Am höchsten bewertete positive Rezension
We still don't know what it is.
am 19. November 1998
If you've ever wondered what is time, where did it come from, does it flow, why does it seem to go in one direction, will it have an end, or is it slowing down, you'll not find your answers in Paul Davies' book "About Time." Neither are you likely to find your answers anywhere else. For me, the most profound knowledge that came from reading Davies' book is the reminder that we really don't know what time is. We live in it, experience it, but really - on a fundamental level - fail to comprehend it.
Davies has subtitled his book "Einstein's unfinished revolution," and he does an excellent job of exposing the reader to some of the unexpected (from a common-sense point of view) conclusions we draw about time from the special and general theories of relativity. He offers an interesting historical perspective on the life of Einstein, and how he developed his theories. Davies also provides some interesting background on experiments that have validated Einstein's space-time, reviewing the qualitative results from some of the more important experiments.
After this introduction to the non-universal time of relativity, Davies takes us to the ultimate time machine: black holes. He offers some interesting explanations about what an imaginary traveler to a black hole might see looking out, and how we - looking in - might view the hapless victim as she neared the event horizon.
As the book progresses, conclusions and examples become less and less concrete. Relative time is a proven fact, and most physicists consider black holes a foregone conclusion. From there, Davies takes us to the very root of some of the biggest issues in cosmology: the origin of time and the age of the universe. Davies clearly believes there are problems with the current Big-Bang theory of the universe, and proposes Einstein's cosmological constant as one possible solution.
Things get weirder still. From cosmology he moves to quantum time and the implications of tunneling and EPR experiments. There is some brief mention of Hawking's imaginary time and, of course, no book on time would be complete without a chapter on possible time travel. Davies looks at all the possibilities, and some of the discussions and speculation runs wild.
For the most part I really enjoyed this book. It is well written, and clear, but sometimes the author fails to define terms properly. He appears to use the term "timewarp factor" synonymously with "time-dilation factor" but the formula on page 58 disagrees with the top figure on page 61. Also, in his discussions about problems with the Big Bang theory, I felt the author failed to give sufficient coverage to inflationary models of the universe that might resolve some of the issues he raised.
Overall, Davies' book is worth the time to read it. It may not answer all the deepest questions about time, but it will help you appreciate how little of the subject we truly comprehend. I'd also recommend his book "The Last Three Minutes."