after indulgng bit more "convenional scifi" it occured to me! Where are the true relics of mankinds glorous past, ringworlds, topopolises, possibly even dyson spheres, where are the planetary/stellar scale megastructures? even the grimd0rk future of 40k should not be able to destroy something as big as those.?

./at0miclich

Topopoli exist. In fact, certain Hive Worlds (including, and most notably, Terra itself) would arguably qualify, plus a number of versions discovered by expeditionary/explorator fleets (the most common is apparently anathema, as it is often maintained by an Abominable Intelligence). Many of them are either under quarantine, or have been subject to various stringent forms of Exterminatus (yes, the Imperium DOES have tech that can crack a planet open. If they just want it not to count as a topopolis, though, sufficient orbital bombardment from regular weapons'd work).

Ringworlds, arguably used to exist (although the example given isn't a Niven-style, but a STL interstellar version of either a Banks-ian Orbital or Habitat, and it was destroyed by an Imperial Expeditionary Fleet during the Great Crusade). And there's a (surprisingly stable) Clarkesque version orbiting a (relatively safe) plane between Hydraphur's ecliptics (it's a complicated solar system); the main difference is that although the station segments are joined together (allowing for some flex) and encircle the planet, it isn't tethered by space elevators.

When we get to Dyson structures, IIRC, there is one in fluff, but it isn't human (in fact, it's possibly pre-human; probably pre-interstellar spaceflight; certainly pre-Crusade). In fact, it's a wholly solid uninterrupted surface, with a C'tan imprisoned inside the star it encloses. This is, of course, impossible. It's part of the torture and imprisonment for said star god.

Aside from that, consider where the Imperium ranks on the Kardashev Scale *- certainly Type I (with many worlds being Type 0), with the capacity to actually destroy planets (well, break them into smaller bodies, most of which are too small to reform into spheroids) giving it at least transient Type II capabilities. Indeed, given the aggregate of Type I planets, we should probably define it at Type II overall, but we don't have the evidence of any megastructures of the kind Dyson proposed. It's not unfeasible that the DAoT/GAoT produced such, but given the impressively rapid rate of expansion humanity had (and the fact that an efficient Dyson sphere/cloud emits very little in the way of coherent radiations and signals), before the rather spectacular fall into Old Night, it is perhaps unsurprising that they haven't been found. For that matter, it wouldn't be too surprising if they had been found, and simply haven't been (widely?) mentioned in fluff.

Likewise, we don't know that humanity ever went for the "efficiency" route. Dyson clouds, ringworlds and similar megastructures only make sense if it isn't relatively easy to just spread out to another habitable system. Admittedly, pre-warp travel (or at least pre-Geller Field), that would be the case, but given we never attempted it in Sol, it seems likely that mankind just writes it off as too much hassle to deconstruct a (significant proportion of) a solar system just to make something more efficient.

*With Type I at the level Lemarchand proposed. I could use Sagan's formula to get closer, but the setting's science is just soft enough to make that impractical)

Thanks for the answer. As I see it mankind in 40k is hellbent destroy any chance it has to survive, as always.

Anyway scenario idea popped up as i read your post. Concept:

"Halo-artefact"(pun intended)

Explorators are are partnered with slightly eccentric astromancer from mechanicus who claims know locatioin of a moving star (it has moved noticeably in last few millenias, and the archives of mechanicus are infallible. Or so they say).

the moving star is actually white dwarf (degenerative star) harnessed as stellar engine and dyson swarm combined with diminutive ringworld (orbiting at 4,5million km and thousand km wide, still having roughly 124 times earths surface area). This structure was built during the golden age, as a (crazy) generation ship to cross the void between galaxies with all the comforts of home (and AI population of thousands to millions). The ship never got to be used on its original purpose due the collapse, luckily its nature makes it hard to spot. As white dwarves rarely have any resources that would interest rogue traders.

Of course the place is a treasure trove of STC technology (it was built as colony ship originally), and it is not defenceless (if you can turn part of stars power into propulsion, i'd hate to think what happens when you turn that power against a starship or fleet or antimatter powered kinetic kill drones.

As an additional complication The Tau have also come to same conclusions that stars don't move on their own. Scenario(this would have ideas for an entire campaign of it's own) begins as players nearly crashland their ship on the ring (rings/swarms automated defences shot them down), now they have to repair their ship. Figure way to lift off without getting shot. Make friends or enemies with rings multitude of inhabitants (and the the Tau propably do the same, "we come in peace, for the greater good"), some visual and neat ideas can be solen from first Halo game.

