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The idea that the Earth orbits the sun is so counter intuitive, that if you where not taught this in school, you will have no way of knowing this. The illusion of sunrise and sunset is impenetrable.

The philosopher Wittgenstein once asked a friend, "How was it that people thought the Sun orbited the Earth for so long"? His friend said, "Because it looked that way". Wittgenstein responded, "What would it look like if the Earth orbited the sun"?

Being locked in illusion himself, Wittgenstein knew the answer was impossible.

Even scientists believe that the sun orbits the Earth but they pretend that they don't.

Kurt Godel, one of the few people who could terrify the brightest minds of the 20th century, wondered why people can be so illogical in believing that the brain produces consciousness. We are locked into this illusion. The illusion is a moving Sun, a Sun set and a sun rise. The illusion is a part of who we are. And the way our language and stories are based on the moving sun, the same can be said for idea the that the brain produces consciousness.

We talk about with this, we feel it, we even tell the kids they will die forever when their brain ages and dies. We tell little kids that dreams are inside their head. We tell them that their brain makes mind like a computer makes software (contradiction intended). We even tell kids that death is annihilation because we are so sure of our illusions. Most of us can't do tensor equations but we convince the kids about illusion. We point, "Look at the sunset". All illusion.

The illusion is solid. The way there is no way out of the illusion of the Sun orbiting the Earth, there is no way out of the illusion of a local mind in the box.

Before the sceptic retorts that brain science gives results. The same can be said for ptolemaic astronomy. Ptolemaic astronomy can predict eclipses. The top minds of the day were convinced, both mathematically and by observation, that Plotemy was correct. This went on for centuries. The hard problem of astronomy was there for all the see, but it was never to be answered. Only when Capernicus came along did the hard problem of astronomy disappear. There wasn't a problem in astronomy, rather, the problem came with the fixtures and fittings, as it where. The system of Plotemy was thrown out and the problem vanished.

There is a hard problem of consciousness. But if we are locked in illusion, we'll never know the answer. I suspect that most people go about their day, doing commerce, playing games and happily living as they've always done without even suspecting there is a hard problem of consciousness because there isn't. The hard problem is in the imagination of the brain scientist who is locked in a ptolemaic jail.

Intuition tells me that I am more than what the brain scientists tell me. Brain science tells me that I am an illusion. Between these banks my life flows.

A little copernican revolution is inside us all!
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on 25 September 2010
Shadows of the Mind is undoubtedly a less populist book than its predecessor "The Emperor's New Mind". It is also significantly more technical in places than the predecessor. Its purpose is to extend the Godel based arguments used in ENM in several directions. Firstly to attempt to address various criticisms of the central argument of the previous book and then to develop some new ones. Also there is a discussion of the application to Robotics. An example of this sort of discussion is whether any capability of a Robot to learn would undo any of the Robot restrictions deduced in his basic argument. After all learning (human or robotic) will imply going beyond previous restrictions and being aware of new facts.

So there is a subtle argument needed to continue to show that despite this, humans will come out on top. If you are interested in this kind of subtlety after reading ENM then this is the book for you.

In effect Penrose is right at the heart of the Mind-Machine debate in this book. I give an overview of this debate as follows:

We need to find a scientific theory of the Mind. So we can examine what kind of cognitive or thinking device it might be, recognising that it also thinks about Mathematics. For that we need a model of cognition sufficiently general: the Turing Machine model is available and generally considered to be that model - there are no obvious rivals. So one can focus on whether the Turing Machine model could really be a model for the Human Mathematical Mind. If the answer is "yes" we would conclude also: Robots could have Minds.

Penrose draws the conclusion about mathematical reasoning that:

G: "Human mathematicians are not using a knowably sound algorithm in order to ascertain mathematical truth".

This statement isn't quite the statement that the Mind is not a Turing Machine (algorithm here), and some critics have attempted to expose the gaps. In this book Penrose discusses several lines of argument to close the gap. A possible rebuttal might be: "could mathematicians just be using unsound algorithms" - the faulty machine argument. This is very close to questions in the foundations of mathematics itself - after all is this suggesting that mathematics itself is fundamentally unsound? If so where is that unsoundness? So Penrose comes round to the conclusion step by step and through 100 odd pages, that the statement G above implies that indeed the Mind is not a Turing Machine.

This latter conclusion however introduces another problem: if the Mind is not a Turing Machine / algorithm then what sort of (scientific) model exists for it? At the end of the book Penrose examines a generalisation of the Turing Machine model (called Oracle Machines and also due to Alan Turing) and determines that a statement similar to G also applies to that model class as well. Thus the story is left incomplete and I would be tempted to say that somewhere a model M exists of which we can deduce:

"Human mathematicians are using M to ascertain mathematical truth"

However Shadows of the Mind ends without a discovery of that model M. So maybe the answer lies in studying Quantum properties, or in other aspects of these obscure machine models? If you want to be able to study this question further Shadows needs to be studied (and "studied" is the word)!
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on 24 December 2003
Shadows of the mind is a terrific book from a brilliant author.
Penrose's argument that conscious thought is not based on computation as we understand it is sound. Whether this can be strictly ascertained from Godel's theorem is still open to question I think.
However his overall conclusion that when we think, we may be using quantum mechanical counterfactuals to take us beyond the limits of computation, is an intriguing possibility.
I would recommend this book strongly to anyone with a reasonably high level of scientific education. Its hard work to read because the questions he asks are so deep and his approach to answering them is so exhaustively rigorous.
Penrose is not an evangelist like Richard Dawkins so his writing style is not as engaging to a popular audience. Nevertheless it is worth ploughing through this book to at least be rewarded in the end with the firm belief that one is definitely not merely a computer controlled robot!
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on 8 February 2001
The purpose of this book is to explore the connection between what is known in the areas of mathematics and physics to the way in which human brains function. Quite apart from this, the book is an excellent commentary on some on the more significant developments in physics and mathematics during the last hundred years. It is written so as to be readable by the non-scientist but those without a scientifc background could find some parts heavy going.
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on 29 April 2013
Shadows of The Mind by Sir Roger Penrose is a difficult read. It is not for everybody. It requires a strong background in mathematics and the physical sciences. The reward is a fascinating peek at the science of human consciousness.

