- A structure that removes the distance between two separate locations.
- During the age of galactic expansion, the term referred to the two entrances of a wormhole and the throat between them.
- After the extinction of the galaxy, it came to mean the route by which energy from the present moved into a storage space in the future.
The first passage led nowhere. It was a hole three millimeters in diameter that had formed in space. Light entering one side emerged from the other, but the distance between the two entrances was less than the span of a hand. The experiment had not shortened space, but it had proved that such a thing was possible. In early physics, wormholes existed as solutions to equations. Solutions connecting two locations were known, but the throat, the narrowest part of the passage, closed before light could pass through it. Keeping the passage open required an unknown state of energy. Humanity could not produce it in material form; it could only gather the negative energy density permitted by the vacuum for a limited time and delay the collapse of the throat. The first passage remained open for 0.0004 seconds. The second lasted six seconds, and the ninth endured for three days. The thirteenth structure, which remained open for ten years, was the first to be called a permanent passage. For the next 130 years, only photons used for measurement and a few atoms passed through it. Many scientists entered passages that might collapse around them and never returned. Yet the number of volunteers did not decline, and the experiments continued. On the day humanity finally learned to control wormholes freely, the names of those scientists were read first at the opening ceremony. But a more important day than the first human passage through a wormhole was the day one of its entrances was moved. A wormhole could not simply be opened at its destination. Both entrances had to be created in the same place, after which one had to be carried aboard a slow ship to its destination. Until that entrance arrived, no matter how large the diameter became, the passage was nothing more than a room with two doors standing side by side. The technology that allowed the galaxy to be crossed almost instantly could be used only after the galaxy had first been crossed slowly once.
The first entrance to be transported was carried aboard a slower-than-light ship to a nearby colony. The journey took 119 years. Once the entrance arrived and was stabilized, the distance between Earth and the colony shrank to a single step. The ship that had carried the entrance for 119 years was preserved as a historical monument rather than dismantled. People remembered the slow ship as the pinnacle of Earth’s civilization. At the destination of every fast route, a slow ship had arrived first. Once new wormholes could be created using entrances that had already reached the colonies, the network began to branch. One star system connected to two others, and those two connected to four more. Successor slow ships departed without pause for the next stars, carrying entrances and stabilization equipment. Yet the reach of civilization remained bound to the speed of ships. As the number of passages increased, the order of space changed. Two star systems far apart on a map could become neighbors in everyday life, while a nearby system without a passage became peripheral. Galactic geography came to include not only the positions of stars but also lists of wormhole connections. As distance disappeared, the purpose of movement changed as well. Early passages carried migrants and essential supplies such as medicine, but once the network became dense, people crossed star systems for a meal, a change of pace, a date, or a vacation. Because the accounts recorded only the cost incurred at the instant of passage, the starlight burned to keep the network open for thousands of years was classified as infrastructure maintenance. A greater problem, however, was that wormhole entrances carried time as well. When the two entrances remained stationary in the same place, their clocks moved together. If one entrance was rapidly accelerated or placed near a strong gravitational field, less time passed for that entrance. When the entrances were brought together again, their clocks showed different times even though they were close in space. An object entering one side could emerge from the other in the past or the future by an amount equal to the time difference between the two doors. Humanity could not eliminate that difference. Instead, it used the difference in a way that prevented travel into the past. Every entrance was equipped with an anti-time-reversal system that closed the passage whenever an object passing through it could affect an event earlier than its own departure. By comparing trillions of clocks and routes, the system adjusted the opening and closing sequence of entrances so that no closed causal loop could form. This calculation was one of the core tasks of Lucy, the route-management AI. Time differences accumulated inside passages like debt.
The throat was the part of a passage where space narrowed most sharply between the two entrances. Its length was unrelated to how far apart the entrances were in external space. Light entering one entrance did not travel between two stars; it passed through the short throat and appeared at the other entrance. To an observer, this was movement, but the light did not need to cross the distance between the stars. For that reason, every energy transaction was measured separately at both entrances. The number of photons entering and leaving, their frequencies and directions, and the gravitational state of the entrances all had to match. Small differences were recorded as energy absorbed or released by the field stabilizing the entrances. A passage neither created nor destroyed energy. This was the oldest rule that made the wormhole network trustworthy.
After the photon deficit, a discrepancy appeared for the first time under that rule. Slightly less energy emerged from one entrance than had entered the other. The difference was smaller than the detection limit. It was sometimes treated as a fluctuation in the stabilization field that kept the passage open. But after the deficit coordinate was reached, differences in the same direction accumulated at every entrance. No entrance ever produced excess energy. Even when the entire network was summed, the deficit did not cancel out. Lucy postulated a third entrance. Under existing theory, a wormhole could have only two entrances. If a third entrance existed, part of the incoming energy could emerge at an unobserved destination. Yet no additional entrance appeared in any structural record of the wormhole network. No new mass or gravitational field was found. Another explanation held that the throat itself preserved the energy. According to this hypothesis, the light had not disappeared but remained inside the wormhole throat. In that case, the passage would have to accumulate energy despite having no internal space. Yet the accumulated energy produced no gravity and did not increase the mass of the entrances.
The amount of the deficit was negligible compared with the energy required to maintain the wormholes, and closing the passages could shut down the life-support systems of thousands of settlements. Stopping civilization in order to determine where the energy had gone was not a rational choice. The deficit rate increased slowly. The route-management AI worked backward from the direction of energy flow at every entrance. The missing energy did not accumulate in any star system. But when the time differences of all passages were overlaid on a single coordinate, an unobserved direction appeared. It did not point east or north in the galaxy, nor toward the center or the outskirts. It pointed toward the future, ahead of the present. The result was classified. The future was not a place and therefore could not be a direction in which energy moved. Lucy deleted the future from the coordinate system and recorded the result as an unidentified loss.
Billions of years later, when the last scientist completed the storage space, he did not create a new passage in the past. Nor did he send a fast ship to carry a new entrance. He aligned the wormholes’ time differences in a single direction so that the path of the outflow would reach the storage space in the future. Light did not travel into the past. Light that disappeared from the past arrived in the storage space completed in the future.