Ideas for the rings inhabitants. How AI's react into both sides.

./atomiclich

There are a few human creations in the Imperium which, if not megastructures, are certainly macro structures.

Off the top of my head, you've got orbital rings - in the Enforcer novels, the Naval Sector command world has a vast orbiting ring structure which girdles the entire planet.

The you've got orbital plates repeatedly mentioned in the Horus Heresy novels. I don't actually know what these are, but I get the impression they're vast space stations the size of continents that link to the planet below by space elevator.

Then you've got militarised moons like the Bastion from Frozen Reaches - that looks to be about 20-50km across.

Then you've got some of the larger Imperial vessels - the Raptorus Rex of the Fire Hawks, the Rock of the Dark Angels and the Phalanx of the Imperial Fists. Ramilles Star Forts are enormous, too. No idea how big these ships are, but the impression I get is that they're notably large, even by the standards of larger Imperial ships, which tend to be around 12-15km long. Most of these are human ships dating from the Dark Age of Technology. One imagines that the Sol system is littered with ancient technological wonders like this.

Note the Imperium does occasionally engage in vast projects almost on the same scale as megastructures, such as moving Deimos (Mars' moon) to orbit Titan instead.

One imagines some space hulks are as large as moons, too.

Xeno artefacts include some examples of megastructures - apart from the Necron home of the Outsider, there aren't many examples of things like Dyson Speres, but there are Eldar Craftworlds (which I picture as being arounf 50-150km across) and, featured in the Sabbat worlds Crusade, you have some artificial planets created by a long lost alien race which are now fought over as fortress worlds.

Then you have Necron worldships (there's one example of this in the canon, which I think was destroyed by an entire chapter of marines sacrificing themselves) and the vast spaceship used by the Cabal in Legion.

Not to forget that greatest of all megastructures of course; the Webway itself.

Also Naduesh, the ruined Hive world which is hinted as being a vast battle station disguised as a planet.

Terra, Luna and Mars are all substantially mechanised, as well as vast orbital docks all over the system, particularly the asteroid belt, Jupitrer and Saturn.

A trio of comments:

Lightbringer, citation for moving Deimos, please? When I read the account of Necron Shrouds raiding Mars, I thought there was a line where they went past Deimos… which implies it's still there.

Eldar craftworlds are big. As I recall, the description in Fallen Suns says they fall into the 'that's no moon' category. Think many hundreds to thousands of klicks across.

As for Naduesh, it is strongly hinted that it is an artificial planet. I didn't see anything about it being a battle station. It had substantial defences, like any sensible world, but that doesn't mean it's a battle station.

Cheers,

- V.

Vandegraffe said:

Edge of the Abyss expands on Naduesh, it states/suggests that the hive ruins are all either laid out like a purely military complex - with vast armouries and barracks, but some of the hive buildings are fakes concealing weapons batteries that "…dwarf those on Imperial Battleships." In short, not only are the defences beyond what even a Hive world might contain, there appears to be no purpose to any of the structures beyond war or camouflage. There's also a rumour that Naduesh was created as a trap for some monstrous foe.

By the Throne, what kinda of monstrosity could require an entire planet of battleship+ sized weaponry to defeat?

WhiteLycan said:

I'm picturing something along the lines of Warp Krakens. as if void krakens werent monstrous enough

Vandegraffe said:

Well… that's no moon.

Vandegraffe said:

Damnit, and I skimmed right past this the first time too.

(and I can't edit anymore)

Isn't the Imperium made up of thousands and thousands of worlds? Far to much information to try and put into a few books IMO. I'm sure there are other megalithic structures and/or worlds/moons that you can create to tailor to your needs. A Paradise moon that floats from planet to planet (albeit slowly) in a system, a ring structure around a planet that it's now at war with due to infighting (or treachery???), a vast monolithic cube the size of 64 (4 across, 4 wide, 4 high) battleships that is the home of the Rak'Gol spawning chambers and shipyards. Who created the last entry even the Rak'Gol don't remember, but they have continued to carry out their masters wishes since upon entering the Halo Stars and waking up from stasis.

Vandegraffe said:

P11, Grey Knight Codex, top right hand side. Deimos is now a small forge world purely in service to the Grey Knights. It now orbits Titan.

