“The Science of Can and Can’t”


I’ve been following Chiara Marletto (and David Deutsch before her) for more than a decade as the idea of a “Universal Constructor” has become an even more generic concept than the “Universal Turing Machine”. A machine that can do arbitrarily creative stuff in the physical world as well as perform arbitrary information processing tasks. (It helps to let go of any mental picture of a machine as a mechanical device or of a computing machine as an electro-mechanical device – rather a machine as any “system” that does stuff.)

Her new book …

“The Science of Can and Can’t”
by Chiara Marletto

… I’ve already mentioned and part/pre-reviewed once or twice as well as referencing numerous interviews about it. (For example, this one with Sean Carroll, this one with The Dissenter – both allow her to describe her ideas at length in her own words.)


[It’s several months since I read and reviewed the “imaginative” introduction – a house move and a new job intervened – but the last few evenings I’ve read it cover to cover. Recommended.]

The subtitle “A physicists journey through the land of counterfactuals” nails her main topic beyond Constructor Theory. That is the idea that most if not all of physical science, and its chances of finding solutions to any number of long-standing problems, is improved by thinking in terms of meta-laws about what’s possible or impossible (counterfactuals) rather than laws about what is (facts).

She works through examples from the physics of simple mechanics to thermodynamics and living systems illustrating how counterfactuals can work and how testable thesis can be derived. It’s written very simply for lay readers and interspersed with thinly-disguised autobiographical (?) fictional passages about formative and inspirational experiences within and beyond physics.

Quite easy for me to sympathise with the meta view of counterfactuals as constraints on the processes of evolution and emergence. I’ll leave it to expert scientists as to whether identifiable scientific leaps are actually enabled.

In many ways I already see Boltzmann / Statistical / Entropic thinking in thermodynamics being about bounds and constraints on the possible rather than exact “what is”, so it is the one area (Chapter 6) where I didn’t quite understand how her counterfactual take is new or an improvement. I might have been left underwhelmed if it were not for the realisation of the importance of the information-theoretic thread running through the whole. (As it is, I will undoubtedly re-read chapter 6.)

The real revelation is not simply that physical process are information-theoretic. In thermodynamics at both human and cosmological scales information-based arguments have been used on the entropic limits to behaviour of matter and energy – from single particles passing through two slits to knowledge of black-hole event horizons. Information is practically the complement to entropy after all – and these already look like counterfactuals, as I say.

No, what she does is show that the counterfactual view brings limits to information and knowledge into physics itself. Knowledge and limits to what can be known cannot be dismissed as matters of human subjectivity. There is a good deal of explanation of the significance of and differences between information and knowledge – the latter being information that sustains itself for re-use as it passes through creative processes. Not new concepts to anyone who has followed information-independent-of-physical-embodiment arguments through physical, biological and mental evolution (a la Dennett say, DNA anyone?) but firmly pinning definitions of information and knowledge as part of physics itself.

Dennett has left information as something disembodied from physics for now, subject to evolution in rational discourse, and many others (myself included) see information as something prior to physics (as well as prior to mental, metaphysics if you like, pan-proto-psychism if you prefer). Marletto bringing it objectively within physics must surely encourage more orthodox scientists to take the information-theoretic view seriously – however sceptical they might be that physics has any specific problem(s) requiring such a solution. An alternative view can’t be a bad thing.

That I think is the masterstroke of The Science of Can and Can’t, bringing information and knowledge within science.

But that’s not all. In her final fictional piece and in her own pen-picture she makes clear not only her physical science credentials and her Italian literary aspirations but also her recognition of the significance of epistemology. Her fictional speculation on the young Alexander being tutored by Aristotle and even planning the library at Alexandria makes clear the importance of the abstract, that discussion and open-ended dialogue beats pedagogy and debate on the tangible.

“The purpose was to have *conversations* with the great philosopher. The boy did not enjoy regular classes that much; but the conversations were a different matter: They were open-ended, exciting and far-reaching.

Abstract does not mean ‘unreal’.”

(Her emphasis in the original.)

Eco meets Rovelli? The literary skills may still be aspirational, but the abstract ideas are second to none.

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