The Accidental Time Machine — Joe Haldeman

Grad-school dropout Matt Fuller is toiling as a lowly research assistant at MIT when, while measuring quantum relationships between gravity and light, his calibrator disappears -- and reappears, one second later. In fact, every time Matt hits the reset button, the machine goes missing twelve times longer.

After tinkering with the calibrator, Matt is convinced that what he has in his possession is a time machine. And by simply attaching a metal box to it, he learns to send things through time -- including a pet-store turtle, which comes back no worse for wear.

With a dead-end job and a girlfriend who has left him for another man, Man has nothing to lose by taking a time-machine trip himself. So he borrows an old car, stocks it with food and water, and ends up in the near future -- under arrest for the murder of the car's original owner, who dropped dead after seeing Matt disappear before his eyes. The only way to beat the rap is to keep time traveling until he finds a place in time safe enough to stop for good. But such a place may not exist...