Excerpt from Starfarers by Poul Anderson, plus links to reviews, author biography & more

Planning and a sketchy run­through had gone before, and the business went more smoothly than might have been awaited. But then, it offered a brief escape from what was outside.

After the cameras had scanned the book­lined room, the battered desk, the portrait of Einstein, while Fleury gave her introduction, "­scientist, mathematical physicist, as famous as he is modest. We'll discuss his latest and greatest achievement. . . " they moved in on her and him, seated in swivel chairs. A projector spread a representation of the galaxy behind them, ruddy nucleus and outcurving blue­tinged spiral arms, awesome athwart blackness. Somehow his slight frame belonged in front of it.

She gestured at the grandeur. 'Alien spacecraft traveling there, almost at the speed of light," she said. "Incredible. Perhaps you, Dr. Olivares, can explain to us why it took so long to convince so many experts that this must be the true explanation."

"Well," he replied, "if the X­ray sources are material objects, the radiation is due to their passage through the gas in interstellar space. That's an extremely thin gas, a hard vacuum by our standards here on Earth, but when you move close to c ­ we call the velocity of unimpeded light c - then you slam into a lot of atoms every second. This energizes them, and they give back the energy in the form of hard X rays."

For a minute, an animated diagram replaced the galaxy. Electrons tore free of atoms, fell back, spat quanta. The star images returned as Olivares finished: "To produce the level of radiation that our instruments measure, those masses must be enormous."

"Mostly due to the speed itself, am I right?" Fleury prompted.

Olivares nodded, "Yes. Energy and mass are equivalent. As a body approaches c, its kinetic energy, therefore its mass, increases without limit. Only such particles as photons, which have no rest mass, can actually travel at that velocity. For any material object, the energy required to reach c would be infinite. This is one reason why nothing can move faster than light.

"The objects, the ships, that we're talking about are moving so close to c that their masses must have increased by a factor of hundreds. Calculating backward, we work out that their rest masses ­ the masses they have at ordinary speeds ­ must amount to tens of thousands of tonnes. In traditional physics, this means that to boost every such vessel, you would have to annihilate millions of tonnes of matter, and an equal amount to slow down at journey's end. That's conversion on an astrophysical scale.

Scarcely sounds practical, eh? Besides, it should produce a torrent of neutrinos; but we have no signs of any."

Fleury picked up her cue. 'Also, wouldn't the radiation kill everybody aboard? And if you hit a speck of dust, wouldn't that be like a nuclear war head exploding?"

A jet snarled low above the roof Thunder boomed through the building, Cameras shivered in men's hands. Fleury tensed. The noise passed, and she found herself wondering whether or not to edit this moment out of the tapes.

"Go on, please," she urged.

Olivares had glanced at the galaxy, and thence at Einstein. They seemed to calm him. "Yes," he told the world. "There would have to be some kind of ­ I'm tempted to say streamlining. The new spaceborne instruments have shown that this is indeed the case. Gas and dust are diverted, so that they do not encounter the object itself, but flow smoothly past it at a considerable distance." An animation represented the currents. The ship was a bare sketch. Nobody knew what something made by nonhumans might be like. "This can, in principle, be done by means of what we call magnetohydrodynamics."

Excerpted from Starfarers by Poul Anderson. Reproduced with the permission of the publisher. Published by Tor Books. No part of this book can be reproduced without permission from the publisher. Copyright (c) 1998 Poul Anderson,