Labyrinths of Reason (2 page)

To anyone with a skeptical turn of mind, the brains-in-vats paradox is both appealing and infuriating. There is something fascinating about the demonstration that, just possibly, everything you know is wrong!

Despite the influence of Penfield and other brain researchers, doubts about the reality of the world are not a uniquely modern malaise. Brains-in-vats is simply a stronger version of older riddles asking “How do you know this isn’t all a dream?” Best known of these is the Chinese tale of Chuang-tzu, dating from the fourth century
B.C
. Chuang-tzu was the man who dreamt he was a butterfly, then awoke to wonder if he was a butterfly dreaming he was a man.

Chuang-tzu’s fable is unconvincing. It is true that we usually don’t realize we’re dreaming in our dreams. But a waking person always knows that he is not dreaming. Doesn’t he?

Opinions differ. In his “First Meditation” (1641), French philosopher and mathematician René Descartes decided he could not be
absolutely
sure he wasn’t dreaming. Most people would probably disagree with Descartes. You’re not dreaming right now, and you know it because experiences in dreams are different from those in waking life.

Saying exactly
how
they’re different is difficult. If waking life is absolutely, unmistakably different from a dream, there ought to be some surefire test you can perform to distinguish the two. For instance:

• There’s the old gag about pinching yourself to see if you’re dreaming. The rationale is apparently that you don’t feel pain in dreams. But I
have
felt pain in dreams, and suspect that everyone must from time to time. Scratch that test.

• Since few dreams are in color, the red rose on your desk proves you’re awake. Again, the dream sensation of color is not all that rare. Many people dream in color, and even if you never have, this could be the first time.

• Real life usually seems more detailed and coherent than dreams. If you can examine the wall before you and see every minute crack, that means you’re awake. If you can add a column of figures, then check the result with a calculator, you’re awake. These tests are more telling though still not foolproof. (Might not you dream about seeing tiny cracks in the wall after hearing that the cracks “prove” you are awake?)

• Some say that the very fact that you are wondering whether you are dreaming or awake proves you are awake. In waking life, you are aware of the dream state, but while dreaming you forget the distinction (and think you are awake). But if that were true, you could never have a dream in which you realize you are dreaming, and such dreams are fairly common with many people.

• I propose this test, based on what might be called “coherent novelty.” Keep a book of limericks by your bed. Don’t read the book; just use it thus. Whenever you want to know if you are dreaming, go into your bedroom and open the book at random (it may of course be a dream bedroom and a dream book). Read a limerick, making sure it is one you have never read or heard before. Most likely you cannot compose a bona fide limerick on a moment’s notice. You can’t do it when awake, and certainly not when asleep either. Nonetheless, anyone can
recognize
a limerick when he sees it. It has a precise rhyme and metrical scheme, and it is funny (or more likely
not
funny, but in a certain way). If the limerick meets all these tests, it must be part of the external world and not a figment of your dreaming mind.
¹

My real point is that you don’t need to use any of these tests to establish that you’re awake; you just
know
. The suggestion that Chuang Tzu’s, or anyone’s, “real” life is literally a nighttime dream lacks credibility.

It may however be a “dream” of a different sort. The most famous discussion along these lines is in Descartes’s
Meditations
. There Descartes wonders if the external world, including his body, is an illusion created by an “evil genius” bent on deceiving him. “I will suppose that … some malicious demon of the utmost power and cunning has employed all his energies in order to deceive me. I shall think that the sky, the air, the earth, colours, shapes, sounds and all external things are merely the delusions of dreams which he has devised to ensnare my judgement. I shall consider myself as not having hands or eyes, or flesh, or blood or senses, but as falsely believing that I have all these things.”

That the demon and Descartes’s mind were the only two realities would be the very pinnacle of deception, Descartes reasoned. Were there even one other mind as “audience” for the deception, Descartes would at least be correct about the existence of minds such as his own.

Descartes’s evil genius anticipates the brains-in-vats paradox in all meaningful particulars. The Penfield experiments merely showed how Descartes’s metaphysical fantasy might be physically conceivable. The illusion in the Penfield experiments was more realistic than a dream or memory, though not complete. Penfield’s patients described it as a double consciousness: Even while reliving the past experience in detail, they were also aware of being on the operating table.

One can readily envision the more complete neurological illusion supposed in the brains-in-vats riddle. The eyes do not send the brain pictures, nor the ears sound. The senses communicate with the brain via electrochemical impulses in the nerve cells. Each cell in the nervous system “sees” only the impulses of neighboring cells, not the external stimulus that caused them.

If we knew more about the original sensory nerve communication with the brain (as may be the case in a century or so), it might be
possible to simulate any experience artificially. That contingency throws all experience into doubt. Even the current embryonic stage of neurology is no guarantee of the validity of our senses. It might be the twenty-fifth century right now, and the forces behind the brains-in-vats laboratory want you to think it’s the twentieth, when such things don’t happen!

The existence of one’s brain is just as open to doubt as the external world. We talk of “brains in vats” because it is a convenient picture, wryly suggestive of bad science fiction. The brain is shorthand for “mind.” We no more know, with unimpeachable certainty, that our consciousness is contained in a brain than that it is contained in a body. A yet more complete version of the fantasy would have your mind hallucinating the entire world, including Penfield, J.V., and the brains-in-vats riddle.

“Brains in vats” is the quintessential illustration of what philosophers call the “problem of knowledge.” The point is not the remote possibility that we are brains in vats but that we may be just as deluded in ways we cannot even imagine. Few persons reach their fifteenth birthday without having some thoughts along this line. How do we know
anything
for sure?

