Friday, August 22, 2014

Ashoke Sen: elementary particles are small black holes

Three string theorists added as Dirac Medal winners

On August 8th of every year, the Abdus Salam Institute in Trieste, Italy chooses up to three recipients of the Dirac Medal. (It's the anniversary of Dirac's 1902 birth. There exist three other awards called the "Dirac Medal" which I will ignore because they're less relevant for this blog's audience.)

Of course, the medal tries to decorate deep minds who are doing a similar kind of profound research as Paul Dirac did which is why dozens of string theorists have already won it. The Dirac Medal shows what the Nobel prize would look like if the committee weren't constrained by the required explicit, dynamite-like demonstration of the physical discoveries.

In 2014, i.e. two weeks ago, the Italian institute avoided all experiments and awarded just three string theorists:
Ashoke Sen, Andrew Strominger, Gabriele Veneziano
Congratulations! Of course, Veneziano is the forefather of the whole discipline (the intercourse that has led to the birth was Veneziano's encounter with the Euler Beta function), Andy Strominger is a lot of fun and a perfectly balanced top thinker in one package and I know him the best of all, of course ;-), and Ashoke Sen is among the most brilliant minds, too. He has previously won the Milner award, too.

The Hindu printed a short yet interesting interview with Ashoke Sen yesterday:
‘Elementary particles may be thought of as small black holes’
It's funny – the title is actually a sentence I have included in almost every general physics talk I gave in the last decade, perhaps 30 talks in total. Sometimes I talk about the panic about the LHC-produced black holes and emphasize that only experts may distinguish a small black hole from an elementary particle such as the Higgs boson – and its evaporation from the Higgs decay etc.

It's true that the Hawking radiation of a "larger than minimal" black hole has a higher number of decay products (particles) so it's more uniform but for the truly minimum-size black holes, there's no difference.

String theory makes this unification of particles and black holes very explicit and elegant and Ashoke Sen has contributed to these wonderful insights a lot. String theory generally predicts an infinite spectrum of particle species – the perturbative "Hagedorn" tower of excited string states is the first glimpse of it, and it gets transformed to black hole microstates for even higher masses where the spectrum gets even denser.

Or you may go in the opposite direction: as a black hole is shrinking, the quantum effects and effects that may be represented as the quantization of its mass eigenvalues get increasingly important and once you get to the sub-Planckian masses, there are just a few black hole microstates and they are identical to the known elementary particles.

The interview mentions his work on S-duality and his research of the black hole microstates. Ashoke was also the #1 soul behind the tachyon minirevolution in the late 1990s but he remained modestly silent about it.

He is also asked about the criticisms directed against string theory that we may still occasionally hear. He reminds everyone of the fact that not just string theory but any theory claiming to clarify the quantum foundations of gravity deals with new phenomena at (at least superficially) experimentally inaccessible scales – the Planck length has been known and known to be ultratiny for more than 100 years (Planck defined the natural units in 1899). So we have two options: either to hang ourselves, or to try to get as deeply as we can with the available knowledge and tools.

String theory is choosing the second option, Ashoke states. Those who are not choosing the second option should at least follow the first option more rigorously so that we don't hear so much unnecessary yelling before they complete their alternative, non-stringy strategy.


  1. String Theorists should stand up for their work and continue it. I think though one hears it intimated that if String Theory fails no other possible unknown strategy will work either, and this is logically false not just wrong.

  2. Dear Billy, I think it's silly to even discuss whether string theorists will continue their work. Of course that they will as long as they will exist. Only loons could think otherwise.

    The problem isn't really whether string theorists will try hard. The problem is that they should be celebrated by the mankind as the true heroes of our epoch but much of the mankind has deteriorated enough not to realize this fact.

    Science isn't about studying "unknown strategies". One can't really study an unknown theory. Science studies tangible phenomena and particular ideas.

    The claim that there are no alternatives to string theory is no "dichotomy". It is one of the most important nontrivial and extremely important results of the last 50 years in theoretical physics.

