Could You Tell If You Were Just a Brain in a Vat?

Movies like 'Total Recall', 'Vanilla Sky' and of course 'The Matrix' have already posed that question. In these movies a hero is trapped in a virtual reality so real he could not know the difference between being and being a brain wired to receive stimulations that create an identical alternative reality.

Being movies, they all ended happily for our prospected "brain in a vat" whether it is Kiano Reeves, Tom Cruise or Arnold Schwarzenegger. Schwarzenegger could tell it was no dream, Tom cruise chose to leave his lucid dream and Reeves, of course, took the blue pill.

But could one really know the difference between being and being a brain in vat? The concept of brain in a vat is a known philosophical thought experiment. In this experiment a brain sits in a lab, wired to a computer of sorts, and receives electrical pulses which stimulate the brains neurons to create a virtual reality full of feelings, smells, sights and sounds. The brain's previous owner is oblivious to its current existence as a brain in vat as reality for him continues on as it has. Would you know you are now a brain in a vat living some scientist's scenario of a life?

Regrettably the only answer to this question is no. This philosophical thought experiment is influenced by Descartes 'Meditations on First Philosophy' from which the famous "I think therefore I am" (Cogito Ergo Sum) quote is taken. Descartes is desperately seeking an anchor for his knowledge and beliefs. Descartes, before reaching his famous conclusion, deduces he can not rely on mathematical truths as some evil demon might have planted those inside him with a firm belief in their a-priory nature.

Another philosophical principle which plays here is Solipsism - Perhaps only I exist and all other are but an illusion. I can be sure of my existence but can I be sure of the others'? Solipsism, as the brain in a vat, has no good reply. One can not argue with the solipsist arguing you are just his imagination (and so are your replies).