new theories of everything
Barrow discusses whether we have any reason to expect that the basics of the universe are describably in terms of a few simple equations. Isn't it possible that there is layer upon layer of complexity, or that we would be unable to comprehend the ultimate nature of the universe? Barrow looks at the analogy of Gödel's incompleteness theorem. He goes on to examine how much of what we see can be deduced from the laws of nature, and how much is a result of the initial conditions, or of broken symmetries introducing random effects. There is a chapter on the constants of nature - can we expect a theory of everything to explain their values? Maybe they aren't constant after all. Barrow also considers anthropic principles and what they can explain. Later chapters look at how much of the complexity of what we see might be explicable from simple underlying rules and how much needs some other form of explanation, such as self-organisation.
This book may well not be what you would expect from the title. Barrow mentions string theory, but doesn't go into great detail, and there's nothing about competing theories such as loop quantum gravity. If that's the sort of thing you're looking for then you'll probably think that this book is too philosophical and rambling. It's best suited to those who like a wide ranging discussion of a topic, linking it to many different subject areas.