[Dorn]

As the Ordo Chronos seems to become a part of official fluff with the new Inquisition minidex, I wanted to ask how u see time travel in 40k. I know in the Eisenhorn trilogy (or was it Ravenour, not completly sure right now) was already a chapter about a time travel, there they encountered Tyranids.

So how does it work? Assumingly using somehow the effects of the warp deforming time... How are the effects of time travel? How may the history of 40k be altered throught time travel?

Can also other races use this effect? Or has it already be used? Maybe Eldar, but travelling through the warp is very dangerous or even impossible for beings with a high psionic emission? Maybe the Tau were made by the Eldar, so they can sent the Tau through the time so they can stop the summounting of Slannesh?

Questions over questions... A lot of stuff for a discussion... So let it beginn...

[MarcoSkoll]

To quote myself from an Ammobunker topic:

The nature of time is pretty flexible in WH40K. It's what TV Tropes would call a Timey Wimey Ball - those rare cases of 40k time travel have few consistent rules; after all, it's the warp!
Paradoxes are not unknown, from the stable Ontological (ships being sent to answer their own distress signals) to the unstable Grandfather (the Ork Warboss who killed himself to get two of his favourite gun)

The above-mentioned Grandfather paradox averted a Waagh, so clearly timelines can change - or at least exist in multiple forms.

However, deliberately going back in time to change things is a no. Time travel is something that only happen on a very rare and entirely unpredictable basis - or at least should only happen on a rare and unpredictable basis.

The moment you introduce stable time-travel to the setting, other than perhaps as something Tzeentch does for giggles*, the time-line is doomed to fall apart.

Ships going back in time unpredictably and the rather unreliable Emperor's Tarot... these work fine, but if you can get in the TARDIS and think "Hey, I'll go kill Horus before he starts the Heresy", the setting suddenly makes no sense.

I am writing a character who made an (unexpected) jaunt back in time, but I plan on treating her future as a possible/parallel one (where she only knows the crudest details of how it came to be that way), thus saving a lot of the potential mix-ups and paradoxes.

* That said, I did once write a plot somewhat inspired by the Terminator films, where a Daemon figures out how to re-emerge in the past and goes about trying to kill someone who'll thwart him in the future (particularly the second film, as he/she/it kept possessing different bodies to disguise itself).
The protagonists in said plot were there partly through luck, partly through hefty doses of prophesy... and were expected to work quite hard to keep up and work out the details behind what the daemon was doing.

[Koval]

To paraphrase Marco... accidental time travel can happen (and in fact that's the whole point of the Ordo Chronos), but deliberate time travel in a setting not dedicated to it will cause major headaches.

I wrote half a short story once (and didn't finish it) whereby Tzeentch catapulted a Dark Angel Fallen back in time to the Drop Site Massacre at Istvaan because he felt like it. It carried with it the explicit proviso that Tzeentch was also making this happen entirely out of continuity. Needless to say, it spiralled out of proportion and I couldn't bring myself to finish it.

In universe, we admittedly have things like distress beacons being answered by the military force that sent them (cf. Desert Raiders, though I wouldn't otherwise recommend it as it's an awful read), or the aforementioned Ork Warboss that wanted more dakka; these are examples where the time travel is entirely accidental on the part of the characters.

Of course, time travel going forwards is possible and entirely expected

[MarcoSkoll]

To paraphrase Marco... accidental time travel can happen (and in fact that's the whole point of the Ordo Chronos), but deliberate time travel in a setting not dedicated to it will cause major headaches.

Nicely summarised.

That's more or less the long or short of it. The Ordo Chronos clears up cases where the warp throws a temporal wobbly - although probably only big temporal wobblies. If the ship complications from the Rogue Trader RPG book are any indication, it's not that rare that a warp engine can be temperamental enough to have ships arrive a week or two earlier than they left on some journeys.

However, the ever-uncertain nature of Imperial dating probably means jumps this small are entirely missed a lot of the time (a lot of planets can't even agree on which year it is*, so a week or two won't be noticed) and of no real consequence - jumping back a couple of weeks doesn't mean a lot unless you know what's happening in those next couple of weeks. Not likely in a universe where interplanetary communication is unreliable, rare, highly censored and far from instantaneous.

*Although, if we're being proper, relativity means there's no such thing as a meanwhile anyway, so no two places are actually at the same time in the first place.

[Dorn]

Warp-travel is also kind of tamed by the navigators? Maybe it would be also possible to use time travel more or less stable... Maybe with some ancient (xenos) technology? Maybe it would be possible to travel at will, but the equipment is too unprecise for a stable use or can be only used for short travels... e.g. one hour backwards. So stopping the Horus Heresy wouldn't be possible...

What kind of Xenos might have tried time travelling? Humans cann't be the only ones...

I just though that maybe some more radical Inquisitors of the Ordo Chronus might have already "saved" the Imperium one or more times by time travelling, but no one had really noticed it.
-> dissapearence/silence of the Ordo Chronos lately

sure, it will cause headaches, but it is in the hand of the writter... I'm right now just thinking about the possibilitys of time travel (Inquisitor McFly and his servant Doc Brown XD )

[MarcoSkoll]

Warp-travel is also kind of tamed by the navigators? Maybe it would be also possible to use time travel more or less stable...

Deliberately trying to invoke warp shenanigans is pretty much by definition not taming the warp.

