Okay then.
I made this page in order to explain some of the unknown terms in my story, like the Skein and the Veil, as well as the layers of the Warp. For the sake of a smooth narration, I will explain the Warhammer's entire cosmology. So bear with me.
Also, it will explain a lot of haxes that will make an appearance in the future. Thus, I want to avoid claims such.
"It was too strong." "It was a wank."
Or something like that.
Now, let us begin. And credit to the account that collects these entire feats and proofs.
First off, we will start with the Materium(Material universe.)
-Materium-
-Materium itself was described as 4-dimensional space-
"Falling down a light-filled tunnel. Rushing motion, sickening vertigo. The sense of being drawn out to a chain a molecule thick. Connection was always difficult, but this… This felt like it was stretching him past breaking point. Then, like taut elastic, he snapped back. Vertigo again. Motion blur, quickly followed by nausea. He fought it, knowing it wasn't real. Inner ear balance that wasn't his. A centre of gravity altered. Someone else's body. New sensations. All unpleasant. Adjust, damn it. Get a grip. The nausea diminished, the sense of dislocation passed. Light and three-dimensional space unfolded. Dimensions had meaning again. The vectors of X, Y and Z restored." - Forges of Mars Omnibus
-It was indeed spatial dimension-
"He was pretty sure that the cliff itself was the problem. Andrioch was the next step in the trek, but they had arrived there too late. The mechnivore, or whatever other rogue behemoth had preyed on the place, had consumed more than just the physical city and the planetary crust beneath. It had eaten data. Not simply the digital data stored in Andrioch's analytic engines, but the raw data of space-time itself." - The Burden of loyality
-But the structure of that 4D was actually just a membrane of infinitely larger dimension-
"The Central conceit is that our visible, four-dimensional universe is restricted to a Brane, that is, a Membrane, inside a higher dimensional space", He begins and I already feel any hope of comprehension fall away "A theoretically infinite number of dimensions of potentially infinite scale occupy other branes, which, in effect, means there can be an endless series of Alternate Realities" - Knights of the Imperium.
-There are several mentions that Materium consists of countless higher dimension-
"Here?' cried Semyon, throwing his arms wide and spinning around like a lunatic. 'You have such a limited understanding of the material world, girl. Words like here and there have no meaning. The myriad dimensions of this material universe cannot be defined by so limited a thing as human language!" - Mechanicum
"The warrior in orange and black armor shouted. The automaton stepped forwards, piston driven limbs shaking the deck. The cannon on its shoulder swiveled. The prisoner could feel the dark energy dancing in the weapon. It knew its shape and taste, old and familiar from wars that had scarred the stars when they were young. The gun weapon drew breath to fire. The prisoner's senses traced the distances between every point in the room and sliced time down until only the decay of atoms marked its passing. The short distance from it to the automaton's gun, from the automaton to its masters, from those masters to the door. Every measured value became like crystal, every facet and plane extending through countless dimensions." -Ahriman: Key to Infinity.
-Many disagree with these feats. But hear me out. The fourth dimension is actually the membrane. And this is how the much higher dimension intersects with their higher counterpart-
"'Give me your hypothesis, Forgemaster,' said Helbrecht. 'I do not believe the cythor are entirely of our realm of existence, my liege,' said the Forgemaster. [Jurisian] 'This stinks of warpcraft,' growled Gulvein. 'This is not the work of the warp. The geometries of the warp defy explanation of any kind. If anything, these dimensions here exhibit a greater complexity. Many of us have noticed the inconstancy of the rooms here, the lack of match between exterior and interior.' 'Aye,' said Helbrecht. 'I have seen it for myself'. Jurisian nodded, the movement accompanied by the faint whirr of muscle bundles. 'Though complex, the dimensions of this place are explicable. This whole habitat is an expression of higher dimensional physics'. 'Explain,' said Gulvein. 'The universe we exhibit comprises four dimensions – height, width, depth and time. These creatures are, perhaps, natives of more'. 'You speak of the warp,' said Bayard. 'I do not,' said Jurisian. 'The warp is separate, unto itself, another realm entirely. There are more dimensions than the four in our own field of existence. It is through these that entrance to the warp is affected, and how some of the greater mysteries of the Adeptus Mechanicus are realised, but these dimensions are not of the warp. They are as real and physical as the heft of your sword, or the roundness of your bolts'. 'I do not understand,' said Bayard. 'Imagine, champion, that you lived in a world of three dimensions instead of our four,' said Jurisian patiently. 'Width, depth and time. You would have no concept at all of up or down, as there would be no height. It would appear perfectly normal to you. But that would not mean that height did not exist, only that you are incapable of perceiving it. So it is here'. 'You speak in riddles. If such a place existed, I would be able to see it. I can see no flat world, and so it is not there!' said Bayard. 'I speak of the greatest mysteries of the temples of Mars. It is not given to you or even to me to understand them, but that does not mean they do not exist'. Helbrecht spoke. 'You posit then a creature that exists as a physical being, not a witch or daemon born out of the warp?'. 'Yes, my lord. These new forms of the cythor are as real as you or I, but possess further dimensionality to them that makes them difficult for us to perceive. Forgive me, my lord, but I am unable to elucidate further. This field of study is the preserve of the greatest of the magi of Mars. My only knowledge of it is practical – the application of these prayer-equations to the proper functioning of field generation and suchlike. I do not know sufficient incantations to reveal the secrets encoded within this man or this building'."
