BIVs

We are brains in vats (BIVs).

The idea that you could be a brain in a vat (BIV) is most likely true. The vat is our scull and the stimulus is from our sensory organs.

Typically it is argued that for a BIV the outside world could be whatever. But this is certainly true about our current situation. There are things in the world that we do not have any direct experience about event though they are completely surrounding us. Take e.g. neutrinos or electromagnetic radiation outside of the visible spectrum as examples. But it is also the case that we can experience things that do not exist is the normal sense. For example the rainbow or phantom pain from a lost limb. Thus, there is no direct or absolute relation between our experiences and the outside world.

However, it is still the case that we can know things about the world. We are physical entities who interact with a physical and stable world. With "stable", I mean that it is ordered and behaves according to rules that are not random. Hence, since we have a capacity to interact with the environment, we can follow that interaction, perform experiments and tests and make theories. There is no limit to how much we can know about the outside world other than in the way our interaction with the world is limited. But any part of the outside world that is not connected to us via interaction is irrelevant. It can never affect us. For if it could, we could investigate those effects and learn about that part as well.

It should be noted that the argument above makes no distinction between our "ordinary" world as we think about it in everyday life, and a more "complex" situation where we really are BIVs. We can follow the interactions in both situations. Hence, we are BIVs. It is just that our body is the vat. But there will be no difference to a can of water and some cables.