"On the Origin of Time" by Thomas Hertog

Subtitled "Stephen Hawking's final theory", this is a 2023 book by his collaborator Thomas Hertog, a Belgian cosmologist, on the theory of everything they developed together before Hawking's death in 2018.

I'm not intending to give a proper review, I'll just say that from a reviewer's perspective it's a curate's egg, the parts dealing with known cosmological theories are good, the parts dealing with the final theory in question are rather hand-wavy, the parts about the process of coming up with scientific theories are interesting, the insights into Stephen Hawking's life are sparse but interesting, and some of the comments on "what it all means" are rather over-excited and new agey (all in my humble opinion, of course). But what I'm interested in is the eponymous theory, and in (perhaps) getting a better grasp on it, should anyone knowledgeable happen upon my comments and care to respond. (I do have a degree in astrophysics, by the way - admittedly from the 1970s, so well out of date, although I endeavour to keep abreast of developments - so I'm not completely ignorant on the subject matter.)

So what's it all about? Hawking has produced four pieces of theoretical insight that seem relevant - his 60s work on demonstrating that, given very general constraints, the big bang must have emerged from a singularity, his 70s work on thermal radiation from black holes, his no-boundary proposal for the big bang (the subject of "A Brief History of Time") and the present theory, which Hertog refers to as top-down cosmology, which attempts to put together these key insights together with some new ones, including inspiration from Andrei Linde, John A. Wheeler and Juan Maldacena, to produce what could be called a theory without laws of physics. Well, sort of, although this is where the hand-waving starts (IMHO).

The book starts with something of a rant against multiverse theories, which I found quite off-putting because it reads less like a scientific analysis than an ideological or political one, as though the author(s) have it in for the string landscape and want to throw every possible doubt at it. Most string theorists would, I think, agree that the ${10}^{500}$ sets of physical laws that can emerge from their (meta-) theory are somewhat daunting and hard to "do science on", but to say that therefore we should abandon this approach is reminiscent of Auguste Comte's 1835 claim that we will never know the chemical composition of the stars, ironically made some 20 years after the first observation of Fraunhofer lines! After all, the universe is under no obligation to make life easy for physicists, and if that's how it happens to work...

Anyway, the theory says that the start of everything is still rounded off into imaginary time, as in A.B.H.O.T., but adds that it involves a lot of symmetry breaking, something that is fairly standard in TOEs. So we get to the current laws of physics via a series of "frozen accidents". And the top-down theory says that a sort of dialogue between our existence and this early symmetry breaking forms a (sort of?) feedback loop. As far as I can tell, the idea is that the questions we ask, using that phrase in a very general sense, feed back in time to cause the symmetry breaking to come out in a manner favourable to us existing.

The alternative, what one might perhaps consider the more "establishment view", is that according to quantum mechanics the symmetry breaking comes out in all possible ways, which either get collapsed into one result at random, as per the "Copenhagen interpretation", or go their separate ways in a multiverse, as per the "many-worlds interpretation". (Technically the Copenhagen interpretation requires a measurement to collapse the wave function, but as Hertog points out, being inside a fog of particles effectively acts as measurements, so the symmetry splitting would decohere very quickly inside a hot big bang.) My problem with this is that it doesn't need the top-down view to explain the outcome. Hertog's section on delayed choice experiments, which indicate that observations can retroactively change the original quantum "decision" to split the symmetry, doesn't apply once the symmetries have been frozen in by the quark soup that followed them. So on the traditional view they were either selected by random quantum events in the big bang fireball, or they went on to form a ... string landscape. Despite all the huffing and puffing about the multiverse being a bad thing, conventional quantum theory plus symmetry splitting can give us one, and the anthropic principle then kicks in to select a "bio-friendly" (but not very friendly, 99.999999% of the universe being hostile to life - which is what we'd expect according to Max Tegmark) patch of spacetime for us to appear in.

Am I missing something?