Man has been trying to understand his universe for quite some time now. It started with basic observations on what was going on around him. The weather, the animals, other humans, all did some strange and wonderful things. As we have become more advanced, we have turned to more complex models and a more detailed study of what is happening in our world. We believe we understand the way the universe was formed and we think we understand the interactions of the building blocks of matter. Yet this study has become so specialized that the general populace has not been able to keep up with the discoveries. This book, "A Brief History of Time: From The Big Bang To Black Holes" by Stephen Hawking attempts to bring much of the latest scientific thought down to a level that the layman can understand. He discusses our view of the universe and the history of that view. Next he talks about the universe on the large scale. After that he goes the opposite direction and talks about the elementary particles in matter. Finally he talks about the attempted resolution of the two theories.
To start with, we need to understand why we view the universe the way we do. Professor Hawking talks about the history of our view of the universe. This starts with Aristotle coming up with the view that the Earth was a sphere. Next came Ptolemy who took Aristotle's idea and came up with a model of the spheres in our universe. The Earth was stationary and the planets and sun revolved around us. This happened to be adopted by the Catholic Church as it allowed for God outside of the sphere of the stars. Nicholas Copernicus came up with a different idea. The sun was the center of our universe and even the Earth orbited it. This was an even better theory than before and matched the observations of the moon and planets motions. Copernicus's theory finally had public adherents in the persons of Galileo Galilei and Johannes Kepler. These people popularized the theory and modified it to state the planets revolved around the sun on elliptical paths instead of circles. From here Newton came up with his work that talked about the motion of planets and the forces that interact with them. In addition he created the branch of mathematics that explained his theories. Years later the idea of a nonstatic universe was theorized and became the norm. Looking backward to the creation of the universe, the two competing theories (and possibly cooperative) are creation by God and the Big Bang. This is discussed in much greater detail by Professor Hawking. His explanation is very lucid and is easily understood. This sets the basis for the rest of the book.
The next couple of chapters talk about the structure of the large scale universe as we know it. Topics from space and time to the expansion of the universe are discussed here. In essence these chapters boil down to this. Light travels at the same speed regardless of the medium. This led to Einstien's Theory of General Relativity which encompasses time. Time as we know it is linear. It proceeds in the direction we know of as past to future. Why this is we don't quite know. However it is important for beings such as humans. However it isn't a uniform flow. As seen by Einstien's Theory of Relativity, the higher up you are the slower time progresses. Or to put it more clearly, if you have two clocks that are exactly equal in marking time, and you take one of them to the top of a mountain and leave the other at the base of the mountain, when you bring them back together there will be a difference in the time they both read. However as time went on, it was discovered that gravity has an important role to play as well. The theory of General Relativity states that light should be bent by gravity and so it is. Now what does all of this mean? The Theories of Relativity and the Laws of Motion have done away with the ideas of absolute positions in space and time. This led to our current view that the universe isn't static which was the common view up until the twentieth century. It had to have a beginning and possibly an end. It does appear at this point that the universe is indeed expanding. This has important implications on the forces we see interacting and the formation of the universe as we know it. It does appear that the universe got its start during a time called the Big Bang. This is a singularity where there was no time because all matter was collapsed into a single infinite point. Upon expansion, time as we know it started and our universe formed. This currently meets with out theories of the universe.
The next section of the book looks into the subatomic portion of our universe. This is extremely important as this is the study known as quantum mechanics. Quantum mechanics can help explain the forces that we know exist but don't understand. Gravity is an example. I found this portion to be extremely difficult to understand. When getting down to the basic building blocks of the universe, we go below the level of proton, neutron, and electron. These particles are know as quarks. Quarks are described in type, color, and spin. They are too small to be seen in the visible wavelength so they couldn't have color as we know it. These are all arbitrary labels to explain the observations of these particles. Nothing is even this simple. Due to the Uncertainty Principal, these particles are both a wave and a particle at the same time. This allows everything I the universe to be described by quantum mechanics. However, quantum mechanics doesn't yet agree with the General Theory of Relativity. In an attempt to rectify this, the study of the forces holding quarks together is being made. Gravity, electromagnetic, weak nuclear force, and the strong nuclear force. All but gravity have been put into a unified theory. Gravity is the least understood of these forces which is why it hasn't been unified. If all of these forces could be combined into a Grand Unified Theory, the belief is it would integrate with the General Theory of Relativity and all would be good in the universe as we would have an understanding of how it all worked.
