Existential Physics: A Scientist's Guide to Life's Biggest Questions by Sabine Hossenfelder
My rating: 3 of 5 stars

Stay in Your Lane

Beware of scientists with philosophical aspirations. Particularly if they write well - as does Sabine Hossenfelder. Especially if they have a contrarian reputation in their own discipline - as does Sabine Hossenfelder. Hidden in plain sight within their lucid prose and controversial interpretations, are some really dodgy arguments. This is the problem with Sabine Hossenfelder, even if one agrees with her conclusions - as I almost always do.

Hossenfelder is an unashamed reductionist. For her the ultimate truth about the world lies in some expression in nuclear physics (but certainly not in cosmological physics which is largely useless, untestable speculation). Specifically there is a hierarchy of scientific enquiry: “Chemistry is underpinned by physics, and that is underpinned by mathematics.” In her theory, the lower down the kind of study the more “fundamental” the enquiry. She wants to focus on the

“… areas of physics that study the fundamental laws as the foundations of physics. Everything else emerges from those fundamental laws, roughly in this order: atomic physics, chemistry, materials science, biology, psychology, sociology…More likely, what’s currently fundamental will turn out to be emergent from yet another, deeper level.[*]”

I find it interesting to note that in the above quotes, mathematics is omitted in the second list as the most fundamental of the sciences. The footnote refers to her first book, Lost in Math: How Beauty Leads Physics Astray which perhaps explains this lapse. There she essentially objects to the criteria used in mathematics which produce things like string theory and other untestable constructions. Mathematics, it seems, has an ambiguous place in her hierarchy.

And indeed mathematics is problematic for Hossenfelder’s theory of the world: “…the closer we look at reality, the more slippery it becomes. Our heavy use of mathematics is a major reason.” So for example, she has to recognise that somehow the gears aren’t meshing between the various ‘emergent’ layers: “failure to distinguish the subjective experience of being inside time from the timeless nature of the mathematics we use to describe it.” Yet mathematics sits there at the ultimate foundation of the scientific enterprise.

The reason for Hossenfelder’s confusion and inconsistency is, it seems to me, obvious to everyone except Hossenfelder. She knows that the map of mathematics is not the territory of reality: “…we can’t assign ‘reality’ to any particular formulation of a theory.” In other words, mathematics does not emerge from reality (a Platonist view she rejects explicitly). In fact, if we accept Hossenfelder’s hierarchy of enquiry, mathematics sits not at the bottom but somewhere near the top of the chain. Mathematics, like all language emerges from the biological/sociological. From that position it then produces the rest of the scientific hierarchy. Mathematics, in other words, is indeed fundamental, but not in the way that Hossenfelder proposes.

So under Hossenfelder’s apparently commonsensical, undogmatic prose lies a dogmatism as rigid as any religion. She wants us to believe on faith that while we can’t demonstrably test the connections between the various levels of scientific enquiry - for example, predicting human behaviour on the basis of quantum theory - this is a matter of available technology not scientific principle. And while she knows that no theoretical description of the world can ever capture its reality, she wants us to share her faith that this doesn’t matter at all. Hers is a sort of militant, evangelical agnosticism suggesting that we follow her fearlessly into the void of knowing more and more about less and less. Sorry Sabine.

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