Gods Themselves — Isaac Asimov

In the twenty-second century Earth obtains limitless, free energy from a source science little understands: an exchange between Earth and a parallel universe, using a process devised by the aliens. But even free energy has a price. The transference process itself will eventually lead to the destruction of the Earth's Sun -- and of Earth itself.

Only a few know the terrifying truth -- an outcast Earth scientist, a rebellious alien inhabitant of a dying planet, a lunar-born human intuitionist who senses the imminent annihilation of the Sun. They know the truth -- but who will listen? They have foreseen the cost of abundant energy -- but who will believe? These few beings, human and alien, hold the key to Earth's survival.