Is the human brain a Turing Machine?
When you ask this question, do you mean to ask "Is the human brain a Turing Machine?" or "Is the human mind a Turing Machine?"
Do you think that the brain and the mind are really the same thing? Or, do you think that there is more to the mind than just the brain?
These are very good questions, and before you answer them, let me tell you what the thoughts were of some famous people.
Alan Turing convinced himself that his brain is just some kind of biological machine that is equivalent to a Turing Machine. The human mind is nothing more than what is already in the brain.
What is written here about Alan Turing is taken from the book A Madman Dreams of Turing Machines (Anchor Books, 2007) by Janna Levin, particularly pages 97 through 108.
This book is a fictional biography of arguably the two greatest mathematicians of the 20th century: Alan Turing and Kurt Gödel. I enjoyed reading this book; although it's a biography, it reads like a novel.
To make it a novel, Janna Levin had to make up some fictional parts. There is a Notes section at the end of the book (pages 223 - 230) where Janna Levin explains what was based on fact and what was fiction. I was surprised to find out how little fiction there was.
At first, Alan Turing believed that there must be more to an individual than just a body with a brain that disintegrates after death with nothing left over. He strongly felt that a person must also have a soul or a spirit that lives for eternity. When his best friend, Christopher Morcom, died, Alan felt that Christopher was still somehow alive, and sometimes even thought he felt his presence. He also considered the possibility that a person's spirit may find a new body, and said this in a letter he wrote to Christopher's mother.
At age 23 (about a year before he published his famous paper), Alan Turing started imagining a machine that could read and write symbols to an infinitely-long strip of paper, and could even make computations of many numbers according to algorithms that were designed into the machine. He also realized, that with the proper algorithm, and with the correct interpretation of the symbols that the machine would write to the tape, such a machine could be designed to play a game of chess--a game that Alan enjoyed very much playing with Christopher.
This type of thinking led Turing to the realization that the human body is nothing more than a biological machine. The human mind, or actually the brain, is nothing more than a machine as well. There is no need to have a soul. There is no spirit. There is no eternal life after death, and there is no God.
Alan Turing held on to this belief for the rest of his life.
Kurt Gödel believed that the human mind is more than just a Turing Machine.
What is written here about Kurt Gödel is taken from Janna Levin's book A Madman Dreams of Turing Machines, particularly pages 7-12, 47-94, and 187-191.
Every Thursday evening in 1931, Kurt Gödel would walk over to a social gathering of philosophers, mathematicians, and other scientists at the Café Josephinum. This was a group of elite professors from the University of Vienna known as the Vienna Circle. They gathered here once a week to discuss and share perhaps some new ideas over a cup of coffee and a snack. The prevailing sentiment here was that the only truths were things that were scientifically observable and verifiable or could be proved mathematically. There was no place here for mysticism, superstition, metaphysics, or religion, and these were deemed to be not true. Among the notable members, the ones worth mentioning here are Otto Neurath, his wife Olga Hahn-Neurath, and most importantly, the founder and leader of the Vienna Circle, Moritz Schlick.
Just two years earlier, at age 23, Kurt Gödel received his Ph.D. in Mathematics at the University of Vienna under the direction of Professor Hans Hahn, the brother of Olga Hahn-Neurath. It was upon his recommendation that Moritz Schlick extended an invitation to Kurt Gödel to join the Vienna Circle.
Kurt was a very quiet type of person, and on these Thursday evenings he would hardly ever say anything but just listened to what everyone else had to say. Yet he was respected by all and recognized as a very talented mathematician--especially by Olga Hahn-Neurath, herself a mathematician.
There was one Thursday, however, when things would be different. Kurt knew he made a profound discovery having to do with an idea that he was working on for some time. He was very eager to announce that he found something that was undoubtedly true yet could not be proved mathematically. He was also very anxious in presenting this to a group dedicated to the belief that only things that can be demonstrated, observed, or mathematically proved are true.
