Existential Physics: A Scientist’s Guide to Life’s Biggest Questions
by Sabine Hossenfelder (2022, Atlantic Books, 248 pages pbk.)
Bursting with opinions
Dr Hossenfelder is a German theoretical physicist and highly accomplished science communicator. She writes popular science books and creates a strong presence on her YouTube channel, with her trademark combative opinions. In this book she takes on the many ideas that are on the fringes of science – not pseudo-science as such, but the different brands of “speculative physics”. I think “speculative” might have made a clearer book title than “existential”, which I don’t really understand in this context.
The author’s work as a physicist has involved leading an academic team who are researching the field of quantum gravity. So she is familiar with the cutting edge of science and is therefore equipped with the experience and mathematical heft that gives her words authority.
She makes clear that she is not religious in any conventional sense, but the book shows that she has no objection to religion. Her main point is to with line-drawing: it is important to clarify the distinction between what is scientific (i.e. a theory that is consistent with observations and is falsifiable) versus what is a-scientific (unobservable, unfalsifiable and often contrary to what is observed). So the focus of her criticisms of other systems of thought, the speculative “scientific” theories which she examines, is that they are the result of sloppy thinking by scientists.
To believe or not to believe
There are several instances when Hossenfelder writes that as long as XYZ doesn’t conflict with what is observable, then a “belief” in XYZ is fine, even if XYZ is an unnecessary or over-elaborate framework for explaining the world. This tolerant attitude surprised me, from what I knew of her strong scientific opinions – I was expecting her to give shorter shrift to beliefs that were unverifiable (or unfalsifiable).
So what are these areas of physics that address the “big questions”? For example, “Does the past still exist?” Perhaps the recently bereaved may wonder “Is there anything of my Grandma’s life still out there?” Through a neat presentation of Einstein’s space-time and the collapse of the notion of simultaneity in the theory of Special Relativity, one can make a case that there are parts of my past and your future that, to another observer, can appear to be simultaneous. There may be no special time that is “Now” – instead it is a matter of perception. So the surprising conclusion is that “past” and “present” are in some way indistinguishable, although we know that they may be practically irretrievable.
This may appear fanciful, but is a serious area of study in the philosophy of space-time, called “eternalism” or sometimes the “block universe”.
Multi-what?!
Chapter 5, “Do copies of us exist?” addresses several species of speculative physics that have been popular and attractive to the popular press, and good click-bait for online content-makers: the Many Worlds Hypothesis, the Multiverse, and the notion that we are all part of a giant simulation.
I am firmly in the camp for whom any mention of these hypotheses leads to sighing and eye-rolling, since 99% of the material available on these ideas is wishy-washy make-believe, cooked up with people who have zero competence in the mathematical structures which spawn these speculative ideas. And yet many eminent and active physicists take these ideas seriously. All of these systems spring from analogies to observable quantum weirdness. For example, the QM concepts of tunnelling or wave-particle duality in which objects appear to be in multiple locations, until they are detected.
Flame Wars
When I read this book, I cannot help but hear it in Sabine’s clipped German accent, and with her confrontational tone, as she presents her excellent videos on her YouTube channel (see below). This is not necessarily a bad thing, but I find that approach tiresome. It reminds me of the “flame wars” that were typical of old-fashioned academic rivalries in the early days of the Internet. So I find myself firmly onside with Dr. Hossenfelder’s assessment of many imaginative ideas swirling around modern physics, I do not like the hectoring style, which does not seem to respect the well-qualified academics who hold opposing views.
Of course there is always the chance that new observations or imaginative experiments will crack open a new vista of understanding, and perhaps show that one of the “fringe” theories of speculative physics prove can suddenly explain the world better. But that’s science! Our best theories now are just the least worst ways to describe what we know, and no doubt the boundaries of ignorance will be rolled back a bit further before long.
Elsewhere
- Sabine Hossenfelder’s eponymous YouTube channel. Described as “As simple as possible, but not any simpler! Science and technology updates and summaries. No hype, no spin, no tip-toeing around inconvenient truths.” [my emphasis] That last phrase signals that here can be found not only clear, accessible explanations, but a LOT of personality. Hossenfelder can be opinionated, direct and dismissive of those she considers to be peddling nonsense.
- Max Tegmark, Our Mathematical Universe: My Quest for the Ultimate Nature of Reality (published by PC, 2020) – I cannot take the conclusions of Tegmark’s book seriously. There is a categorical error in his leap from showing how well mathematics describes the Universe, to his theory that the Universe IS mathematics, and that we are all part of a theoretical construct or simulation. I’m more comfortable with “turtles all the way down” than this!
- At the Cutting Edge – OffTheShelf – JohnJoe McFadden, Life is Simple: Occam’s Razor, the essential tool for weighing up scientific theories.
- Carlo Rovelli, Anaximander and the Nature of Science – this is a small but thought-provoking book which argues that insights in the 6th century BCE amounted to the most profound revolution in the history of science. [review forthcoming]
At the far end of the scientific bookshelf, the Times obituary for Erich von Däniken is a good read if you have access to it. He wrote the follow-up to Chariots of the Gods while serving a sentence for fraud in a Swiss prison. As Carl Sagan wrote, ‘Every time he sees something he can’t understand, he attributes it to extraterrestrial intelligence, and since he understands almost nothing, he sees evidence of extraterrestrial intelligence all over the planet.’ I wish I could write like that.