Warhammer 40,000 and Time Travel

[Elheru Aran]

I think the only alien race that can count on being able to get anywhere they want to go reasonably reliably, consistently faster than the Imperium is the Necrons.

There is also the Eldar with their Webway Portals. The GEoM had a plan to phase out warp-capable craft and the Navis Nobilites (Navigators) with a human made webway because how of reliable and fast that system is.

Only works if there's a webway portal at both ends, though. Getting in and out of the webway without a portal is a tricky business, perhaps impossible for anybody who's not Eldar. Czevak is the only Imperial I know of who's reliably used webways, and that's because he spent like 40 years in the Black Library or something.

[NecronLord]

It's never been implied that the Emperor wanted to abolish Navigators with the Imperial Webway, presumably he would use both, as both are useful. Even the eldar use navigators when they can (Farseer has an example of an ancient pact between House Belisarius and Craftworld Ulthwe for instance) get them, for travel outside the web.

[SilverDragonRed]

Only works if there's a webway portal at both ends, though. Getting in and out of the webway without a portal is a tricky business, perhaps impossible for anybody who's not Eldar. Czevak is the only Imperial I know of who's reliably used webways, and that's because he spent like 40 years in the Black Library or something.

You're right about that limitation. If you go by Dark Crusade, Taldeer brought a ship with an onboard portal so she link it to one they were building on the planet, so she could bring in reinforcements from Ulthwe. So they do contingencies for places without a portal available.

It's never been implied that the Emperor wanted to abolish Navigators with the Imperial Webway, presumably he would use both, as both are useful. Even the eldar use navigators when they can (Farseer has an example of an ancient pact between House Belisarius and Craftworld Ulthwe for instance) get them, for travel outside the web.

He didn't want to outright abolish Navigators, but he did want to curtail their political power.

[Cykeisme]

The 40k material I've read lines up pretty perfectly with Sea Skimmer's statements about the Imperium's strategic response to threats.

The local system monitor ships, orbital defense platforms, surface-based anti-starship weapons and PDF regiments are expected to be able to drive off (or at least slow down) most threats, and if they can't handle it, they call for help.
The Imperium's response depends on how great the threat is, and how important the system is. Since there's always a demand for military intervention somewhere, the degree of response offered to each warzone needs to be prioritized.
I've seen clear descriptions that escalating response will increase the radius in which military forces are drawn in. It can go up to sub-sector level, sector level, and in rare occasions, forces are drawn from across the entire Segmentum or from other Segmentums (the galaxy is divided into four Segmentums).
Again, on top of the delays in the various levels of government (sub-sector, sector, Segmentum, Terra itself) processing the information coming out of the threatened planet, there's also the time taken to muster the response forces. And then there's the topic of the OP itself, the vagaries of warp travel.

If a threatened planet is lucky, there are also the Space Marines that might show up within weeks, or even days, after a call for help goes out. They're good at rapid response and quick mobilization, and that sort of thing.

Hence there is no need for the instant next-day kind of response that Purple was asking about; it doesn't exist, but it's already accounted for.

Edit: Crap, just noticed the previous post was October 17th. Thread was still on the first page, but my bad

[Eipok_Kruden]

There is also the Eldar with their Webway Portals. The GEoM had a plan to phase out warp-capable craft and the Navis Nobilites (Navigators) with a human made webway because how of reliable and fast that system is.

Only works if there's a webway portal at both ends, though. Getting in and out of the webway without a portal is a tricky business, perhaps impossible for anybody who's not Eldar. Czevak is the only Imperial I know of who's reliably used webways, and that's because he spent like 40 years in the Black Library or something.

That was the entire point. The Emperor was planning on building a human-made webway infrastructure, likely with portals in every subsector. Of course, he was so consumed with that vision that he was blind to Horus' Betrayal, and when Magnus attempted to warn him, Magnus inadvertently destroyed the under-construction Webway Nexus on Terra and earned the Thousand Sons the Space Wolves' axe. Whole plan went to shit, but it was a nice idea.