On that Thursday evening, Kurt went to Moritz and said in a clear voice "I have thought more about the Liar's Paradox, about the liar who says This statement is false." Otto and Olga, upon hearing this, made light of it with humorous comments. Olga added laughingly "Half the lies they tell about me are true." Kurt tried to explain that it was this paradox that led his thinking to the discovery of a truth that could not be proved. Alas, everyone just wondered why Kurt would be uttering such nonsense.
That Thursday, and perhaps some subsequent Thursdays, Kurt tried to convince everyone that he was right. Sometimes he directed his arguments more to Olga than others; perhaps because she was blind and unaware of the visible expressions of doubt around the room; perhaps because she was a mathematician and had the best chance of understanding him; but mostly perhaps because Kurt felt that she, more so than others, respected him and valued his opinions. (Of course, Kurt must have known, that it was practically impossible to present a rigorous explanation in the time allowed for a casual conversation.) At one point, Otto asked "Are you saying Moritz is wrong?" to which Kurt replied "Yes." Kurt pleaded with Moritz "We cannot prove it is true, but we can recognize that it is true. Our minds can see truth. See it even when mathematics cannot. Our minds are bigger than that. Our minds are bigger."
That same year, Kurt Gödel published the paper in which he presented a rigorous proof of what became famously known as Gödel's Incompleteness Theorem. The logic in this paper was flawless, so that mathematicians all over the world had no choice but to accept (sometimes very reluctantly) that Gödel was right.
Many years later, in 1977, when Kurt Gödel was at the Institute for Advanced Study at Princeton, he confided to his good friend Oskar Morgenstern that he was writing an article refuting Alan Turing's thesis on the limits of the mind. He agreed with Turing that algorithmic reasoning could be completely replaced by a Turing Machine, but we cannot equate a human soul with a Turing Machine. He asked Morgenstern if he would publish this article for him in case he died before he completed it.
Gödel told Morgenstern that he was also working on a formal proof of the existence of God, but this one should not be published before he finished it, or else their colleagues would think he was crazy.
Oscar Morgenstern died on July 26, 1977. Kurt Gödel died on January 14, 1978, before he could complete and publish either of these last two papers.
Roger Penrose presumes that the human brain is much more than a Turing Machine. In addition to the algorithmic thinking of a Turing Machine, the brain is somehow capable of consciousness and the emotions that humans have. All of these human abilities reside in the brain, so that everything in the human mind is already in the brain.
What is written here is taken from the book The Emperor's New Mind (Oxford University Press, 1989) by Sir Roger Penrose.
This is truly an excellent book! The Excel-based Turing Machine that you can download from the Home page of this website was designed using the description in Chapter 2 of this book.
Proponents of Strong AI believe that the day will come when computers and robots will be able to do anything that humans can do. Penrose refutes this belief by asking whether human insight or consciousness can be programmed into a robot that's equivalent to a Turing Machine. You can sense that this is the purpose of the book The Emperor's New Mind right from the begining--as soon as you read the Prologue.
But, do we need more than the brain to exhibit human thinking? Is there a need for a mind that's more than the physical brain? Certainly, the brain plays an indispensible role in human thinking, as we're all aware that a serious injury to the brain can have an adverse effect on thinking. What is particularly interesting are the split-brain experiments (as described in Chapter 9 of Penrose's book) which seem to show that two halves of a split brain are independently conscious.
But, can the entirety of human thinking, to include consciousness, somehow reside in the human brain, which is viewed by many people as a collection of neurons, in pretty much the same way as a computer is a collection of transistors? Penrose predicts that someday we may be able to explain how consciousness comes from the brain; however, to do so we may first need to discover a new theory, which is really a bridge between quantum physics and classical physics.
This book is a fictional biography of arguably the two greatest mathematicians of the 20th century: Alan Turing and Kurt Gödel. I enjoyed reading this book; although it's a biography, it reads like a novel.
To make it a novel, Janna Levin had to make up some fictional parts. There is a Notes section at the end of the book (pages 223 - 230) where Janna Levin explains what was based on fact and what was fiction. I was surprised to find out how little fiction there was.
This is truly an excellent book! The Excel-based Turing Machine that you can download from the Home page of this website was designed using the description in Chapter 2 of this book.
Ok! Now it's your turn!
Which of the following do you think is correct?
Version 1.0 -- April 23, 2017