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Positivism vs Realism: Hawking vs Penrose

March 29, 2021

In a famous debate about the nature of space and time between Roger Penrose and Stephen Hawking, Hawking saw there to be no problem in quantum theory that needed extra explanation. Schrodinger’s cat and the measurement problem was not such a big problem, because we could view quantum theory purely operationally, based on experimental results. This is the route of positivism. Penrose took the route of realism where he insisted that something must be missing in quantum theory, something akin to the unfinished revolution of Einstein.

Many people have written about and tried to tackle this debate that started with Einstein’s attempts through various thought experiments to undermine quantum theory by finding some inherent paradox or contradiction contained within some of its consequences. David Bohm, John Stewart Bell, Paul Davies, Roger Penrose, and most recently Lee Smolin has written a book with this very title. What Einstein wanted was some coherent and consistent realist picture or model of what is happening with quantum phenomena that can be seen as objectively true, independent of observers.

The first attempt was the pilot wave theory of David Bohm and De Broglie, the next effort was in the development of the notion of Beables in the work of John Stewart Bell, who also proved a very important theorem in quantum mechanics, to the effect that if there are hidden variables guiding the wave, they must be non local. So we find ourselves in the position of having to understand how to reconcile realism and non local influence.

This has made the path difficult for the likes of Penrose, Lee Smolin and other more recent proponents of realism in science. The problem is that the basic Newtonian principle of action and reaction is lost by allowing non local influences. And this principle is a foundational tenet of traditional realist and mechanical approaches and is continued on even in Quantum field theory. An option favoured by Penrose is that there is some sort of collapse of the wave function triggered by the gravitational fabric of curved space-time-matter itself, whenever there is a certain degree of curvature present. Penrose sees some hope for his view in the theory of Hawking radiation and evaporation of black holes. I think he sees this potential asymmetry caused by strongly gravitational objects as indicative of a collapse of the wave function caused by gravity, and so of an explanatory dependence of quantum theory on some general relativistic interpretation of quantum gravity.

It is ironic that Stephen Hawking himself came to reject this view about black holes and argued later that energy is conserved and there is no evaporation of black holes. In both these cases and some others you can see how Hawking is guided more by positivistic and operationalist considerations, while Penrose is motivated by trying to preserve some connection with realism in our fundamental physical theories.

So, where would I place myself in this discussion? Well, the recent book I read and reviewed and talked about on here in previous posts by Julian Barbour provides a good alternative way to view many of these things. The only question that remains then is how, within a relationalist view of space and time to quite account for the reality of space time curvature and hence, also the reality of singularities and black holes, because if space-time is purely relational, there is no independent “thing” there to which we can apply the property of curvature, just a network of relations between things. But those networks, it makes no sense to apply curvature to them, variation is provided instead by evolution and development of different configurations of networks of relations.

I think these questions still remain to be considered in more thorough detail and greater clarity to solve some of these quandaries about how exactly to describe and delineate the reality-status of our fundamental physical theories. Hawkings positivistic approach may be a safer way to hedge your bets and not commit to a metaphysic or view of reality, but I think its clear that some metaphysic always slips in whether we adopt one consciously or not, so it may be better as Penrose is trying, to adopt realism and aim to choose our metaphysic wisely. And also is the effort of Smolin in his latest work.

I have reservations though about how both of them interpret realism, as well as reservations about the timeless Platonia of Julian Barbour. Penrose’s realism seems to rely on a non-relationalist view of space and time which may conflict with basic principles of human reason, while Smolin’s realism seems to involve various postulations of extra entities that are added on to quantum theory arbitrarily rather than having a clear physical role. Their role seems only to be to save realism. Barbour’s realism is a pure Platonic realm of changeless forms. And, as appealing as that may be aesthetically, I tend to agree with Smolin, Rovelli and others in preferring to give primacy to the reality of time and processes, rather than to static things.

On that point, Carlo Rovelli has a newly released book called Helgoland presenting and arguing for a process view of quantum theory and it will be interesting to explore that one. The debate is ongoing, but it is refreshing to see these kinds of serious consideration and respect being shown by top theoretical physicists to questions of the ontolological status and implications of their physical theories. For, I think they realise well that without some physical basis and platform for their theories that we can all point towards, the danger is that the subject would become reduced to the creation of mathematical models and pure mathematics. less and less in touch with a serious grounding in physical reality.

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