Was your original postulation a hypothetical reality in which we all would be simultaneously co-existing in? Because I'm speaking of a specific theoretical scenario of which would apply to only an individual mind.
I am sorry for the late reply. Well, the brain in a vat thought experiment implies that either all or a few humans could have had their brains removed by an evil scientist & plugged in to a super computer while the brains. That super computer would provide them with impulses that an embodied mind generally receives deluding those beings in to believing that the world it exists in is the real one. That being would have a body, but that body isn't physical, it's virtual. It's argued that such a being would have no method to figure out that it was being tricked.
Unfortunately, this experiment fails to take humoral signals in to account. Those signals are the ones carried by the blood stream. In order to ensure that the brain experiences life exactly as an embodied being, the diabolical controller would have to provide it with a circulatory, respiratory, excretory system, etc. Remember that adequate blood supply for instance is crucial for the brain & is often referred to as functional hyperemia. Basically, this necessitates a need for a body, the body would have to be functionally coupled with the brain itself so that it regulates & is regulated by the nervous system itself. This surrogate body does not have to be organic but it needs to be as complex as an organic body no matter how simplified it turns out to be. Things like respiration for instance have to be under the control of the conscious mind even in the surrogate body.
The provision of this surrogate body implies that this experiment to delude that being would fail.