Brain thriving in vat on emergency stirrups wired to a computer running simulation of the universe could be an ideal situation as to know the reality of the universe which we perceive somehow to be overwhelmingly big and real but could not be the case so. The brain in vat is running on life support and poses the ethical question do I exist? The brain on its own might never exist but it opens the doors to questions like does brain work in isolation severed from the other processes which on the outset seems false but could actually be true?
The important thing is how would the brain know whether its connected to the computer through neurons or is located inside the skull? There must be a mechanism to know if the brain is conscious of the environment and that the consciousness exists. But it could be assumed the brain is sending electrical signals to the computer and thus creating the simulation of the universe. That seems proper but is the consciousness about the body or independent of it? All the above questions arise merely out of the fact the brain having severed from the body is thriving. All the questions are skeptic and treats the world as an illusion of reality.
The conclusion drawn could be that the brain actually is wired in isolation in the skull such that the world appears as an illusion of space and time which both are relative to the observer. So our universe instead of being big and real emerges as puny and unreal such that nothing could precisely be known but the divine energy that permeates time like ether could be thought of permeating space as an abstraction of itself. The space must have come out of something and that something is an abstraction of pure consciousness which is not possible with the brain in vat. The pure consciousness is the source of all abstractions of space and ether occupying the space is one among them.