''The good news is, we can visit other Earths.''
''The bad news is, somebody out there doesn't like us.''

Something that looks like TimeTravel combined with [[AlternateReality alternative world]] hopping. ''GURPS: Infinite Worlds'' is the default TabletopGame/{{GURPS}} 4th edition setting, loosely inspired by Creator/HBeamPiper's "Literature/{{Paratime}}" novels. The successor to the Third Edition sourcebook ''GURPS Time Travel'' and its supplement ''TabletopGame/GURPSAlternateEarths''.

The basic concept is this: A Parallel Earth (that calls itself "Homeline") develops the technology for travel to other timelines. It is controlled by the UsefulNotes/UnitedNations, which effectively becomes a World Government (an opinion not every nation and corporation agrees with). They secretly explore and exploit the other Earths (in ''relatively'' benign ways - buying resources from Earths that have plenty, for example, and dumping wastes on Earths that never developed life) and forms an organization known as "The Infinity Patrol" for the purpose of keeping "The Secret" (that is, the existence of TheMultiverse) from those Worlds that do not know about it (the vast majority discovered so far).

The reason is twofold. First, worldlines that learn The Secret may either be aggressive timelines, or become the victim of one, creating another reality-hopping danger. But the second deals with "echo" timelines that mirror Earth's past -- changing an echo by interfering too much may cause that reality to "shift" closer or farther away from Homeline (that is, it becomes more or less easy to access.) In fact, Homeline's biggest rival, Centrum, a World that also has "cross-time" technology but with a [[strike:Communist-type]] socialist technocratic society, seeks to draw worlds "closer" to themselves so they can influence them into developing similar governments. Occasionally, "outtimers" (slang for people from outside Homeline) are recruited to join Infinity if they are judged worthy. This is similar to a TimePolice setting genre except it involves parallel worlds instead of the actual past or future. (The book also includes a separate, Time Travel setting called "Project Timepiece" as well as settings such as The Order of the Hourglass, a pulp setting where adventurers [[MentalTimeTravel travel through time via their minds]].)

Oh, by the way there's a third up-and-coming player in the multiverse that recently extracted The Secret from a crashed Homeline conveyor. Homeline's name for their timeline? [[StupidJetpackHitler Reich-]][[OhCrap 5]].

This setup allows GURPS game masters to permit {{Crossover}}s between different genres. For example, the Earth of "IST" from the original ''TabletopGame/GURPSSupers'' has been recently discovered, which could allow for crossovers between the two settings. This also gives both the player and GM a huge sandbox to play with. This is to some degree, the purpose of the setting, as it literally allows the game master and the players to goof around, err... that is police the infinite multiverse where literally anything is possible (that includes some very weird possibilities) without worrying about actual time-travel (unless you want to, of course) The sheer complexity and size of the multiverse and the parachronic physics is probably the main reason The Secret can be maintained with any success at all.

The publisher's Web page for the book is [[http://www.sjgames.com/gurps/books/infiniteworlds/ here.]]
!!This, as a setting for TabletopGame/{{GURPS}}, shares many tropes with TabletopGame/{{GURPS}}.

!! '''Other tropes''':
* AlienNonInterferenceClause: There's no general bar, but Infinity enforces individual ones for individual worlds. TheMasquerade needs to be upheld on ''all'' worlds, travel to worlds with advanced technology (in other words, potentially able to develop parachronics) is restricted, and cultural contamination, cargo cults and colonialism are to be avoided. Also, meddling with "echo" worlds (worlds identical to time periods in Homeline's past) is forbidden, but that's because their temporal physics are unstable. Other than that, trade and "benevolent guidance" happen all the time.
* AlienSpaceBats: Centrum and Homeline do a ''LOT'' of this, as often as not as a part of their ongoing conflict. More worryingly, it seems that they may not be the only ones who do this, as the no less than 18 Gothas (parallels that all suffered a ZombieApocalypse with a common source) seem to point to [[MysticalPlague a common origin]].
* AllohistoricalAllusion: There is a mercenary outfit called Alternate Outcomes Inc. that works as the only PMC allowed to carry out out-time operations. The first PMC was [[UsefulNotes/SouthAfrica South African]] Executive Outcomes.
* AlternateHistory: The point of the exercise, most of the time.
* AlternateUniverse: Where all these alternate histories (and some worlds so weird they're barely recognizable as Earth) can exist.
