Дэймон Найт - Orbit 5

“Please, Zin, do we have to settle it tonight?”

“No, it’ll wait.” He rose reluctantly. “Just following up something occurred to me after the track meet.”

“What’s the velocity of light got to do with a track meet?”

“Nothing, probably. Still, time . . . distance . . .light, all tied up together, you know.”

“I know we’re going to catch it from our wives if we don’t get a move on. Now get your coat and flash some speed in the direction of home.”

Zinner caught the English professor a few days later as he was coming down the steps of the cafeteria. He wasted no time in polite chitchat.

“Seen the new JOSA?”

“The new which?”

“Journal of the Optical Society of America —-what else?”

“Didn’t know the Optical Society of America had a journal.”

“It’s got Barker’s new value for the velocity of light. Know what he gets?”

Alyson raised a restraining hand. “Now don’t tell me. Let me guess.”

“He gets a weighted mean of 329,542.4 kilometers per second with a probable error of 0.2. It breaks the record for a new high.”

“Please convey my heartiest congratulations.”

“Best part is it fits right in with my track-meet hypothesis!”

“Don’t tell me we’re back on that again.”

“This new value looks high,” Zinner said, letting his voice fall. “Only it’s not really high.”

“Ah! I suspected there was something underhanded—

“Measuring the speed of a light beam is not so different from timing a man in a race,” Zinner hurried on. “Galileo was the first to try it. Here—you be Galileo.” He seized Alyson and backed him up against the wall.

“I’m his assistant over here somewhere. We’ve both got lanterns. Galileo uncovers his lantern. Soon as I see his lantern I uncover my lantern. Galileo measures the time for the round trip. Say it’s 300,000 kilometers per see-ond.” 1 1 In his classic experiment Galileo made no attempt to measure the time. He relates that he was unable to determine with certainty whether the appearance of the opposite light was instantaneous or not, but states that “if not instantaneous it was extraordinarily rapid.” (Dialogues Concerning the Two New Sciences by Galileo Galelei, I, 1638.)

He paused for dramatic emphasis.

“ ‘Hmmmm. Looks kind of low,’ Galileo says. ‘I’ll give it another try.’ He doesn’t know I’d gotten tired and started back home. Since we’re closer now he gets 301,000 kilometers per second. ‘The velocity of light has increased,’ he announces. But, no, it wasn’t that the speed of light increased— it was the distance that decreased”

Alyson had been showing signs of distress.

“D’you suppose I could be Galileo some other time? I’m already late for my seminar on Pope and his contemporaries.”

Zinner stared in undisguised amazement.

“Are you fellows still muddling around with those old dopes? Honestly—”

“Some of those old dopes said some things that are very cogent to our present situation,” Alyson informed him coldly.

Zinner continued staring after the man of letters until he was out of sight within the decrepit old Humanities Building.

When Alyson returned from his seminar late that afternoon he found Zinner with his feet on his desk, thumbing through a worn copy of Pride and Prejudice.

“This gal Jane Austen sure turned out some red-hot stuff,” he commented, with a shake of his head.

“Was that what you came all the way over here to tell me?”

Zinner laid Jane Austen aside.

“Al, old man. I’ve decided you need a change.”

“Thoughtful of you.”

“You need to get away from this poisonous atmosphere down here laden with coal-tar products ... all this corruption and sordid lust.”

“Corruption and lust always seemed like rather fascinating subjects for investigation.”

Zinner shifted his feet to the floor.

“Seriously, how would you like to spend some nights on the mountain with me? I’ve got a big observation coming up. Pluto’s going to occult a fifteenth-magnitude star. Nearly central this time.”

The offer was tempting. Several times before he had kept the astronomer company while working at the big reflector, and had always enjoyed the experience. It was a welcome change from the routine of classwork. And as it happened, his wife was away, so there would be no conflict on the home front.

“What’s more, not only is this the best occultation in years,” said Zinner, “but it furnishes me with a splendid opportunity to test my shrinking solar system hypothesis.”

It was Alyson’s turn to stare with a wild surmise.

“First it was the hundred-yard dash in the Rose Bowl. Next it was the velocity of light. Now you’ve got us out to Pluto.”

Zinner smiled with goodnatured tolerance.

“Living here as you do in the cloistered shelter of the Humanities, immersed in Jane Austen and her contemporaries, I dare say this sudden excursion to Pluto comes as a bit of shock. Actually it is a natural step, following logically upon the others.”

He hesitated as if uncertain how to proceed.

“Pluto’s the outermost planet but don’t think I can’t find it. I’ve got that little old planet nailed down tight. 2 2 Zinner was justified in referring to Pluto as a “little” planet. His work on the perturbations arising from the close approach of Uranus to Pluto late in 1967, yielded for the mass of Pluto the value 0.089 x Earth. This gives 3.54 gm/cm 3 for the density of the planet, replacing the former ridiculous value of 50 gm/cm 3 . The prediction of an occultation involves a correction for ‘light time,’ the time light takes to travel from Pluto to Earth. Planetary aberration’s another name for it. Light time for the sun is about eight minutes. For Jupiter at opposition about thirty-five minutes. But for Pluto the light time’s around three hundred minutes—five hours.

“I’m assuming the solar system has shrunk by ten per cent. The distance from Pluto to Earth is then shorter by ten per cent. So the light time is correspondingly shorter. Which means the occultation should come early by about thirty minutes, an amount not easy to ignore.”

“Well, that sounds reasonable,” Alyson agreed. “Even I can understand it.”

Zinner gave him a curious look.

“You know what would really cinch this thing? Some observations taken right here on the planet Earth.”

“What kind of observations?”

“Observations of velocity in a race.”

“Shouldn’t think that would be difficult,” said Alyson. “You’ve got the time . . . you know the distance . . .”

“But that’s just what we don't know,” Zimmer said. “Is the distance a hundred yards? Or is it only ninety yards? The tape measure won’t tell. We need a very special kind of velocities— Doppler velocities. Velocities derived from displacements of spectrum lines to the red or violet, the way we measure line-of-sight velocities in stars. We don’t need a tape or stop watch for these measures. All we need is a photograph of the star’s spectrum.”

Alyson didn’t seem to understand.

“Then why not pretend your boys are stars? You set up your spectroscope down the track . . . measure their violet shift. . . and voilà!”

“Wouldn’t work. Lines in stellar spectra originate in glowing gases. Stars shine because they glow. A track star may shine but he never glows.”

“Hang a lantern around their necks.”

“Afraid that wouldn’t work either,” Zinner said.

They were silent for several minutes pondering this unhappy state of affairs. Finally Zinner got to his feet.