I was originally going to write this as an addendum to my not-so-recent post, The problem with physics, but it became obvious that it deserved a post of its own.
It so happens that Sabine Hossenfelder has posted a video relevant to this topic since I published that post. She cites a paper by some renowned physicists, including Lawrence Krauss, that claims a theory of everything (TOE) is impossible. Not surprisingly, Godel’s Incompleteness Theorem for mathematics forms part of their argument. In fact, the title of their paper is Quantum gravity cannot be both consistent and complete, which is a direct reference to Godel. This leads to a discussion by Sabine about what constitutes ‘truth’ in physics and the relationship between mathematical models, reality and experiments. Curiously, Australian-American, world-renowned mathematician, Terence Tao, has a similar discussion in a podcast with Lex Fridman (excellent series, btw).
Tao makes the point that there are 3 aspects to this, which are reality, our perception of it, and the mathematical models, and they have been converging over centuries without ever quite meeting up in a final TOE. Tao comes across as very humble, virtually egoless, yet he thinks string theory is 'out of fashion', which he has worked on, it should be pointed out. Tao self-describes himself as a ‘fox’, not a ‘hedgehog’, meaning he has diverse interests in maths, and looks for connections between various fields. A hedgehog is someone who becomes deeply knowledgeable in one field, and he has worked with such people. Tao is known for his collaborations.
But his 3 different but converging perspectives is consistent with my Kantian view that we may never know the thing-in-itself, only our perception of it, while such perceptions are enhanced by our mathematical interpretations. We use our mathematical models as additional, complementary tools to the physical tools, such as the LHC and the James Webb telescope.
Tao gives the example of the Earth appearing flat to all intents and purposes, but even the ancient Greeks were able to work out a distance to the moon orbiting us, based on observations (I don’t know the details). Over time, our mathematical theories tempered by observation, have given us a more accurate picture of the entire observable universe, which is extraordinary.
I’ve made the point that all our mathematical models have limitations, which makes me sceptical that a 'final' TOE will be possible, even before I’d heard of the paper that Sabine cited. But, while mathematics provides epistemological limits on what we can know, I also believe it provides ontological limits on what’s possible. The Universe obeys mathematical rules at every level we’ve observed it. The one possible exception being consciousness – I am sceptical we will ever find a mathematical model for consciousness, but that’s another topic.
Tao doesn’t mention the anthropic principle – at least in the videos I’ve watched – but he does at one point talk about the infinite monkey theorem, which is a real mathematical theorem and not just a thought experiment or a pop-culture meme. Basically, it says that if you have an infinite number of monkeys bashing away on typewriters they will eventually type out the complete works of Shakespeare, despite our intuitive belief that this should be impossible.
As Tao points out, the salient feature of this thought experiment is infinity. In his own words, ‘Infinity absolves a lot of sins’. In the real world, everything we’re aware of is finite, including the observable universe. We’ve no idea what’s beyond the horizon, and, if it’s infinite, then it may remain forever unknowable, as pointed out by Marcus du Sautoy in his excellent book, What We Cannot Know. Tao makes the point that there is a ‘finite’ limit where this extraordinary but not impossible task becomes a distinct possibility. And I would argue that this applies to the evolution of complex life, which eventually gave rise to us. An event that seems improbable, but becomes possible if the Universe is big and old enough, while remaining finite, not infinite. To me, this is another example of how mathematics determines the limits of what’s possible.
Tao has his own views on a TOE or a theory for quantum gravity, which is really what they’re talking about. I think it will require a Kuhnian revolution as I concluded in my second-to-last post, and like all resolutions, it will uncover further mysteries.
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