I was thinking for a while on what you are saying and I think it is neat issue.

I see no problem in a person becoming aware of the anthropic principle while being in a vat… it is pretty abstract principle, and doesn’t depend on becoming aware of real individual things or kinds.

One problematic thing would be however the existence of the exact physical laws and types of elementary particles which we “find” while under perpetual illusion. Though given those exact physical laws, and types of elementary particles, the physical constants have to be as they are for life to appear, the issue is still there if maybe there could be some different physical laws and elementary particles. Further, is a world possible, where there wouldn’t be physical particles, and physical laws at all?

Thinking about it this way, maybe we could include the anthropic principle in those things about which we can think a priori (even if in the vat), i.e. add it to our metaphysical conclusions.

I’m very interested in this line of thought, because I’m interested in this relation between the becoming aware of real things (in the external manner), and what further can we become aware of about those things. While it seems to me that this first – becoming aware of real things, is something which we can’t have while subject of perpetual illusion (by definition), the further we go away from this direct acquaintance with individuals, we in fact deepen our understanding. But it is interesting that the further we go from this direct acquaintance, it also seems more possible that we could become aware of the same things even if subject of perpetual illusion (so without direct acquaintance).

So, yes, your words made sense, and I can now only hope what I said made sense too! :)

For instance, if you can do science in the perpetual illusion-world then you can investigate the anthropic principle. The anthropic principle states that if the universal constants were any different, we wouldn’t exist, so wouldn’t the universal constants have to be the same if we were in a vat, because either way, there would have to be an underlying substratum of physical matter for there to be vats at all.

So, I would say that if you can do science while under perpetual illusion and trace a causal history stretching back from the big bang to the current day, then strictly speaking, there couldn’t be any existential difference between the two realities due to the anthropic principle.

Does that make sense?