Inside Cover Blurb
- Roger Penrose's original and provocative ideas about the large-scale physics of the Universe, the small-scale world of quantum physics and the physics of the mind have been the subject of controversy and discussion.
- These ideas were set forth in his best-selling books
→ "Penrose (Roger) - The Emperor's New Mind", and
→ "Penrose (Roger) - Shadows of the Mind".
- In this book, he summarises and brings up to date his thinking in these complex areas. He presents a masterful summary of those areas of physics in which he feels there are major unsolved problems. Through this, he introduces radically new concepts which he believes will be fruitful in understanding the workings of the brain and the nature of the human mind.
- These ideas are then challenged by three distinguished experts from different backgrounds - Abner Shimony and Nancy Cartwright as Philosophers of Science and Stephen Hawking as a Theoretical Physicist and Cosmologist.
- Finally, Roger Penrose responds to their thought-provoking criticisms.
- This volume provides an accessible, illuminating and stimulating introduction to Roger Penrose's vision of theoretical physics for the twenty-first century. His enthusiasm, insight and good humour shine through this brilliant account of the problems of modern physics.
- CUP, Cambridge, 1997. Paperback.
- Based on the 1995 Tanner Lectures.
"Longair (Malcolm) - The Large, the Small and the Human Mind: Foreword"
Source: Penrose - The Large, the Small and the Human Mind
"Penrose (Roger) - Space-time and Cosmology"
Source: Penrose - The Large, the Small and the Human Mind, Chapter 1
"Penrose (Roger) - The Mysteries of Quantum Physics"
Source: Penrose - The Large, the Small and the Human Mind, Chapter 2
"Penrose (Roger) - Physics and the Mind"
Source: Penrose - The Large, the Small and the Human Mind, Chapter 3
"Shimony (Abner) - On Mentality, Quantum Mechanics and the Actualization of Potentials"
Source: Penrose - The Large, the Small and the Human Mind, Chapter 4
"Cartwright (Nancy) - Why Physics?"
Source: Penrose - The Large, the Small and the Human Mind, Chapter 5
"Hawking (Stephen) - The Objections of an Unashamed Reductionist"
Source: Penrose - The Large, the Small and the Human Mind, Chapter 7
- To start with, I should say I’m an unashamed reductionist. I believe that the laws of biology can be reduced to those of chemistry. We have already seen this happening with the discovery of the structure of DNA. And I further believe that the laws of chemistry can be reduced to those of physics. I think most chemists would agree with that.
- Roger Penrose and I worked together on the large-scale structure of space and time, including singularities and black holes. We pretty much agree on the classical theory of General Relativity but disagreements began to emerge when we got on to quantum gravity. We now have very different approaches to the world, physical and mental. Basically, he’s a Platonist believing that there’s a unique world of ideas that describes a unique physical reality. I, on the other hand, am a positivist who believes that physical theories are just mathematical models we construct, and that it is meaningless to ask if they correspond to reality, just whether they predict observations.
- This difference in approach has led Roger to make three claims in Chapters 1-3 that I strongly disagree with.
- The first is that quantum gravity causes what he calls OR, objective reduction of the wavefunction.
- The second is that this process has an important role in the operation of the brain through its effect on coherent flows through microtubules.
- And the third is that something like OR is needed to explain self-awareness because of the Gödel Theorem.
- To start with quantum gravity, which is what I know best. His objective reduction of the wavefunction is a form of decoherence. This decoherence can come about through interactions with the environment or through fluctuations in the topology of spacetime. But Roger seems to want neither of these mechanisms. Instead he claims that it occurs because of the slight warping of space-time produced by the mass of a small object. But, according to accepted ideas, that warping will not prevent a Hamiltonian evolution with no decoherence or objective reduction. It may be that accepted ideas are wrong but Roger has not put forward a detailed theory that would enable us to calculate when objective reduction would occur.
- Roger’s motivation in putting forward objective reduction seems to have been to rescue Schrodinger’s poor cat from its half-alive, half-dead state. Certainly, in these animal liberation days, no one would dare suggest such a procedure, even as a thought experiment. However, Roger made a point of claiming that objective reduction was so weak an effect that it could not be experimentally distinguished from decoherence caused by interaction with the environment. If that is the case, then environmental decoherence can explain Schrodinger’s cat. There’s no need to invoke quantum gravity. Unless objective reduction is a strong enough effect to be measured experimentally, it can’t do what Roger wants it to do.
- Roger’s second claim was that objective reduction had a significant influence on the brain, maybe through its effect on coherent flows through microtubules. I’m not an expert on the operation of the brain, but it seems very unlikely, even if I believed in objective reduction, which I don't. I cannot think that the brain contains systems that are sufficiently isolated that objective reduction could be distinguished from environmental decoherence. If they were that well isolated they wouldn’t interact rapidly enough to take part in mental processes.
- Roger’s third claim is that objective reduction is somehow necessary because Gödel’s Theorem implies that a conscious mind is not computable. In other words, Roger believes that consciousness is something special to living beings and that it couldn’t be simulated on a computer. He didn't make it clear how objective reduction could account for consciousness. Rather, his argument seemed to be that consciousness is a mystery and quantum gravity is another mystery so they must be related.