* AncientConspiracy: The Cabal, which since it's mostly made up of sorcerers and assorted supernaturals with amoral, inscrutable ([[WeAreStrugglingTogether and often conflicting]]) goals, [[MagicVersusScience is an unwelcome wild card in the conflict between techno-centric Homeline and Centrum]]. [[StrawVulcan Centrum especially]], as their ingrained pragmatism and logic has a hard time coping with a concept as irrational as magic (they tend to pretend it's not there until it goes away, get rid of it by any means necessary if it doesn't, or [[ScrewThisImOuttaHere just pull out]] if neither option works).
* AntiVillain: Centrum really isn't evil, just with [[BlueAndOrangeMorality alien social values]] (what we might term "ruthlessness", they term "practicality"). There's a section explicitly allowing the GM to decide if they should be ALighterShadeOfGrey or ADarkerShadeOfGrey, and another that mentions the possibility of an EnemyMine with Infinity to fight Reich-5 if it ever becomes a major player.
* ArabianNightsDays:
** Caliph twists this. It's a world mostly covered by Islamic nations in the 1600s, except that the magic is technological... and the worldline is by far the most advanced of any that either Infinity or Centrum have ever discovered.
** A more classical example is Burton, an anachronistic myth parallel that exists in a StableTimeLoop that coincides with the reign of Caliph Harun al-Rashid where the folktales are true.
* AwakeningTheSleepingGiant: There are several sleeping titans in this setting:
** Reich-5 was originally presented as a sleeping giant, but while it's awakened, it suffered DiminishingVillainThreat between its initial presentation and the exposure of parachronics, and the latter event occurred in such a way that most of the Nazi hierarchy is unaware of the situation, so the Armanen and Raven Division are more of a GoldfishPoopGang right now than a match for Homeline or Centrum. However, they're still very nasty, and if their superiors ''did'' find out what's going on...
** Merlin's another partially-awakened giant: a world with technology equal to that of our own Earth, but with access to advanced {{Magitek}} as well (in fact, the world of the ''GURPS: Technomancer'' supplement). A blunder with Gate magic and Infinity's response to it made America's CIA aware of parachronics, and they've started spying on Homeline back (though Homeline is as of yet unaware of this); however, they are not necessarily hostile. More worrisome, [[ArgentinaIsNaziland the Condor Group Nazis in control of Argentina]] have made an alliance with Reich-5's Armanen.
** Caliph is a mostly-peaceful world of Islamic CrystalSpiresAndTogas, but its technology is centuries ahead of anything that Infinity and Centrum have, and both sides want it. Of course, any intrusion risks telling Caliph about the existence of parachronics, and that centuries-advanced technology makes Caliph into quite possibly the most powerful single worldline in existence.
** Most horrifying of all possibilities is Shikaku-mon. A dark, overpopulated {{Cyberpunk}} world where democracy never happened, over half of which is ruled by an UsefulNotes/ImperialJapan that christianized and modernized early on, it would be a likely threat to Homeline for that alone. What makes it worse, though, is that parachronic projectors may work on that worldline, meaning that [[ParanoiaFuel if they develop parachronic technology, they can reach Homeline]]. Also, the existence of Shikaku-mon is ''not'' a secret on Homeline, so it may be only a matter of time before the {{Masquerade}} breaks on this world as well. Sweet dreams!
** The ''Worlds of Horror'' supplement introduces another Sleeping Giant that is potentially far, '''''far''''' worse: Taft-1. Both Infinity and Centrum think that the point of divergence is Truman's early death and the election of Robert A. Taft in 1948. It's not.
* BewareOfHitchhikingGhosts: A double inversion. Troubled people might get picked up by a mysterious stranger who gives them life-affirming advice before dropping them off. Turns out he's some kind of supernatural being (not necessarily a ghost) who drives across worlds for this very purpose.
* BrokenMasquerade: The wheels are starting to come off in Quantum 3. Reich-5 is out of the bottle (though their parachronics are limited to a GovernmentConspiracy within the declining Reich) and has begun invading other worlds, while due to the emergency circumstances of first penetration, Merlin's U.S. government has discovered Infinity and is in the process of trying to infiltrate Homeline back.
* CanonWelding: The 4e version of the setting has absorbed several campaigns from the 3e Time Travel book that were originally entirely separate settings.
** In a more general sense, just about every other GURPS setting has a corresponding world mentioned in the book. Including the licensed ones (yes, Infinity agents can visit Literature/{{Discworld}}, [[Franchise/ConanTheBarbarian Hyboria]] and Literature/WitchWorld). From a meta perspective, the ''Infinite Worlds'' setting basically exists to facilitate {{Massive Multiplayer Crossover}}s.
