## Sunday, March 05, 2017

### NYT: Randall reviews Rovelli's oversalted book

Lisa Randall has argued in her review in The New York Times that
A Physicist’s Crash Course in Unpeeling the Universe
that reality isn't always what it seems to those who read Carlo Rovelli's book, Reality Is Not What It Seems, a popular text that was successful in Europe, translated to English, and that I discussed in January.

Randall says that the best popular books bring something both to the beginners as well as the readers who already know something. However, Rovelli only chose the audiences without any physics background and adjusted his writing appropriately. He nicely communicated the grandiose revolutionary changes that took place in the recent century or so. Because of the adjustments and other things, the result isn't great.

The main trouble with the book, as Randall sees it, may be divided to several overlapping bullets:
1. Mistakes in established physics
2. Presenting some claims that are considered highly controversial even within the controversial loop quantum gravity community as facts – more generally, the failure to separate science and speculation
3. Romanticization of physics – too much poetry in which the precision is being lost, and it's therefore analogous to an oversalted food
4. Inability to see that centuries or millenniums ago, thinkers had different ideas (and even questions) than top 20th century physicists
5. Rovelli's implicit and sometimes explicit claims that the same ingredients guarantee the same thing – his refusal to see that the way how the ingredients are arranged is actually the essence of physics
I think it makes sense for Randall to have found at least one example of Rovelli's lousy fact-checking and she did succeed.

At some point, Rovelli discussed the big difference between the huge size of the Universe and the tiny fundamental length scale:
It is around 10120 times greater than the Planck length, a number of times that is given by a one followed by 120 zeros. Between the Planck scale and the cosmological one, then, there is the mind-blowing separation of 120 orders of magnitude. Huge.
First, the web-based New York Times write 10120 and 1060 instead of 10120 and 1060. Many other newspapers have the same problem. It may be just a poor text conversion but the mistakes could have arisen because the journalists don't really understand the concept of a power – or at least they believe that the exponent can't be greater than roughly two or three.

But let's focus on the Rovelli-vs-Randall issues here. Rovelli repeats that the size difference is huge and mind-blowing etc. and to make sure that you hear, he repeats that there are 120 orders of magnitude between the two scales at least thrice. The only problem is that there are only 60 orders of magnitude in between,$R_{\rm universe} \sim 10^{60} \ell_{\rm Planck}.$ You may get 10120 if you square this ratio – so the Planck and cosmic-horizon areas have this ratio. Because of the proportionality of area and entropy in quantum gravity, it also follows that the de Sitter entropy of the visible Universe is about 10120. But Rovelli unambiguously talked about lengths and his ratio is wrong by 60 orders of magnitude. A huge mistake. There's a sense in which the mistake is small because none of the readers will ever do any calculation that would depend on any such number – so they just don't care.

Concerning the non-separation of speculations and facts, Randall mentions Rovelli's statement that the Big Bounce – a pre-Big-Bang shrinking of the Universe followed by the Big Bang – follows from loop quantum gravity. This is presented as a fact. But the justification of this statement is only found in several vague speculative loop quantum gravity papers and the percentage of the people in loop quantum gravity who believe that the Big Bounce existed is similarly low. So it's bad that Rovelli sells these speculations if not pseudoscience as science that is almost on par with general relativity.

You know, I have read probably all Lisa's popular books before they were published and I would keep on annoying her if she wrote e.g. that "dinosaurs were killed by a dark matter disk" as it were a statement on par with some confirmed predictions of GR etc. (And similarly with warper extra dimensions and other things.) The weakening of some statements may make it harder to sell millions of copies of a book but it's still critical if the author wants to preserve his or her image as an honest scientist.

Randall comments that loop quantum gravity doesn't even pass the test of explaining some ordinary gravitational phenomena. Even if it predicted something like the Big Bounce, it would be very likely a prediction for a "completely different Universe", one that is inhospitable to life if not inconsistent. Just to be sure, Rovelli completely ignores string theory and all related research of quantum gravity that is some 1060 times more justified and solid than loop quantum gravity (and he would write the ratio as 10120 if he weren't applying double standards).

