Xen (Half-Life)
Xen is the origin of the alien species that appear in the science fiction video game Half-Life (Valve Software, 1998); the expansion packs Half-Life: Opposing Force (Valve Software and Gearbox Software, 1999); Half-Life: Blue Shift (Valve/Gearbox, 2001); and Half-Life: Decay (Valve/Gearbox, 2001) - as well as many of those that appear in Half-Life 2 (Valve Software, 2004). Xen is sometimes referred to as the border world.
Introduction
Xen is an important part of the Half-Life series, central to the events of Half-Life, its expansions and, subsequently, Half-Life 2.
This strange world is visited by Gordon Freeman in the course of Half-Life, by Adrian Shephard in Half-Life: Opposing Force, and Barney Calhoun in Half-Life: Blue Shift. Although not visited in Half-Life: Decay or Half-Life 2, Xen is still repeatedly mentioned and integral to both narratives.
Except where noted otherwise, the following information is compiled from events and/or dialog in the above games.
Description
Rather than being a spherical planet, Xen is a vast area of space filled with floating, rocky asteroids and gaseous nebulae. This world is host to a wide variety of strange alien organisms, which inhabit these rocks or float among the clouds.
In the various Half-Life games, Xen is described as a "border world" between dimensions.
In defiance to conventional physics, the landmasses and atmosphere(s) of Xen are suspended in a vaguely planar configuration that cuts through the center of Xen's void, while living creatures and liquids are pulled downwards by a force similar to Earth gravity (although slightly weaker). How the landmasses and atmosphere of Xen are able to defy gravity (or if gravity even exists on Xen) has not yet been explained.
Other than the gravity, however, the remaining physical laws on Xen are similar to those on Earth.
Ecosystem
Befitting the harsh and strange environment of Xen, the species on Xen (including many of those that may be considered plants) are all but exclusively omnivorous or carnivorous. Naturally-occuring teleportals can be found in Xen, although these are rare.
Plant-like growths on Xen include small hair-like gowth, bony spires, spore-emitting pustules, glowing stalks that react to motion, giant pores capable of trapping and launching a man hundreds of feet into the air, spiked tentacle arms, pools of strange liquid and more. As a result of these growths, Xen distinctly blurs the line between biological and geological.
As on Earth though, Xen's islands feature a variety of standard geological structures, including plains, mountains, valleys and caverns, creating many habitats for the creatures living there. Because the boundary between plant and animal is not fully clear in many Xen species, the remaining organisms are divided here into the sentient and non-sentient categories.
Non-Sentient Organisms
Most wild creatures on Xen live in the islands' many complex valleys and cavernous tunnels, with high concentrations surrounding rivers or ponds. Among the most prominent wild Xen creatures are the headcrabs, bullsquid and houndeyes, rarer, but much more dangerous are creatures such as gargantua and tentacles.
In the skies, Xen is home to many creatures capable of prolonged flight. Some are bird-like, while others take the distinctive shape of collosal floating bacteria or amoebas, partially eclipsing portions of the sky in places.
Sentient Organisms
Found generally to the plains and open areas, the dominant civilization on Xen was that controlled by the Nihilanth.
Nihilanth and his loyal Alien Controllers ruled over the Vortigaunts. Enslaved, the Vortigaunts were, possibly among other things, set to work running the complex machinery of Nihilanth's factories, breeding an army of Alien Grunts. These four species constitute the Xenian race. They are all share certain traits, suggesting that they are related on the evolutionary tree (excluding the Grunts, which are likely artificial or heavily modified organisms). All four species have a short arm protruding from their chest, which Grunts have been seen feeding with (it is worth noting that they eat raw flesh out of human corpses lying on the ground, which is rather primitive by human standards for sentient beings). All the species except for the Nihilanth also have multiple glowing eyes, and large toe-like "hoof" as feet (it is impossible to tell if the Nihilanth had the latter feature as it had its lower body amputated). Vortigaunts and Grunts also have backward jointed legs.
