“Certainly,” Dana said. She appeared a bit nettled, and Weinbaum decided to give her the full dose at a more rapid pace. After all, she could be assumed to be better informed than the average layman.
“What we’ve needed for a long time, then,” he said, “is some virtually instantaneous method of getting a message from somewhere to anywhere. Any time lag, no matter how small it seems at first, has a way of becoming major as longer and longer distances are involved. Sooner or later we must have this instantaneous method, or we won’t be able to get messages from one system to another fast enough to hold our jurisdiction over outlying regions of space.”
“Wait a minute,” Dana said. “I’d always understood that ultrawave is faster than light.”
“Effectively it is; physically it isn’t. You don’t understand that?”
She shook her dark head.
“In a nutshell,” Weinbaum said, “ultrawave is radiation, and all radiation in free space is limited to the speed of light.
The way we hype up ultrawave is to use an old application of wave-guide theory, whereby the real transmission of energy is at light speed, but an imaginary thing called “phase velocity” is going faster. But the gain in speed of transmission isn’t largeby ultrawave, for instance, we get a message to Alpha Centauri in one year instead of nearly four. Over long distances, that’s not nearly enough extra speed.”
“Can’t it be speeded further?” she said, frowning.
“No. Think of the ultrawave beam between here and Centaurus III as a caterpillar. The caterpillar himself is moving quite slowly, just at the speed of light. But the pulses which pass along his body are going forward faster than he isand if you’ve ever watched a caterpillar, you’ll know that that’s true. But there’s a physical limit to the number of pulses you can travel along that caterpillar, and we’ve already reached that limit. We’ve taken phase velocity as far as it will go.