When Good Brains Go Bad, or "The Brain in the Vat"

Philosophers have often used variants of a modern, science-run-amok retelling of Descarte’s Demon—the Brain in the Vat scenario—to pose thought experiments to students and non-philosophers, or to anyone who just has a few hours to kill and wants to flex some mental muscle. The scenario, written in 1988 by philosopher Michael F. Patton, Jr., of Syracuse University, involves a runaway trolley approaching a fork in the track. At the wheel of the trolley is a brain in a vat, which is somehow hooked up to the trolley so that it can determine whether the trolley should take the right fork or the left fork. And therein lies the root of the problem.

In its simplest explanation, the trolley problem is this: on each side of the track is a railroad worker, so no matter which fork the brain chooses to take, someone will be killed. When one of those workers is killed, his death will affect the lives of five or ten other people in either positive or negative ways, or a combination of ways. The effects on the lives of those five or ten other people will then cause a further ripple affecting the lives of another group of people. And the ripples don’t stop there; the brain’s decision will ultimately result in a war either way, but each side of the fork will result in a different type of war with a different outcome. And ultimately, the decision the brain makes, whatever it turns out to be, will serve as an example to other brains-in-vats and so the effects of his decision will be amplified even further.

Hilary Putnam responded to the Brain in a Vat scenario by arguing that a brain in a vat would have no true beliefs. Although a brain in a vat, hooked up to receive the same inputs it would receive from a human body, would in theory believe the same things we believe, the brain would have no language and therefore no public referent for making a decision one way or the other. Judith Jarvis Thompson posed an analogous problem in her article, "Killing, Letting Die, and the Trolley Problem." The case Thompson came up with is called the transplant problem, and requires you to decide whether you would kill one person whose organs could be distributed around to save the lives of five other people who are about to die if they do not receive the organs. Most people to whom the transplant problem is posed are adamant that they would not sacrifice the one person to save the five others, yet those same people admit they would have no problem steering the trolley onto one of the rail workers to save five people.

Both philosophical conundrums offer valid arguments for a variety of sides of each issue, and both can easily provide fodder for hours of deliberation and contemplation, and result in healthy and rousing debates of the ethics involved in opposing decisions. The traditional "brain in the vat" trolley problem is designed to show the plausibility of radical skepticism—the thesis that there is no such thing as certain knowledge. If people were merely brains in vats, hooked to computers, all of our experiences would be indistinguishable from what we consider to be "real life experiences," but we would have no hope of discovering that we were actually brains in vats and not real people.