Tau zero - Poul Anderson

Fifty men and women set out in the twenty-third century from Earth aboard an interstellar craft to travel to a planet some thirty light-years away. The ship will approach the speed of light and so (as Einstein predicted) subjective time on board will slow and so the journey of several decades will be of much shorter duration for the crew.

But the ship's deceleration system is irreparably damaged when it hits a cloud of interstellar dust and acceleration continues toward light speed, tau zero. Soon the ship is speeding through galaxies and eons are passing on board the ship in the blink of an eye ...