- Personally, I get uneasy when people, especially theoretical physicists, talk about consciousness. Consciousness is not a quality that one can measure from the outside. If a little green man were to appear on our door step tomorrow, we do not have a way of telling if he was conscious and self-aware or was just a robot. I prefer to talk about intelligence which is a quality that can be measured from the outside. I see no reason why intelligence should not be simulated on a computer. We certainly can't simulate human intelligence at the moment, as Roger showed with his chess problem. But Roger also admitted that there was no dividing line between human intelligence and animal intelligence. So it will be sufficient to consider the intelligence of an earthworm. I don't think there’s any doubt that one can simulate an earthworm's brain on a computer. The Gödel argument is irrelevant because earthworms don’t worry about Π1-sentences.
- The evolution from earthworm brains to human brains presumably took place by Darwinian natural selection. The quality selected for was the ability to escape enemies and to reproduce, not the ability to do mathematics. So again the Gödel Theorem is not relevant. It is just that the intelligence needed for survival can also be used to construct mathematical proofs. But it is a very hit and miss business. We certainly don’t have a knowably sound procedure.
- I have told you why I disagree with Roger’s three claims that there is objective reduction of the wavefunction, that this plays a role in the operation of the brain and that it is necessary to explain consciousness. I had better let Roger reply.
COMMENT: See "Penrose (Roger) - The Large, the Small and the Human Mind: Responses to Shimony, Cartwright & Hawking" for a reply.
"Penrose (Roger) - The Large, the Small and the Human Mind: Responses to Shimony, Cartwright & Hawking"
Source: Penrose - The Large, the Small and the Human Mind, Chapter 7
RESPONSE TO STEPHEN HAWKING
- Stephen’s comments about his being a positivist might lead one to expect that he, also, would be sympathetic to a ‘patchwork’ picture of physics. Yet he takes the standard principles of U quantum mechanics to be immutable, as far as I can make out, in his own approach to quantum gravity. I really don’t see why he is so unsympathetic to the genuine possibility that unitary evolution might be an approximation to something better. I am, myself, happy with it being an approximation of some kind - as Newton’s superbly accurate gravitational theory is an approximation to Einstein’s. But that, it seems to me, has very little to do with Platonism/positivism, as such.
- I do not agree that environmental decoherence alone can un-superpose Schrodinger’s cat. My point about environmental de-coherence was that once the environment becomes inextricably entangled with the state of the cat (or with whatever quantum system is under consideration), then it does not seem to make any practical difference which objective reduction scheme one chooses to follow. But without some scheme for reduction, even if it is merely some provisional FAPP (‘for all practical purposes’) scheme, the cat’s state would simply remain as a superposition. Perhaps, according to Stephen’s ‘positivist’ stance, he does not really care what the unitarily evolved cat-state actually is, and he would prefer a density matrix description for ‘reality’. But this does not, in fact, get us around the cat problem, as I showed in Chapter 2, there being nothing in the density matrix description which asserts that the cat is either dead or alive, and not in some superposition of the two.
- With regard to my specific proposal that objective reduction (OR) is a quantum gravitational effect, Stephen is certainly correct that ‘according to the accepted physical ideas, [space-time] warping will not prevent a Hamiltonian evolution’, but the trouble is that without an OR process coming in, the separations between the different space-time components can get larger and larger (as with the cat), and seem to deviate more and more from experience. Yes, I do believe that accepted ideas must be wrong at this stage. Moreover, although my ideas are far from being fully detailed as to what I do believe must be going on at this level, I have at least suggested a criterion which is in principle subject to experimental test.
- With regard to the likelihood of the relevance of such processes to the brain, I agree that this would seem to be ‘very unlikely - were it not for the fact that something very strange is indeed going on in the conscious brain which appears to me (and also to Abner Shimony) to be beyond what we can understand in terms of our present-day physical world-picture. Of course this is a negative argument, and one must be very cautious not to go overboard with it. I think that it is very important to look into the actual neurophysiology of the brain, and also other aspects of biology, extremely carefully to try to see what is really going on.
- Finally, there is my use of the Gödel argument. The whole point of using this kind of discussion is that it is something that can be measured from the outside (i.e., I am concerned with the A/C or B/C distinction, as I mentioned earlier, not the externally non-measurable A/B distinction). Moreover, with regard to natural selection, the precise point that I was making was that a specific ability to do mathematics was not what was selected for. If it had been, then we would have been trapped within the Godelian straight-jacket, which we are not. The whole point of the argument, in this particular regard, is that it was a general ability to understand that was selected for - which, as an incidental feature, could also be applied to mathematical understanding. This ability needs to be a non-algorithmic one (because of the Godelian argument), but it applies to many things other than mathematics. I don’t know about earthworms, but I am sure that elephants, dogs, squirrels and many other animals have their good share of it.
COMMENT: Reply to "Hawking (Stephen) - The Objections of an Unashamed Reductionist".
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