Death's End

At first blush, it seemed impossible to give advance warning for photoids, because they moved at close to the speed of light. This meant that they moved almost as fast as the radiation they generated, and reached their target almost simultaneously. In other words, the observer was outside the event’s light cone.

But reality was a bit more complicated. Any object with rest mass could not achieve lightspeed. Although a photoid’s speed approached lightspeed, it was still slightly slower than true lightspeed. This difference meant that the radiation from the photoid moved just a bit faster than the photoid itself. If the photoid had to travel a long distance, this difference was magnified. Also, a photoid’s trajectory to the target wasn’t an absolute straight line. Since it wasn’t massless, it couldn’t avoid the gravitational attractions of nearby celestial bodies, and its path typically ended up being slightly curved. The curvature was much greater than the curvature of light through the same gravitational field. For the photoid to strike the target, its trajectory had to take this effect into account. This meant that the path traveled by the photoid was longer than the path taken by its radiation.

For these two reasons, the radiation from the photoid would reach the Solar System before the photoid itself. The twenty-four-hour estimated warning period was calculated based on the maximum distance at which photoid emissions could be observed. By the time the radiation reached the Earth, the photoid itself would still be about 180 AU away.

But that was merely the ideal scenario. If the photoid were launched from a nearby spaceship, there would be almost no warning—like what had happened to Trisolaris.

Thirty-five observation units were planned for the Solar System advance warning system. These would monitor the sky in every direction for photoid emissions.

Broadcast Era, Year 8 Fate’s Choice

Two days before the false alarm; Observation Unit #1

Observation Unit #1 was in fact just the Ringier-Fitzroy Station from the end of the Crisis Era. More than seventy years ago, it was this observation station that had first discovered the strong-interaction space probes—the droplets. The station was still located on the outer edge of the asteroid belt, but all its equipment had been updated. Take the visible light telescope, for instance: The lenses were even bigger, and the first lens’s diameter had increased from twelve hundred meters to two thousand meters, big enough for a small town to fit on it. These gigantic lenses were made from materials taken directly from the asteroid belt. The first one was a medium-sized lens five hundred meters in diameter. After that was finished, it was used to focus sunlight on asteroids so that the melted rock could be made into pure glass and then formed into additional lenses. In total, six lenses floated in a ten-kilometer-long column in space, far apart from each other. The observation station itself was located at the end of the column of lenses, and could only hold a crew of two.

The crew was still made up of a scientist and a military officer. The officer was responsible for monitoring photoid emissions, while the scientist conducted astronomical and cosmological research. Thus, the tradition of fighting for observation time begun three centuries ago by General Fitzroy and Dr. Ringier continued.

After this, the largest telescope in history, had completed its shakedown tests and successfully taken its first image—a star forty-seven light-years away—Widnall, the astronomer on the crew, was as excited as if he’d just had a son. Laymen did not understand that previous telescopes could only amplify the luminosity of stars outside the Solar System, not reveal any shapes. No matter how powerful the telescopes were, the stars always showed up as tiny point sources, only incrementally brighter than images taken by lesser telescopes. But now, in the view of this ultrapowerful telescope, a star showed up as a disk for the first time. Though it was small, like a Ping-Pong ball seen from tens of meters away, and one couldn’t see any details in the disk, this was still an epochal moment in the history of the ancient science of visible-light astronomy.

“The cataracts have been removed from the eyes of astronomy!” said Widnall dramatically, wiping his eyes.

But Sublieutenant Vasilenko wasn’t impressed. “I think you need to remember our role here: We are sentries. In the old days, we’d be perched atop a wooden watchtower on the frontier, a desolate desert or snowfield around us. Standing erect in the frigid breeze, we’d be gazing in the direction of the enemy. As soon as we saw tanks coming up the horizon, or men on horses, we’d make a call or light smoke signals to inform the homeland that the enemy invasion had begun…. You need to get into that mental space. Don’t think of yourself as being in an observatory.”