an area that science did not understand.
The author insists upon the fact that if universe is self contained, with no singularity or boundary, then it has profound implications on the role of God as Creator. Einstein once asked, "How much choice did God have when constructing the universe?" If the no boundary proposal is correct then He had no choice at all. He would still have the freedom to choose the laws that the universe obeyed.

The one important point of this book is Stephen Hawking's answer to Einstein's famous comment: "God does not play dice". The reader is encouraged to find out what was Stephen Hawking's answer to this comment in this book.

Stephen Hawking completes the book with following lines:
"... why it is that we and the universe exist. If we find the answer to that it would be ultimate triumph of human reason - for then we would know the mind of God."