Quite frankly, most of this discussion, which is far more understandable in the book, was beyond me. The biggest problem I had with it was with the quarks. A chart or a picture would have made it comprehensible for me and I suspect for anyone else as well. Still this is nitpicking as it does indeed explain the fundamental elements of the universe and their functions as we know them.
The next few chapters discuss black holes and the fate of the universe. This may seem unrelated but it draws upon the work in the previous chapters. The importance of black holes is in the theory of the origin of the universe and in the study of time. A black hole is also known as a singularity. In a singularity, gravity is so massive a force that even light cannot escape. All matter inside a black hole is compressed until it is down to a single point. This gravity will curve light, space and time. This is as close to our theory of the beginning of the universe as we can come up with. With the current theory of the Big Band, all matter was compressed in a single point. Time had no meaning because time didn't start until the Big Bang took place. It is possible that the interior of a black hole is similar. It is impossible to find out for a couple of reasons. Anything sent into a black hole would be unable send signals back to us. Once it passed the event horizon nothing could escape the force of gravity and return to us. Another reason is the force of gravity would be so strong that it would destroy anything sent into it. However, the theory behind a black hole matches the basic concept and observations we have of them. It also matches what we think happened at the Big Bang.
In effect the beginning of the universe was a very hot singularity. The heat was caused by the density of matter. When it expanded the temperature of the universe should have cooled (It cools by half as the size doubles). In the interim, the particles exploding out of the singularity have so much energy they can escape into the universe. As they cool and lose energy they can begin to clump together and form matter. Those that strike each other before they cool have enough energy to either create new particles or annihilate each other. Eventually the universe cooled enough that we have particles clumping together to form planets and gas clouds and stars. Why did the universe form the way it did? That leads into the theories of chaotic boundary conditions or the anthropic principles. Chaotic boundary theory says either the universe is infinite in Boundary or there are an infinite amount of universes and we just don't see them. The anthropic principle has two forms, weak and strong. The weak anthropic principle says the universe is infinite in space and/or time but there are finite regions in it. These finite regions are set up so certain conditions would prevail. In our case the conditions are perfect for our kind of life. In other words, we shouldn't wonder why our universe is set up where life like ours would exist because if it didn't we wouldn't be here to ask the question. The strong anthropic principle is that all of creation came about with just the right values to create life. For example electrons have an electric charge that is constant throughout the universe. If that charge had been different by even a small amount then stars wouldn't be able to burn hydrogen into helium and the universe as we know it wouldn't exist. Therefore humans wouldn't exist but some other life form that conceivably is asking the same questions we are.
So how does this all add up? What Professor Hawking has done is discuss the basic background of all of the currently accepted theories of how the universe works. He went into the history of these theories. He went into the discussion of the people involved and what they added to this pool of knowledge. This knowledge is based on observation and repeatable experiments. It has lead to tow complementary theories that don't quite mesh but are as close as we have come to understanding the universe in enough detail that we can predict what will happen. Through it all Professor Hawking has given us detailed insights into these theories. He has done it in laymans terms so that anyone interested can read this book and get an understanding of what are the basic theories. For this alone it is an excellent work. However it is also well organized. Every section is about a certain topic, clearly stated, and how that topic integrates into the whole of the book. Examples and humor help to make these topics even more understandable. The end of the book then takes everything discussed and puts it together into a unified picture. There is even a small biography on the principle players in modern pphysics and a glossary of relevant terms in the book. I found it to be clear, concise, and understandable. The only part I didn't understand really well is as much a limitation of my ability to conceptualize the theory as the way the subject was written. While he book is now ten years old and somewhat out of date, it is an excellent starting point for anyone wishing to understand the fundamentals of our universe.