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Kip Thorne’s Black Holes and Time Warps is an essential paperback (Papermac, £10, ISBN 0 333 63969 3). He examines Einstein’s inheritance in the hands of his followers in lucid and clear prose: for example showing the problems and pleasures of estimating the enormous randomness of black holes; why it makes sense to treat them as membranes; time travel; and the chancy nature of reality, conditioned, as the poet Lawrence Durrell had it, by one’s position in space and time. One step in either direction, and reality changes.