The field of hep-th has always been quite faddish, with many of the fads easily recognizable just from looking at the buzzwords appearing in paper titles. In recent years “entanglement” is a buzzword that has been all the rage, and John Preskill has some data here (slide 3) on how many hep-th papers have it in their title. Extrapolating from 62 in 2011, 119 in 2013 and a projected 220 this year, long before we see a new accelerator, all hep-th papers will have “entanglement” in their titles. Another very visible trend is that an increasingly large fraction of these and other papers in hep-th (which used to mean high-energy particle physics) are now about low-energy non-particle physics topics.

I make periodic attempts to listen to talks or read papers explaining the hot topics at issue, but have to confess that I tend to lose interest, not seeing anything relevant to the standard model or unification, or to the kind of deep mathematics that in the past has provided insights into those topics. Suggestions of what to read to follow these latest fads are welcome, when I have more free time I’ll look into them. In the meantime, I’m just reporting a trend, will leave it to others to decide what it all means.

This brave new world of hep-th is generating a lot of activity. The week before last saw a big “The Information Universe” conference in the Netherlands, that addressed questions such as

– Is the universe one big information processing machine?

– Is there a deeper layer in quantum mechanics?

– Is the universe a hologram?

– Is there a deeper physical description of the world based on information?

Last week was the kick-off meeting of the It from Qubit collaboration, which is supposed to bring together quantum information theory and fundamental physics. This is an extremely large effort, very well-funded by the Simons Foundation. They just announced that they’re planning on hiring a dozen or so postdocs this year. If you get one of those jobs, there’s a warning that you’ll have a “significant burden” of having to travel to collaboration meetings in places like Bariloche, but at least on long flights you’ll be flying business class.

For a detailed explanation of the plans of It from Qubit, see here.

After the Simons-funded meeting a few days ago at Stanford, this weekend there’s yet another quantum information/entanglement/HEP meeting at Stanford, this one funded by the Templeton Foundation. The program for the Templeton Program meeting is here.

**Update**: It seems that this page has been edited this weekend to remove reference to the It from Qubit collaboration travel policy, however you can still find it here.

**Update**: For popular expositions of these ideas, there’s a new article in Science News, and a book coming out by George Musser, reviewed today by Sabine Hossenfelder. I haven’t seen the book, but the Science News article doesn’t help me understand much: all I get out of it and the papers its links to are some very vague conjectures about understanding quantum gravity via AdS/CFT. Standard facts about quantum mechanics on the CFT side become more exciting sounding conjectures about gravity on the AdS side, but it remains unclear to me exactly how any of this is supposed to really work. For one thing, we don’t live in AdS space.

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I saw Leonard Susskind give a lecture as long ago as 2013. I vaguely remember, he said something like ‘… by the way, we’re undergoing some kind revolution in entanglement… every day [week?] there’s a new paper out…’

Modelling the fadishness of HEP-TH titles might actually be an interesting little project. Am wondering if each fad (information, firewalls, multiverse, etc) follows the same initial geometric increase followed by a plateau and decay.

The fadishness of technology has been well-captured in the Gartner Hype Cycle.

http://www.gartner.com/technology/research/methodologies/hype-cycle.jsp

It is likely that the curve they draw is of validity for scientific topics as well.

I like it when they have these conferences at kitp, because then all of the videos are available and promptly posted. Thanks for pointing this meeting out.

Well, Peter seems to be being finicky with posts about this, but here’s a try. I read the it from qubit writeup pretty carefully, and found it quite scary. Does that really pass for science now? It reads like a press release trying to sell a new piece of software. Conjectures are theorems. Completely open problems are discussed as if there is some sort of established theory about them. Rigor is completely absent. There is no expectation that anyone will have to prove anything, ever, mathematically or via experiment. HEP has jumped the shark.

Jeff M,

Physicists have never been much interested in rigor or proof, so you can’t really criticize this project on those grounds. Some parts of what they are doing though seem to be completely divorced from any contact with experiment, so a real question arises as to how you evaluate work like this if the usual standards of neither mathematics nor physics apply. That their proposal leads off with some pretty extreme hype (“A rapid change is taking place in our thinking about fundamental physics that amounts to a nascent paradigm shift.”) and also makes an argument based on the exponential increase in use of a buzzword, isn’t really confidence inspiring.