That's a bit like asking a trained pilot to try some stunts in a hurricane. Not even an insane pilot would try it, because it won't work and is going to result in very undesirable consequences.
(It's worse on an Imperial ship, as you have hundreds of crew that you have to get to cooperate in an exercise they know has worse consequences than death).

I just though that maybe some more radical Inquisitors of the Ordo Chronus might have already "saved" the Imperium one or more times by time travelling

If you introduce the possibility of predictably changing things via time travelling, then everyone would be trying it. Xenos, Heretics, Traitors, etc... clearing up after the huge damage that they'd be causing wouldn't be the demesne of an Ordo Minoris.

The absolute blunt answer to this is that time travel in WH40K is something that only happens on a notable scale through exceptionally rare accident or a very, very, very, very, very occasional case where a literal god rips a hole through time for the sake of it, but it is not something mere mortals can play with.

Take it further than that and the setting just falls to bits.

[Koval]

What kind of Xenos might have tried time travelling? Humans cann't be the only ones...

Arguably the Necrons, given the level of stasis technology and dimension-folding gubbins* they have at their disposal. However, I'd posit that although they can sort of control the passage of time (on a local level), actual time travel is most likely beyond even them, given that we haven't heard anything about it whatsoever.

*Which, incidentally, is why Matt Ward's suggestion that they need to hijack the Webway of all things to cross the galaxy is not really something that can be taken all that seriously.

[Macabre]

What kind of Xenos might have tried time travelling? Humans cann't be the only ones...

One of the three alien races I created, the Omicron (short for ordo xenos species designation Omicron/456-N), were very adept at manipulating time and created advanced technology that could very easily bend chronological laws (their stasis and temporal acceleration/deceleration technology was second to none), eventually this technological mastery led them to designing a device capable of directed, controllable time travel...

...On its first test the entire Omicron species and its minor empire was erased from all periods of existence.

The only members of the Omicron that survived were a hundred or so personages of, a very prescient, science cadre. They foresaw this distaster and were vocally opposed to meddling in such areas of science. They created Temporal Arks, personal suits of technology that act as a quantum anchor, stabilising their existence. They are strictly pacifist, searching for a way to undo their species annihilation. An end to their goal must be near at hand, for random pieces of their fallen civilisation have begun to appear again; artifacts of such rarity that have made their way into the avaricious hands/claws/appendages of collectors. Yet the remain hidden until their restoration is complete...

...After all, who would look for a xenos race that has never existed.

[SwordlordRoy]

Only really bothered with time travel forward for the background for my Imperial Guard Homeworld and it's patron Saint...but I also committed that Darkest of Heresies by also trying to incorporate the old Rogue Trader lore of Half-Eldar (borrowing the 40ktheories Haemonculus idea), so make of it what you will.

In particular said that a trade fleet got sent forward to the Great Crusade from the start of the Age of Strife due to the latter's Warpstorms.

[Heroka Vendile]

A Perpetual used an Athame to time travel while working for the Cabal in the Horus Heresy stories.
Although obviously this makes it incredibly rare and powerful artifact that's realistically way beyond the practical scope of an Inquisitor campaign - it'd be akin to discovering the creators of the Blackstone Fortresses, to use a recent example.

[mcjomar]

...but I also committed that Darkest of Heresies by also trying to incorporate the old Rogue Trader lore of Half-Eldar (borrowing the 40ktheories Haemonculus idea), so make of it what you will.

Xenology covers that this is physically impossible, so I'm assuming this is either a chaos mutant, or something forcibly created by a renegade magos biologis or inquisitor in a lab?

We have a binary helix, and eldar have a quintuple helix - to the eldar it would be akin to trying to mate with a banana, and just as likely to result in conception (though I wouldn't put it past some dark eldar...).

[MarcoSkoll]

I don't necessarily know that the existence of

Although obviously this makes it incredibly rare and powerful artifact that's realistically way beyond the practical scope of an Inquisitor campaign

I would probably agree about an athame specifically, but it's worth saying that idea of some other powerful artefact that enables some degree of time travel isn't so far beyond the realm of plausibility that it's definitely off limits. (Obviously, we've sort of used them in the forum Dark Heresy group).

Xenology covers that this is physically impossible

I wouldn't object to the idea that an individual was rumoured to have Eldar ancestry, but more than that becomes an issue.

While whether it's biologically possible can always be answered with something like "Fabius Bile", "Haemonculus" or "Tzeentch did it", any suggestion that the idea is any more credible than mere rumour (and I suspect it'd be blooming hard to hide being a half Eldar) would probably result in a prompt burning at the stake.

[SwordlordRoy]

Considering the character I tried to apply this to specifically died during the Horus Heresy...with the Circumstances of their birth being in that Shadowy time known as the Dark Age of Technology. Any potential proof of any claims of Eldar Blood are kinda just rumors at this point...Maybe an Eldar or two know the truth, maybe a Perpetual...but beyond that, Emperor only knows.

Back to the Topic at hand, I'd say be careful about Time Travel, even accidental. Space Hulk populated by Humans from the Dark Age of Technology and Orks who react to the small, feathery Xenos these humans call "Chickens" the same way Klingons react to Tribbles: Hilarious and could provide an interesting campaign, but major finds of note should be the macguffin of an entire story arc and should probably not be Imperium-shaking. Remember, technology is kinda so backwards that Two Guardsmen where given a planet each for finding an STC for a Knife.