Pebble in the Sky

By Isaac Asimov

Joseph Schwartz was just a regular guy, a retired tailor living in Chicago who found himself, through no fault of his own, catapulted 50,000 or more years into the future and, again through not fault of his, embroiled in a deadly plot to overthrow galactic government.
Coming from the past to an Earth that is now radioactive and partially ruined, Schwartz finds nothing recognizable and doesn't even figure out until quite a bit later that he is in the future and on Earth. He falls into the hands of an enterprising scientist who subjects Schwartz to a medical procedure that vastly improves Schwartz's intelligence, even to the point of giving him the power to read people's minds.
The people of Earth live in virtual quarantine, viewed as pariahs by the civilized worlds of the galaxy. Because of Earth's degraded environment, population is strictly controlled with only a very few exceptional individuals allowed to live past their sixtieth birthday. Everyone else at that age is killed to make room for the next generation. It is not a happy world and the galactics just ignore the misery of people on Earth. Plus they refuse to admit the humankind originally came from Earth. All of this creates great resentment on Earth.

This was an OK book. I found some parts of it a bit dull and the plot against galactic government didn't make much sense to me. But other than that it was interesting reading about Schwartz finally getting a handle on where he was and what was going on and learning to use his new mental powers to help himself and his friends.