now studying this phenomenon are located very close to the source, which is why they have managed to draw a very detailed picture. Now we know very well what we should be looking for, and we didn't have to wait long for a result."
MacQueen nodded.
"OK, let's get back to the phenomenon."
"Yes. Knowing its signature, we set out to search for similar phenomena in our galaxy. If you remember, as a result of the shape of the Milky Way and the position of our Solar System in it, a great part of it is concealed from us by stellar dust and gas clouds. Any radiation is to a greater or lesser extent absorbed by this barrier, so a great part of our galaxy is hidden from our eyes on the other side of the gas-dust cloud.
"Gravity waves differ from electromagnetic waves in that they are not absorbed by these clouds. To be precise, it seems that they are not subject to absorption by matter at all. Therefore we have succeeded in detecting such beacons not only in those regions we have already studied by the classical methods, but also in looking where we could not look before.
"And now we come to the most interesting part. The following law became obvious to us. The beacons are not scattered uniformly over the cosmos, but form certain clusters in certain sectors of the Milky Way. These clusters are most likely to be found, firstly, close to stable star systems; that is, systems in which the central star is in the quiet stage of its life cycle. And secondly, near those star systems which have planets in the habitable zone.
"On this basis, we draw the conclusion that this source of gravity waves is something like a beacon, integrated into the cosmic infrastructure of the incomer's civilisation. Since we did not know of the existence of such a phenomenon close to us before the Solar System was visited, it can be assumed that the incomer activated some kind of a mechanism which created this beacon during its visit. It is quite possible that setting up this beacon was the real aim of its visit. The contact with us may simply have been a distracting manoeuvre."
"Interesting. As a military man, the first analogy that comes to mind is that this phenomenon is something like a marker, as often used by clandestine groups to correct missile fire and bombing strikes."
"That may be so. But to me, as a civilian, another analogy comes to mind. I called the source of the gravity waves a beacon. But beacons, at least in our civilisation, act as landmarks in space. In other words, they are part of our transport infrastructure.
"If you remember, the alien ship came into our telescopes' field of vision while it was still beyond the orbits of the Solar System's planets. At first it was moving slowly, and only later picked up a fair bit of speed. Yet it is not rational to overcome interstellar distances at low speeds, or its journey would take tens of thousands of years.
"This leads to the thought that the incomer started from some kind of base located somewhere outside the orbit of Pluto. Or its starting point might not be a base, but some element of a transport infrastructure making it possible to overcome cosmic distances faster than at the speed of light. If this supposition is true, the gravity radiator may denote the location of a portal for fast travel which the incomer was using.
"This would also explain the radiation of gravity waves, because, as I said, they are not in the least subject to absorption by matter. Therefore the dust clouds filling our galaxy are no obstacle to such beacons. They can be seen everywhere and from anywhere."
"These portals... To what extent are they possible, from the point of view of contemporary science?"
"From the point of view of our science, they are pure fantasy. We know that at sub-light speeds, the mass of a rocket begins to grow perceptibly. The closer to the light barrier, the greater it becomes. Therefore we require more and more energy to impart more speed to the ship. As it approaches the speed of light, the mass value rises to infinity, which means we would require an infinite quantity of energy to continue accelerating the ship. Naturally, this is impossible, which is why it is impossible for any object with a mass of more than zero to travel even at the speed of light. It is customary in science to call the effect of the increase in mass and other phenomena which appear at sub-light speeds 'relativistic'. These effects are a consequence of the properties of our space-time.
"But as we know, the aliens are able to manipulate space-time itself. Who knows how far they have succeeded in that? Therefore the existence of such portals cannot be excluded.
"Nor should we forget that the incomer, when it left the Solar System after our attack, selected a flight trajectory towards the phenomenon. This could hardly have been a coincidence. I think we ought to consider the portal theory the most probable, although we shouldn't exclude your marker theory either."
"All right, then let's take the theories of beacons and portals as starting points," proposed MacQueen. "It seems they've built a space highway to us. That means that sooner or later we are going to have numerous guests."
"You're probably right."
8
That morning, Clive's face was despondent, and there were many empty glasses on the table. Steve knew what that meant. Clive had not closed his eyes all night, but had been sitting at his calculations after finding something which didn't add up. That was how problems usually began.
"Hey, what's up?" asked Steve, sitting down next to him. "Are my calculations about the shape wrong?"
Clive grinned.
"No, your calculations are correct. So are mine."
"So what's the matter then?"
"When I put them together, it produces a contradiction."
The day promised to be a lousy one. If Clive had been sitting over his calculations for several hours, it would not be easy to find the error. The worst thing of all is when two sets of calculations are both true, but lead to mutually exclusive results. You could spend months looking for the solution. Something similar had happened a few times with the telescope. Just remembering those cases was enough to give Steve a headache.
"All right, let's go through it again together," proposed Steve.
"It's no good. I've already rechecked a hundred times. There are no errors in your figures."
"And yours?"
"Not in mine either."
"But it has to be somewhere, doesn't it?"
"I know that without you telling me," snapped Clive.
When Clive was in this state, it was best to leave him alone. Steve turned to his own console and set about rechecking his calculations. A visualisation of the anomaly in space was revolving on one of the auxiliary displays.
Due to the relatively low resolution capability of the apparatus for detecting gravity waves, the size and shape of the anomaly were only known roughly. The data on which the visualisation was based were approximate, and were extrapolated in several sectors.
Steve was fascinated by the picture. On the visualisation, the gravity anomaly was rocking slightly from side to side, or even rotating. It was quite possible that it was shuddering in space, slightly changing its state, but due to the imprecision of the data, the computer was interpreting this as rotation.
The rotation looked unnatural, somehow. The cuboid, which had recently been looking more and more like a cube, the edges of which were denoted in the visualisation by fine lines, seemed to be rotating around its axis, but after making a half turn, it jumped sharply back to its original position. This sudden jump did not look like a natural movement. Maybe that was the crux of the problem.
"Does anything about the visualisation seem strange to you?" asked Steve after several minutes' thought.
Clive raised his eyes, red from lack of sleep, to the auxiliary display.
"It's rotating in a strange sort of way. It keeps twitching," he replied.
"But it isn't a sticking pinion, to twitch like that."
"It's the low resolution of the instruments distorting the result, that's why it's twitching."
"No, hang on. Shelby sent us the theoretical calculations of the anomaly in the form of a portal between two points in space, right?"
"Well, so what? It's
pure fantasy. The lads from the theoretical physics faculty gave free reign to their imagination. From the practical application point of view, their description is worse than useless."
"All the same, they did construct the mathematical model."
"Not every mathematical solution to a system of equations makes sense in terms of physics. Speaking purely mathematically, time goes backwards at superluminal speeds. That doesn't mean it will be like that in the real world."
"Well, look at it this way. It follows from their calculations that the portals are connected to each other in space, right?"
"Well... yes. Only they call it hyperspace, because the tunnel exists in five or more dimensions."
"It doesn't matter what they call it. They postulate a space with a larger number of dimensions than ours. If they are right, then the portal is partly in our space and partly in hyperspace. That's so, isn't it?"
Clive thought for a second or two.
"Well, if you mean within the framework of their theory, yes. So?"
"Then we aren't seeing the whole portal, but only part of it, as a three-dimensional projection."
Clive thought again, and his eyes suddenly came alive.
"There's something in that..."
He turned back to his own console and started rapidly working his magic on it. Then he transferred a picture to the main screen in which a number of different strange-shaped figures were rotating. Steve had already seen this many times in lectures on hyperbolic geometry. They were