Timeline for Can Loop Quantum Gravity connect in any way with string theory?
Current License: CC BY-SA 4.0
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| S Feb 13 at 11:32 | history | suggested | Kasiéobì ùdumágà | CC BY-SA 4.0 |
A couple of grammar corrections
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| Feb 13 at 4:35 | review | Suggested edits | |||
| S Feb 13 at 11:32 | |||||
| Jan 27, 2011 at 13:30 | comment | added | Lawrence B. Crowell | cont: String theory is much richer in structure that LQG. The LQG camp formulates theory far closer to GR, while string theory is formulated from elementary particle QFT work. The LQG side has background independence, though there are funny issues with classical-quantum correspondence. I see this as important, though maybe not sacrosanct. So this “connection” I ponder is whether it is possible that LQG might provide a system of constraints on string theory. In other words, might physical solutions in string theory in part be provided by Lagrange multipliers in the action for LQG? | |
| Jan 27, 2011 at 13:29 | comment | added | Lawrence B. Crowell | It is interesting to read Lubos and Carlos on degrees of freedom. Classical gravity is indeed a continuous metric, but for that reason one does not count degrees of freedom in each infinitesimal region where one sets up Gaussian intervals. Quantum mechanically the LQG spin connections in spacetime are dense and the problem of a Planck density of energy or entropy remains with LQG. Duality and holography reduces these enormously. | |
| Jan 27, 2011 at 11:05 | comment | added | user346 | issues with this approach, as there are with any current approach to QG. But I do not know of a simpler way to get from the microscopic theory to the EH action. One might suggest String Theory. However, there one requires the introduction of extra-dimensions and SUSY for the quantum theory to be anomaly free. LQG imposes no such additional requirements. BTW this does not imply that LQG is incompatible with extra dimensions and SUSY, only that its minimal formulation does not require these ingredients. | |
| Jan 27, 2011 at 11:00 | comment | added | user346 | that is a great answer. I disagree only with your take that LQG it is hard to calculate anything because it does not give a classical limit that looks like smooth spacetime. This is incorrect. The basic dynamics in LQG - as in any quantum theory - are given by the expression for the vertex operator. There are several versions to choose from. One then has a well-defined procedure to obtain a semi-classical limit in the limit of either large spins $j \gg 1$. These calculations yield an effective action containing the Einstein-Hilbert action among other terms. Of course there are | |
| Jan 27, 2011 at 10:42 | history | answered | Philip Gibbs - inactive | CC BY-SA 2.5 |