“We could wait for them at any of the lower levels, of course, but the geometry involved means that when they reach the highest point there is a period when they almost stop moving vertically with reference to us. I see from the chart that, luckily, there has been a lot of excavation around that level. What we have to do is spread out laterally as much as possible—probably just one person to a tunnel—and look for buildings materialising. We’re not so much interested in the Avernians themselves at this stage, but we do want to find buildings.”
“I seem to have missed something,” Snook said, setting down a pot of coffee. “Why are buildings so important?”
“They represent our best chance of establishing contact with the Avernians, and even then it may not work. The only reason we were able to detect them is that a mine is a pretty dark place, and so the conditions were good for seeing ghosts. In daylight they might never have been noticed.”
“We were able to see Thornton’s Planet in daylight,” Culver said.
Ambrose nodded. “True—but in its own universe. Thornton’s Planet is a very dense assembly of antineutrinos and is emitting neutrinos in four-pi space at a very high rate. The planet Avernus is less dense, in its own universe, and therefore its surface appears to us as the milky luminance which Gil and George described. The inhabitants of Avernus are less dense again—just the way my hand is a lot less solid than a steel bar—so their neutrino flux is even more attenuated, and they are therefore much harder to see. Okay?”
“I think I get it, but does that explain the way the Avernians were seen gradually emerging bit by bit from the floor? If we see them by virtue of their neutrino emission shouldn’t they be more or less visible all the time? Shouldn’t we see them right through the solid rock?”
“No. Not to any important extent anyway. The neutrino flux decreases according to the inverse square law, and if you start off with a weak emitter, like an Avernian being, the flux soon attenuates to below the threshold level at which the Amplites will produce an image. The glasses aren’t a very efficient way of seeing the Avernian universe—at best they leave us desperately short-sighted.”
“But they’re super-efficient in this universe,” Quig put in.
“Even in the dark they would give you a good image of the floor and that could blot out faint images of what was below the floor.”
“Correct.” Ambrose nodded his agreement. “It’s a bit like not being able to see stars in the daytime sky, even though they’re there just the same.”
“And the reason we’re hoping to find structures,” he continued for Snook’s benefit, “is that it might be dark inside an Avernian building, and that would give them a better chance to see us. Don’t forget thati as far as they’re concerned, we are the ghosts. Right now, sitting in this room, we’re sailing along in their atmosphere. The rotation of the two planets means that we’re on a kind of glide path which will intersect with their equivalent of Barandi just before dawn.”
Prudence raised her head. “Is it night time in Avernus?”
“In this hemisphere, yes.”
“Then maybe they know about us. Perhaps they can look up in the sky and see us.”
“No. If you look at the two circles again you’ll notice that the Avernians are under the surface of the Earth, so all they would see, if they see anything, is a general radiance—as happened when Gil and George sank under their surface. The only time we can communicate with them is when the two surfaces are roughly coincident.”
“Hell! I’ve just thought of something which wrecks the whole plan,” Culver put in, slapping his forehead. “We would never have detected the Avernians at all if our miners hadn’t been wearing magniluct glasses. So the Avernians would need special viewing aids to see us, wouldn’t they. And the chances that they’d just happen to be wearing them are bound to be millions to one against.”
“Good point.” Ambrose smiled at Culver, obviously pleased at the question having arisen. “But, fortunately, the relationship between the two universes is not symmetrical, and the advantage is on our side. What it boils down to is that we are better emitters than they are. I’ve done a few sums and it looks to me that if we stand in an intermediate vector boson field it will have the effect of making us glow fairly strongly in their universe.”
“Bosons? That’s a funny kind of radiation, isn’t it?”
“Yes, but it should be the Avernian equivalent to a shower of photons.”
“Will you need a Moncaster machine? Des and I have a friend at the power station who uses one sometimes.”
“A lab model would be too big and heavy. I brought some portable equipment with me from the States—it creates a low-intensity field, but it should be good enough for our purpose. I only had room for one so we’re going to need good communications in the mine. Anybody who finds what he thinks is an Avernian building will signal the others and we’ll get the radiation equipment to him as fast as we can.”
Des Quig put up his hand, like a boy in class. “If we need communicator sets I can rig up something at the plant.”
“Thanks, but we’re too short of time. That’s why I brought as much commercially available equipment as I could get in the few hours I had—pulse code modulation sets and…”
“Hey! It sounds as if you’re planning to talk to the ghosts.”
Ambrose looked surprised. “Of course! It’s technically feasible, isn’t it? If they can see us and we can see them, that means light is being exchanged. All you have to do is modulate it to get sound communication.”
“That’s assuming Avernians use speech among themselves, that they are a technical race at the same level as ourselves or more advanced, and that we can get the idea of light-to-sound conversion over to them. And all that’s on top of assuming we will even manage to make them see us.”
“Correct. I know I’m rushing a lot of fences, and I know that being wrong in any one of the assumptions you mention will wreck the whole scheme, but we’ve got to make the effort—starting tonight.”
Quig burst out laughing. “Where did I get the idea that astronomers were patient, slow-moving types? Why all the hurry?”
“We’re hurrying because it was a stroke of pure luck that the Avernians were seen in a deep mine, and it has given us a few days’ grace in which to try making contact.” Ambrose tapped the sectional chart again.
“Let me remind you of the geometry of the situation. We’re dealing with two kinds of movement. One of them is the separation of the two worlds—Avernus is emerging from the Earth at a speed of just over five hundred metres a day. This creates a problem in itself because they rise that much higher each time we see them. At dawn this morning they’ll get to about fifteen hundred metres from the surface, tomorrow morning it will be a thousand metres from the surface, the morning after five hundred, and the morning after that they’ll be visible on the surface—right out there among the trees and mine buildings, or here in this room.” Ambrose paused and smiled as Prudence gave a theatrical shiver.
“That’s the stage at which the surface of Avernus coincides with the surface of the Earth—from then on the Avernians will start rising into the sky above us, five hundred metres higher every day, as the planets begin to separate. That would be awkward enough, but the daily rotation of the two worlds complicates everything even further because it is translated into vertical movement between corresponding points on the surfaces of the two spheres.”