Lisa thinks that Rovelli's book is intellectually oversalted much like food in P.F. Chang's (I guess that this metaphor should also be understood as Lisa's not so great relationship to the Asians LOL) – or like food of cooks who are smokers who tend to add too much salt for that reason (I guess that smoking reduces your sensitivity to tastes). Note that she has previously mentioned that the text is also peppered with Einstein, Newton, Plato, Aristotle, Democritus, Galileo, Dante, and Lucretius. So it makes sense to say that the food is both oversalted and overpeppered.

The big role that these ancient thinkers and writers play in the book was clearly about as provoking for Lisa as it was for me. Ancient Greek or renaissance thinkers could have had big goals and they could talk about some of the same objects as modern physicists and some of the same most general ideas that survived, but all the details how these ingredients were organized were completely different than e.g. in Einstein's papers. The final theory, like soufflé or general relativity, isn't the same as a generic mixture of the ingredients, like egg and flour.

The way how you treat and organize and connect all the dots is actually even much more important in physics than it is in the kitchen. Rovelli's presentation of the ancient writers' thoughts as "being the same" as the ideas discovered by Einstein is just pure demagogy. There is nothing equivalent between the two. It's really silly to combine them into one book because the progress has been long and deep. Most of the ideas solved by modern physicists at some moment would only be comprehensible to their colleagues who live a few years or at most a few decades before them. It means and doesn't mean that physics isn't solving "eternal problems". They're eternal except that centuries or millenniums ago, no human was able to even formulate most of these problems.

In effect, Rovelli is selling newly created kitsch (more precisely, a thousand-dollar couture adorned with beads and feather) as if it were an actual object with true cultural and historical relevance, Lisa crisply writes.

You know, there are two completely different reasons why some people's ideas are considered "worth studying" today. Texts by ancient philosophers are important and valuable because they came from the times when the top-level thinking was only done by a small number of people, the number of intelligent texts is small and they're therefore precious, and in some way, these people's thoughts may be considered ancestors of many later ideas in a tree of intellectual and cultural evolution. We often like to worship our history, roots of our culture, and ancestors and that's really why most of these things continue to be valuable. It's the importance rooted in humanities.

But theories in modern physics – including Einstein's theories etc. – are important for a different, scientific reasons. We still really take many of these ideas very seriously. They're operating within the engines we still use for driving. So they're important because they're still competitive. They work. The positive evaluation has nothing to do with humanities: it is all about the natural science, the logic, the cohesion of the arguments with themselves and with the empirical data. It's just wrong to confuse the "importance because of humanities and history" and "importance due to the scientific meritocracy" and Rovelli is confusing them all the time. One could say that the whole concept of his book – and his life-long approach to popularization of science – is mainly built on this confusion.

The last point – the whole is more than the sum of the parts – was already discussed. But Lisa adds that the beauty of physics really hides in its precise statements. One can only be truly excited as a physicist – even excited about some simple or old finding of physics – if she formulates and verifies some statements or patterns with a really high precision. If something "works" even at the verbal level without the appropriate, nearly professionally mathematical, precision, then it is just not physics.

So the goal to bring the beauty of physics to millions of the laymen is noble, Randall praises Rovelli, but the goal would be better served if Rovelli were more careful. I have serious doubts whether any of the truly lay readers of such popular if not populist books – who avoid proper textbooks etc. – learns anything about the actual physics. The details and precision are very important in physics so if one is excited about something that boils down to ambitious words or links with the ancient thinkers, it's almost certainly not the same reason that makes physicists thrilled when they discover (or at least understand) some idea explaining the working of Nature.

Physics ultimately depends on the balance and neverending fight between the hot and ambitious, philosophically and sometimes religiously sounding, speculations and the cold hard data that cruelly filter all the ideas. Populist books on physics – and books linking physics to ancient philosophers, religions, and other parts of humanities and other human emotions – only sell the former. There's just no tough contest in between the ideas, no precise tests that verify the predictions of a theory etc. So people following this "big mouth" school aren't really doing physics and they're not excited by the same things as physicists because physicists are only excited when some details are actually found to work. Books they read may sometimes use some physical terminology but they're books in the humanities and that's the case of Rovelli's book, too.

Rovelli posted a response to Randall's review. I will only mention that it's a full-blown crackpot's rant based on obfuscation, ad hominem attacks, and conspiracy theories, and I won't honor it with a longer reply.