One imagines Eldar Craftworlds vary quite a lot. Iyanden is probably a lot bigger than Kaelor, for example. Some are going to be moon sized, some are going to be smaller.

Lightbringer, thanks for the reference. I don't have the Grey Knights Codex, so I'll have to take your word for it.

Speaking of megastructures, we've all overlooked one of the biggest: Commoragh. It's home to the entire Dark Eldar race, and is described as being too big for any one planet to contain. Yeah, that's got to have some size to it. Mind you, it's not the sort of place I'd like to visit…

Cheers,

- V.

True dat, Vandegraffe, I'd forgotten Commorragh. In fact it's a prime example of the kind of mega-engineering we're talking about on this thread, as I believe that it uses captive suns to generate power and light - all held immobile within the webway.

On a related note, where are we with speculation on the Dyson sphere in the original Necron Codex? As I recall this is a vast object at least one AU across with what is described as "an albedo range approaching infinite." My understanding of albedo is that it's a measure of reflectivity, meaning that the sphere has a mirror finish. A sort of giant disco ball of the stars.

The sphere had become linked to the 4th Major named C'Tan (in the original pantheon), the Outsider, with an indication that this particular C'Tan was insane and trapped withi the sphere. Has there been any more mentions of this within the canon that I've missed?

The whole Dyson sphere (well, I'm assuming it's a Dyson sphere) issue intrigued me, and it would be nice to know more…who built it? The Necrons? Rival Necron factions? The Old Ones? An extinct race?

If C'Tan were truly invincible (as appears to be suggested) and can only be shattered into shards, then perhaps another way to dispose of one would be to imprison it forever?

Whoa- "an albedo range approaching infinite"? An object's albedo is a measure of it's reflectivity, yes, but the scale ranges from 0 (a perfect black body- no radiant energy reflected) to 1 (a perfect white body- all radiant energy reflected). Any albedo greater than 1 would result in the object losing energy by reflecting greater amounts of energy than strikes it. This is, of course, impossible.

Wait- we already established that that particular megastructure was impossible. Never mind. It's now merely several different flavours of impossible.

Two words for those pondering the ramifications of things in GW products meaning what they say:

Depleted Deuterium.

Alasseo said:

Interesting. As I have no science background (As far as I'm concerned, electrical devices might as well be powered by tiny sparkling pixies) where would a perfect mirror finish score on an Albedo range of 0-1? Surely a mirrored surface would have a greater albedo rating than a pure white one?

I suspect (reading between the lines) that the writer of that part of the codex probably just wanted us to infer that the sphere was perfectly reflective, with a mirror finish. That's my supposition, anyway.

I see where you're coming from, Lightbringer, and the answer is along the lines of "yes, but…", I'm afraid. A "white body" doesn't actually have to be white- the term merely means that it reflects all (or virtually all, depending on how close it is to the ideal) incident radiation. It's to contrast with "black body", which again, don't have to be black (note, a cold black body would be black- so much so that we couldn't be able to see it directly; occluded stars/objects behind it, yes, observed gravitational pull, yes, but any light or other forms of EM radiation would simply fall into it. A hot black body could simply put out greater energy than reflects off it- meaning incandescent objects like the sun are actually the closest things to true black bodies we can see).

Next, I'm going to differentiate between "mirror" and "shiny": A mirror finish depends on the coherence of the reflected energy- the more coherently the incident radiation is reflected, the clearer the resultant image (obviously, there'd be distortion/aberration depending on the shape of the reflector). Arranging such a reflection is inherently less energy efficient than letting it scatter (2nd and 3rd Law of Thermodynamics; a coherent image has less entropy than randomly scattered photons. To maintain the the amount of entropy at a lower level, you have to put more work/more energy in, which decreases the efficiency). Therefore a mirrored surface is actually less efficient at reflection than a surface that simply bounces every photon that strikes it in a random direction.
However, a shiny surface, you're quite right, is more likely to reflect more photons than a dull surface. Logically, therefore, a shiny white surface is going to be even more effective (remember that the colour of an object is a function of which frequencies of light it reflects more efficiently, and white light is a combination/superposition of all frequencies of light.

I'll also note that the composition of the surface matters a lot- a white painted lump of wood will have a lower albedo than snow, because the wood will absorb more of the energy striking it.

But yeah, the guy writing it probably meant "impossibly shiny and reflective"

Or, in the opposite direction, completely matte and unreflective. Either would be possible for ancient xenotech.