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

Fleury whistled. "How can we do this?"

Olivares chuckled. "I'll leave that to the laboratory physicists, and afterward the engineers. In principle, though, it must be by means of what I'll call a quantum field gate. We can use a Bose­Einstein condensate to generate a certain laserlike effect and bring all the atoms in two parallel, superconducting plates into the same quantum state. The consequences are nonlinear and result in the creation of a singularity. Through this the energy of the substrate flows. Presumably it will distribute itself evenly through any connected matter, so that the acceleration is not felt."

"Hoo, you're right, this is kind of technical." A touch of practicality should liven it. "How does the, um, pilot get the ship headed the way he/she/it wants to go?"

'A good question," Olivares approved. "I'm glad you know the difference between a scalar and a vector. I think the velocity vector must increase or decrease linearly. In other words, when the ship acquires the new energy, she continues in the same straight­line direction as she was moving in. I'm still working on the problem of angular momentum."

"More technicalities," Fleury said ruefully. "You mentioned having this energy for a period of maybe hours. Must it then go back?"

Olivares nodded. "Yes, just as with the familiar vacuum, a loan from the substrate must be repaid. The product of energy borrowed and time for the loan is a constant. However, with the substrate the constant is immensely larger ­ a multiple of the Planck energy, which is itself enormous. The quantum field collapses, reclaiming the borrowed energy for the substrate."

"But the ship can take out another loan right away?"

"Evidently. The instruments have, in fact, detected flickerings in the X­ray outputs that correspond quite nicely to this. From the inverse proportionality of energy and time, it follows that every jump is of the same length. My preliminary calculations suggest that this length is on the order of a hundred astronomical units. The exact value depends on the local metric­" Olivares laughed. "Never mind!"

"Maybe we can talk a little about what a voyage would feel like, aboard a ship like that," Fleury proposed.

"Why not? It'll take us back to less exotic territory."

"Could you review the basic facts? For some of us, our physics has gotten kind of rusty."

"It's simple enough," Olivares said, quite sincerely. "When you travel at relativistic speeds, you experience relativistic effects. I've mentioned the increase of mass. The shortening of length in the direction of motion is another. Of course, you yourself wouldn't notice this. To you, the outside universe has shrunken and grown more massive. And your observations are as valid as anybody else's."

"What about the effect on time? I should think that'd matter most to the crew."

'Ah, yes. Time dilation. Loosely speaking, if you're traveling at close to c, for you time passes more slowly than it does for the friends you left behind you. One of those spacecraft may take several hundred years to cross the several hundred light­years between her home port and her destination. To those aboard, whoever or whatever they are, a few weeks will have passed."

Before she could head him off ­ but it could be edited out later if need be ­ Olivares continued: "The new theory modifies this a bit. If you travel by way of the quantum field gate, you never get the full time dilation you would if you accelerated to the same velocity by ordinary, impossible rocket means. However, at high energies the difference becomes too small to be worth thinking about. Contrastingly the less energy you borrow from the substrate, the worse the ratio is. You could take an extremely long time by your clocks ­ theoretically forever ­ to transit the fixed distance of a jump at an ordinary speed. You'd do better to use a regular jet motor.

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,