The whole of our experience is a stream of nerve impulses. The sheen of a baroque pearl, the sound of a dial tone, and the odor of apricots are suppositions from these nerve impulses. We have all
imagined
a world that might account for the unique set of nerve impulses we have received since (and several months before) birth. The conventional picture of a real, external world is not the only possible explanation for that neural experience. We are forced to admit that an evil genius or a brains-in-vats experiment could explain the neural experience just as well. Experience is forever equivocal.

Science places great faith in the evidence of the senses. Most people are skeptical about ghosts, the Loch Ness monster, and flying saucers, not because they are inherently stupid notions, but only because no one has produced unquestionable sensory evidence for them. Brains-in-vats turns this (apparently reasonable!) skepticism inside out. How can you know, by the evidence of your senses, that you are not a brain in a vat? You can’t! The belief that you are
not
a brain in a vat can never be disproven empirically. In the jargon of philosophy, it is “evidence-transcendent.”

This is a serious blow to the idea that “everything can be determined scientifically.” At issue is not some bit of trivia such as the color of a tyrannosaurus. If we cannot even know whether the external world exists, then there are profound limitations on knowledge. Our conventional view of things might be outrageously wrong.

Ambiguity underlies a famous analogy proposed by Albert Einstein and Leopold Infeld. In 1938 they wrote:

Descartes’s evil genius was the starting point of an investigation into how we know what we know. Descartes wrote: “Some years ago I was struck by the large number of falsehoods that I had accepted as true in my childhood, and by the highly doubtful nature of the whole edifice that I had subsequently based on them. I realized that it was necessary, once in the course of my life, to demolish everything completely and start again right from the foundations if I wanted to establish anything at all in the sciences that was stable and likely to last.”

Descartes wanted to address the problem of knowledge in much the same way that Euclid had treated geometry two thousand years earlier. All of Euclid’s geometry is deduced from a set of five
axioms
. An axiom was, in Euclid’s time, a statement so obviously true that one could not imagine a world in which it was false (for instance: “A straight line can be drawn between any two points”). All the
theorems
—provably true statements—of traditional geometry can be derived from Euclid’s five axioms.

Descartes wanted to do the same thing with the facts of the real world. He needed first to identify a set of facts known with utter certainty. These facts would be the axioms of his natural philosophy. Then he would establish valid rules of inference. Finally, Descartes
would use those rules to deduce new facts from the original set of incontestable facts.

Unfortunately, almost any statement about the real world has some degree of doubt. Descartes found the ground floor of his natural philosophy vanishing beneath his feet: “So serious are the doubts into which I have been thrown as a result of yesterday’s meditation that I can neither put them out of my mind nor see any way of resolving them. It feels as if I have fallen unexpectedly into a deep whirlpool which tumbles me around so that I can neither stand on the bottom nor swim up to the top.”

This dizzying “whirlpool” aptly describes
ontology
, the study of what is most real. The first thing to realize in constructing an ontology is that the accepted, everyday “facts” of the external world are disputable. You can almost always think of a scenario in which unquestioned beliefs could be wrong. Is Paris the capital of France? Very likely it is, but still, there is a sliver of doubt that never vanishes. It’s barely conceivable that our government is a totalitarian conspiracy that, for reasons of its own, does not want its citizens to know the
real
capital of France. They’ve rewritten all the history and geography books, and force teachers to indoctrinate each new generation of children with the Paris fiction. You say you went to Paris last summer and saw a bunch of official-looking French government buildings there? That could have been a theme-park simulation maintained by our government to give its citizens the illusion of freedom of travel.

Wild fancies like this should not obscure the fact that some things are more disputable than others. By most people’s standards, the Loch Ness monster is less real than a tyrannosaurus, and both are less real than the elephant you saw at the zoo last Sunday. What is most certain of all?

A popular answer is the truths of logic and mathematics. Even if your first-grade teacher was the dupe of a conspiracy bent on teaching you falsehoods, you cannot doubt that 2 + 2 is 4. Right now you can picture two things, and put two more things beside them, and see that the total is four. This deduction seems obviously true in any possible world, be it the external world we believe exists, the brain-in-vats laboratory, or something stranger yet.

There are two problems with this answer. First of all, you can take the ultra-skeptical position that even logic and mathematics are an illusion. Just because you don’t see how you could be wrong about 2 + 2 = 4 doesn’t guarantee that it’s right.

Your brain is evidently in a certain state when you come to a
valid conclusion of logic or mathematics. What’s to stop the brains-in-vats overlords from deluding you about arithmetic as well as the physical world? Possibly 2 + 2 is 62,987, but by stimulating your brain in a precise way, the mad scientists have you thinking it’s 4, and even thinking that it’s
obvious
it’s 4 and you can
prove
it’s 4. Maybe somewhere they’ve got a whole row of brains in vats, each one believing in a different sum for 2 + 2 and immersed in a different “reality” consistent with that sum.

Philosophers rarely take skepticism that far. There are enough other things to doubt in the world. The other, more pragmatic problem with restricting certainty to logic and mathematics is that it leaves us with no way of justifying beliefs about the physical world. Certainty about arithmetic is not going to tell us what the capital of France is. So, are there any facts, aside from logic and mathematics, about which we can be certain?

Descartes had some interesting ruminations on this point. He noted that there are limits to imagination, possibly including that of evil geniuses. The fantastic objects of a dream or a surreal painting are based on real objects. “For even when painters try to create sirens and satyrs with the most extraordinary bodies, they cannot give them natures which are new in all respects; they simply jumble up the limbs of different animals,” wrote Descartes. (Are there
any
mythical beasts which aren’t simple pastiches of nature? Centaurs, minotaurs, unicorns, griffons, chimeras, sphinxes, manticores, and the like don’t speak well for the human imagination. None is as novel as a kangaroo or starfish.)