The vastest system ever built by Terragens, the wormhole nexus is a modular and ever expanding network of artificial wormholes, which already spans much of explored space. More than six millennia old, it is still growing at an accelerating pace that shows no signs of abating. While there are several smaller nexi still unconnected to the main network, when one speaks of the Nexus there is no doubt what is being referred to.
The Nexus is more than just a multi-millennial ongoing project, and more than all the billions of physical and exotic matter structures and the quadrillions more support structures, superstructures and maintenance and service ai. It is the symbol of Civilization itself, trumpeted at isolates and xenos and even at other ordinary Terragens, to prove that Sephirotic civilization is the largest, mightiest, greatest empire ever! It allows even the most humble baseline to cross from one end of the known galaxy to the other in only five or six standard months of shipboard transit interspersed with instantaneous wormhole 'jumps'. It is the circulatory system of the entire Terragen bubble, conveying goods, services, data streams, and sentients of all kinds to where they are needed, or where they wish to go.
And yet, for all of its size, cost, and miraculous technology, the Nexus is something that most beings in the galaxy hardly give a second thought to. It is there, always functioning smoothly, allowing the wonderful Terragen civilization to exist and flourish. It works quietly, in the background, like the Known Net. All sophonts are assured that if they want to go somewhere, and provided they have the monetary credit to pay the very reasonable tolls (in those polities that use them) then they can do so without fear to life or limb. While tolls vary from non-existent to exorbitant, depending on the local polity, it is a fact that travel through the Nexus is often easier than travel from one end of a planet or megahabitat to another!
The topology of the Nexus is tree-like, extending outwards from the Inner Sphere and the imperial capitals. The oldest wormholes connect the inner sphere worlds. From the "bridge" worlds, worlds with many stargates (mainly imperial capitals and special systems) wormholes extend to major provincial capitals. These link to their provinces and more remote regions, where the network becomes more random. Out here there are very few connections between branches, while they are more common the closer you go to the Inner Sphere.
The number of wormholes one needs to traverse varies according to the trip taken. In case of travel from Sol to Kepleria, the Lonely Galaxy Guidebook gives the following advice:
From Sol take the venerable Einstein Bridge to Tau Ceti, the Akiyoshidai to Djed, and then the Kepler Arc to Kepleria. Just three jumps. The trip would mostly involve resting in light stasis in a shuttle connecting to grapeships moving through the wormholes - it is only a few weeks stopover in each system at most. In the case of a longer journey from Vast Endeavour to the Chronos Cluster, things are more complex. Again citing the Lonely Galaxy travelbook:
At Vast Endeavour you first take the wormhole to Alauda, a minor NoCoZo world (a wormhole link directly to Merrion is intended to arrive shortly in the Bazaar project, which will render the Alauda link obsolete). Alauda connects to Frei (very central), which connects to Merrion. Merrion has a direct link to Pardes, where you can go to Nova Schiaparelli (capital of the West Cygnus Region), Sy (intermediary system in the outer Veil region) and finally to Orwell in the Chronos cluster. Seven jumps; generally this should be fairly quick although there are administrative troubles at Sy.
The first wormhole nexus to be discovered was the Taurus Nexus, created by a very early a-human transapient civilisation in the First Federation era. Later parts of the alien nexus built by the Tunh were discovered, although the component parts of this nexus have mostly disappeared and the few that remain have drifted far apart. Other entirely independent nexi have been built, such as the Diamond Nexus and the Panvirtuality Nexus, and the later Lirantiq nexus which has since been connected to the main network.
Wormholes come in two main kinds:
Traversable wormholes, which use a modified Morris-Thorne-Kuhfittig metric. These are very large: traversable wormholes are consistently 327 Astronomical Units (A.U.s) in radius from the region of flat-space to the wormhole mouth. This kind of wormhole uses a relatively small quantity of negative (exotic) ANEC-violating energy. This is the kind of wormhole often referred to as a stargate.
Hayward class wormholes which are much smaller, but use a much larger amount of negative (exotic) ANEC-violating energy. They are only useful for transmitting em-beams containing data, but this data transfer is very important to the existence of civilisation in the Terragen Sphere.
Chronology Protection - Text by Anders Sandberg The universe seems to counteract attempts to produce time machines, for example due to Visser decay and related vacuum phenomena undermining other forms of time communication. Although the strict Chronology Protection Conjecture by the information age physicist Hawking was subsequently disproved, the chronology protection theorems of Lang, Picard and Joel-5 showed that this tendency can be explained from the consistency theorems, information physics and (eventually) vacuum physics.
Fargate, The - Text by Todd Drashner Wormhole of presumably alien manufacture discovered in the Metasoft volume in 10233. Travel through the gate transports one to a location in intergalactic space. The exact location in relation to the Milky Way galaxy is unknown since instruments sent through the portal have been unable to pinpoint any familiar configurations of galaxies. It is hypothesized that the Fargate may exit beyond the current universal Event Horizon or even into another universe. There is of course no evidence for this and most serious researchers are confident that the coordinates for The Other Side, as it is called, will be pinpointed eventually.
Sagittarius Project - Text by Anders Sandberg Major exploration project backed by a number of research and colonization megacorporations in the Establishment and early Consolidation era. The Sagittarius Project attempted to set up wormhole links to the Sagittarius arm and continue inwards to the galactic core. Over time, the Project developed into a megacorp-house like most others (eventually becoming the Sagittarius Sphere), and the thrust towards the core was replaced by exploiting the many new worlds found in the Sagittarius arm. Some research vessels are still on their way towards the core, and are expected back in a few millennia.