The Causal Angel by Hannu Rajaniemi (3.5 stars)

The final in the trilogy started by the fantastic Quantum Thief. Unfortunately neither of the subsequent books could match the first, and this is the weakest of the three. My view is somewhat coloured by having 3 years in between the Fractal Prince and my reading of this book, and I hate re-reading.  So I went into the complicated Hannu-verse cold...and it's not the sort of book you want to do that with.

Nonetheless, I pushed on and remembered most of the important points, but I'm sure I missed plenty of references. The book is full of action, is incredibly complicated, and has zero exposition. I'm a big fan of this style of book in general, but I felt like Hannu lost control of his ability to put the ideas in his head down on paper in a way that someone else can actually comprehend. I'll admit to being completely confused about what is a simulation, who has a body, what weapons are physical/virtual, what is happening in the physical universe, and even if this entire story is part of a larger simulation.

Partly this is the point, that the physical universe matters less than the virtual. But when characters and copies of characters are constantly shifting around in, and creating, nested virtual realities it is really, really confusing, to the point where I essentially stopped caring.

There's some nods to physics nerds and sci-fi fans, which are entertaining:

And it seems some people can’t tell their Fitzgerald from their Lovecraft. So don’t be surprised if you see a few flapper Deep Ones tonight.

It was an idea they already thought of in the twentieth century, that spacetime could compute. They tested it, in the last days of the Large Hadron Collider, when they learned how to make tiny black holes. Encode computations into their event horizons, then probe the information paradox by smashing them together, see if quantum gravity is more powerful than Turing Machines or their quantum cousins. Something to do for the humming LHC, still warm from finding the first Higgs. 

Gene Wolfe-level of unexplained complexity, but with more physics.

3.5 stars