A Brief History of Time by Stephen Hawking is about modern physics for general readers. Its aim is not just listing some topics, but introducing modern physics by examining current scientific answers, although not complete, to fundamental questions like: Where did we come from? Why is the universe the way it is? Was there the beginning of time? Is there an ultimate theory that can explain everything? We don’t have such a theory yet.
I have read the first edition when I was a high school student around 1990, and this book is the revised version (revised in 1998). Compared to the first version, there are little changes. But there is one noticeable change in his point of view on the ultimate theory. According to him, recent findings on “dualities” seem to indicate that it would not be able to express an ultimate theory in a single fundamental formation. Instead, we may have to apply different theories to different situations, but in the areas which they overlap, they must coincide.
The book has a lot of merits. Firstly, non-native English users including myself would feel comfortable and find it easy to read. He doesn’t use difficult words and his writing style is clear. In the sense, he is better than other English scientific authors like R. Penrose, J. Gleick and I. Stewart. Secondly, the level of the book is well-chosen for general readers and the total page number is just less than 200 pages. If they read the book, at least, they would be able to learn more about how the universe began, how the stars have been formed, and how we have come here as the result of the evolution of the universe. More than that, the book contains interesting stories of some Nobel Prize winners in physics with their results related to the mentioned fundamental questions. This will help readers understand the 20th century’s progress in physics.
Thirdly, among the physicists who have contributed in searching an ultimate theory, the author himself is distinguished. He showed that a black hole radiates light, so we can say that a black hole is not completely black. Up to the time he presented this theory, everyone believed that a black hole can only absorb everything around it, but radiates nothing. To find the ultimate theory, we have to consolidate general relativity and quantum mechanics, but the two theories are inconsistent in many cases. But Hawking skillfully applied both of them to black holes, and obtained the result. The physicist, L. Smolin regards his finding as a starting point toward the ultimate theory. That we can read a book where Hawking himself explains about his theory for general readers is thrilling.
As I mentioned above, this is my second reading of the book. When I first read the book as a high school student, it was impressive for him to explain that at the beginning of the universe, there was a singularity where the energy density is infinite, and so the law of physics including general relativity, cannot hold. But at the second reading, I found out that what Hawking really wanted to say was not that we cannot know the beginning of the universe, but that we need another theory that can explain the beginning by considering both general relativity and quantum mechanics. Actually, in the book, he introduces his “no boundary” theory which explains it without the singularity. But this theory has been neither verified nor disproved by experiments until now.
Here is my advice for a reader. Don’t think that you have to understand every word and sentence. Less than 200 pages, the book contains a lot of things and the author does his best in explaining them easily. For example, its explanation about the history from the beginning of the universe to the first living things on earth is outstanding. And about time travel, its arguments are ever clear and reasonable for me. But, in a few parts, the explanations are just sketchy, so if a reader is not already an expert, he could not fully understand them. When you meet such parts, just move forward. The most important thing is to learn some things and enjoy the reading.