-These higher dimensions are stated to be explicitly extensions of 4-D reality, and just as real as the 4 Dimensions that mortals perceive.-
-There is also planets within warp storms described as Higher-Dimensional.-
"From realspace, Sacgrave appears to be a fist-shaped gnarl of black rock barely the size of a small moon. Sacgrave's Warpshadow, however, is out of all proportion to its physical presence. It stands athwart the third fluvial extension where its anomalous presence breaks that comparatively calm channel into the raging fifth and sixth interstices."
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Now. Let's head next into the Veil and the Skein.
-There was a veil that separates the MAterium and Immaterium-
"There was no blazing light of the Astronomican to sail by. In Imperium Nihilus, he must rely on more esoteric means of navigation, following streams of thoughts and fears. The direction of etheric winds and their eddying revealed mass concentrations on the other side of the veil dividing Materium from immaterium." - Darkness in the Blood
-Seemingly from the interaction between the Materium and Immaterium at their nexus point that is the Veil, fate itself is created along the 'surface of time'.-
"Hyalhi let his mind shimmer outwards, touching the veil that separated reality from the warp. It was there that the threads ran, criss-crossing the surface of time. The threads – not truly threads, that was just the concept that Hyalhi used to comprehend them – were the substance of fate. Few spoke of fate as anything but a metaphor or a curse, for in the minds of a non-psyker fate was something without meaning" - The World Engine
"This was the part Corswain hated the most, in sensation most alike to the disembodied lurch of teleportation. For an endless moment the Invincible Reason was held between two dimensions, perched on the precipice between the material and immaterial like a wanderer standing at the crossroads of fate. A moment before, it had been adrift on the tides of the warp, cocooned within a bubble of reality kept intact by its Geller field. Now it was in the true universe, plucked from the unnatural currents, its Geller-borne reality imploding as real space engulfed the vessel."- The Primarchs.
-Fate is essentially the 'thread' or timeline of a soul in the Materium, these innumerable threads combine together to form 'The Skein'. Basically, the Skein was an amalgamation of various timelines or rather realities that came together and overlapped.-
"As Bielanna's senses flowed into the Skein, she followed the threads of the warriors back into the past, seeing shadowy ghost-figures spinning and leaping around her. Their every movement was fluid, economical and deadly. The phantom shapes spun around her with ever greater fury as she looked down at the wraithbone runestones in the sand. The Scorpion and the Doom of Eldanesh. Both lying atop the Tears of Isha. The pattern was familiar to her, each one tracing the line of fate's weave. Between them they represented skeins of futures that had already been realised, that were yet to be, and which might never be. They braided together in innumerable threads, and each one was – in turn – made up of a dizzying number of potential futures, making the task of interpretation and manipulation almost impossible." - Forges of Mars Omnibus.
-Every single beiangs have their own fate/thread. Note again the 'hell-dimensions of the Othersea' the 'voidspawn' come from is explicitly described as different to the 'World of Nightmare'-
"Where the weapons' deadly beams terminated, pricks of light as bright as stars appeared along the line of voidspawn. They twisted in on themselves, expanding with flares of purple and green ghostlight, briefly lived portals opening up onto the hell-dimensions of the Othersea. Where the distortion weapons hit directly, voidspawn exploded, torn apart by the forces at work within them. Others were pulled off their feet and dragged wholly through the veil that separated this world from the next. Hundreds were sent into the world of nightmares this way. The sense of horror built until Iyanna thought she would collapse, and then the portals slammed shut. Iyanna could still sense the enemy on the other side of the thin veil of reality. Torn from their hive mind's great rope of being, the creatures briefly showed as feeble fibres on the skein, before winking out."- Valedor.
-The Skein is connected to the space-time of the universe. Unravelling the Skein causes it's threads to unwind. Past, Present and Future crash onto one and other undoing a universes laws causing it to literally unravel at the seams. So the arguement that Breath of the Gods only capable of destroying the entire galaxy was false here.-
"'Yes, yes of course', said Kotov, trying hard to keep the excitement from his voice. 'Space-time is being violated on a fundamental level. Put bluntly, Sergaent Tanna, Telok's machine is undoing the basic laws of the universe in order to achieve miraculous results.'
