## Saturday, January 10, 2015 ... /////

### The Dirac roundtable

The latest Dirac medal went to string theorists Gabriele Veneziano, Ashoke Sen, and Andrew Strominger. See TRF, August 2014.

This October 2014 roundtable with the winners was hosted by Atish Dabholkar, a physicist at the Abdus Salam Institute for Theoretical Physics.

At the beginning, Veneziano is fighting the myth that he found his formula by randomly searching through mathematical books in the library. Just to be sure, this is no straw man. For example, go to 1:02:10 of the TV documentary with Brian Greene, The Elegant Universe, and you may check that it's routinely said that this is how string theory was born.

As the story goes, he happened on a dusty book... and in it, he found the [Euler formula]. ...And he was famous ever after for this accidental discovery.
Even though Veneziano was allowed to say a few words to denounce this "happy accident" story after that, I guess that he must have hated this (otherwise great) documentary!

Back to the roundtable. Andy Strominger said that Veneziano's memories are interesting because the history keeps on repeating itself. After some critical findings, scientists are disappointed to find out that their newly discovered theory doesn't describe what they wanted it to describe – but they often see that it actually describes something more important afterwords. The message is that the wisdom of the laws of Nature is more powerful than our imagination. The successes that replace those failures are more wonderful (in absolute value) than the failures.

Similarly, in 1985, it would have been unimaginable to foresee that string theorists would solve the large $N$ 't Hooft limit of gauge theories, unmask mysteries of black holes, find new realms of mathematics, glimpse a new holographic structure of spacetime – everything coming from analyzing those funny little oscillators. It would have looked crazily optimistic.

Dabholkar then turns to Sen and asks an incoherent question about something – mentioniong Sen's contributions in a disorganized way (I hope that you find my summary accurate, Atish!). Dabholkar also says that Sen should predict where it will go. Sen is capable of returning to the order, ignore most of Dabholkar's words, and use the last ones to reiterate the point by Veneziano and Strominger in a different way – it's dangerous to predict, especially the future, where the field is going.

At any rate, Sen adds the comment that black holes have become a crucial laboratory for testing the ideas about all these fundamental puzzles. Of course, Sen knows very well that Strominger would agree, too. Dabholkar and Strominger then agree that most of the claims about the unitary evolution of black holes etc. remain misunderstood. I would probably disagree with that although Dabholkar's proposition wasn't terribly sharp. Veneziano mentions the singularity as the main thing that is misunderstood according to his view.

Dabholkar says that the victories haven't been quite transferred from the SUSY realm to the SUSY-breaking one, and quotes Strominger as someone who tries to extend the results. I disagree with this picture, too. In my opinion, he talks from a viewpoint of a technocrat who doesn't quite understand the role of some technical work within the broader picture. It's an understandable fact that supersymmetric objects and SUSY-preserving phenomena are simply more calculable (or easier to calculate) than the SUSY-breaking ones and this fact will never change. On the other hand, the evidence is clear that in principle, all these things work in the absence of SUSY, too. Strominger effectively agrees. It was reasonable to start in the safe, SUSY territory, and then to deviate from the safe territory, step by step, he says.

Strominger sees the simplest, Schwarzschild black hole and the universality as the main blocks that are not understood. I think that I understand the universal law pretty well, too, but for understandable reasons, one has to use more informal rules and formalism of quantum gravity, not a *specific* string-theory-based formalism. This limitation is inevitable because the universality wants to be independent of a particular formalism! ;-)

Andy said that the measurement of the inflationary tensor-to-scalar ratio – a quantum gravity quantity – would have looked unimaginable a few years ago.

Veneziano thinks that the inability to explain the cosmological constant is a disappointment. He is not a fan of the landscape – the large number of solutions. But it's still a possibility that a large number of them will survive, he admits. He wants one vacuum – the right one or at least "a" viable one – to be found. There isn't even an existence proof that the Standard Model comes from string theory. Most string phenomenologists surely disagree with that statement.

Sen emphasizes something that I have often emphasized – that if it turns out that there are many solutions or even that we live in a pretty random one, it cannot be used as an argument against string theory. It would just mean that this is how Nature works, this feature would become a part of the stringy picture. One must buy a theory with all the derivable features of it, as a single package, Veneziano agrees. Almost all the critics are deluded about this elementary point.

Dabholkar says that holography – and perhaps other dualities – is extremely deep and the depth is arguably not being properly communicated, even to people in adjacent disciplines of physics. Sen says that many people in those fields seem to be aware of the depth; hydrodynamics is mentioned as his example. They say that the dominant flow of wisdom allowed by AdS/CFT is that classical gravity is mostly used to study strongly coupled dynamics of non-gravitational systems but the arrow may be reverted in the future.

Strominger says that the area-proportional entropy of the black hole is mysterious, understood well in a few examples, and should be understood in the full generality.

Dabholkar thanks them and it's over.

#### snail feedback (6) :

I liked Strominger's statement that the reality is much more wonderful than anything we can imagine.

Dear Lubos
nice post; beware Dabholkar is not director of ICTP

reader Jimmy Neutron said...

Completely irrelevant: how about those chairs making everyone appear to be slouching? Also, contrary to popular myth, these geniuses know how to dress well. GR to GQ.

It must be nice to have a cushy job @ some Institute, be clueless and babble nonsense and still get highly compensated for it.