Wednesday, November 29, 2017

Pop science meets Edward Witten

Off-topic, science: China's DAMPE's dark matter signal

Natalie Wolchover is among the best popular writers about theoretical physics. But when I read her interview with Edward Witten at the Quanta Magazine,
A Physicist’s Physicist Ponders the Nature of Reality,
the clash of cultures seemed amusingly obvious to me. Witten is much smarter than myself and he also loves to formulate things in ways that look insanely diplomatic or cautious to me but I can still feel that his underlying sentiments are extremely close to mine.

They have discussed the conceptual and, I would say, emotional aspects of the (2,0) theory, M-theory, dualities, Wheeler's "it from bit", tennis, a hypothetical new overarching description of all of physics, and other things. It looks so obvious that Wolchover "wanted" to hear completely different answers than she did! ;-)




OK, let me start to comment on the interview. Wolchover explains he is a physicists' physicist, geniuses' genius, and a Fields Medal winner, among other things. She managed to interview him but he managed to make her invisible on the stone paths. Well, I felt some dissatisfaction already there. We were told about the children's drawings and piles of papers in Witten's office, not to mention a picture of a woman's buttocks in a vase. After some introduction to dualities and M-theory etc., we we told about her first question.




OK, Wolchover asks why Witten was interested in dualities which physicists sometimes talk about recently. Here it's not quite waterproof but even in the first question, I could hear her "why would you study something so boring and ugly like dualities?". Well, exchanges that appear later in the interview have reinforced this initial impression of mine. I surely think that Wolchover is totally turned off by dualities and, like almost all laymen, she doesn't appreciate them at all.

Witten answered that dualities give you new tools to study questions that looked hopelessly hard. Some examples are sketched, including a few words on the AdS/CFT. Wolchover asks about (AdS) holography but Witten redirects the discussion to a more general concept, the dualities of all the kinds, and says that it's often more than two descriptions that are dual to each other. Again, I think that you can see tension between the two people concerning "what should be discussed and/or celebrated". In this situation, Wolchover seems eager to repeat some of the usual clichés about holography in quantum gravity while Witten wants to emphasize some more general features of all dualities and what they mean.

The following question by Wolchover is the aforementioned confirmation of her negative attitude towards dualities:
Given this web of relationships and the issue of how hard it is to characterize all duality, do you feel that this reflects a lack of understanding of the structure, or is it that we’re seeing the structure, only it’s very complicated?
Do you see her proposed two answers? Both of them are "negative". Either dualities mean that we're dumb; or they mean that the structure is "complicated" by which she rather clearly means "disappointingly ugly". But both of these propositions are completely upside down. Dualities mean that physicists are smart, not dumb; and they imply that the underlying structure is more beautiful, robust, constrained, and exceptional than we have thought. I am pretty sure that Witten would basically agree with these words of mine but there's this tendency of his to avoid any disagreements so he prefers not to address the apparent underlying assumptions of such questions directly. He wants the people – e.g. Wolchover in this case – to find the wisdom themselves. But can they? Does it work? If you don't tell Ms Wolchover that dualities should be studied and celebrated rather than spitted upon, can she figure it out herself? I doubt so.

Witten's answer is interesting. He doesn't know whether there is some "simplified description" i.e. one that would make dualities and other things manifest. We don't have it so it's obvious that we must accept the possibility that no such description exists. Nati Seiberg seems to believe that such a description exists. It's a matter of faith at this point.

But Witten makes a general important point (which I have made many times on this blog, too): It's not only mathematics that is central in theoretical physics. It's mathematics that is hard for mathematicians. For mathematicians, it's even hard to rigorously define a quantum field theory and/or prove its existence. It's even harder with the concepts that string theory forces you to add. Why is it so? Well, I would say that the need for "mathematics that is hard for mathematicians" simply means that the Universe is even more mathematical than the contemporary mathematicians. Contemporary mathematician still discuss objects that are too close to the everyday life while the concepts needed to discuss the laws of physics at the fundamental level are even more abstract, more mathematical.

After Wolchover asks him about the relationship between mathematics and physics, Witten returns to the question about the simplified formulation of quantum field theories etc. and says that he tends to believe that nothing of the sort exists, he can't imagine it. What is Wolchover's question right afterwards? You may guess! :-)
You can’t imagine it at all?
Witten has just said that he couldn't imagine. Why would you ask "can't you imagine it at all"? Wasn't his previous sentence sufficiently clear? Or does she believe that the words "at all" provide the conversation with an exceptionally high added value? It's clear what's going on here. The statement that "the simplified universal definition of quantum field theory probably doesn't exist" is a heresy. It's politically incorrect and the question "you can't imagine it at all?" means nothing else than "recant it immediately!". ;-)

If "I can't imagine such a description" is so shocking to Ms Wolchover, can we ask her: And do you know what such a description should look like? ;-) Obviously, she can't. No one can. If someone could, Witten would have probably learned about it already.

