It's not an empirical fact that a brain-in-a-vat has subjective experience. It's a thought experiment. Thought experiments don't establish empirical facts.
"It's not an empirical fact that a brain-in-a-vat has subjective experience."
If we could watch what the BIAV gets up to in its simulated world, we could see it interacting with its simulated environment. This would give us the same level of confidence in its having subjective experience as we have for any normal person.
From Michael Eisen's blog:
Yuval Levin, former Executive Director of the President's Council on Bioethics, has an op-ed in Tuesday's Washington Post arguing that Obama's new stem cell policy is dangerous. Levin does not argue that stem cell research is bad. Rather he is upset that Obama did not dictate which uses of stem cells are appropriate, but rather asked the National Institutes of Health to draft a policy on which uses of stem cells are appropriate:
Lost in this superficially unobjectionable - if banal - assertion of the complexity of ethical issues involving science is Levin's (and many other bioethicists) credo: that the moral complexity of scientific issues means that scientists should not make decisions about them.