Tuesday, August 09, 2005

The Fifth Dimension, is the Spacetime Fabric

Perhaps Quantum Gravity can be Handled by thoroughly reconsidering Quantum Mechanics itself? by Gerard t' Hooft

I was attracted to Nigel Cook's statement on Peter Woits blog entitled, "Panel Discussion Video" by the quote of his taken here below. What immediately struck my mind, was the Bekenstein Bound and how "temperature" would have been seen from that perspective.

Bekenstein Bound:
Superstring theory rules in the 5-D spacetime, but a so-called conformal field theory of point particles operates on the 4-D hologram. A black hole in the 5-D spacetime is equivalent to hot radiation on the hologram--for example, the hole and the radiation have the same entropy even though the physical origin of the entropy is completely different for each case.


Lee Smolin post given at Peter Woit's site was a ressurrection of "Three Roads to Quantum Gravity", and I like the fact that he wants cohesion amongst physicists and theoriticians alike. But if stauchly held to any position, then you have divisive comment about the ways in which to approach things. It can't be helped. But asking for more clarity this might be a good thing, and a approach by Lubos to qualify the string theorist position.

Lubos Motl:
The holographic conjecture, based on the Bekenstein's bounds and the Bekenstein-Hawking entropy of the black hole,has been first proposed by Gerard 't Hooft and discussed in more detail by Lenny Susskind:


But before consider Nigel's comment, I wanted to quote something from Lee Smolin.

Consider any physical system, made of anything at all- let us call it, The Thing. We require only that The Thing can be enclosed within a finite boundary, which we shall call the Screen(Figure39). We would like to know as much as possible about The Thing. But we cannot touch it directly-we are restrictied to making measurements of it on The Screen. We may send any kind of radiation we like through The Screen, and record what ever changes result The Screen. The Bekenstein bound says that there is a general limit to how many yes/no questions we can answer about The Thing by making observations through The Screen that surrounds it. The number must be less then one quarter the area of The Screen, in Planck units. What if we ask more questions? The principle tells us that either of two things must happen. Either the area of the screen will increase, as a result of doing an experiment that ask questions beyond the limit; or the experiments we do that go beyond the limit will erase or invalidate, the answers to some of the previous questions. At no time can we know more about The thing than the limit, imposed by the area of the Screen.


Page 171 and 172 0f, Three Roads to Quantum Gravity by Lee Smolin

Nigel Cook:
'Caloric’, fluid heat theory, eventually gave way to two separate mechanisms, kinetic theory and radiation. This was after Prevost in 1792 suggested constant temperature is a dynamic system, with emission in equilibrium with the reception of energy.


Yet I understand this call for bringing a string theorist into the fold of Lee's, but I would remind him, that such cosmological approaches are well on their way with the course ISCAP set for themselves and how comsological realization, are still important features that string theory would like to get a hold of.



Juan Maldacena:
The strings move in a five-dimensional curved space-time with a boundary. The boundary corresponds to the usual four dimensions, and the fifth dimension describes the motion away from this boundary into the interior of the curved space-time. In this five-dimensional space-time, there is a strong gravitational field pulling objects away from the boundary, and as a result time flows more slowly far away from the boundary than close to it. This also implies that an object that has a fixed proper size in the interior can appear to have a different size when viewed from the boundary (Fig. 1). Strings existing in the five-dimensional space-time can even look point-like when they are close to the boundary. Polchinski and Strassler1 show that when an energetic four-dimensional particle (such as an electron) is scattered from these strings (describing protons), the main contribution comes from a string that is close to the boundary and it is therefore seen as a point-like object. So a string-like interpretation of a proton is not at odds with the observation that there are point-like objects inside it.