Kotov paced on the edge of the gorge, his head hazed with the excess heat bleeding from his cranium as his cognitive processes spun up to concurrently across tens of thousands of inloaded databases.
'If I am understanding... Bielanna correctly, the Breath of the Gods feeds it's vast power demands by siphoning it from the future and the past, most likely from the hearts of dozens of stars simultaneously. It then uses that power to accomplish it's incredible feats of stellar engineering.' said Kotov, his mechandrites tracing complex temporal equations in the air. 'But the fallout from employing the machine created the many spatial anomalies Magos Tychon detected at the galactic edge, stars dying before their time, others failing to ignite and so forth. In all Likelihood, the Breath of the Gods probably created the Halo Scar in the first place.'" - Forge of Mars Omnibus
"This was the doom she had seen ensconced within the Speranza. Space and time were coming undone, ripping apart like the solar sails of a wounded wraithship. Doom had come to this world, but that was the least of the danger. The rift beginning here was pulling wider with every passing second, drawing every thread within the skein to it. Like a weavers's shuttle reversing through the warp and weft of a loom, ,the future was unravelling to it's omegapoint." - Forge of Mars Omnibus.
-The Skein is described as residing within the 'Not-yet formed' concept and the process of reaching it requires one to almost entirely lose sense of their own existence-
"In the Skein there is nothing. There are no names and there are no beings. This is where the mind originates. There is the mind but nothing is physical. Forms obtain the mind and thoughts are created. This is called Passing. In the not-yet-formed the Skein divides and splits but there is no time passing. This is called Being. There is an energy that gives life to all things, allowing form to obtain mind and create thought. Forms that create thought share in this energy. This is called Life. Let slip Life, and become Being. Let slip Being and become Passing. Let slip Passing and become Mind. Become Mind and be one with the Skein."- Path of the Seer.
-The quotes 'beyond the galaxy' was a mere perspective. The Skein is a place where time loses its sense-
Past and future. Then and now. Temporal anchors. Intellectual conceits, they allowed a farseer to cling to the present. Such linear terms had no meaning or place within the Skein, but they had their uses. Bielanna fought to cling on to the present as past and future collided, hurling her sight into potentialities that could never come to be and times she had never lived. Infinite vistas of the psychic landscape surrounded her, golden ocean depths filled with glittering, frond-like threads. Each shone brightly as it flared and was then extinguished, only to be replaced by hundreds more. A billion times a billion lives lived in the blink of an eye. And these were just the ones she could see. She drifted, watching each tightly woven thread split into fractal patterns of innumerable futures as she approached. The Skein's tides were unpredictable at the best of times, and to see one individual destiny was next to impossible. But that was what she had trained her entire life to do. Farseers spent centuries reading the Skein's ebb and flow, but not even the greatest were entirely safe from capricious undertows or spiteful squalls. In this place beyond the galaxy, where the warp and weft of space-time were playthings shaped by the will of a madman, it was all too easy to forget that. Bielanna struggled against the tug of fear, hatred and grief: interleaved emotions that would damn her as surely as relaxing her grip on the thread leading back to her body of flesh and blood." - Forges of Mars Omnibus .
