A good book by GregEgan, ISBN:006105481X

It starts off with questioning our reality after testing a downloaded person in a simulation.  The gist is that after each simulation has ended it seems as if it is still going on creating realities that are more and more suspicious for the main character.  Finaly deciding that the simulations do infact keep on going after they are stopped he embarks on a grand project to simulate a computer architecture that is self replicating without limit and downloads some who wish to live forever and initiates the brief simulation.

Of course the fun comes into it in that there are a couple of hitchhikes as well as one of the people downloaded runs a sim in the sim of an entire (if simplified) self consistant universe with the goal of evolving life.

[A fair while since I read this so could someone who has it more fresh please re-flesh it out --AndrewMcMeikan]

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