Thursday, November 22, 2007

Two dimensional string theory

Promotion has sapped the output of my favorite physics bloggers, so I'm grateful to FMH for my physics fix:
Shadow World: Science News Online, Nov. 17, 2007

....Since 1997, physicists have proposed countless variations on Maldacena's theme, all of which interpret a string as a swarm of particles living in a small number of dimensions. Perhaps the easiest case to visualize is when that number is two. In such a scenario, anything that takes place in your many-dimensional, stringy universe has a sort of shadow representation in terms of particles moving on that universe's 'sphere at infinity.' This esoteric-sounding concept is actually similar to the familiar celestial sphere of the night sky as seen from Earth: It's the two-dimensional surface spanning all possible directions one can point to infinitely far in space...
So this re-representation of string theory has been popular for 10 years -- but I don't recall reading about it.


Sciam did cover this in Nov 2005 ("The Illusion of Gravity"), but I wasn't a subscriber then. (SciAm is the only periodical I subscribe to does not give archival access to current print subscribers. It's their right, but I do hold it against them.)

Wikipedia presents the theory more technically:
Juan Martín Maldacena (born September 10, 1968) is a theoretical physicist born in Buenos Aires, Argentina. Among his many discoveries, the most famous one is the most reliable realization of the holographic principle - namely the AdS/CFT correspondence, the successfully tested conjecture about the equivalence of string theory or supergravity on Anti de Sitter (AdS) space, and a conformal field theory defined on the boundary of the AdS space.
and on AdS/CFT correspondence:
In physics, the AdS/CFT correspondence (anti-de-Sitter space/conformal field theory correspondence), sometimes called the Maldacena duality, is the conjectured equivalence between a string theory defined on one space, and a quantum field theory without gravity defined on the conformal boundary of this space, whose dimension is lower by one or more...
Now, as we all know one of the primary challenges of the last 80 or so years of physics has been quantizing gravity. So, as a hobbyist reading this, I'm thinking the mathematical trick is to make the problem more tractable (and perhaps more constrained?) by taking gravity out of the picture. Hence the SciAm title - the "illusion of gravity".

This might be a bit like the old polar vs. cartesian coordinate transformation in Physics 101. Neither is "truer" than the other, but in some problems solutions are much easier. Or maybe the the Maldacena view will turn out to be the "better" model of "reality" (whatever that slippery beast might be).

I'll have to look around for some other popular summaries ...

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