Then last novella written by Arthur C Clarke, one of the greatest writers of the classic science fiction age, ended with almost an open invitation. Its protagonist, Howard Falcon, half man, half machine was to be an ambassador between humanity and a machine culture, which was not the focus of that story, “in the troubled centuries that lay ahead”. Two of the biggest names in the British sci-fi scene have taken up the challenge of chronicling those troubled centuries. Baxter, off the back of his Long Earth series written jointly with the late Sir Terry Pratchett, and Reynolds revisiting some of the themes from his recent space opera trilogy – Poseidon’s Children. The first thing to say about The Medusa Chronicles is that, without being slavish, Baxter and Reynolds have tried to capture the feel of 1960s science fiction. Although it dips heavily into some ideas from modern physics, the book has a ’60s feel. This is both to their credit and, ultimately to the book’s detriment. The whole narrative exists in an altered imagined future in which a joint space effort in the late ’60s to avoid global disaster kickstarted a much more vigorous space exploration program, landing a…