After completing the quest Arniel turns into some kind of a ghost that you can summon by striking some kind of soulgem with Keening, but why? Some ideas on why he turned into that ghost thing, or what this quest says about the disappearance of the dwemer. And can this somehow be linked to the fact that you encounter dwemer ghosts in Morrowind?

Arniel tried to recreate the experiments of the Dwemer on a smaller scale.
The Dwemer absorbed themselves into Numidium to become a living god.
Arniel never really understood what he was doing, and when he uncreated himself his shade was bound to the nearest recepticle, in this case the dragonborn.

We are only lucky Arniel was completely inept, only had one tool (that had lost a lot of its potency), and used a simulacrum instead of the actual Heart, otherwise he probably would have bound the entire Breton race to the dragonborn.

Consider Baladas Demnevanni on the Dwemer:

"It was unfashionable among the Dwemer to view their spirits as synthetic constructs three, four, or forty creational gradients below the divine. During the Dawn Era they researched the death of the Earth Bones, what we call now the laws of nature, dissecting the process of the sacred willing itself into the profane. I believe their mechanists and tonal architects discovered systematic regression techniques to perform the reverse -- that is, to create the sacred from the deaths of the profane."
"As the Dwemer left no corpses or traces of conflict behind, I believe that generations of ritualistic 'anti-creations' resulted in their immediate, but foreseen removal from the Mundus. They retreated behind math, behind color, behind the active principle itself. That the Dwemer vanished during a conflict with Nerevar and the Tribunal is merely coincidence."
"Yes, I can now translate these books. This first one is Bthuand Mzahnch's refutation of a popular theory from Nerevar's time. A few tones of Dwemer believed that using the power Lorkhan's Heart was an unjustifiable risk. "The Egg of Time" contains Bthuand's arguments against this idea, many of which are quite compelling. The next book, "Divine Metaphysics," is an explanation of how the Dwemer tried to make a new god, Anumidium, using Kagrenac's tools and the sacred tones on Lorkhan's heart."

I see. But doesn't that make it somewhat "easy" to eliminate races? ("Easy", you just need Kagrenacs tools and the heart of a god...)

The Heart is no longer available, its enchantments were shattered in Morrowind.

All races are basically subgradiated Ehlnofey, who are subgradients of Aedra.
The Dwemer attempted to reverse this downward spiral and return to what they saw as the perfection before creation by turning their entire race into a god.

The interesting thing is that the Thalmor have the same goal, to return to the first brushstroke of Anu and Padomay, but via very different means.

So yes, you could say that creation is unstable.
It can be altered, and has been, in many ways since the Dawn time.

So, how does the Thalmor intend to do so without the heart?

What appears to be an Altmeri commentary on Talos:
To kill Man is to reach Heaven, from where we came before the Doom Drum's iniquity. When we accomplish this, we can escape the mockery and long shame of the Material Prison.
To achieve this goal, we must:
1) Erase the Upstart Talos from the mythic. His presence fortifies the Wheel of the Convention, and binds our souls to this plane.
2) Remove Man not just from the world, but from the Pattern of Possibility, so that the very idea of them can be forgotten and thereby never again repeated.
3) With Talos and the Sons of Talos removed, the Dragon will become ours to unbind. The world of mortals will be over. The Dragon will uncoil his hold on the stagnancy of linear time and move as Free Serpent again, moving through the Aether without measure or burden, spilling time along the innumerable roads we once travelled. And with that we will regain the mantle of the imperishable spirit.


Talos is a pillar of the Mundus.
The Thalmor believe that his removal from mythic awareness will destabilise creation enough for them to do something to Auriel/ Akatosh.

I know that I'm starting to get really off topic, but if Talos once was a man how can he now be an aedra? Or can he be one of the divines without being an aedra? And if that is the case, then why does his presence fortify the wheel of convention? After all, he didn't really contribute to the creation of Mundus.

Talos mantled a god and therefore is one, to put it very simply.

And if you don't put it simply?

The enantiomorph(s) of Hjalti Early-Beard, Ysmir Wulfharth and Zurin Arctus used the Mantella to mantle the Aedra Lorkhan.

Simply put: Down, down, down and up again.

Unsimply, I put it like this on another thread:

It all goes down and down and spiraling down.
From Anu and Padomay to the Et'Ada is a downward spiral.
Enter Lorkhan who tricks or convinces Magnus to draw a plan to cease the downward spiral and create something no one Et'Ada is capable of.
Instead of one splitting to form many lesser, many will join to create a greater.

But on the Nirn everything goes down, down, down again.
The overarching pattern is repeated and the Aedra become many lesser beings or things, such as the Ehlnofey and Earthbones just in order to make the centre hold.
Enter Talos.
Talos goes up, reaches towards the sky, transcends mortality, is an amalgam of many avatars of Lorkhan* who each played their part in mirroring the story of creation.
Talos is a big giant YES towards Nirn, a spoke in the Wheel of Creation.

The Thalmor Altmeri view creation as a prison and a trap.
Therefore they seek to tear down the foundation, even if said foundation was laid after the structure was built.

*Talos is an oversoul, a joining of many avatars of Lorkhan, Wulfharth, Hjalti, Ysmir, Talos, Arctus and Septim. Through their lives and fates they re-enacted the story of creation so perfectly that in a mythic sense there is no difference, apart from size.

Ninja'd before I even came back to answer. lol.

Thanks!