Personally I’m dubious that quantum information theory is going to revolutionize our understanding of fundamental physics (eg. the SM and gravity), or our understanding of QFT (it seems more likely that our understanding of QFT may revolutionize quantum information theory). I see not a hint here of anything addressing the problems of the SM or unification, and the problem with claims to have a quantum theory of gravity has always been that, in isolation from the rest of physics, quantum gravity theories seem to be untestable. But, that’s just me, in a few years we’ll see what emerges from this activity, and maybe it will be clear if there’s anything to the revolutionary claims. The danger is that the claims will just get a lot more exposure, with the problem of evaluating whether this is a useful paradigm shift never solved.

While I don’t think it’s going to be a revolution in physics, quite possibly some interesting things will come out of this research. Hopefully part of what the grant will fund will be some readable expository literature, such that one can learn what people have found without having to wade through mountains of hype.

Musser has a Cliff’s Notes summary of his book in the latest SA. I read it twice and still got nothing out of it. I am a bit reluctant to invest my time reading his book until someone whose opinion I respect, like Peter, tells me it is worth my time.

On it from bit, I don’t understand why this is a promising path other than the fact that Shannon’s theorem is a transformation of the Second Law.

Off Topic.

Nautilus magazine has a good article on Sloane’s encyclopedia of number sequences.

http://nautil.us/issue/29/scaling/how-to-build-a-search-engine-for-mathematics

Peter

I completely appreciate that physicists don’t do proof (it’s a running joke among us mathematicians) but I had hopes for rigor. Perhaps I’m misremembering, but when I worked through the field equations of GR or Dirac’s equation for the relativistic electron I seem to remember a lot of rigor. Ah well, perhaps it’s good you’re in the math department đź™‚ As for Jim Akerlund and Sloane’s Encyclopedia of Integer Sequences, it’s an amazing resource. I was working on something and we got this sequence, we plotted it and stared at it, and knew it had to be something, but no one we talked to had ever seen it. Plugged it in to EIS, found out it was Stern’s sequence, discovered in the 1840’s, used to help make watches, more or less lost by the 20th century (though used to construct the rationals). Lots of fun to reference a paper written in the middle of the 1800’s…

Neil wrote:

>On it from bit, I donâ€™t understand why this is a promising path other than the fact that Shannonâ€™s theorem is a transformation of the Second Law.

I think even that is an over-statement: I’ve done some work involving information theory (I hold some patents on implementations of error-detection-and-correction systems). The way I’d put it is that anything that involves multiplicative counting (you know m choices followed by n choices, etc.) lends itself to taking logarithms, and then it inevitably looks a little bit like entropy. Of course, Shannon chose to use the word “entropy,” hence he encouraged this sort of over-statement. But, I don’t think Shannon’s theorem really is a transformation of the Second Law.

By the way, I am not attacking you personally: I know that your statement is a widely accepted view. I’m just pointing out that, in my experience working in both physics and information theory, that widely accepted view is misleading.

However, like Peter, I am open to being shown to be wrong: I’ve always been curious about “It from Bit” (I went to a lecture by Wheeler pushing the idea way back in the mid-’70s), even though I’m skeptical.

Dave.

Dave,

Yes, I misspoke. I meant Shannon’s equation is a variant of Boltzmann’s entropy equation. But, as you point out, that could just reflect that they both deal with combinatorics.

Dave and Neil,

Wikipedia has a pretty good discussion of this very topic. By now it has a long history.

If you wish to learn more about Â¨It from BitÂ¨ from WheelerÂ´s perspective, I suggest reading his autobiography – Geons, Black Holes, and Quantum Foam. His work is also mentioned in Amanda GefterÂ´s book – Trespassing on EinsteinÂ´s Lawn. An archive of his papers can be found at jawarchive.wordpress.com.

Please, enough about “It from Bit”, which, as far as I can tell, has little or nothing to do with “It from Qubit”. I would be interested in hearing more about this second topic from someone who understands recent developments. Personally I’ve never seen anything interesting coming out of the first topic, but replacing bits by qubits does seem more promising.

