"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.