Note: I was unaware when I wrote this review that the English-born Charles Sheffield, both a physicist and a fiction writer himself, died in November last year, aged 67.
Science Fiction and Fantasy Writers of America, Inc. published a fine obituary, while a bibliography of Dr Sheffield's prolific work is at Fantastic Fiction.

Nancy Kress dedicates 'Probability Sun' to "Charles Sheffield, founder, the Charitable Foundation for the Promotion of Scientific Literacy Among People Purporting to be Science Fiction Writers."
Who happens to be her late husband.
Then comes a potentially intimidating acknowledgement of

"a large debt to Brian Greene's fascinating Elegant Universe. Greene's explanations of superstring theory provided the bases, both factual and speculative, for the even more speculative and eccentric theories of my character Dr. Thomas Capelo."

Superstring theory? Maybe Kress's readers have reason to say thanks to Sheffield too, because she does a fine job with tough ideas.
This is the branch of physics to which friend François gave me a long lunchtime introduction at the pizzeria a while back with some dazzling designs on the tablecloth.
But to begin at the beginning, it's probability theory which lays the groundwork in Nancy Kress's stunning first in a trilogy, 'Probability Moon' (2000, Tor Books; paperback since September last year).

Kress's future is one where humanity, still divided among itself, has leapt into the far reaches of the universe not through any faster-than-light technology of our own devising, but the discovery of the first of a network of "tunnels", found beyond Neptune in the exploration of our solar system.
In the half-century following the passage of a first ship through Space Tunnel #1, the scientists and the military have made use of this legacy from a mysterious, long-gone civilisation, but with no more than a speculative grasp of how it works.
Humankind has found that it is far from alone in a universe home to more than 30 known races whose genetic make-up is very similar to our own.
With one exception.
We have been found by the Fallers and know little about them — apart from the troublesome fact that this incommunicative alien race has just one goal regarding humanity: systematically to annihilate it.

In 'Probability Moon', the human race is losing the war against genocide. Kress launches straight in with a paragraph which told me at once that this was going to be the next one to enjoy and review:

"The aide materialized beside General Stefanek at a most inconvenient moment. The girl with him was too schooled to react; she had been with her company for two years now, and it was the most popular and discreet first-class company on Titan. The girl took no notice of the intrusion, but the general lost his erection.
'I'm so sorry, sir,' the holo said, averting Malone's eyes, 'but there is a level-one message.'"

A message important enough to swing the Solar Alliance Defence Council into sending scientists to a remote, newly discovered planet on a mainly anthropological study. What the field researchers aren't told is that their trip is a cover for a military mission which could change the course of the war against the Fallers.
The people of World have a peaceful, pre-industrial civilisation, and they enjoy an inexplicable common mindset they describe as "shared reality". More intriguing still, one of the seven moons of their distant planet is a remarkable artefact, probably made by the unknown designers of the space tunnels, and conceivably a weapon of immense power.