-The space or lack thereof that the Skein resides in is described as 'potential' and eldritch voidspawn are specifically described as not beings of the warp seep in through the small cracks within the Skein. These obvious references to Cosmic horror appear to crawl through the cracks they make in the stacked planes of the Skein and exist merely as 'Suggestions.-
"In the Skein, Bielanna fought to control her feelings. The mon-keigh knew nothing of the universe's secret workings, and for the briefest moment, she envied them their ignorance. Who but the Eldar could mourn lives that had not even been born? 'I am Bielanna Faerelle, Farseer of Biel-Tan,' she cried into the oceanic depths. 'I am master of my soul and I bring only balance in my heart and thoughts.' Everything in the Skein rejected constancy. It sensed her lie. This was a place of dreams and nightmares, where all things were infinite. To give something a name marked it as not of the Skein. And that was dangerous. It drew things that hid in the cracks between destinies. She saw them ooze from half-glimpsed shadows. That shadows could exist in this realm of absolute light was a measure of their threat. These were not the crystalline web-forms of warp spiders, nor yet the glimmer of future echoes moving from potential to reality. These were things twisted out of true by the tortured nature of space-time beyond the galaxy's edge. They defied the tyranny of form, mere suggestions of grub-like null-spaces that existed only to consume. She moved onwards, far from their questing, sphincter-like mouths and blind, idiot hunger."- Forges of Mars
-The Skein is beyond Materium-
"Battle-sign had made no mark here, for the doom of the shrine kept war from its halls both in the material plane and on the mess of potentialities that made up the skein."- Valedor
-The Skein is almost explicitly described as residing within an even higher plane then the totality of reality. Reality merely being an image on the surface of the Skein. Eldar Farseers memories of projecting themselves into it, are described as 'Flat' compared to the full grandeur of truly residing within it. It should be noted, the process of the threads of Fate twisting together into a Skein is essentially how a universe is created.-
"The beauty of the Skein never failed to move Taec, and now, when the burning hand of Khaine hovered in his mind's eye, it moved him all the more. The threat of destruction added to his appreciation. The Skein defied description. The Eldar tongue, for all its complex shades of nuance, could not encompass it. Even psychic communication and shared recollection could only hint at the Skein's glories, for all that was passed over was the seer's subjective impression of it. Only pure mind could comprehend it, and then only while it was upon the Skein, for when form and mind were one again, memories of the Skein became flat. But to be in it! All of reality was laid out before him. Threads twisted into yarns woven into tapestries depicting universes of possibility. Shards of infinitely shattering mirrors, each fragment showing the same event in different perspective; ripples alive with images on the surface of a lake, its depths also ablaze with scenes that were, could be, and had been. There were many ways of seeing the Skein." -Valedor
"A world of leaping flames and broken stone extended away from me on all sides."... "I see the future in their dust dance. Possibilities and unborn fates spin before my eyes, each one a universe that shall live, or shall remain unborn."- Ahriman the Omnibus
-Each possibility and choice forms a new universe and the Skein is described as residing within 'overlapping planes of destiny' layered like panes of glass on top of each other.-
"She found herself in a realm of light and movement. She could see the flicker of other eldar around her, like candles in twilight. A tracery of white, the infinity circuit, linked every other light together, stretching on without horizon into the impossible distance. Energy flowed along the maze, back and forth, surging and ebbing, binding everything together with its movement, linking the eldar with one another. And beyond. Beyond was something even more spectacular, defying rationalisation. Beyond were the constantly shattering panes of existence; the overlapping planes of destiny; the interwoven threads of fate. The present surrounded Thirianna, but just out of reach was the future, and in the darkness behind was the past. Every life, every thought, every movement, every motive, every emotion, weaving together in a dazzling tapestry of cause and effect. It branched out, splitting and dividing like cells, spawning entire new universes and possibilities with every passing moment. This was the Skein, and it was beautiful. And too much. Too much to see, to comprehend, to understand." - Path of the Seer
-These 'Panes' of existence have a lot of similar characteristics of the warp. It has no dimensionality/geography, save for that imposed by its residents and it is fundamentally structureless. It is described as an ocean with ebbs and tides.-
"She had followed the threads of these humans in order to cut them and restore her future of motherhood, but the greater threat of this new power demanded precedence. Past, present and future were on a collision course, pulling together into a convoluted knot that would tear the fabric of space-time apart as the universe attempted to undo this violation of its natural order. Taking a series of calming breaths, Bielanna fell back on the gentle gifts of Farseer Tothaire, recalling his meditative exercises that unbound spirit from flesh and material attachments from spiritual awakening. She let out a soft sigh as her spirit slipped its moorings and lifted into the outermost edges of the Skein, letting its familiar mosaic of pasts and futures wash over her and renew her with its liminal beauty. It had no geography, save that which she imposed upon it, though its fluid, structureless immensity was only fleetingly visible through the many barriers that separated her from its depths. Bielanna sought something familiar in the web of possibility that surrounded her, threads she could cling to and follow, pathways to lead her into the oceanic vastness of the Skein. The golden threads of her assembled warriors surrounded her, but each time she tried to follow their paths into the future, they skittered away like a pack of startled Warp Spider" -Forges of Mars omnibus.
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Conclusion. Indeed, the Materium only consist of four dimensional plane. But that dimension is directly intersect with countless others, forming a kin of membrane. Like what I gave earlier, the mortals only fully understand four dimensional space.
The Veil is basicall a gap dimension that separates the Materium and Immaterium. And in that veil, fate has become a thread that if the fate itself overlapping, it will form the Skein. It transcends the physical universe, a fundamentally structureless plane, the fate of the individuals within the physical universe, merely appearing as an image on the Skein. Furthermore acts akin to a 'veil' that protects a related universe from the warp pushing into it and consuming it, the Chaos Gods needing to corrupt a universe from within to break down it's related Skein, destroying it's Space-Time, Laws and Fate, sort of akin to a cell membrane protecting the main body from. Dimensionality is merely imposed by the essence of beings that can interact with and view this, with infinite Skeins for each universe.