Well, after her "recant it", Witten didn't recant it. He said "No, I can't". If he can't imagine it, he can't imagine it. Among reasonable scientists, there just can't be similar taboos about such questions. Of course the view that such a description doesn't exist is entirely possible. It may very well be true. Wolchover asked a question about the (2,0) theory in 5+1 dimensions – it seems to me that it was a pre-engineered, astroturf question because it doesn't seem natural that she would need to ask about the (2,0) theory. And Witten says that it's a theory that we can't define by Lagrangian-like quantization of a known classical system. But there's a huge body of evidence that the theory exists and its existence also makes lots of the properties of theories in lower-dimensional spacetimes manifest – e.g. the \(SL(2,\ZZ)\) S-duality group of the \({\mathcal N}=4\) supersymmetric gauge theory in \(D=4\).

Witten ends up saying that the question "is there a six-dimensional theory with a list of properties" is a more fundamental restatement of the statements about the dualities. Well, it's also a "deeper way of thinking" than just constructing some quantum theories by a quantization of a particular classical system. The previous sentence is mine but I think he would agree with it, too.

Wolchover's jihad against dualities apparently continued:
Dualities sometimes make it hard to maintain a sense of what’s real in the world, given that there are radically different ways you can describe a single system. How would you describe what’s real or fundamental?
Great. So Witten was asked "what's real". She clearly wants some of the dual descriptions of the same physics "not to be real", to be banned or killed and declared "unreal" or "blasphemous in physics" – so that the dualities are killed, too. Well, all of the dual descriptions are exactly equally real – that's why we talk about dualities at all. But she doesn't reveal her intent explicitly so the question is just "what's real".

Needless to say, "what's real" is an extremely vague question from a physicist's viewpoint. Almost any question about physics, science, or anything else could be framed as a version of a "what's real" question. "What's real" may be asked as an elaboration building on basically any previous reason. People may ask whether something is real just to confirm that they should trust some answer they were previously given. People may ask whether the eigenvalues of Hermitian operators are real and they are, in the technical sense of "real". They may ask whether quarks are real – they are even though they can't exist in isolation. They may use the word "real" for "useful scientific concepts", for "gauge-invariant observables". Lots of things may be said to be "real" or "unreal" for dozens of reasons that are ultimately very different.

The question doesn't mean anything, not even in the context of dualities – except for the fact that I mentioned, namely that concepts used to describe theories on both or all sides of a duality are equally real. OK, what can Witten answer to a question "what's real"? He's not your humble correspondent so he doesn't explode in a profound and vitally important tirade about Wolchover's meaningless vague questions. Instead, he said:
What aspect of what’s real are you interested in? What does it mean that we exist? Or how do we fit into our mathematical descriptions?
This is just Witten's way of saying "Please think about the rubbish question you have asked. Can you see that it has no beef and it can mean anything?" OK, so Witten said that her question could very well be interpreted as a question by the New Age religious people who are constantly high and who ask whether the Universe is real at all, and so on. But he gave her another option: Do you want to keep on discussing our mathematical description of the Universe?

I can only see the written interview, not the emotions. But I would probably bet that the adrenaline was elevated. Wolchover reacted to Witten's answer by a special tweet:


The tweet sounds like "Witten has given the most original answer (a counter-question) to the question what's real" in the history so far. (Well, I actually respond in almost the same way to "what's real" when I am expected to be polite.) But what I actually read in between the lines is "look, Witten has answered my very deep philosophical question disrespectfully, please help me to spread the idea that he's quite a jerk". ;-)

OK, so which kind of "what's real" do you want to discuss, Ms Wolchover? The latter, the mathematical descriptions, she answers.

Witten keeps on talking about the hypothetical "simpler unified description that clarifies everything". At this point of the interview, it's already staggeringly obvious that Wolchover tries to impose the faith in the existence of this description on Witten but shockingly enough, she finds out that Edward Witten doesn't automatically accept beliefs provided by popular writers to him. Witten's answer is a damn good argument – which I have been well aware of for decades – why this whole search for a single universal description of a TOE may be misguided:
Well, unfortunately, even if it’s correct I can’t guarantee it would help. Part of what makes it difficult to help is that the description we have now, even though it’s not complete, does explain an awful lot. And so it’s a little hard to say, even if you had a truly better description or a more complete description, whether it would help in practice.
The point is that we already have some descriptions that simply must be correct at some rather high level of accuracy. They may be close enough to some observations – they are really helpful to explain the observations. So if you add a new, at least equally correct description of all of physics, you must still explain why that new description basically reduces one to the known and successful ones in some situations or limits. In practice, we will always use the limiting, old descriptions when they work and they will almost certainly be the descriptions of choice for some situations even if we find a deeper description.

