Poul Anderson had a strange tendency. When his story could be made into a long novel, he made it small (like this one). On the other hand, when his story could be told in 100 pages (boat of million years) he bloated it into something like 600 pages. This story is of course something poul wrote in 2 months, or rather 1, probably to pay a mortgage or smt. It is a little promising, a little of a pager turner and not much more. The notion of the all male/all female spaceships is dated. The deus ex machina earth physicist who discovers the new physics is a very tired and used to death platitude to overcome SF problems. The aliens are too terrestrial. So, read this only if you don't have to pay for it. But better, skip it for Anderson's best novel Tau Zero.