Beyond the Hallowed Sky - Ken MacLeod (The Lightspeed Trilogy Book 1)

When a brilliant scientist gets a letter from herself about faster-than-light travel, she doesn't know what to believe. The equations work, but her paper is discredited - and soon the criticism is more than scientific.

Exiled by the establishment, she gets an offer to build her starship from an unlikely source. But in the heights of Venus and on a planet of another star, a secret is already being uncovered that will shake humanity to its foundations.