  3. At the cost of sounding like a (virtually) traveling salesman: Hyperresonance theory is a viable extension of string theory (not really an alternative, but still... it complements string theory):

  4. kashyap vasavadaAug 22, 2014, 6:09:00 PM

    Congrats to Sen for Dirac medal. Now black holes do radiate energy by Hawking radiation. My question is: how does Sen explain stable elementary particles?

  5. The electron isn't a black hole. It's a chiral bispinor "optical vortex". You can make it out of light in pair production, you can diffract it, and when you annihilate it you get light again.

  6. Dear Kashyap, a good question but the answer is that there is nothing wrong about stable black holes as long as they have a nearly vanishing entropy. It really means that the temperature is T=0. Classically, extremal black holes have T=0. Once SUSY is broken, it must be possible for all black holes to decay, to avoid black hole remnants

    so there must exist tiny black holes - elementary particles - with mass/charge ratios exceeding the extremality bound. But some of those may be stable. There's really nothing wrong about it even from the black hole perspective. ;-)

  7. IMHO, the smallest black hole could be interpreted as stringy quantum knot produced by electro
    magnetic interference at the solar surface being the start of small comets or
    by the so called sprites above thunderclouds. See:
    Ball Lightning, Micro Comets, Sprite-Fireballs, Solar Bright Points and Xray/ Gamma
    Flashes According to Quantum FFF Theory.
    And : The Impossible Zero Point Electric Black Hole as the Origin of New Physics even for
    Comets like 67P,C-G.

  8. Congratulations to them!

    This good message in the form of a very nice TRF post saves my day :-)

  9. How does a black hole carry an electrical charge? Does the string theory explain why leptons carry an integral charge and quarks 1/3 or 2/3?

  10. With an open mind I searched for evidence for string theory. The first serious site:
    Nothing much listed there.
    No doubt Lubos has covered this issue at length already.
    It would be nice for new readers to have a quick summary of evidence so far. Otherwise I might suggest 10^-33 dancing penguins as a better base unit.

  11. In a certain sense one could have asked "what is the evidence for Maxwell's equations?" . After all the electricity and magnetism laws that it incorporated successfully already did the job of describing the data, as the Standard Model does for the elementary particle data. The equations are validated with the incorporation of light/radiation naturally in its formulation.

    I think string theoretical models are at the point of being able to incorporate the successful Stndard Model of particle physics which describes the nature of elementary particles, ( i.e. the encapsulation of practically all existing data) but not yet at the point of predicting new phenomena and correlations that would validate carrying the complexity of a string theoretical model as a TOE ( theory of everything).

    I do not know of another candidate theoretical model for a TOE that is so inclusive of particle data .

    Do you think penguins would would dance around the Standard Model?

  12. Thanks for the reply.
    "...string theoretical models are at the point of being able to incorporate the successful Stndard Model of particle physics which describes the nature of elementary particles"

    If so, that is excellent. I have not followed the field of string theory. Is the "at the point of" a true reflection of the situation? I am reminded of software developers who use this term a lot, yet their projects never complete.

    Is the theory without fudges, infinity cancellations, arbitrary constants? Is it "beautiful" as Einstein would have us believe is a characteristic of nature. Maxwells equations fit this bill.

    I always considered that the move from particles to strings was an arbitrary choice, hence my reference about penguins. What was the basis for choosing strings as fundamental objects?

  13. It started back in the 1960s or so with Regge pole theory, where the resonances discovered in particle physics were found to be like excitations of a string. Lubos will have the history someplace in this large blog. My experimental thesis was studying Regge poles ! They fell by the way when the quark model was so successful in organizing everythin in the symmetries of SU(3)xSU(2)xU(1) ( the standard model). In searching for theoretical models that that could quantize gravity they were discovered again , and string theory is the only one that I have heard that quantizes gravity and in addition contains the SU(3)xSU(2)xU(1) symmetry structure naturally. As I understand it the problem with the theories is theoretical in the sense that there exist thousands of possibilities which have to be sifted in order to find a specific model that could make predictions. One general prediction is that supersymmetry should manifest at LHC ( that takes care of infinities and is natural in string theories), and I expect it will.

    A phenomenological string model that predicted large dimensions for the compacted ones has not manifested at the LHC energies so that model seems to be off the books.

  14. It's very Zen that both string theory and hanging need string.