Yippee!

Aetherium was introduced in Skyrim specifically, if I remember correctly. It’s basically a crystal that attunes especially well to sonic waves, which makes it a core component in tonal architecture, a form of magic that’s basically alchemical transmutation that’s based in sound. So this magic is extremely important because the whole thing about the elder scrolls universe is that it’s a sort of cosmic song. Everything has frequencies to it, and the dwarves learned that they can not only hear them, but manipulate them on a small scale. Aetherium most likely acts like a resonator on a guitar, amplifying the magic. Which means it most likely was present at the construction site of the Numidium.

Now the kicker with the brass god of NO and IS NOT is it’s original power source: the Heart of Lorkhan.

Basic rundown: Anu (Stasis, Time) and Padomay (Change, Space) created avatars of themselves named Auriel (elven ancestor-god of time) and Lorkhan (trickster demiurge). Lorkhan tricked Auriel and the other elven ancestor-spirits into creating the world (becoming Aedra, spirits who contributed to the creation of the world, and lost a large amount of their power; not to be confused with Daedra, spirits who chose not to contribute in the creation of the world, and thus held onto their power), thus binding themselves to it in the process. This was not known to the ancestor-spirits, and they killed Lorkhan for it, ripped out his heart, and Auriel tied to an arrow and shot it out into the sea where Red Mountain then rose out of. But Lorkhan could not die because he was tied up in the creation of the planet just like them, and so long as the planet still existed, he would exist in some way. This technically makes Lorkhan an outcast and dead Aedra, the only one to be either, the only one to be both. There is a theory that does suggest he is a Daedric Prince, and Nirn is his Sphere (Molag Bal with Coldharbour, Mehrunes Dagon with the Deadlands, Sheogorath with the Shivering Isles, etc…), but this is posed by Mankar Camoran, the leader of the cult that whipped out the Septim Dynasty and began the Oblivion Crisis as seen in TES IV: Oblivion, so take it with a grain of salt. Dude was a scary wacko.

It’s to be noted that Lorkhan’s name literally translates from Altmeridoon (high elven language) as “Doom Drum”. It’s also to be noted that “Doom” to the elves and their ancestor gods is being trapped/born in flesh and blood bodies, and thus subject to the concept of mortality. Lorkhan as the Doom Drum means he is the tempo of this cosmic song, driving it forward, bringing it out of an eternal chorus and into the verses, and the inevitable end. Most elves see him as Satan-adjacent, while most men see him as a chief creator god. Both are technically true.

The dwarves found the Heart of Lorkhan in Red Mountain while tapping into the geothermal energy there. Now with them being elves, you’d think they would try and destroy it, but the dwarves were devout anti-theists. They believed the gods (infernal and divine) existed, yes, because in this fantasy universe there is hard evidence that they do (auriel’s bow and shield, the amulet of kings, ebony, heart stones, etc…). They just decried their godhood. To the dwarves, the gods were just outerplanar beings subject to outerplanar laws that made them seem especially powerful in comparison to the denizens of the planet. And they’re 100% correct. Their problem is that this knowledge made them catastrophically arrogant.

There was a sect of tonal architects, led by a dwarf named Kagrenac, who hypothesized that since tonal magic could alter existing frequencies, it could conceivably also negate them with equal, opposite frequencies (think in mathematical terms of 1 + -1 = 0).

So, when you’re an aggressively anti-theistic elf that’s happy to gloat over how smart and right you to all your religious cousins, and you have the heart of a dead god that created the entire world… you build a fucking Eva Unit with intent to kill the gods just to prove that you can.

Where and how this fucked them up into fundamental nonexistence was that tonal magic was used for mass telepathy, making them a pseudo hive mind. The second Kagrenac struck the Heart with his tools, the Nimidium’s quasi-conscious flooded the mindscape with the knowledge of apotheosis.

Apotheosis in TES Lore is fucking crazy because it’s literally a character in the game becoming aware that they are a character in the game, and it has three outcomes: zero sum, CHIM, and Amaranth.

Zero sum occurs when a character cannot rationalize that reality as they know it- themself included- is a simulation. They do not exist, thus the newfound godly power is used reflexively to erase themselves from the simulation.

CHIM is when a character becomes aware of the simulation, but is able to hold onto their sense of self. Since they know that they are code and that the world around them is also code, reality within the bounds of the simulation becomes an extension of their being to be used and manipulated at will.

Amaranth is a possible natural progression of CHIM in which a character who has been made aware of the simulation becomes aware of who built the simulation, this builder being referred to as the Godhead (which is you, the player). The character who achieved CHIM- if they so desire- then creates their own simulations and becomes a Godhead, playing their own games. Vivec, the warrior-poet God-King of the dark elves, is the only known individual to have achieved Amaranth, and only in out of source text created by Michael Kirkbride (former artist and lore writer for Bethesda. You can thank him for Morrowind being the coolest kind of acid trip).

Kagrenac struck the Heart, the Numidium spread apotheosis through the tonal magic telepathy like a mindplague, the entire race of the dwarves (at least the ones that were in the plane of Mundus at the time) zero summed.

But since the Numidium was only a quasi-conscious echo of the dead god Lorkhan, it could not zero sum. Every time it gets powered on without a Shezzarine (mortal avatar of Lorkhan) present to control it, it goes fucking berserk. It’s following out preinstalled instructions to cancel out reality that were only meant for alpha testing. It’s fundamentally tied to the Heart, and thus to Lorkhan, so it cannot be destroyed by mortal or godly means, only dismantled as a stopgap. The Numidium has been reassembled and disassembled multiple times, has disputed itself out of existence and disappeared, and then reappeared after disputing its nonexistence, and has turned time nonlinear on multiple occasions in history. It’s a buggy bit of code that’s glitching the cornfed flying fuck out of reality whenever it’s activated.

The “space elves” you mention are actually the dark elves of the out of canon 9th Era (also penned by Michael Kirkbride), who fled to one of the moons after the Numidium was reassembled and powered on (again) and turned the planet of Nirn both physically and metaphysically uninhabitable. It was finally, FINALLY destroyed by one of these dark elves, Jubal-lun-Sul, who realized that it wanted to die, and convinced it to kill itself. And since dying and being unmade were contextually different enough things, it stayed dead.