* CrapsackWorld: Not as bad as most other cases and not immediately apparent, but the more you read, the more obvious it is that there are a LOT more crappy parallel worlds than reasonably nice ones (from the [[ColonyDrop Lucifer parallels]] to the [[StupidJetpackHitler Reich parallels]], with the disturbingly common [[ZombieApocalypse Gotha parallels]] and many others in-between), and even the nice ones tend to have ugly caveats - Gernsback, for example, has world peace under the League of Nations (both TheGreatDepression and UsefulNotes/WorldWarTwo were averted) and awesome RaygunGothic SchizoTech thanks to UsefulNotes/NikolaTesla's inventions, but due to not having had those experiences, racism, sexism and colonialism are still firmly entrenched at pre-1940's levels in most inhabitants' minds. It still is one of the most positive parallels overall.
** Nergal, where the Assyrian Empire destroyed the Hebrews and Phoenicians, prevented the rise of Persia and set a very bloody standard for every empire to follow. Nearly every local culture practices human sacrifice, paper and alphabetic writing disappeared from history, and the world is slowly descending into an anomalous Ice Age that's hinted to be a result of dark magic. It's bad enough that Infinity has decided to throw TheMasquerade to the wind; Nergal lacks the technology to replicate parachronics, and to quote the book, "frankly, the Patrol would like to cause as much cultural contamination here as possible."
* DeathWorld: Several parallels qualify, even appart from the aforementioned Gotha and Lucifer parallels, many of them colloquially called [[NamesToRunAwayFromReallyFast Hell Worlds]]. The causes run the gamut from [[DepopulationBomb incredibly deadly]] [[ThePlague epidemics]] to [[GreenAesop man-made ecological meltdown]] to [[NukeEm nuclear war]] to [[AlienInvasion Alien]] [[{{Ultraterrestrials}} (or maybe not)]] [[AlienInvasion Invasion]], but probably the most worrisome (i.e. most likely to be completely and irreversibly quarantined) are the (thankfully few) parallels that seem to exist in a CosmicHorrorStory universe. One of these parallels may have the Things back-tracing the parachronic trail from a Homeline Scout team.
* {{Demonization}}: A literal example in Azoth-7. When the Spanish Inquisition unexpectedly managed to summon Spain's tutelary angel to prevent an English invasion, the English accused them of making a pact with [[DemonLordsAndArchdevils Samael]] instead. This is ''probably'' not true.
* DiminishingVillainThreat: In ''Alternate Earths'', Reich-5's Imperial Japan, especially their ''[[SecretPolice Kempei Tai]]'' organization, were every bit as deadly an adversary as the Nazis. In ''Infinite Worlds'', Japan is decaying into warlord states and the ''Kempei Tai'' have, within a single generation, gone from being the guys who gave the Gestapo nightmares to a bureaucratic tar pit.
** The Reich itself plays with this; while the Nazi regime is no longer the unstoppable Orwellian terror that it used to be, a faction within the decaying Reich [[OhCrap now has world-jumpers at their disposal]].
* DoingInTheScientist: Some of the nuttier sorts at Paralabs think that parachronics ''actually'' runs on ClapYourHandsIfYouBelieve. This hasn't been proven either way, owing to the one field test disappearing into thin air.
* DoingInTheWizard: Inverted, as there are several parallels where magic clearly exists, making it kinda hard to deny (though Centrum tries). There is even a loose group of powerful magic-users and monsters that also travel through realities, the Cabal (from ''Gurps Cabal'', natch). ''However'', the Merlin parallels play this straight by providing a scientific explanation for GURPS' default magic system, which is heavily tied in with parachronic travel itself.
* EnemyMine: One suggestion in the book is that Infinity and Centrum could ally against Reich-5. On the other hand, a vignette in the book suggests that Centrum might take advantage of "the Irrationalist sect from Bavaria" to draw off Infinity resources.
* EqualOpportunityEvil: Centrum is explicitly called out as finding the concept of discrimination based on race and gender very strange. They're a little more lenient on social divisions, but that's because they're [[AsskickingEqualsAuthority meritocrats]].
* EvilerThanThou: What may happen when Centrum and Raven Division finally meet. Centrum are EqualOpportunityEvil meritocrats, while Raven Division... [[StupidJetpackHitler are]] [[{{Ghostapo}} Nazis]].
