The Hugo and Nebula Award-winning novel.

In the year 2100, the invention of the Electron Pump - an apparently inexhaustible supply of free energy - has enabled humanity to devote its time and energies to more than the struggle for survival, finally breaking free of the Earth.But the Electron Pump works by exchanging materials with a parallel universe, and such unbalancing of the cosmos has consequences. Humans and aliens alike must race to prevent a vast nuclear explosion in the heart of the Sun - and the vaporisation of the Earth exactly eight minutes later…