Do Loops Explain Consciousness? Review of I Am a Strange Loop Martin Gardner I Am a Strange Loop H o f s t a d t e r , a Douglas Hofstadter professor of cogni- 2007, Basic Books, New York tive science at In- US$26.95, 412 pages diana University, ISBN-13: 978-0-465-03078-1; is best known for ISBN-10: 0-465-03078-5 his Pulitzer prize- w i n n i n g G ö d e l , Barmaid: “Would you like some wine?” Escher, Bach, or GEB Descartes: “I think not.” as he likes to call Then he vanishes. it. His new book, as —Anonymous joke brilliant and provoc- ative as earlier ones, Our brain is a small lump of organic molecules. is a colorful mix of It contains some hundred billion neurons, each speculations with more complex than a galaxy. They are connected passages of autobi- in over a million billion ways. By what incredible ography. An entire hocus-pocus does this tangle of twisted filaments chapter is devoted become aware of itself as a living thing, capable of to a terrible tragedy of love and hate, of writing novels and symphonies, that Hofstadter is still trying to cope with. His wife feeling pleasure and pain, with a will free to do Carol, at age 42, died suddenly of a brain tumor. good and evil? The preceding chapter links his love for Carol to David Chalmers, an Australian philosopher, has a fantasy he once conceived about a mythical land called the problem of explaining consciousness he called Twinwirld. Its inhabitants are identical twins, so nearly alike that they think and act like the “hard problem”. The easy problem is under- single individuals. standing unconscious behavior, such as breathing, I suspect Hofstadter will be surprised to know digestion, walking, perceiving, and a thousand that L. Frank Baum, in his non-Oz fantasy The other things. Grappling with the hard problem has Enchanted Island of Yew (you?) imagined a similar become one of the hottest topics facing philoso- land he called Twi. Everything in Twi is duplicated, phers, psychologists, and neuroscientists. Accord- like seeing the world through glasses that produce ing to philosopher John Searle, reviewing Nicholas double images. Residents of Twi, like those of Humphrey’s Red: A Study of Consciousness (New Twinwirld, are identical twins. The rulers of Twi York Review of Books, November 2005), Amazon are two beautiful girls who think and speak as a lists 3,865 books on consciousness. The most single entity. recent, published this year by Basic, is Douglas In his heart-rending chapter on Carol, Hof- Hofstadter’s I Am a Strange Loop. stadter makes clear why he preceded it with a de- scription of Twinwirld. He and Carol were so much Martin Gardner wrote Scientific American’s Mathematical alike they they resembled a pair of Twinwirlders. Games column for 25 years. His most recent books are Unable to find consolation in hope for an afterlife, The Annotated Hunting of the Snark and Are Universes Hofstadter’s only solace is knowing that for at least Thicker Than Blackberries? 852 NOTICES OF THE AMS VOLUME 54, NUMBER 7 a time Carol will in a way live on in the memories In Chapter 21 Hofstadter introduces a disturb- of those who knew and loved her. ing thought experiment, involving human identity, I Am a Strange Loop swarms with happy memo- that has been central in dozens of science-fiction ries. One vivid recollection, not so happy, concerns tales. A man is teleported by a process made fa- a time when Hofstadter was fifteen and asked to mous by Star Trek. Officers of the Enterprise are select two guinea-pigs to be killed for a laboratory beamed down to a planet, later beamed up again. experiment. Faced with the task, he fainted. This This is done by apparatus that scans a person mol- aversion to animal killing led to his becoming a ecule by molecule, then transmits the information vegetarian. For a while he allowed himself eggs and to a distant spot where it creates an exact duplicate fish, but later became a vegan, avoiding all food of animal origin. He refuses to buy leather shoes and belts. Like Baum’s Tin Woodman, to whom the Wiz- ard gave a fine velvet heart, Hofstadter has twinges of guilt when he swats a fly. One of his heroes is Albert Schweitzer, who whenever possible avoided killing an insect. Many pages in I Am a Strange Loop express the author’s great love of music. Hofstadter plays a classical piano. Bach, Chopin, and Prokofiev are among his favorite composers, Bartok among those he dislikes. Another passion is for poetry. He has translated from the Russian Pushkin’s great poem Eugene Onegin, as