Book review: A Brief History of Time (2017 edition), by Stephen Hawking

Read 6/23/2024–7/2/2024

Review title: Nice overview of cosmology and its development

As one would expect of a book that spent many weeks on the New York Times best-seller list, this book is well written, descriptive but not too technical, and sprinkled with humor. It is just over 200 pages long and introduces the reader to the history of the development of modern cosmology as well as the author’s discoveries and involvement in the discipline. Readers will learn about important discoveries and how they shape our modern understanding of the universe. I especially appreciate how faith-friendly the author is, respectfully allowing room for Christians and other theists to infer God’s Providence in the universe. I also found Hawking’s attitude delightful given his sizable contribution to this field of study, full of wonder and excitement for learning, rather than arrogant or condescending.

Chapter 1: Our Picture of the Universe

“The concept of time has no meaning before the beginning of the universe. This was first pointed out by St. Augustine. When asked: ‘What did God do before he created the universe?’ Augustine didn’t reply: ‘He was preparing Hell for people who asked such questions.’ Instead, he said that time was a property of the universe that God created, and that time did not exist before the beginning of the universe.’” p8. “One may say that time had a beginning at the big bang, in the sense that earlier times simply would not be defined.” p9. “They would say that God, being omnipotent, could have started the universe off any way he wanted. That may be so, but in that case he also could have made it develop in a completely arbitrary way. Yet it appears that he chose to make it evolve in a very regular way according to certain laws. It therefore seems equally reasonable to suppose that these are also laws governing the initial state [of the universe].” p11.

Chapter 2: Space and Time

“Newton’s laws of motion put an end to the idea of absolute position in space. The theory of relativity gets rid of absolute time.” p34. “Space and time are now dynamic quantities: when a body moves, or a force acts, it affects the curvature of space and time — and in turn the structure of space-time affects the way in which bodies move and forces act.” p34.

Chapter 3: The Expanding Universe

“Our modern picture of the universe dates back to only 1924 when the American astronomer Edwin Hubble demonstrated that ours was not the only galaxy.” p38. “We live in a galaxy that is about one hundred thousand light-years across and is slowly rotating; the stars in its spiral arms orbit around its center about once every several hundred million years.” p39. In 1929, Hubble published his findings that “the size of a galaxy’s red shift is not random, but is directly proportional to the galaxy’s distance from us. … And that meant that the universe could not be static, … but is in fact expanding; the distance between the different galaxies is growing all the time.” p41. The Cosmic Microwave Background Radiation discovered in the mid-60s is from the early hot dense universe. “The expansion of the universe meant that this light should be so greatly red-shifted that it would appear to us now as microwave radiation.” p44. “So in the end our work became generally accepted and nowadays nearly everyone assumes that the universe started with a big bang singularity. It is perhaps ironic that, having changed my mind, I am now trying to convince other physicists that there was in fact no singularity at the beginning of the universe — as we shall see later, it can disappear once quantum effects are taken into account.” p53.

Chapter 4: The Uncertainty Principle

“In general, quantum mechanics does not predict a single definite result for an observation. Instead, it predicts a number of different possible outcomes and tells us how likely each of these is. … Indeed, it has been an outstandingly successful theory and underlies nearly all of modern science and technology. … The only areas of physical science into which quantum mechanics has not yet been properly incorporated are gravity and the large-scale structure of the universe.” p58. “We do not yet have a complete consistent theory that unifies general relativity and quantum mechanics, but we do know a number of the features it should have.” p63.

Chapter 5: Elementary Particles and the Forces of Nature

“Force carrying particles can be grouped into four categories according to the strength of the force that they carry and the particles with which they interact. … Ultimately, most physicists hope to find a unified theory that will explain all four forces as different aspects of a single force.” p72. “However, just as in the case of the electromagnetic and weak unified theory, there are low-energy consequences of the theory that can be tested.” p77. Experiments have shown that the laws of physics are not quite the same for particles and antiparticles; they are not completely symmetrical.

