"Why should you?"
"I'm an astronomer too."
"I thought you were an electronicist."
He pumped his head up and down. "Yeah ... at the radio astronomy
observatory at Greenbelt. Project OZMA. Where do you work?"
"Lick Observatory ... with the 120-inch reflector."
"Oh ... an _optical_ astronomer."
"Certainly."
"You're the first optical man I've met." He looked at me a trifle
queerly.
I shrugged. "Well, we've been around a few millennia longer than you
static-scanners."
"Yeah, guess so."
* * * * *
"I didn't realize that Project OZMA was still going on. Have you had
any results yet?"
It was Rizzo's turn to shrug. "Nothing yet. The project has been
shelved for the duration of the emergency, of course. If there's no
war, and the dish doesn't get bombed out, we'll try again."
"Still listening to the same two stars?"
"Yeah ... Tau Ceti and Epsilon Eridani. They're the only two Sun-type
stars within reasonable range that might have planets like Earth."
"And you expect to pick up radio signals from an intelligent race."
"Hope to."
I flicked the ash off my cigaret. "You know, it always struck me as
rather hopeless ... trying to find radio signals from intelligent
creatures."
"Whattaya mean, hopeless?"
"Why should an intelligent race send radio signals out into
interstellar space?" I asked. "Think of the power it requires, and the
likelihood that it's all wasted effort, because there's no one within
range to talk to."
"Well ... it's worth a try, isn't it ... if you think there could be
intelligent creatures somewhere else ... on a planet of another star."
"Hmph. We're trying to find another intelligent race; are we
transmitting radio signals?"
"No," he admitted. "Congress wouldn't vote the money for a transmitter
that big."
"Exactly," I said. "We're listening, but not transmitting."
Rizzo wasn't discouraged. "Listen, the chances--just on statistical
figuring alone--the chances are that there're millions of other solar
systems with intelligent life. We've got to try contacting them! They
might have knowledge that we don't have ... answers to questions that
we can't solve yet...."
"I completely agree," I said. "But listening for radio signals is the
wrong way to do it."
"Huh?"
"Radio broadcasting requires too much power to cover interstellar
distances efficiently. We should be _looking_ for signals, not
listening for them."
"Looking?"
"Lasers," I said, pointing to the low-key lights over the consoles.
"Optical lasers. Super-lamps shining out in the darkness of the void.
Pump in a modest amount of electrical power, excite a few trillion
atoms, and out comes a coherent, pencil-thin beam of light that can be
seen for millions of miles."
"Millions of miles aren't lightyears," Rizzo muttered.
"We're rapidly approaching the point where we'll have lasers capable of
lightyear ranges. I'm sure that some intelligent race somewhere in this
galaxy has achieved the necessary technology to signal from star to
star--by light beams."
"Then how come we haven't seen any?" Rizzo demanded.
"Perhaps we already have."
"What?"
"We've observed all sorts of variable stars--Cepheids, RR Lyrae's, T
Tauri's. We assume that what we see are stars, pulsating and changing
brightness for reasons that are natural, but unexplainable to us. Now,
suppose what we are really viewing are laser beams, signalling from
planets that circle stars too faint to be seen from Earth?"
In spite of himself, Rizzo looked intrigued.
"It would be fairly simple to examine the spectra of such light sources
and determine whether they're natural stars or artificial laser beams."
"Have you tried it?"