After reading this book, the first thing I did was to go and look up the author to see if Asaro knew what she was talking about.
She has an MA in physics from Harvard and her publications include - "Complex speeds and special relativity," Catherine Asaro, Am. Jour. Phys. April 1996
So, I think I'll read the space propulsion section of the book more carefully next time around - because this is a book that would repay a second reading even without the physics.
The novel has a few minor glitches in the writing style, especially early on when there's rather more 'telling' than 'showing'. This soon smooths out a lot, and besides, it was her first novel.
This novel shows us a complex future in which empathic abilities are closely tied into the operation of ftl craft. This creates a cruelly ironic world where the people necessary to be the really high-tech military are also those who most feel the pain of another person's death.
Asaro works this neatly into her work and this alone would make a good novel. However, what I really enjoyed was that she wrote a romance that avoids the clichés. There was a point early on where I groaned and thought: "Oh Lord, standard romance cliche number four coming up - and it didn't happen!" I found the avoidance of the clichés greatly increased my enjoyment of the book as I was unable to predict what would happen next.
This is a book that I'll happily recommend to anyone who wants hard SF with a dash of romance.
Primary Inversion can be legally read online