Chapter 6: Black Holes

“The event horizon, the boundary of the region of space-time from which it is not possible to escape, acts rather like one-way membrane around the black hole.” p92. “General relativity predicts that heavy objects that are moving will cause the emission of gravitational waves, ripples in the curvature of space that travel at the speed of light.” p92. “Black holes are one of only a fairly small number of cases in the history of science in which a theory was developed in great detail as a mathematical model before there was any evidence from observations that it was correct.” p95.

Chapter 7: Black Holes Ain’t So Black

“Quantum theory tells us … that the particles [radiated from black holes] do not come from within the black hole, but from the ‘empty’ space just outside the black hole’s event horizon.” p109. This radiation is equivalent to the entropy of the black hole and proportional to its mass.

Chapter 8: The Origin and Fate of the Universe

“He [the Pope] told us 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.” p120. About the hot big bang model Hawking says, “This picture of a universe that started off very hot and cooled as it expanded is in agreement with all the observational evidence that we have today.” p125. “God may know how the universe began, but we cannot give any particular reason for thinking it began one way rather than another.” p141. “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?” p146.

Chapter 9: The Arrow of Time

“The increase of disorder or entropy with time is one example of what is called an arrow of time, something that distinguishes the past from the future, giving a direction to time.” p149. Initially, Hawking thought entropy would decrease in a contracting universe. He says, “What should you do when you find you have made a mistake like that? … It seems to me much better and less confusing if you admit in print that you were wrong.” p155. “To summarize, the laws of science do not distinguish between the forward and backward directions of time. However, there are at least three arrows of time that do distinguish the past from the future. They are the thermodynamics arrow, the direction of time in which disorder increases; the psychological arrow, the direction of time in which we remember the past and not the future; and the cosmological arrow, the direction of time in which the universe expands rather than contracts.” p156.

Chapter 10: Wormholes and Time Travel

Quantum theory seems to allow for time travel on the microscopic scale. “Does quantum theory allow time travel on a macroscopic scale, which people could use? … It is not yet clear… thus the possibility of time travel remains open. But I’m not going to bet on it.” p169.

Chapter 11: The Unification of Physics

“It seems that the uncertainty principle is a fundamental feature of the universes we live in. A successful unified theory must, therefore, necessarily incorporate this principle.” pp11–172. “A necessary first step, therefore, is to combine general relativity with the uncertainty principle.” pp172–173. String theories are an attempt to unify physics but there are several proposals, none of which resolve everything. “On many occasions we have increased the sensitivity of our measurements or made a new class of observations, only to discover new phenomena that were not predicted by the existing theory, and to account for these we have had to develop a more advanced theory.” p184.

Chapter 12: Conclusion

“We now know that Laplace’s hope of determinism cannot be realized, at least in the terms he had in mind.” p188. “The question remains, however: how or why were the laws and the initial state of the universe chosen?” p189. “Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe.” p190. “If we find an answer to that, it would be the ultimate triumph of human reason — for then we would know the mind of God.” p191.

Next in the book are very short biographies of Einstein, Galileo, and Newton followed by an appendix, glossary, acknowledgments, and index.

“More significantly, we have now determined that the precise pattern of variation [in the cosmic microwave background radiation] agrees with the specific predictions I and others made by combining inflation with the no boundary proposal.” p202. “Perhaps the most striking trend is one that many find uncomfortable: the no boundary proposal and eternal inflation point increasingly strongly to the idea that our universe is one of many.” p207. “Despite the vastness of the multiverse, there is a sense in which we remain significant: we can still be proud to be part of a species that is working all this out. With that in mind, the coming years should be just as exciting as the last twenty.” p208.

Although I was familiar with most of the topics discussed in this book, I found the presentation to be a very nice overview and I would highly recommend this book to anyone wishing to understand the basics of cosmology and what we know about the formation of our universe. Even more than that, I wish the general population, and especially pastors and teachers understood how the scientific process leads to the descriptions of the universe found in this book. We live in a wondrous, complex, and beautiful universe filled with amazing phenomena. I found the enthusiasm of the author contagious and I look forward to learning more.