Tuesday, January 11, 2005

Nastase: RHIC produces black holes

There are interesting papers today on the arXiv, and one of them is by Horatiu Nastase - the "N" from "BMN":
He extends his previous ideas about the AdS/CFT duality applied to QCD at low energies. Polchinski and Strassler started to investigate the high-energy scattering in QCD using the AdS/CFT correspondence: this high-energy scattering should be dominated by black hole production - these black holes live in the dual AdS space.

Horatiu argues that this regime may be described by the effective pion model - and the black hole is a nonlinear soliton of this pion field. From the pion model, he can calculate the temperature of the soliton, and the result is
  • 176 MeV times "a"
where "a" is the Nastase parameter, an undetermined dimensionless constant. For the most natural value "a=1", the predicted temperature is simply 176 MeV, although one should admit that other values are probably equally acceptable.

So this is what the string theory dual of QCD predicts for the temperature of such black holes. Can we test string theory experimentally, at least this string theory dual to QCD? Can we produce these dual black holes? Yes, this is what RHIC is good for. So Horatiu looks at the RHIC data and he sees that they have produced fireballs whose temperature is
  • 176 MeV
String theory is now proved, is not it? ;-)

QCD, string theory, and its uniqueness

Let me clarify the situation a little bit: Horatiu's ideas and similar approaches, even if they work, are not testing the "full" string theory. They are testing some particular mathematical methods applied to approximate descriptions of Nature, such as QCD. The dual dynamics is a not-quite-geometrical theory in the anti de Sitter space, although many of the conclusions we would make in a geometrical anti de Sitter setup will be qualitatively correct.

QCD is not the full theory of Nature, and correspondingly its dual string theory is not the same type of a solution of equations of string theory that we consider to be the theory of everything. The realistic backgrounds of the full string theory can predict everything, including gravity and black holes in the actual spacetime - which are different objects than the "dual black holes" in the "dual string theory to QCD".

For example, using string theory I can predict that Peter Woit would only have read the beginning of this article, before he will submit the first comment under this article. Moreover, in his comment, he will state an incorrect conjecture that I think that string theory is just a "dual of QCD". I definitely don't think that.

Note that it is easy to make physical predictions about simple physical systems - for example low-energy gravitons in 11 dimensions, fireballs, or Peter Woit - but it is harder to calculate the properties of more complicated systems, such as the proton.

I also predict that in his second posting, Peter Woit will ask whether the existence of the "string theory dual of QCD" contradicts the uniqueness of string theory. I actually think that this is a good question. But it seems that the answer is "no": these "different string theories" are just different vacua of the same theory, and it is conceivable that some of them are not solutions of string theory at all.

The dual string theory to QCD is moreover a very peculiar type of background - as string theory, it is a highly curved five-dimensional space. We would certainly not consider this background to be a full description of our Universe including its gravity simply because the characters of the gravitational forces in these two backgrounds are very different. But it is not quite a trivial question whether the dual string theory to QCD is a solution to the same theory that also describes the full world around us. Whatever the answer is, it can't invalidate the uniqueness of string theory: on the other hand, it is - of course - an example of the multiplicity of solutions of string theory.


  1. Hi Lubos,

    Glad to see that you've finally come around to the point of view that string theory is just a dual theory to QCD!


  2. But wait a minute, I thought string/M theory was a completely, absolutely unique framework with no choices one could possibly make. Are you trying to tell me that there are actually lots and lots and lots of different possible string theories?

  3. One would think Lubos has found predictive quality that we can now engage particular thought patterns with consistancy? Solitons, as Tachyon Condensation?? Owww spooky?:)

    It's true, Peter was comment one, but Lubos did not predict two comments?:) So maybe fifty fifty ,unless he had the ability to go back in time and change what could have appeared as prediction under the guise of editorial challenges?:)

    Anyway, I think Sean Carroll is posting a interesting comment about research and focused attention? Moving forward, to more focused dialogue about the differences of opinion can always be more enlightening if the motivation can be understood with regard to the direction you might want this science to go?:)

    Remember, the root of all evil?:)

  4. The paper you cited:
    is a completely total crap!

    The derivations leading up to Equation (7) used nothing more than the standard arguments for a 4-D blackhole, and so equation (7) is still correct. The problem occurs during the transition from Equ. 7 to Equ. 8, during which the author used a big "IF" for which no reasoning is given:

    "...IF we have Equ. 8 with M1 the mass of KK (Kaluza-Klein) graviton...we get Equ. 8"

    I do not know where that IF came from and how come it is true. But to get Equ. 8 from Equ. 7, regardless what M1 is, it must depend on M, the mass of the blackhole, in a inverse proportional relationship. (Remember Rh, the black hole radius, is calculated by 2GM/C^2, so d(Rh^2) is proportional to M*dM.)

    So M1 definitely can not be a constant if Equ 8 is to be true. That is where the trouble starts. Equ. 9 and Equ. 20 are essentially the same, so we can skip the discussions in between. The author merely replaced M1, which is supposed to be inverse proportional to blacm hole mass M, and is so not a constant, with the average pion mass, which is a constant. No reasoning is given why he can replace variable in such an arbitrary way.

    So the whole thing is a totally illogical numerology crap. Since the Lubos string theory consistently gives predictions that Lubos will always erase any anti-string messages, I am going to cross post this message to other Blogs, before Lubos had a chance to erase it.


  5. Dear Quantoken,

    I agree that the paper now looks mostly as numerology, but I am not sure whether I agree with your specific criticism.

    The equation 8 simply that the decrease of the entropy - the left hand side - is equal to the decrease of mass expressed as multiples of the lightest KK units - the entropy of one particle is assumed to be of order one, so to say.


  6. Further, the author started with standard Hawking Blackhole Temperature arguments, and end up with something totally ridiculous, by secretly replacing a few variables with something else that is totally unrelated.

    The presumed 176MeV temperature, if it were Hawking temperature, corresponds to a blackhole of roughly sixty million tons of mass. Such a small black have nothing to do with pion, or any presumed black hole pairs generated in any vacuum excitation, which should be at Planck Scale. See:



  7. Lubos:

    I am glad you are beginning to at least listen and reason, instead of simply deleting anything associated with the name "quantoken". So you are still hopeful, I think :-)

    You said: "The equation 8 simply that the decrease of the entropy - the left hand side - is equal to the decrease of mass expressed as multiples of the lightest KK units - the entropy of one particle is assumed to be of order one, so to say."

    If that interpretation of Equ. 8 is true, then the equation is wrong. We know the Hawking entropy is porportional to the surface area, which is porportional to the square of the radius, which is porportional to the mass. So for a black hole, the entropy is porportional to the mass squared, not proportional to the mass.

  8. Quantoken,

    you realize that the "black hole" lives in
    dual space. It is already in the title "Dual black holes ..."
    Thus you cannot argue the way you do.

    Best regards,
    Wolfgang Beirl

  9. Wolfgang said:
    "you realize that the "black hole" lives in
    dual space. It is already in the title "Dual black holes ..." Thus you cannot argue the way you do."

    Then you can not discuss your dual space black hole using standard arguments we use for regular black holes existing in 4-D spacetime, either. You can not use Hawkings arguments and formulas, which are good for regular blackholes living in the real 4-D spacetime world, not for your strange ones living in the "dual space".


  10. Quantoken,

    you wrote:
    > Then you can not discuss your dual space black hole
    > using standard arguments

    Why not ?

    Wolfgang Beirl

  11. I predict that Lubos will soon write a paper using quasinormal modes to prove that the ratio of the Nastase parameter to the Immirzi parameter is always precisely the log of the square root of 7.