well as the work of other foreign bards. On page 94 Hofstadter offers a clever six-stanza poem by a friend that commemorates an event he later considered symbolic. One day he grabbed Photograph by Pete Rimbey. Pete by Photograph a batch of empty envelopes and was puzzled by Carol and Doug Hofstadter touching one another’s noses. what seemed to be a marble wedged between them. The marble turned out to be a spot where a thick- of the person. If this destroys the original body ness of paper felt like a marble. In a similar way, there is no philosophical difficulty. But suppose he believes, we imagine a self wedged somewhere the original is not destroyed. The result is a pair between the neurons of our brain. of identical twins with identical memories. Is the The marble provides the central theme of I Am a teleported person the same person or someone Strange Loop. The soul, the self, the I, is an illusion. else? It is a strange loop generated by a myriad of lesser loops. It is a minute portion of the universe, a glob The dilemma goes back to Plutarch. He imagines of dead matter within our skull, not only observing a ship that is slowly replaced, piece by piece, until itself, but aware it is observing itself. the entire ship is reconstituted. The original parts Hofstadter has long been fascinated by self- are then reassembled. Each ship can claim to be reference loops. He sees them everywhere. They the original. are at the heart of Gödel’s famous undecidability Baum introduces the same problem in his his- proof. They lurk within Russell and Whitehead’s tory of the Tin Woodman. As all Oz buffs know, a Principia Mathematica. They are modeled by such cruel witch enchants Nick Chopper’s ax, causing logic paradoxes as “This sentence is false.” and by it to slice off parts of Nick’s meat body. Each part the card that says on one side “The sentence on the is replaced by Ku-Klip, a master tinsmith, until other side is true,” and on the flip side says “The Nick is made entirely of tin. In The Tin Woodman sentence on the other side is false.” Similar loops of Oz the tin man visits Ku-Klip’s workshop where are such lowly mechanisms as flywheels, thermo- he converses with his former head. Ku-Klip has stats, and flush toilets. He reproduces Escher’s preserved it in a cupboard. Who is the real Nick famous lithograph of two hands, each drawing Chopper? The tin man or his former head? the other, and suggests modifying it by having one Hofstadter has little interest in such conun- hand erase the other. drums. Another topic that infuriates him is free Many photographs in the book depict recursive will. Unlike his good friend philosopher Daniel loops. One shows a carton closed by four flaps, A Dennet, Hofstadter denies that free will exists. It is on top of B, B on top of C, C on D, and D on A. In another mirage, like the marble in the envelopes. another picture Doug and Carol are each touching Other topics drive Hofstadter up a wall. One is the other’s nose. An amusing photo shows a grin- the “inverted spectrum” paradox. How can we be ning Doug with nine friends, each sitting on the certain that our sensation of, say, red is the same lap of a person behind. as that of another person? What we experience AUGUST 2007 NOTICES OF THE AMS 853 as red could be what she experiences as what we threshold to become aware of what it is doing. No call blue. chess program, however advanced, will know it is Another topic Hofstadter considers frivolous playing chess anymore than a washing machine is the concept of a zombie. Zombies are persons knows it is washing clothes. Today’s most power- who think, talk, and behave exactly like ordinary ful computers differ from an abacus only in their people but are entirely lacking in all human feel- power to obey more complicated algorithms, to ings and emotions. The concept arises in relation twiddle ones and zeroes at incredible speeds. to computerized robots. Baum’s wind-up robot A few mysterians believe that science, some Tik-Tok, who Dorothy rescues in Ozma of Oz, glorious day, will discover the secret of conscious- has a metal plate on his back that says, “Thinks, ness. Penrose, for example, thinks the mystery may Speaks, Acts, and Does Everything but Live.” It is yield to a deeper understanding of quantum me- hard to believe, but entire books have been written chanics. I belong to a more radical wing. We believe about zombies it is the height of hubris to suppose that evolution Consciousness for Hofstadter is an illusion, has stopped improving brains.