This book is a follow-up of Sir Penrose's first book The Emperor's New Mind. It is divided into two parts. In Part I, using Gödel's incompleteness theorems as he did in his first book, Sir Penrose argues that the human mind, unlike an electronic computer, is non-algorithmic and hence non-computational. In plain English, artificial intelligence based on electronic computers is impossible, no matter how advanced computers become. His argument is terribly dry and mathematical. The point I took from Sir Penrose's argument here is that the human mind works in a way distinctly different from that of an electronic computer. His non-computational thesis is contrary to mainstream theories that the mind emerges from the brain as a result of complex computations at the synapses of the neurons.

The book becomes interesting in Part II, where Sir Penrose explains the "puzzle mysteries" and "paradox mysteries" as well as various aspects of quantum mechanics. But the most fascinating is his theory of how consciousness arises at the human brain, which he co-developed with Dr. Stuart Hameroff, an anesthesiologist and a professor at the University of Arizona. The theory is later called Orchestrated Objective Reduction or Orch-OR. Basically Orch-OR proposes that consciousness is the result of the self-collapse of a quantum wavefunction induced by quantum gravity at the microtubules of the neurons. The theory of Orch-OR complies with Sir Penrose's non-computational aspect of the human mind. He further proposes that the self-collapse of the wavefunction to a definite state (or objective reduction) is not random but rather influenced by "Platonic values" embedded in the fundamental fabric of space-time geometry at the Planck scale, and hence the objective reduction is "orchestrated". These Platonic values include mathematical truth, aesthetic and ethical values. Orch-OR is controversial but it represents a fascinating new approach in the science of human consciousness (See my comment below).

Sir Roger Penrose is a brilliant mathematical physicist, but he is a terrible science writer. He doesn't know how to simplify a complex concept to the degree that a layman can grasp, like Stephen Hawking does. Mathematics becomes a shackle in the book that holds back the reader. Five star for Penrose the scientist, two for Penrose the science writer.
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"Shadows of the Mind" addresses first, all of the arguments Professor Penrose had to counter regarding the assertions he made in "The Emperor's New Mind." He then goes on to hint at an approach to the subject of consciousness, the great puzzle that science has heretofore been unable to tackle, and has therefore denied.

It provides an exceptional mental excursion into the questions surrounding the subject of consciousness, as well as the peculiar nature of matter.

Why is it that a physicist is the one to tackle this subject as opposed to a biologist?

Professor Penrose suggests that physicists may be in a better position to comprehend how matter really behaves than biologists are.

Read it for yourself to see whether he is right.
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on 19 November 2015
Wow. Roger Penrose at his best - is he ever at anything else? He really never leaves a stone unturned. Anyone who has read "The Emperor's New Mind" (he calls it ENM in this later book) will be thrilled with this. He refuses to "run with the crowd". It really stimulates one's thinking.
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on 3 June 2001
Penrose's book expels the myths surrounding artificial intelligence and in doing so also reveals a great deal of physics to the layman. He gives an expose of the twin pillars of modern theoretical physics, namely quantum theory and relativity and uses this scientific knowledge to justify his views on the nature of consciousness. A sequel to his previous book "The Emperor's New Mind", Penrose covers subjects as diverse as superstring theory and brain neurology, in an attempt to justify his conviction that algorithmic computers cannot truly achieve artificial intelligence or consciousness. Along the way, "Shadows of the Mind" also offers tentative suggestions for the way forward in fundamental physics and much of its contents would therefore be of interest to students of the subject.[A more pictorial approach to some of these subjects can be found for example on"Special Relativity: A concise guide for beginners."]
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on 30 September 2014
I would say its just as good as "The Emperor's New Mind". Its technical, and some of it goes over my head, but the reasoning is excellent. I like his style of writing.
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on 17 November 2000
Penrose writes lucidly, and while not as engaging as some other pop science writers (e.g. Dawkins) is still easy to read.
However he is also a grossly mistaken man who has strayed far from his own field - a good Mathematical Physicist he may be but he's no Philosopher or Psychologist.
The main argument of the book centres around Godel's Theorem (or rather Turing's formally equivalent version) to show that mathematical reasoning is non-computational.
This basically begins with the premise 'assume that A is the algorithm which can decide if any given algorithm will terminate' and ends with the contradiction 'if A terminates then A never terminates'.
Penrose concludes that therefore A never terminates and that we must have used a non-algorithmic method for telling this ourselves (since A is the best algorithmic method).
However Penrose has misrepresented Godel, the actual conclusion is the falsity of the premise (that there could ever actually be an algorithm which would tell us if any algorithm terminates).
If Penrose is right and A never terminates then he has violated the initial premise of what A does and invalidated the whole argument.
The whole book then flows from this failure of logical reasoning to a far-out theory of consciousness that is highly implausible and scientifically naive.
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