* EvilIsDeathlyCold: Nergal's oncoming Ice Age appears to be a result of the gates of Hell opening. It's anyone's guess just how literally to take this.
* ExpendableAlternateUniverse: Neither Infinity nor Centrum quite view people from other worldlines as real people. Among other things, it notes that some Homeline filmmakers have taken to filming real battles on other worldlines with thousands of people dying to use as footage in their historical epics.
* FantasticRankSystem: Centrum dispenses with individually named ranks almost entirely[[note]]Unattached are a special case of Grade 7[[/note]], using a numbered scale that starts at Grade 1 (the default for every citizen) and ends at Grade 7 (top-level coordinators of each Service that set policy for Centran society and have some authority even across Service lines).
* ForScience: Apart from the Gernsback parallel, which plays this straight (if mostly benevolently), there's an interesting variation with the Cabal (For Magic!).
* FromBadToWorse: Many on Homeline in the know consider Reich-5's discovery of parallel worlds to be this; while their own version is, so far, ''much'' less performant than that of Homeline or Centrum, it could potentially end up forcing Homeline in a two-front conflict, as the latter's dimensional coordinates are between the other two.
** A potentially much, much worse case happened recently on the former myth parallel once designated Oppenheim: Once an Edwardian/WWI-era world with some myth parallel elements,
* {{Ghostapo}}:
** Reich-5's Raven Division uses quite a bit of Aryan magic to facilitate their world-hopping.
** The Condor Group from Merlin are Nazi mages who fled to Argentina after UsefulNotes/WorldWarII and formed an alliance with the Peróns. They've recently formed a low-level alliance with Reich-5's Armanen Order.
* GreyAndGrayMorality: The conflict between Centrum and Homeline, where neither can be easily categorised as pure good or completely bad.
* HellOnEarth: Nergal is implied to be in the beginning stages of this. All of its surviving gods demand HumanSacrifice, and the world is descending into an [[EvilIsDeathlyCold anomalous ice age]] couched in melodramatic terms.
* TheHouseOfNormandy: Where Centrum's history splits off from Homeline's; Henry I's son and heir [[http://en.wikipedia.org/wiki/William_the_Aetheling William the Aetheling]] doesn't die in a shipwreck, and the Angevin Empire [[AlternateHistoryWank becomes even more of a world-spanning power than real-life Great Britain did]].
* KilledToUpholdTheMasquerade: Stringently averted by the Time Patrol; Centrum has less scruples, but there are few situations where they'll bother (see just below).
* Myth/KingArthur: The "Camelot" designation used to be used to describe worlds with King Arthur, but it's since been dropped. In just about any world between 400 and 600 AD, there's almost certain to be some kind of King Arthur up in Britain, whether it's Artorius the Romano-British warlord, King Arthur Pendragon of the Round Table, or a weirder variation. Also, [[ForScience just out of curiosity]], Infinity is keeping a close eye on an echo that's currently in 410 AD.
* LizardFolk: The chief inhabitants of the United States of Lizardia evolved from [[UsefulNotes/StockDinosaursTrueDinosaurs troodons]] -- though, rather bizarrely, [[InSpiteOfANail their recent history still closely parallels Homeline's]].
* TheMagicComesBack: The Merlin worlds, parallels where Hellstorms locally warped the fabric of reality and brought magic back to modern-day Earth.[[note]]Two of these parallels are the settings for ''TabletopGame/GURPSTechnomancer'' and ''GURPS: WWII: [[{{Ghostapo}} Weird War II]]''.[[/note]]
* {{Magitek}}: Exists on worlds where magic and technology have both been developed.
** Merlin has the most advanced version yet seen, to the point where magic has been seamlessly integrated into the world's technological infrastructure.
** Azoth-7 has a weird version, where alchemical developments have led to something that looks rather like Victorian science fiction, only a hundred years earlier and with a completely different form of technology.
** Homeline's Paralabs have been trying to develop some, but it's mostly seen as a curiosity rather than a serious pursuit, as Infinity is mainly a technological organization. For example, they came up with a really weird conveyor that ran on ClapYourHandsIfYouBelieve... and it and its inventor vanished in the first test.
* TheMasquerade: Infinity policy is to not reveal "the Secret" of parachronics to any outsiders, and to actively sabotage anyone else's attempts to do so; people who learn the Secret may be kidnapped and sent to [[PenalColony Coventry]]. Centrum is less anal-retentive about it; they only care if the natives learn about them on planets advanced enough to develop parachronics. However, when that happens, they tend not to let technicalities (like the right to live) get in the way of business.