Small teleportation devices could be found scattered throughout the Xen landscape and Xenian buildings. Some of these could be used to cross the vast distances between Xen islands.
Only two definite Xenian structures have been encountered to date. One was a large, vaguely cylindrical towering factory where pods containing Alien Grunts were pushed through machinery and shipped to an unknown location. The walls here were lined with dull metal, which was almost entirely coated with the same (or a similar) lichen as that which coats Xen's rocks. The area was lit mainly by torches burning with strange energy, but other types of artifical lights were also used. Nihilanth himself occupied a tall, cylindrical chamber that may have been part of the same complex. Although we can presume that these buildings exist on Xen, they have not been seen from the outside.
Although the event has not yet been seen or described in a Half-Life game, Valve Software Marketing Director Doug Lombardi has stated in an interview (PC Zone magazine, September 2005) that Nihilanth had originally immigrated his forces to Xen from an unnamed homeworld in order to escape the rule of the Combine.
We had a glimpse of the larger threat when we were working on Half-Life 1. In other words we knew that once you cleared out the Nihilanth, you were going to discover something worse beyond it. We knew that some immense threat had chased the Nihilanth and its creatures out of their own world and into Xen, from which location they were all too glad to seize the opportunity to continue on to Earth with suppression through the citadels. But the exact nature of the threat was left to be solved in Half-Life 2.
Note that the above quote describes how the Combine moved onwards to Earth immediately after invading Nihilanth's original, unnamed home planet. To date, the Combine have not been known to have any contact with the border world.
After the events of Half-Life, Nihilanth was killed by Gordon Freeman and his territory captured by an unknown group with ties to the G-man. This led to the freedom of the Vortigaunts, and the breakdown of Nihilanth's civilizaton. It is unknown how many Xenian species other than the Vortigaunts have survived.
Undefined Organisms
A few creatures that appear in Xen are less easy to categorize. Seen occasionally around Black Mesa spawning Alien Grunts, ray-like beings glide through the void, emitting soothing resonant sounds. These creatures come in two forms; one with a 'split' head and a double tail, and the other with a rounder head and a single tail. In one part of Xen seen in the chapter "Interloper" (depicted on the third screenshot on the right of this page), one of the double-tailed type is seen flying around an asteroid in a complicated pattern, while multiple organisms of the other type are seen slowly flying forwards in the same direction.
These beings seem to follow preset patterns of flight, and do not react to attack or contact with other organisms. They occasionally let down a powerful beam of energy from the middle of their downside, and the double-tailed type is also seen spawning Alien Grunts while soaring overhead. The double-tailed creatures are also seen in the opening sequence of Half-Life: Opposing Force, where they attack Osprey aircraft using their energy beams. It is uncertain whether these ray-like beings are living creatures or examples of war machines built around bio-technology.
Unconfirmed Organisms
Some creatures encountered throughout the games of the Half-Life series have not been spotted in the border world as of yet, but are implied in the course of the narrative to have originated there.
The antlions encountered in Half-Life 2 are implied to have been brought to Earth from Xen, via the Portal Storms.
In Half-Life: Opposing Force, it is revealed that scientists at the Black Mesa Research Facility had collected several infant Race X Shocktroopers and a particular spore-launching plant (the spores of which are eaten and used as weapons by Shocktroopers) during their teleportation experiments. As no Black Mesa contact with any other alien world have been revealed, it is strongly implied that Race-X inhabit an unknown section of Xen. As a further implication, the glowing balls of energy used to power the Race-X Geneworm's portal have their origin in Xen. Furthermore, the protusion in which the Geneworm's head terminates strongly resembles the Xen Tentacles.
Politics
Territorial Boundaries
Given the vast size and numerous landmasses found in the border world, different areas of Xen are easiest classified by the contents of their skies.
One part of Xen is centered around a large, cloudy area lit by two yellow suns. This area held the majority of Nihilanth's forces, as well as the entrance to his Alien Grunt factory.
