The Large, the Small and the Human Mind: Responses to Shimony, Cartwright & Hawking
Penrose (Roger)
Source: Penrose - The Large, the Small and the Human Mind, Chapter 7
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RESPONSE TO STEPHEN HAWKING

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.

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