Monday, February 20, 2006

Dantas discussion forum for Smolin lectures

Dr Christine Dantas has an interesting discussion forum for Dr Lee Smolin's lectures on quantum gravity here. It has some interesting comments, a few extracts follow:

'You don't take General Relativity as a basis and apply quantization recipes. Because, after all, it is the quantum gravity that is the fundamental theory of spacetime and Gen Rel is merely an APPROXIMATION to it. Instead, [Smolin] says, what is basic is differential forms - that is, fields that you can define without resorting to a METRIC or a setup geometry. So let's find out about form theories - BACKGROUND INDEPENDENT field theories like BF, in other words - and then lets play around ... and then (I guess) he pulls a form theory of gravity out of his hat.' - Dr Who

'I want to think in physical terms on how to understand causality in a discrete, background independent framework.' - Dr Dantas

'In Lecture 1, Smolin introduces the important idea of a HISTORY and he gives a toy model example with unlabeled graphs instead of the spin networks of regular LQG and a HISTORY is simply a series of MOVES (each one with an amplitude, a complex number) and it is a series of moves that get you from the INITIAL graph to the FINAL graph and the AMPLITUDE of any given history is just the PRODUCT of the series of amplitudes of each move, step by step. And the PATH INTEGRAL is simply the sum of all those products - the sum of the amplitudes of each history that gets you from the initial graph to the final graph. So understanding the toy model he gives in Lecture 1 really comes down to getting a feel for MOVES.

'Oh, another thing, a history can be visualized as a foam. The path of a changing network describes a foam-like complex - drag a graph through a time-like dimension and it describes a honey-comb looking cellular complex of 2D cells. In regular Quantum Gravity, spin foams are the HISTORIES of evolving spin networks. So a spin foam is what you get if you apply MOVES to get from an initial spin network to a final one. NO ONE SHOULD HAVE TO UNDERSTAND ALL THIS in one sitting, or in one lecture. So in Lecture 1 what Smolin did was basically make us familiar with the idea of an unlabeled network and the idea of a move.' - Dr Who


Thursday, February 09, 2006

Dr Dantas has LQG reading list...