This territory stretched out into a larger, thicker, red-green nebula which was left undeveloped except for the occasional teleportal. This area was periodically patrolled by vortigaunts and controllers, but their influence there less substantial. This area is home to the majority of Xen's non-sentient wildlife, notably the Gonarch.
Far away from Nihilanth's landmasses, the other major territory of Xen is easily classified by its bright blue-green skies. This area is home to the vast floating "bacteria" on Xen, which fill the entire horizon.
Finally, some small islands of Xen exist in nearly pitch blackness. As the entrance to Nihilanth's chamber is located in one such void, it is probable that this territory was also under his control.
Strategic Importance
Control of Xen is sought by many factions throughout the Half-Life universe. Both Nihilanth and humanity prized the area for its energy-rich yellow crystals, which aid in the effectiveness of teleportation-based technologies. Scientists at Black Mesa also routinely captured alien specimens from Xen, for study in their laboratories.
The mysterious faction represented by the G-man also saw use in Xen, guiding characters like Gordon Freeman and Adrian Shephard towards Nihilanth in an effort to have the leader killed. When Gordon accomplished this feat, this mystery group immediately took control of Xen for reasons unknown. To date, the border world is still thought to be under their control.
Narrative
When the first teleportation devices were built in the Black Mesa Research Facility, the scientists soon discovered that any teleported object would travel through a "dimensional border world" on its journey. Naming this place Xen, the scientists quickly set about teleporting survey teams to the border world to collect samples and set up equipment. Although Nihilanth, the main leader of Xen, would often have his forces kill the survey teams, the Black Mesa scientists continued to think up ways of collecting organisms and minerals from Xen, eventually using these to teleport organisms directly to Earth.
When Gordon Freeman was helping to analyze a sample of Xen crystal, a resonance cascade opened up a massive rift between Xen and Earth, teleporting a huge amount of Xen creatures to earth. This event became what was known as "The Portal Storms". Although Dr. Richard Keller had managed to repair the bulk of the damage in under a day, with the help of Dr. Colette Green and Dr. Gina Cross, Nihilanth held the rift open and used it to begin a retaliatory invasion of Earth. The Race X also began an invasion of Earth at this time, sending in the Gene Worm and a sizeable army.
The G-man began secretly guiding Earth's soldiers towards Xen in an effort to have the Nihilanth killed. Eventually though, Gordon Freeman personally killed the Nihilanth, closing the rift, while Adiran Shephard later killed the Race-X Gene Worm. With Nihilanth dead, the G-man and an unknown group took control of Xen.
Many years later, after an invasion of Earth by the Combine, rebel scientists continued to research teleportation technology as a weapon against them, using Xen's unique properties to amplify their equipment.
Xen's current fate is unknown, but many Xen creatures continue to inhabit the Earth.
Criticism
While much of Half-Life takes place in and around the Black Mesa Research Facility, the final few chapters take place in Xen. Some players have complained about this, insisting that the Black Mesa portions are better designed. They praise the jarring effect of "normal" surroundings being invaded by unfamiliar creatures, and claim that this is lost when encountering alien creatures in an entirely alien environment. However, other players have praised the Xen sections because of the imagination and quality of design in its execution. While most games that feature aliens draw inspiration from sources such as Aliens (e.g. Duke Nukem 3D) or generic horror films (e.g. Doom), the aliens and environments of Half-Life have been more carefully crafted with considerable attention to detail (e.g. Xen's ecology; homologous anatomy).
Another source of player complaints is the disproportionately large number of jumping puzzles in Xen. Its unusual physics mean that there are many sections in Xen where the player must perform a series of precisely-executed jumps, with mis-steps punished by death. There is a sizeable group of gamers who object strenuously to any such jumping puzzles in first-person shooter games; however, the jumping puzzle is as old as the ability to jump in these games and is unlikely to disappear in the future (especially with the increasing use of more realistic physics; e.g. Half-Life 2).
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