Quantum Time (Quantum Series) / Phillips, Douglas

Everyone knew time travel was impossible. Then reality intruded.

A dying man stumbles into a police station and collapses. In his fist is a mysterious coin with strange markings. He tells the police he’s from the future, and when they uncover the coin’s hidden message they’re inclined to believe him.

Daniel Rice never asked for fame but his key role in Earth’s first contact with an alien civilization thrust him into a social arena where any crackpot might take aim. When the FBI arrives at his door and predictions of the future start coming true, Daniel is dragged into a mission to save the world from nuclear holocaust. To succeed, he’ll need to exploit cobbled-together alien technology to peer into a world thirty years beyond his own.

The third book of the Quantum series goes far beyond extra dimensions of space to expose the curious paradoxes of time in a wild ride along the edges of scientific knowledge.