A singular theory

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The last 50 years have seen a myriad of -so far- unsuccessful attempts at unifying General Relativity and Quantum Field Theory. Loop Quantum Gravity is one of them, even though not by far the most favored amongst physicists. The theory postulates space is actually made of tiny loops which connect to each other, eventually building the whole universe we see.

Along with some of Lee Smolin’s books -i.e. The trouble with Physics– Bojowald does a pretty good job of explaining the intricacies of a theory which is still in the baking. He explains how Quantum Loop Gravity can be used to analyze the Singularity at the Big Bang and make it disappear; then, he rises the astonishing possibility that the Big Bang may just have been an intermediate phase between two universes.

Bojowald’s book is dense in some parts, fascinating in others. Sometimes one misses a little more detail in the explanation, even though that has probably more to do with Quantum Loop Gravity not being a complete theory than with Bojowald’s explanatory skills. Some of the theory’s ideas will be difficult to accept for physicists: for example, the fact that his equations are not (explicitly, at least) covariant and time has a special status, which conflicts with the lessons learned from General Relativity, or its prediction of a non-constant speed of light. These apparent weaknesses, however, may be in fact a blessing, for right now Quantum Loop Gravity is the only theory which actually makes any testable predictions about our universe and, thus, brings a ray of hope to the increasingly frustrating field of theoretical Physics.

The last sections, with discussions on the nature of time and even a brief historical overview of Cosmology, may be a little basic for physicists with some knowledge of their discipline’s history, but will be enjoyed by the great majority of the general public.

In general, this book can be enjoyed by anyone, and is especially recommendable for people with some background of popularized Physics who want to expand their horizons and get to know the new candidate for a Unified theory.

Martin Bojowald. Once before time: a whole story of the universe. Random House. New York, 2010. 320 pages.

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