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 ...