On the Equality of All Things - Carlo Rovelli ****

There is a wide gulf between the worldviews of physicists and philosophers. Many physicists present a rather sweetly naive, child-like view of the world, where philosophers bring a distinctly more adult, cynical tone. This being the case, it can be a little worrying when a physicist dips a toe into the philosophical mire. Infamously, in The Grand Design, Stephen Hawking and co-author Leonard Mlodinow told us that philosophy was now dead because science could deal with anything it had previously been needed for.

Thankfully, Carlo Rovelli is not trying to do away with philosophy, though it has to be said that when he veers into the topic that physicist's naivety can make it feel like the philosophising of an earnest eighteen-year-old. Take the opening paragraph, which tells us 'electrons and minds, stones and laws, judgements and galaxies do not essentially differ in nature from one another. They are notions that illuminate each other'. I almost expected a Pink Floyd soundtrack. But though Rovelli doesn't say philosophers are redundant, he does delight in telling them they're wrong, for example 'I feel there is a whole branch of contemporary philosophy that is trapped inside this mistake. The mistake is to believe that the concepts we have are necessarily adequate for understanding reality, even beyond the context in which these concepts were shaped.'

It might seem, given this concern, that I've over-rated the book, but where he primarily focuses on the physics - which is more of the book than you might think, Rovelli absolutely deserves those four stars. Admittedly, as always, his presentation of physical theory does not give us an objective broad picture of the current debates, but only his own personal viewpoint - but he does that very well and approachably, giving considerably more detail than he has often done in these short books.

One major basis of his thesis is the relational interpretation of quantum theory, which builds on the idea that very few physical observations can be made in isolation - we always have to consider a physical system in its context. (This feels very much in opposition to the traditional physics approach of pretending we can deal with perfect isolated systems.) Inevitably this also brings in relativity. It was particularly interesting comparing Rovelli's section on 'the flow of time' with some very different views in Jim Al-Khalili's recent On Time.

Occasionally things seem to go a little adrift. At one point we are told that there is no such thing as absolute certainty of anything - effectively, there are no facts. Can’t I be certain that my entire body is not currently inside my own stomach? Even Rovelli seems not to be convinced by his own statement as soon after he states a physical observation is a 'fact'.

All in all, for me despite the dips into philosophical noodling, this book had far more meat to it than most of Rovelli's compact hardbacks. Probably his best book yet.

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Review by Brian Clegg - See all our online articles or subscribe to a weekly email free here