I've enjoyed Joe Haldeman's work for many years. I even have a couple of his Attar the Merman books written under some pen name or other. So when a friend recommended this book, I picked it up.
Matt Fuller is a grad student at MIT and kind of a loser. He's never going to finish his dissertation, which he realizes isn't much good, anyway. But then he accidentally discovers a time machine. It works only in one direction, and each time it leaves, it goes farther into the future. He tries it with a turtle, and then, when things go downhill for him, he goes himself. After that, he lands in a number of different futures, and in one of them he falls for Martha, who accompanies him on his next trip and gives him a chance to grow up a little. What Matt really wants to do is get back to his own time, but no society he lands in has the capability to send him there. At least not until he lands in a far-distant future.
I wouldn't want to spoil the fun by telling you what goes on, but I'll give you one thing: Matt has a troubling encounter with Jesus. There are more surprises along the way, too.
I saw this novel on the Locus list of recommended books, and Haldeman's effortless prose and satirical take on the various futures makes if fun to read.