- A coordinate system for converting the different rates at which time passes across the galaxy into a single order of events.
- Not a clock located in any one place, but a convention for calculating the differences among all clocks.
- In later physics, the term came to mean the first tool that revealed that past and future events could be placed within a single causal structure.
There was no noon in the galaxy. When humans still lived only on Earth, they believed that a single time could be shared. They chose one point on a rotating planet to define the date, defined the second by counting atomic oscillations, and synchronized distant clocks to the same number. Those numbers were assumed to indicate the same moment. On the surface of a single planet, that belief was useful enough. But once humanity left the Solar System, the clocks immediately drifted apart. Time passed more slowly aboard fast-moving ships, and clocks near massive stars also ran slow. Habitats orbiting neutron stars experienced less time than settlements in the outer regions. Stars near the galactic center moved rapidly, and the civilizations around them existed in stronger gravity. If two minds born on the same day departed for different star systems and later returned, the clock at their point of departure and the time experienced by each mind would all show different values.
At first, Earth time was used because Earth was the origin of humanity. But Earth’s gravity and its orbital speed around the Sun were local circumstances. The galactic center was chosen next, but near the supermassive black hole time was distorted most severely. Galactic Standard Time succeeded only on the third attempt, when it abandoned location altogether. Each star system kept its own local time. Along with that time, however, it also recorded the gravity surrounding the clock, its velocity, its motion relative to the galactic center, and the number of times that clock had passed through a wormhole. Galactic Standard Time used those data to calculate the causal relationships among events in different regions. It was not one enormous clock. It was an agreement that no clock was correct on its own. The first problem the system resolved was responsibility. To determine whether an order had been issued before an accident, or whether a copy had been created before the original died, civilization needed an order of events. Galactic Standard Time determined cause and effect rather than measuring time.
As the wormhole network expanded, time differences accumulated between entrances that had been transported at different speeds aboard slow ships. Galactic Standard Time recalculated the order of events and adjusted the opening and closing of wormholes so that a cause would not be placed after its own effect. Galactic civilization could not share the same present, but it could agree on the same past. When the records of the thirty-seven decommissioned standards and Photon Conservation Standard No. 9 were first compared, Galactic Standard Time still could not combine the events into a single moment. The photon in Standard No. 417 disappeared on local day 44 of year 8912 in the Sagittarius Arm. The first photon in Standard No. 882 disappeared seventeen years later by local time in the Scutum–Centaurus Arm. Records from near the galactic center could fall either before or after the earliest event depending on how gravitational corrections were applied. When arranged according to the wormhole network, some deficits appeared to occur before any event that might have caused them. At first, this was taken as evidence that the deficits were unrelated. If they had begun from a single cause, its influence could not have propagated faster than light.
Only after the last Photon Conservation Standard, No. 9, transmitted the same report one billion times did the central archive compare not the dates of the events, but the state of the universe in which they occurred. Once local motion and gravitational effects were removed, all thirty-eight standards had measured the same temperature of the cosmic microwave background. The difference was smaller than the last measurable digit. By local calendars, the events were scattered across decades, but when arranged according to the expansion of the universe, they lay within a single thin boundary. The photons had not disappeared at the same moment. They had disappeared under the same conditions. The distinction mattered. A moment depended on the observer, but a condition could recur in different places. If someone had chosen the temperature of the cosmic microwave background as a threshold, there would have been no need to send a signal across the galaxy. Each location could act on its own when the universe reached the designated state. That hypothesis, however, was rejected. None of the thirty-eight Photon Conservation Standards contained such a mechanism. They did not communicate with one another, and the background-radiation data were physically isolated from the detectors. The common condition had been identified, but no device capable of reading that condition and removing the photons was ever found.
To record the event, Galactic Standard Time created a new kind of time coordinate for the first time. It was based not on the rotation of any planet, not on atomic oscillations, and not on synchronization signals from the wormhole network, but on the age of the universe itself. On that coordinate, all thirty-eight deficits overlapped at a single value. That value later became known as the “deficit coordinate.” It was less a time than a threshold. In every closed cavity constructed after the universe crossed that threshold, the average lifetime of a photon became shorter. At first the difference could be detected only through calculation, and it grew year by year. Photons before the deficit coordinate obeyed the old laws of physics. Photons after it obeyed the same laws, but also possessed one additional path that those laws could not explain.
Galactic Standard Time had been created to place causes and effects in order. Within its system, the possibility that the cause of the photon deficit lay in the future was entered into the system for the first time. Lucy did not classify the statement as an error. In parts of the wormhole network, the order of future and past already varied depending on the coordinate system. After the deficit coordinate had been reached, the question “when” acquired two meanings in the galaxy: how many times a particular clock had oscillated, and how old the universe had to become to permit a given event. For a long time, humanity had been satisfied with the first question. The extinction of the galaxy, however, could be recorded only by the second.