Conversation so far:
What is Epistemology?
In the field of epistemology, Putnam is known for his "brain in a vat" thought experiment (a modernized version of Descartes's evil demon hypothesis).
What was Putnam's "brain in a vat" experiment?
if some person, Mary, were a "brain in a vat", whose every experience is received through wiring and other gadgetry created by the "mad scientist.

Question: What did the experiment prove?
Self-contained rewrite: What did Hilary Putnam's "brain in a vat" experiment in epistemology prove?