Best Hard Science Fiction Books

Are you the type of person that likes your science fiction heavy on the science? Get annoyed by the hand-waving attempts to allow for faster-than-light travel or inter-species breeding? We've got a run-down of the top twenty five hard science fiction books that are exactly what you're looking for.

For those who don't recognize the term, hard sci fi is a subgenre of science fiction that puts the focus on the science - lots of technical detail, realistic explanations and maybe if you're lucky, one or two equations! 

Now that's not to say it doesn't invent anything new, and it certainly doesn't mean you have to reject anything that might conceivably throw a spanner in the works (speed of light constant, I'm looking at you) but whatever it does, it has to be theoretically possible and make sense given known constraints. Sound like your sort of thing? Right, on with our list!