The Great Time Machine Hoax
Keith Laumer
 Chester W. Chester IV inherits a run-down mansion and millions in back taxes. In order to pay the taxes, he initially decides to auction off the mansion and its contents, including a massive computer (the Generalized Nonlinear Extrapolator, or "Genie"). However, while examining the mansion and the computer with his friend Case Mulvihill, he finds the computer can solve complex problems involving historical fact and display realistic images of them. He hits on the idea of using its capabilities to create an elaborate hoax ... a fake time machine. Accordingly, he asks the computer to show him "real, three-D, big as life dinosaurs and plenty of em - and how about a four-wall presentation?" The computer asks if it should employ a method of doing so that "is a purely theoretical approach, which might prove simpler, if feasible, and would perhaps provide total verisimilitude..." Chester tells the computer to "go to it" and the computer does. However, the computer has managed to actually transport the two through time, and on their second trip back, before they realize that they actually do have a time machine, they make the mistake of leaving their arrival area, and become trapped in the past. Even when they manage to return to the present, their actions in the past have altered it completely, but they are able to use the computer to (perhaps, more or less) restore everything to the way it was.