A good introduction to the subject, but still difficult to understand,
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This review is from: The Elegant Universe: Superstrings, Hidden Dimensions and the Quest for the Ultimate Theory (Kindle Edition)
This book by Brian Greene, a professor of physics and mathematics, is focussed on string theory. Regrettably, it's a book I wasn't able to finish because I found it got more and more complicated as it progressed. It started off well with some excellent explanations of quantum theory and relativity, although most of this I was already familiar with. It then progressed to string theory, and the first few chapters, all covering new ground for me, were well presented. However, I started to get into difficulties as the author tried to explain how the five different string theories may all be variants of a single theory. I struggled to follow much of this and gave up part way through chapter 12, so I didn't make it to understanding M-theory. Consequently, I never got to read the subsequent chapters on black holes or cosmology.
I could have struggled on but one factor in the back of my mind was that the Kindle edition I was reading, which was purchased from Amazon in January 2014, was derived from a book published as long ago as 2000 so I felt it was likely that string theory would have moved on since then. Consequently, I was conscious that some of the more advanced concepts may have been updated or replaced in the intervening years and I might have been wasting my time trying to understand something that was no longer considered valid. These thoughts were somewhat demotivating.
But from what I learnt, or at least as it was understood in around 2000, string theory is highly theoretical, with only approximate (and usually multiple) solutions to what are sometimes just approximate equations. There is no strong experimental evidence to support the theory, and neither is the theory of much value in predicting experimental results. Nevertheless, the theory does try to make sense of, and rationalise, the numerous fundamental particles making up the standard model. It also seeks to unite quantum theory with general relativity and gravity. It therefore has the potential to solve problems that have faced physics since the quantum and general relativity theories were first formulated in the early 20th century.
It's undoubtedly a complex theory but Greene does a good job of explaining much of the basics. I particularly liked the way that for many tricky concepts he explained them from two different angles, often using analogies. Therefore, I found that if I didn't quite understand one explanation, there was often a second explanation from a different perspective that made more sense to me. I found this double attack approach very useful for enforcing many of the basic ideas.
String theory requires more dimensions than we are familiar with in our everyday lives, these extra dimensions being very small and curled up. It's difficult to visualise what this means but Greene provided an excellent (although simplified) explanation of these curled up dimensions using the example of an insect walking along a hose pipe, where the length of the hose pipe represents a dimension we're all familiar with, and which can be seen from afar, but the cylindrical cross-section of the hose pipe is a curled up dimension, only visible from close-up.
Although I didn't manage to finish it, I'm still awarding this book 4 stars because I doubt that many authors could better Greene's treatment of this difficult subject. His approach is entirely non-mathematical, which is a challenge for a theory based entirely on mathematics, yet he manages to present many complex ideas in an understandable manner.
Looking on Amazon today I discover that the 2000 Kindle edition I was reading has been replaced by a 2011 edition. A sample I downloaded looks very similar to what I've already read but I'm wondering if some of the chapters may have changed.