"And what about the message for the future?" asked Keith.

Hek pointed to one of the cube's sides. "We've incised it into the cube's faces," he said, his barking echoing in the bay. "It begins on this side. As you can see, it consists of a series of boxed examples.

Two dots plus two dots equals four dots; a question with its answer.

The second box, here, has two dots plus two dots, and a symbol. Since any arbitrary symbol would do, we just used the English question mark, but without the separate dot underneath; that might confuse one into thinking it was two symbols rather than one. Anyway, that gives us a question and a symbolic representation of the fact that the answer is missing. The third box shows the question symbol, the symbol I've established for 'equals,' and four dots, the answer. So that box says, "The answer to the question is four. Do you see?"

Keith nodded.

"Now," continued Hek, "having established a vocabulary for our dialogue, we can ask our real question." He waddled around to the opposite side of the cube, which was also incised with markings.

"As you can see," said Hek, "we have two similar boxes here. The first one has a graphic representation of the shortcut, with a star emerging Ifrom it. See that scale mark showing the width of the star, and the series of horizontal and vertical lines beneath? That's a binary representation of the star's diameter in units of the box's width, in case there's any confusion about what the image represents. And then there's the equals symbol, and the question symbol. So it says, 'shortcut with star emerging from it equals what?' And beneath it is the question symbol, the equals symbol, and a large blank space: "The answer to the above question is…" and a space implying that we want a reply."

Keith nodded slowly. "Clever. Good work, gentlemen."

Azmi pointed to one of the cube's other faces. "On this face, we've incised information about the periods and relative positions of fourteen different pulsars. If the shortcut makers in the future — or whoever it is who finds this — have records going back this far in time, they'll be able to identify the specific year in which the cube was created from that information."

"Beyond that," said Hek, "they might also assume, quite reasonably, that the cube had been created shortly after the green star emerged from this shortcut — and presumably they'll know what date they sent that star back to, as well. In other words, they've got two independent ways of determining when to send any reply back to."

"And this will work?" Keith asked.

"Oh, probably not," said Azmi, smiling. "It's just a bottle in the ocean. I don't seriously expect any results, but I suppose it's worth a try. Still, as Dr. Magnor has told me, if we don't get a good explanation, and if we decided the stars are a threat, we can use the Waldahud space-flattening technique to evaporate the shortcuts.

Granted, stars may be popping out of thousands of exit points, so we probably can't do much to stop them. But if they know we have the capability to interfere to some degree, perhaps they'll provide an explanation rather than have us do that."

"Very good," said Keith. "But what will make the cube conspicuous?

How can you be sure someone will find it?"

"That's the hardest part of all," barked Hek. "There are only a few ways to get something to stand out. One is to make it reflective. But no matter what we make this box out of, it will have to endure perhaps ten billion years of scouring by interstellar dust. Granted, that's only a few microscopic impacts per century, but the net effect over that much time would be to dull any reflective surface.

"The second possibility we'd considered was to make the time capsule big — so that it's eye-catching; or heavy — so that it warps spacetime. But the bigger you make it, the more likely it is to be destroyed by a meteor collision.

"The final possibility was to make it loud — you know, by broadcasting a radio signal. But that requires a power source. Of course, right now the green star is close by, and we can use simple solar cells to generate electricity from it, but the star has a respectable proper motion relative to the shortcut. In just a few thousand years, it'll be a full light-year from here, much too far away to provide significant power. And any internal power source we use would exhaust its fuel, or have most of its radioactives decay to lead, long before the target date."

Keith nodded. "But you said you were using starlight converted to electricity to power the attitude-control system?"

"Yes. But there's almost no spare power for a beacon of any sort.

We're just going to have to assume that whoever built the shortcuts will have detectors that will find the cube regardless."

"And if they don't?"

Hek moved all four shoulders up and down in a shrug. "If they don't — well, we've hardly lost much by trying."

"All right," said Keith. "It looks good to me. Is this a prototype, or the actual time capsule?" "We'd intended it as just a prototype, but everything came together perfectly," said Azmi. "! say we might as well go ahead and use this one."

Keith turned to Hek. "What about you?"

The Waldahud barked once. "I concur."

"Very well," said Keith. "How do you propose to launch it?"

"Well, it has nothing but ACS jets," said Azmi. "And I don't dare put it out there on its own with those dark-matter creatures swarming around; it would probably get sucked into their gravity. But we've already seen that the dark-matter beings have some mobility, so I'm assuming they won't be in this exact spot forever. I've programmed a standard payload carrier to take the cube away from here, but come back in a hundred years and dump it about twenty klicks from the shortcut.

After that, the time capsule's own ACS jets should be able to hold it in place relative to the exit point."

"Excellent," said Keith. "Is the launcher ready, too?"

Azmi nodded.

"Can you launch it from down here?"

"Of course."

"Let's do so, then."

The three of them exited the bay, and took a lift up to the docking control room, which had angled windows that overlooked the interior of the cavernous hangar. Azmi took a seat in front of a console and began operating controls.

Under his command, a motorized flatbed rolled into the bay, carrying a cylindrical payload carrier. Mechanical arms mated the cube to the clamps on the front of the Carrier.

"Depressurizing the bay," said Azmi.

Shimmering forcefield sheets started to close in from three of the four walls and the floor and ceiling, forcing the air in the bay out through vents in the rear wall. When all the air had been swept up and compressed into tanks, the forcefield sheets collapsed, leaving an interior vacuum.

"Opening space door," Azmi said, operating another control. The segmented curving outer wall began to slide up into the ceiling.

Blackness became visible, but the glare of the bay's internal lighting washed out the stars.

Azmi touched some more buttons. "Activating time-capsule electronics."

He then tapped a key, initiating a preprogrammed sequence for the tractor-beam emitter mounted on the rear bay wall. The payload carrier lifted off the flatbed, flew over the floor plates, passed the spindly form of a repair skiff that was parked inside the bay, and headed out into space.

"Powering up carrier," said Azmi. The cylinder's end lit up with the glow of thrusters, and the contraption rapidly receded from view.

"And that," said Azmi, "is that."

"Now what?" asked Keith.

Azmi shrugged. "Now just forget about it. Either this will work, or it won't — probably won't."

Keith nodded. "Excellent work, guys. Thank you. It's-"

"Rissa to Lansing," said a voice over the speakers.

Keith looked up. "Open. Hi, Rissa."