* MegaCorp:
** Infinity Unlimited is structured as a corporation, though in practice it functions more as a U.N. agency.
** White Star Trading was Paul Van Zandt's original crosstime trading firm and the main source of seed capital for Infinity.
** Consolidated Mines, Unlimited was formed by a [[RichardNixonTheUsedCarSalesman parallel-world Cecil Rhodes]], who combines low-tech and high-tech mining techniques to bring home more raw materials than anyone else. Rhodes himself made a move to get elected to the Infinity board of directors, and took advantage of the [[NoJustNoReaction expected outcry from Africa]] to [[ManipulativeBastard split his operation off from Infinity]].
** The Yugorovsky Group are a [[TheMafiya Mafiya]]-affiliated mining conglomerate known for being [[CorruptCorporateExecutive ruthless, deadly]] and [[GovernmentConspiracy tied into the Russian government at the highest levels]]. They often engage in proxy wars with CMU.
** Johnson Crosstime Inc. has invested itself so heavily in Rome-2 that they effectively run the place, having turned the Roman Empire of that world into a massive tourist trap.
* MentalTimeTravel: World Jumpers.
* TheMultiverse: Of GURPS.
* MultiversalConqueror:
** Both Centrum and Reich-5's Raven Division count, for different motives: Centrum [[WellIntentionedExtremist thinks they're civilizing alien realities]], Raven Division because they're [[ThoseWackyNazis greedy Nazis]].
** On Homeline, Infinity generally tries not to act like this... but there is no AlienNonInterferenceClause, and they're not against [[GovernmentConspiracy behind-the-scenes guidance]] of non-Homeline humans, or stealing technology and art from other parallels for Homeline's benefit. They also have to ride herd on sharp entrepreneurs who have their own ambitions:
*** Johnson Crosstime, Inc. ended up taking over Rome-2 because Infinity didn't read the fine print on his business license. By the time they realized what he was doing, the situation had become insane enough that they threw up their hands and ratified his buyout of the Roman Empire.
*** The Yugorovsky Group and TheMafiya send a lot of their members out to primitive worlds to "play czar," taking over nations to exploit them for their Homeline masters.
*** Infinity themselves have drawn up plans for the [[GodzillaThreshold annihilation of the governments of Reich-5]], in concert with Homeline's militaries. Operation Firefall was shelved because it was too risky and promised an appalling number of casualties even if Homeline won.
*** For some reason it seemed like a good idea to Infinity to put an alternate Cecil Rhodes in charge of mining operations on multiple Africas. There's no evidence he's become one of these ''yet'', but some people in Infinity think it's just a matter of time.
*** Infinity has an operation going on in the South Africa of Nergal, where they pose as gods and wizards who rule over the local Zulus and occasionally lead them in SlaveLiberation raids against the other nations of Nergal. This is presented as [[TheExtremistWasRight a good thing]], as the other nations of Nergal all practice HumanSacrifice and are possibly leading the world to ruin through their magic.
* NGOSuperpower: Infinity Inc. is probably the most powerful entity on Homeline economically and politically. Only a partial example, as Infinity is technically a U.N. member organization. (In practice, Infinity doesn't answer to anyone.)
* NiceJobBreakingItHero: The snafu that resulted in the Reich-5 SS discovering parallel worlds and how to reach them was originally a Russian attempt to aid the partisans of the Reichsostland.
* NonindicativeName:
** The "Gotha" parallels, and the plague named after them. The name came about because the first such world that Infinity discovered was just a particularly bleak Dark Ages parallel where Visigothic berserkers had destroyed every city in their path. It was only later that Infinity discovered that things were [[ZombieApocalypse far darker than that]].
** A poetic-to-the-point-of-nonindicative name is the "Lucifer" series of worlds. No, these are not worlds defined by the presence of [[{{Satan}} Big Red]], they're worlds that have become or are becoming uninhabitable through [[ColonyDrop a meteor strike]].
* ObviousCrossoverMethod: As mentioned under the Canon Welding entry, the setting itself was basically built to allow crossovers to happen by way of interdimensional travel.
* ReedRichardsIsUseless: Averted. Parachronics are making Homeline a better place in many ways -- one of the most obvious is the fact that with a seemingly unlimited number of uninhabited parallels to exploit, resource conflicts have become a thing of the past. Nevertheless, Homeline's seedier elements are finding ways to use the infinite worlds to support ''their'' agendas as well.
