This book is excellent. The science is tight, mixing elements of physics and biology into an intelligible, compelling problem. And the plot, pacing and characterization are dead on.

The story is set in two time frames: 1962-1964 and 1998. In 1998, an environmental disaster is tearing Earth apart. Two scientists believe they can contact the past and possibly prevent the disaster, but all available funds for scientific research are being spent on the crisis. They beg, plead and scavange for resources and support in an increasingly tense social and political climate. In 1962-1964, a young assistant professor is struglling to establish his academic career, in the face of heavy competition from older professors and industry bigwigs. In both time frames, the story concentrates on the social and political problems that prevent and/or encourage the various scientific endeavors.

Benford takes the literary tale a further step, and uses the social interactions among the characters to reinforce the scientific explanations. For example, in one scene, a possible shift in time is explained in terms of physics, and then one observer experiences a physcial sense of the world buckling around him. This style works quite well: the fiction and science work together to tell the tale.

This book was first published in 1980, so there are a few things Benford imagined wrong about 1998. But these don't in any way detract from the story, and other than those few instances, nothing about the book feels dated. I highly reccomend this book, giving it a +.