Dualities relate so many different environments and vacua that the underlying hypothetical "universal description" must be extremely flexible. It just can't say anything "particular" about the spectrum of particles and other things because those properties may be extremely diverse. So if such a deeper universal description exists, it has to be "at most" a paradigm that justifies the known descriptions – and perhaps allows us to compute tiny corrections in these theories even more accurately or completely precisely (at least in principle). But you simply shouldn't expect a new description that is both universal and directly useful (or even "simplified") to analyze the particular situations!

Another exchange is about M-theory. Witten says that it's totally settled that the theory exists today but we still don't know too much more than in the mid 1990s what the theory is. Some new progress in the bulk-based description of gravitational theories would be useful – I completely agree (too much focus has been on the boundary CFT description in this duality) – but Witten doesn't have too much useful stuff to say except that it's probably more abstract and vague about the spacetime than we are used to from existing descriptions. This "I have nothing useful to say" is a sentence he modestly says often. Well, most other people have 500 times less useful things to say but they present themselves as if they were megagods flying above Witten. The contrast between monster mind Witten's almost unlimited modesty and lots of speculative mediocre minds' unlimited hype and narcissism couldn't be more obvious.

Witten mentions that some days ago, he read Wheeler's "it from bit" texts. Now, he's more tolerant towards similar vague stuff, we hear, because he's older. When Witten was younger and wrote his 36th paper, the best thing in the world was immediately the planned 37th paper, of course, and so on, we learn. ;-) But now he's ready to read some less serious stuff such as Wheeler's "it from bit". This increased tolerance may be partly due to the lower relative difference between the numbers 363 and 364, relatively to 36 and 37. ;-)

Nevertheless, his reactions are still basically the same to mine. Wheeler's comments about physics – "information is physical" – are hopelessly vague and carry no information, Witten reacts in the same way as your humble correspondent. On top of that, Wheeler talked about "bits" but he must have meant "qubits" – the term wasn't usual in those times but Wheeler hopefully meant it, otherwise the text would have been really dumb.

And while the spacetime is probably emergent, that's not a good reason to abandon the continuum of the real numbers. Like your humble correspondent, Witten sees evidence that you should better not try to throw away the continuum from physics. Discrete physics with no connections to the continuum just can't do almost anything. To get rid of the reals is an unpromising starting point. Witten also mentions a self-observing Wheeler's picture of an eye and suggests that the observer's being a part of the world that is observed could hide some extra wisdom to be understood. Well, I am agnostic about some ill-defined progress of this kind, I am just pretty sure that the particular ideas that have been proposed to prove this meme are bogus.

One of the last questions by Wolchover was "Do you consider Wheeler a hero?". And Witten just answered "No". Witten just wanted to see what "it from bit" could have meant but I am afraid he just confirmed his expectations that the essay had no beef at all. Witten described Wheeler as a guy who wanted to make big jumps by thousands of years while Witten has been doing incremental advances. Well, 100,000+ citations worth of those, I would add. That's how Witten confirms Wolchover's point that he preferred progress through calculations than vague visions. He also mentioned he likes to play tennis although he doesn't expect to win Wimbledon for several more years.

To summarize, I think that Wolchover must have seen that she comes from a culture that constantly hypes and worships some vague and would-be ambitious statements by big mouths, that constantly needs to worship authors of such vague visions, that is annoyed by mathematics and everything that looks complicated or that has many aspects or many solutions, and so on, and she was forced to see that the methodology and the value system of a top-tier physicist – and, indeed, most top-tier physicists – is extremely different.

And that's the memo.

P.S.: At this moment, there are 8 comments under the interview. By the Pentcho Valev crackpot, by another crackpot who fights QCD, another one that thinks that he has a theory competing with string/M-theory, the fourth crackpot who believes that dualities contradict mathematical logic, and a few more. There's quite a company over there. I am fortunate to have some of you, the brilliant readers, because if I only saw comments like on those websites, I would surely conclude that any writing like that is a waste of time.

P.P.S.: There are 20 comments now. A Vietnamese thinker has an "educated guess" that Carlo Rovelli is more impressive than Witten. ;-) Zarzuelazen talks about Sean Carroll and "nonlocality", and random mixtures of entropy with other things. Someone else quotes Hossenfelder's seven theories of everything – six cranks who are Witten's peers because it was written somewhere in the cesspool of the Internet. Indeed, quite a company.

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