Three roads to quantum gravity. (Q2735599)

This book contains almost no formula, but a lot of figures, one of them relates the notion of causality with the fall of the Berlin Wall. Nevertheless, it is not a popular book in the classical sense: In principle, the reader should know the formulas not written in this book to understand the words written by Smolin, or the reader simply wants to see what kind of questions are discussed in the search for quantum gravity. One learns, for instance, that the ``Ashtekar formulation of Einstein's theory'' is due to Amitaba Sen; but this is, nevertheless, not a misnomer, because Abhay Ashtekar was the one person to take Sen's equation seriously.NEWLINENEWLINENEWLINEFrom the topics covered, the part on canonical loop quantum gravity is the easiest to follow: The graphs given to present spin networks are drawn; the edges of the graphs are labeled by numbers representing the spin of the corresponding particles. Each spin network represents one possible quantum state for the geometry of space. The nodes of the graph carry discrete units of volume.NEWLINENEWLINENEWLINEOther discussed approaches include Roger Penrose's twistor theory, string theory, M-theory, and Alain Connes's noncommutative approach to geometry.