* RichardNixonTheUsedCarSalesman: In what may just be the Most Triumphant Example, the director of the Infinity Patrol's secret ISWAT special task force is... an alternate [[http://en.wikipedia.org/wiki/Otto_Skorzeny Otto Skorzeny]]. However, this alt-Skorzeny was, in his home parallel, a freedom fighter for the [[RagTagBunchOfMisfits multi-national and -denominational]], proto-democratic [[TheRepublic Republican]] [[TheAlliance Alliance]] (in this timeline, European monarchies endured almost unopposed until the collapse of the Austro-Hungarian Empire in the 1930's), and really, really ''hates'' ThoseWackyNazis (especially when they're other hims), and so uses live-fire sabotage missions against them [[TrainingFromHell as part of the standard ISWAT training]].
** Par for the course to have a bunch, really. It's even possible to meet your own alternate-universe self, who likely as not can have a very different life experience.
* [[SpaceColdWar Spacetime Cold War]]: Infinity vs. Centrum, although the presence of Reich-5 may or may not end up provoking a cross-temporal equivalent of World War II.
* StupidJetpackHitler: Reich-5, a world where the Nazis have taken over and developed some [[AppliedPhlebotinum superscience]]. They don't have world-hopping technology yet, but ''do'' have some innately gifted people who can do it.
* TheThemeParkVersion: Deliberately invoked by Johnson's Rome, where Johnson Crosstime Inc. has all but bought out the local Roman Empire, and then gleefully pumped up the "fun parts" of the already pervasive decadence it was riddled by (fortunately for the locals, Johnson is both practical and modern in his outlook, so he's also arranged for a gradual phasing-out of the more unsavory aspects
* TimePolice, alternate-history style.
* TimeTravel: But to [[AlternateHistory alternate timelines]] instead of the actual past or future (unless the GM decides to mix it up), partly to avoid TimeyWimeyBall-related problems like those nasty {{temporal paradox}}es.
* TrainingFromHell: The Academy; one year spent in the middle of an Ice Age. The big weeding drill in the middle is being dumped in the middle of the frozen wilderness [[WithThisHerring in your sleepwear, with whatever you can grab five minutes after the alert]] and told to find your way back home.
* UsefulNotes/UnitedNations: Though the UN itself is being usurped by Infinity, which essentially doesn't answer to anyone.
* TheUsualAdversaries: Homeline's Infinity and Centrum's Interworld Service serve as this for each other, as their respective worlds are the only ones that have full access to parachronic tech. They are directly competing against one another to spread their influence and secure any potential "back doors" into their homeworlds.
* WeAREStrugglingTogether: Possibly Infinity's greatest handicap in its parachronic operations (especially compared to the mostly unified front Centrum presents) is that a LOT of Homeline's various governments, corporations, [=NGOs=], and even criminal groups have access to parachronic tech (legally or otherwise) and use it to push their often wildly conflicting agendas across the parallel worlds. Consequently, a lot of their ressources are tied up monitoring, policing and otherwise cat-herding all these groups.
** The Cabal is another example, as it's basically made of several different groups of supernaturals and magic-users with often widely divergent goals and philosophies. To its more technologically-inclined rivals Infinity and Centrum, this doesn't make it any less threatening, though, as this (among other things) makes it the biggest WildCard of the setting.
* WeirdnessMagnet: Worlds in which Robert A. Taft is/was president have either magic, an artificial spacecraft of unknown origin in orbit around Saturn or a peculiar sterilizing radiation whose source is heavily implied to be ''[[Franchise/CthulhuMythos Azathoth]]''.
* WellIntentionedExtremist: Centrum's default moral status. They're ruthless, hegemonic cultural imperialists, but they're trying to save each parallel they're operating in from undergoing their own versions of the [[TheEndOfTheWorldAsWeKnowIt Last War]].
* TheWorldAsMyth: There are more than a few parallels based on explicitly fictional settings, called "myth parallels."
* ZeppelinsFromAnotherWorld: The random timeline generation has a specific result that produces these, by the book's own admission (see the quote on that page) driven by RuleOfCool.
* ZombieApocalypse: The Gotha parallels. Gotha zombies are [[TechnicallyLivingZombie carriers of a prion-based disease]] that mutated from the pneumonic plague, which retain some of their previous intelligence and memory, as well as just enough wherewithal to hold onto old cultural beliefs (usually with a strong slant towards fatalism and death worship). Thus why the zombies discovered on Gotha-1 were described as Visigothic berserkers; another Gotha parallel had zombie Thuggee in India.