Sabine Hossenfelder 2021. Existential Physics. A scientist’s guide to live’s biggest questions. London: Atlantic Books, 248 pp.

Physicists are the magisters who proclaim what we can objectively know of the world around us. Or supposedly. Thus, for example, one mantra of Hossenfelder is that “the future is fixed except for occasional quantum events that we cannot influence”. On this and similar topics (multiverse, for example) she convinces, although I was already convinced, or at least ready to be. This Sabine Hossenfelder is a lot more hard-nosed that the Max Tegmarks of the world. As should have been obvious from her first book which I’ll now get hold of.

But, the magisters remain fallible and Hossenfelder gently admonishes (for example) Sean Carroll, Carlo Rovelli, even Stephen Hawking for wandering from her narrow objective path into dark seductive ascientific realms. Throughout the book she intersperses conversations with senior physicists (notably Penrose, Deutsch) who she also declines to agree with since their claims to the contrary invoke quantum events without evidence, eg Penrose on microtubules although pleasingly she allows doubt to intrude. She is not well disposed towards most philosophers (except Nietzsche?).

Predicably (!), Hossenflelder also rejects (or abstains as ascientific) from the simulation hypothesis and has plenty to say about how physics makes this improbable (eg how a Simulator would struggle to simulate consciousness). But I think she is also fallible and in one telling instance has completely missed the boat, led astray by her hard-nosed competence with this world; she fails to understand that Kant’s transcendental noumenon (even if he later equivocated) amounts to something ascientific and thus beyond critiques based on physics of phenomena. (Also telling that Kant gets no meaningful mention.)

Although this book inevitably covers ground that is familiar from many similar “popular physics” books, these are topics that can do with plenty of reinforcement. I found Hossenfelder’s to be especially interesting, well written, thoughtful, and - despite the comments made above - easy to agree with. It’s a pity the chance to chat with the author won’t arise. Each chapter is a question and for each the final paragraph is a useful summary.

Those chapters being: Does the past still exist? How did the universe begin? Is math all there is? Why doesn’t anyone ever get younger? Are you just a bag of atoms? Do copies of us exist? Has physics ruled out free will? Was the universe made for us? Does the universe think? Are humans predictable? What’s the prupose of anything anyway? [interviews omitted]

Once we get to know the author the answers to each chapter question are pretty obvious, predicable! - typically of the form “yes, free will/multiverses/simulations/mind-body dualism etc. don’t exist, but don’t worry about it”.

A few simple truisms illustrate the kind of book this is, and are worth trying to remember:

Nietzsche: free will is an “uncaused cause” and “the best self-contradiction that has been conceived so far”.

If you could predict the growth of knowledge, your knowledge wouldn’t grow.

We improve scientific theories by simplification.

We get older because that’s the most likely thing to happen.