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marcus
#38
Sep22-09, 03:23 PM
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Someone steering a boat may pick a mark on the horizon or shore "to steer by". It might not be the actual destination, but it temporarily it serves as one.

To me it seems as if Hermann Nicolai has indicated what might serve as provisional goal for a line of 4D quantum gravity development.
Does this make sense to you?

As a rough paraphrase, Meissner and Nicolai (M & N) are saying if you can give a quantum 4D geometry for them to define fields on, which has a certain kind of symmetry in the flat classical limit, then thereon they can construct a version of the Standard Model QFT with all troubles pushed out beyond Planck scale. The model will predict that you take it all the way to Planck scale without finding new physics----then, as expected, lots of new Planck scale physics.

So incidentally it can be falsified in a completely straightforward manner! If new physics shows up at some intermediate scale, long before Planck, then this minimalist theory is wrong.

It looks like a reasonable provisional target. What would it take for a QG to satisfy M&N? One could try heading that way, and maybe some progress in the right general direction would be made, even if it ultimately turns out not to be the final destination.

Could any of the half-dozen QG approaches we've been looking at be adapted or modified in the desired way? How close or far are they from providing the missing piece in M&N's picture? Do any have a reasonable chance of filling that role?

Here is some background on the Meissner Nicolai papers, and Nicolai's talk at the Planck Scale conference.
http://physicsforums.com/showthread.php?t=339154
If for some reason you don't like the M&N approach, please let me know.
They are offering it as something that deserves to be worked out, which can be checked for consistency and possibly tested experimentally. It is subject to experimental refutation. So it is not being presented as The Answer, but as an interesting minimalist theory.

Quote Quote by marcus View Post
Here are five papers by Kris Meissner and Hermann Nicolai:
http://arxiv.org/find/grp_physics/1/.../0/1/0/all/0/1
"... in a UV finite theory of quantum gravity, if the latter admits a flat space limit which is classically conformally invariant. The mass spectrum and pattern of couplings observed in elementary particle physics could then have their origin in quantum gravity."
What prospects do any of our half-dozen approaches have of admitting a flat space limit that is conformally invariant?