Peter,

Most of the “It from Bit” presentations going way back that I remember seeing did in fact invoke quantum mechanics — certainly Wheeler did so, and I remember even old sci-fi novels that did so.

And, the idea of tying in wormholes to quantum entanglement also has a long history, at least going back to Dave Deutsch’s famous Phys. Rev. article, which tied his theory of quantum computation into wormholes, time travel paradoxes, and parallel universes: certainly the most interesting case for many-universe theory I’ve ever seen, even if it was a bit, let us say, speculative (I always wondered how he managed to get the Phys. Rev. editors to approve it for publication!).

Dave

I feel like the entanglement and more generally “information” angles are sort of under-delivering. It’s not clear to me what, if anything, has been gained by focusing on the “information” of a quantum system or a putative analogies with computation (Lloyd: “the universe is a quantum computer, computing itself”…gee thanks for that!) With entanglement the goal is to see spacetime “emerge” from specific forms of entanglement, but we already see this kind of entanglement in the states of a standard QFT, and it doesn’t seem to be particularly helpful (so far) to think of this is as creating the spactime.

Well I think it’s unwise to ignore the fads or hot topics of hep-th since plenty of smart people obviously think they are promising, but I do think these two may be not as promising as hoped.

An interview with Abhay Ashtekar of general interest.

http://thewire.in/2015/10/29/good-scientists-solve-problems-but-great-scientists-know-whats-worth-solving-14279/

A little clip about string theory:

Thereâ€™s even been talk of â€śpost-empirical scienceâ€ť.Yes. There was another Strings conference in India at TIFR, in 2001. I happened to be in India at that time â€“ people had just discovered that the universe is going through accelerated expansion, so that the cosmological constant may be positive. And I saw in newspapers that Tom Banks and Edward Witten had said that, no, the cosmological constant cannot be positive because it is incompatible with string theory. It has to be negative, they said. And that these observations are premature. They were completely wrong. The fact is that nobody goes back to these things and says, well, let us be a little more modest about it.

Itâ€™s like shifting the goal post.Exactly! There is nothing wrong with making the statement. But then ignoring completely that you made that statement â€“ that is wrong. And then to say that this is the only theory. It has not had hard experimental/observational success, and it has not made that much progress in quantum gravity.

Abhay Ashtekar supposedly said

“And I saw in newspapers that Tom Banks and Edward Witten had said that, no, the cosmological constant cannot be positive because it is incompatible with string theory. It has to be negative, they said. And that these observations are premature. They were completely wrong.”

This comment makes no sense. Witten’s talk – available at http://arxiv.org/abs/hep-th/0106109 – was about quantum gravity in de Sitter space. He discusses theoretical difficulties but certainly does not conclude that it’s impossible. As for Tom Banks, I don’t see him in the Strings 2001 program but the claims make even less sense in his case, since he was already writing papers specifically about adapting string theory to do Sitter space.

Well, Jan 1, 2002, Dennis Overbye wrote in the NYTimes:

http://www.nytimes.com/2002/01/01/science/the-end-of-everything.html

which means that at sometime, per the newspapers, Witten thought that the result must be wrong, etc.

Anyway, Ashtekar (elsewhere in the interview) remarks on S. Chandrasekhar’s powers of memory, and disclaims having any such.

Mitchell Porter,

Witten had this to say at the time

â€śThis means that there is no classical way to get de Sitter space from string theory or M-theoryâ€¦ In fact, classical or not, I donâ€™t know any clear-cut way to get de Sitter space from string theory or M-theory. This last statement is not very surprising given the classical no go theorem. For, in view of the usual problems in stabilizing moduli, it is hard to get de Sitter space in a reliable fashion at the quantum level given that it does not arise classicallyâ€ť.

Ashtekar may not be quite accurate, but do you have any doubt that if the data showed the universe to be AdS, this would now be heavily advertised as evidence for string theory?

The It from Qbit hype is certainly over the top, partly due to the personalities involved, some of whom have a habit of declaring their own work revolutionary based on very little that is solid. There have been various fads over the years proclaiming new theories of spacetime, including non-commutative geometry, deconstruction, two dimensional gravity, et cetera. They have each been interesting in some ways, but none really lived up to the claims of proponents.