Quantum Space: Jim Baggott *****

There's no doubt that Jim Baggott is one of the best popular science writers currently active. He specialises in taking really difficult topics and giving a more in-depth look at them than most of his peers. The majority of the time he achieves with a fluid writing style that remains easily readable, though inevitably there are some aspects that are difficult for the readers to get their heads around - and this is certainly true of his latest title Quantum Space, which takes on loop quantum gravity.

As Baggott points out, you could easily think that string theory was the only game in town when it comes to the ultimate challenge in physics, finding a way to unify the currently incompatible general theory of relativity and quantum theory. Between them, these two behemoths of twentieth century physics underlie the vast bulk of physics very well - but they simply can't be put together. String theory (and its big brother M-theory, which as Baggott points out, is not actually a theory at all but simply a conjecture) has had much written about it. But the main alternative theory, loop quantum gravity has had far less coverage. As I mentioned in another review (and Baggott also picks this up), in one whole book on gravity, loop quantum gravity is only mentioning in an endnote. Yet in many ways, loop quantum gravity has a lot more going for it than string theory.

One major strand of Quantum Space is a biography of two key players in the field - Lee Smolin and Carlo Rovelli, both good writers for the general public in their own right, but neither has been able to come close to what Baggott does in trying to make the ideas of loop quantum gravity accessible at a deeper level than a summary, hand-waving description. It’s also the first complete and approachable account I’ve seen of how both approaches to a quantum theory of gravity were derived. The only downside of the way it's structured is that I think if you’re going to be comfortable with the level of detail Baggott gives, you probably don’t need the first 100 pages or so giving background on quantum theory and general relativity.

My only real concern apart from that unnecessary opening material, which makes the book a little too long for my tastes, is that there could have been more unpacking of how loop quantum gravity represents reality - the jump from the introduction of spin networks to anything resembling a theory that can be applied to a real world where things happen is overwhelming. I had to resort to the much valued advice of one of my supervisors at university who said 'Don't worry if it doesn't all make sense, just keep on with it and hopefully it will all come together.' It almost all did all come together, but I was left with a nagging doubt that I couldn't really grasp the foundation of the whole idea.

As well as coming out of reading this book with significantly more respect for Rovelli (whose popular science writing I find flowery and overrated), I feel that Baggott has done a huge favour for anyone who really wants to understand modern theoretical physics, giving a much better understanding of this fascinating attempt to deal with a central requirement to explain the workings of our universe. It's a triumph.

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Review by Brian Clegg