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marcus

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## Main Question or Discussion Point

the intent of this thread is to gather links and other information that can

help us gauge the progress being made towards a TESTABLE

theory of QUANTUM GRAVITY WITH MATTER (QG/M) specifically in the "covariant" sum-over-histories or PATH INTEGRAL version.

(I am classifying Freidel's group field theory variant of spinfoam QG as essentially a path integral approach because of its equivalence to spinfoam)

if you have information to share about the status of research along these lines, please consider contributing some online references.

it doesnt matter if you think progress in this direction is slow or fast, in this thread I am not looking for arguments to prove some particular case.

I especially want to look at some recent papers of Laurent Freidel and people that co-author with him or work on similar research. Freidel has a path integral approach that includes matter and appears to work in 3D which he is hopeful can be extended to 4D.

one interesting feature is that the same mechanism that provides for the quantum spacetime dynamics (the QG part) also provides feynman diagrams for the particles of matter---so it is really QG/M, if I understand correctly what he says.

another interesting feature is that a form of DSR is derived from the 3D QG/M theory----so there is energy dependence of the speed of gammaray photons. It is important to emphasize that the DSR is not merely assumed or postulated or guessed but rather it is logically derived. For this Freidel QG/M theory to work there must be a slight energy dependence-----if I understand correctly----and would make the 4D version TESTABLE, if the same DSR thing carries over.

So if Freidel and the others succeed with their program of extending the already proven results from 3D to 4D, then they will have a theory that predicts something that might or might not be observed. One will be able to look at a Gammaray burst (GRB) and see whether or not the more energetic photons are arriving a little bit earlier (after traveling for a billion years) so that the spike is skewed. And if one does not observe this, it is evidence against the theory.

So what this example shows is that it is a

And we might also look at recent work of Carlo Rovelli which is also path integral, and is in preliminary stages of including matter. Maybe there are some other developments towards a testable path integral approach to QG/M, which we should know about.

I will start by getting some links and some quotes about Freidel's program. These will take some time to assemble---- I think they'll show that they aren't at the goal, but will give some basis for telling if they are getting to where they have a shot at it.

help us gauge the progress being made towards a TESTABLE

theory of QUANTUM GRAVITY WITH MATTER (QG/M) specifically in the "covariant" sum-over-histories or PATH INTEGRAL version.

(I am classifying Freidel's group field theory variant of spinfoam QG as essentially a path integral approach because of its equivalence to spinfoam)

if you have information to share about the status of research along these lines, please consider contributing some online references.

it doesnt matter if you think progress in this direction is slow or fast, in this thread I am not looking for arguments to prove some particular case.

I especially want to look at some recent papers of Laurent Freidel and people that co-author with him or work on similar research. Freidel has a path integral approach that includes matter and appears to work in 3D which he is hopeful can be extended to 4D.

one interesting feature is that the same mechanism that provides for the quantum spacetime dynamics (the QG part) also provides feynman diagrams for the particles of matter---so it is really QG/M, if I understand correctly what he says.

another interesting feature is that a form of DSR is derived from the 3D QG/M theory----so there is energy dependence of the speed of gammaray photons. It is important to emphasize that the DSR is not merely assumed or postulated or guessed but rather it is logically derived. For this Freidel QG/M theory to work there must be a slight energy dependence-----if I understand correctly----and would make the 4D version TESTABLE, if the same DSR thing carries over.

So if Freidel and the others succeed with their program of extending the already proven results from 3D to 4D, then they will have a theory that predicts something that might or might not be observed. One will be able to look at a Gammaray burst (GRB) and see whether or not the more energetic photons are arriving a little bit earlier (after traveling for a billion years) so that the spike is skewed. And if one does not observe this, it is evidence against the theory.

So what this example shows is that it is a

**reasonable goal**to develop a testable QG/M path integral theory. And we can also look at Renate Loll's CDT which is path integral QG, and see how close she is to including MATTER and to being TESTABLE, which she must do to be in this race.And we might also look at recent work of Carlo Rovelli which is also path integral, and is in preliminary stages of including matter. Maybe there are some other developments towards a testable path integral approach to QG/M, which we should know about.

I will start by getting some links and some quotes about Freidel's program. These will take some time to assemble---- I think they'll show that they aren't at the goal, but will give some basis for telling if they are getting to where they have a shot at it.