Carlo Rovelli – A Fresh Spin on Fundamental Physics

Interesting to see today’s news on standardisation of units of measure, that time, distance and mass are now to be unified through the Caesium clock with application of the speed of light (c) and Planck’s constant (h). (Hat tip to Jim Al-Khalili on Twitter). Fascinating article in itself, however yet more evidence that the accepted standard models of physics are ever more solid and dependable. The scales of everyday life really are gounded in quanta.

I say interesting, because the cosmic gravitational scales of relativistic space-time nevertheless remain disconnected from such models. Quantum gravity has been the holy grail of physics for several decades, ever since the two extremes seemed sound in themselves despite failing to communicate with each other.

Interesting today particularly, because last night I finished Carlo Rovelli’s latest “Reality is Not What it Seems – The Journey to Quantum Gravity” and was already composing this post.

I’m sympathetic to Rovelli’s outlook, have been for several years, because I appear to share his metaphysics. As I said only in my previous post – on the topic of gender, race and religious identity politics, not physics:

“Significant differerence”
is THE fundamental “particle” of the universe,
the source of all information and all things.

Rovelli’s hero, from beginning to end, is Democritus. The original source of the idea that the universe is made of bits of very small but finite size, points of closest-possible but finite separation. Indivisible a-toms.

One thing I did learn from Rovelli’s latest is that the “loops” of quantum loop gravity (QLG) are closed curves in space-time around which solutions to the fundamental maths of physics have well-behaved (non-infinite) solutions. The other thing is that in the limit – the smallest curves around individual or small finite numbers of quanta – the values of these solutions resolve to multiples of the half-integers of “spin”.

As an aero-engineer myself, I couldn’t help but see the parallel with (Navier-Stokes equations) integrals in aerodynamic flows around the infinities of (virtual) sources and sinks used to model circulations (vortices) imposed on otherwise steady flow fields. In fact the QLG posits that all fields are quantised – in all the material particles and force fields in the standard model in space-time there are no zero properties or dimensions involved.

To cut to the chase, the fundaments of Rovelli’s QLG physics are information; small, finite, significant, differences of possibility. Claude Shannon is in there with the more expected heroes of physics and natural philosophy. Information is the key. The Ontology of reality really is limited by the epistemology of what can be known. What can be known is in the limit of quantised physics.

“A vision of reality
entirely independent of the observer
is impossible.”

Rovelli dismisses many hopeless fallacies around fundamental physics, string theory in its entirety being one of them, but also popular conceptions around the collapse of the Schroedinger wave function, often used to gloss over the observer-world interactions.

Time and causation are root problems in understanding how fundamental physics works. Time, says Rovelli, doesn’t exist. He means it doesn’t exist as some fundamental thing underlying the behaviour of the rest of physics. An independent fundamental variable – a part of “space-time”. Like the rest of physics, it’s an emergent, quantised and relative property. Time is within the QLG model, like everything else.

As we already knew, time is the direction of increasing entropy, in general, on average. Life is the efficient local means of reversing entropy and increasing or maintaining form and order. The more intelligently evolved life, the more efficient the entropic processes.

Positing a physics based on forces relative to points of finite separation also sounds a lot like Boscovich, an early influencer of Mach and hence Einstein.

I’ve said before, one of the things I like about Rovelli as a scientist is that he has time for philosophical thinking, and cites many early philosophers. He’s pretty scathing however, about the qualitative aspects of Plato – what is for the best:

How completely off track the great Plato was here!

But on the whole he takes a sympathetic reading of the intended thinking of many ancient philosophers from Anaximander to Spinoza. He doesn’t cite any modern or present day philosophers. Rovelli’s pedigree comes in part via Lee Smolin with whom a lot of this metaphysics is shared. Smolin of course published an important major work recently in collaboration with political philosopher Roberto Unger. I’d be really interested to see some current philosophers take on Rovelli’s work. I’m thinking of you Dan Dennett, Rebecca Goldstein, Julian Baggini and Massimo Pigliucci?

(Aside – Would also love to tie up Rovelli’s take on QLG with Deutsch & Marletto’s thinking on constructor theory, and with Mersini-Houghton, but I digress.)

After his exposé on QLG, itself preceded by a potted history of physics to date, Rovelli ends with several short qualifying chapters on where we stand and what needs to be done. He is particularly careful about what makes for science and evidence. He is at pains to reiterate that the unknown is much greater than the known, but creativity needs to be based on clues in or problems with what is believed to be known, rather than flights of complete fantasy into the unknown. Empirical disconfirmation remains the key distinguishing feature of science – taking its exams – whatever the process of arriving at hypotheses.

In some sense I think he doth protest too much in his final warning against arguments from authority and ancient wisdom, since his whole book proceeds step-wise from what was previously hypothesised to be known. All steps are relative, nothing is cast in stone, but every step needs a foundation, even one that redefines or undermines previous foundations. That the great thinkers and scientists are proven wrong, doesn’t stop them being great. It’s what makes them great. Not being provably wrong is science’s biggest problem. It’s belief without explanatory understanding that risks reification into dogma.

An absolutely excellent book. So many more notes on topics I’ve not mentioned here: cosmic expansion and multiple sequential big-bounce universes, black holes and Hawking radiation and the hype over Higgs and Super-symmetry as examples. Rovelli’s own selection of important people in the history of natural philosophy is itself interesting. Great read and I suspect will turn out to be an important book in the history of fundamental physics.


[Post Note: “It from Bit” – More on the informational basis of reality – New Scientist from earlier (May) this year, and Erik Verlinde’s “Entropic Gravity” from 2010. Hat tip to Jaap van Till. (Latest May 2018 thoughts on Verlinde et al.) Interesting that Verlinde is a string theorist, so the time <> entropy <> gravity relationship is a deep issue for all sides here. Rovelli says “Time isn’t real”. Verlinde says “Gravity isn’t real”. They seem to be saying the same thing. Nothing is fundamentally real other than quantised information, all else is emergent in higher level patterns. If it works with quanta, not sure why we need strings, but hey.

Information (significant differences)
and patterns (negative entropy)
have been Psybertron’s focus since 2001.


[Post Note: See also this review of James Gleick’s History of Time Travel, by John Lanchester in the New York Review of Books. Hat tip to Massimo Pigliucci on Twitter. A long read on the inescapability of time; everything from Joe Campbell’s monomyth to fundamental physics via H G Wells. Metamyth.]