Can the Holographic Principle make predictions

[Michael27]

I have been following the online lectures of Leonard Susskind regarding the holographic principle and entanglement.see Holographic Principle Lecture Part2
The universe can be seen as two-dimensional information on a cosmological horizon. (see https://en.wikipedia.org/wiki/Holographic_principle)
My question is: Can the holographic principle make predictions on the size and shape of such a horizon? If so does the information projected on the horizon change the shape and size of this horizon?

Does the holographic principle/string theory state anything about the projection of the information on the horizon implying the physics of the universe or are the physics independent of the way the information is projected/stored?

 

[Urs Schreiber]

Just going by the headline of your question: A key observation was that the holographic principle in its precise incarnation as AdS-CFT duality allows to say something about the shear viscosity in N=4 SYM, and by a suitable approximation then also in quark-gluon plasmas in QCD. This observation was originally due to

• G. Policastro, D.T. Son, A.O. Starinets,
  "Shear viscosity of strongly coupled N=4 supersymmetric Yang-Mills plasma",
  Phys. Rev. Lett.87:081601, 2001 (arXiv:hep-th/0104066)

and has since spawned a lot of discussion.

I suppose there remains some debate among solid state physicists how much this really helped to make predictions in their field. I am not expert enough on the fine detail to judge this. For review about this application to condensed matter physics see the references here.

Also beware that this takes the opposite point of view on holography than you seem to have in mind: In this application the observable physics corresponds to the boundary theory, and it is the bulk theory which is an auxiliary device for reasoning about the boundary theory.

 

[Fra]

As far as I understand this there are two components in this discussion

1) holographic principle as a mathematical realtion between theories, which can be used as a calculational tool as the two theories have different computational complexity. This in itself is very interesting (physics aside). AdS/CFT is one explicit example.

2) Then is the physical interpretation of this, like is this telling us something about nature? or the nature of physical law? or about inferential systems used in physics?

In particular (2) is very fuzzy, but extremely interesting, but i think there is no consensus!

Black Holes, AdS, and CFTs, Donald Marolf
"This brief conference proceeding attempts to explain the implications of the anti-de Sitter/conformal field theory (AdS/CFT) correspondence for black hole entropy in a language accessible to relativists and other non-string theorists. The main conclusion is that the Bekenstein-Hawking entropy S_{BH} is the density of states associated with certain superselections sectors, defined by what may be called the algebra of boundary observables. Interestingly, while there is a valid context in which this result can be restated as "S_{BH} counts all states inside the black hole," there may also be another in which it may be restated as "SBH does not count all states inside the black hole, but only those that are distinguishable from the outside." The arguments and conclusions represent the author's translation of the community's collective wisdom, combined with a few recent results. For the proceedings of the WE-Heraeus-Seminar: Quantum Gravity: Challenges and Perspectives, dedicated to the memory of John A. Wheeler."
-- https://arxiv.org/abs/0810.4886

As for shapes of boundaries (interpreted in a wider meaning), i also see a possible connection to linking extremal black holes to elementary particles.

Black Holes as Elementary Particles, C.F.E. Holzhey, F. Wilczek
"It is argued that the qualitative features of black holes, regarded as quantum mechanical objects, depend both on the parameters of the hole and on the microscopic theory in which it is embedded. A thermal description is inadequate for extremal holes. In particular, extreme holes of the charged dilaton family can have zero entropy but non-zero, and even (for a>1) formally infinite, temperature. The existence of a tendency to radiate at the extreme, which threatens to overthrow any attempt to identify the entropy as available internal states and also to expose a naked singularity, is at first sight quite disturbing. However by analyzing the perturbations around the extreme holes we show that these holes are protected by mass gaps, or alternatively potential barriers, which remove them from thermal contact with the external world. We suggest that the behavior of these extreme dilaton black holes, which from the point of view of traditional black hole theory seems quite bizarre, can reasonably be interpreted as the holes doing their best to behave like normal elementary particles. The a<1 holes behave qualitatively as extended objects."
-- https://arxiv.org/abs/hep-th/9202014

I think these papers are food for thought, in pondering about (2). Once these things are more understood, THEN, maybe there are more implications beyond (1). But there are more, like those arguing that the "holographic principle" is rather emergent as a dynamic equlibrium.

/Fredrik