marcus

Science Advisor

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I see the suggested directions you offer as a "mixed bag".

As I said: "...But who knows? Some of them might suddenly jump up in importance.

==quote==

I see different directions:

- technical: reformulation in terms of spinors, twistors, group field theory, ...

- technical: fixing the issues with quantization (both canonical and PI/SF) + their equivalence

- dynamics! (once the SF and H are rigorously constructed)

- boundary Hilbert spaces and holographic principle (get rid of the bulk)

- coarse-graining / Kadanoff's renormalization group approach / certain other related limits

- matter d.o.f., unification, possibly the Sundance Bilson-Thompson approach

- exotic smoothness, PL manifolds, 'non-diffeomorphic defect-structure', ... relation to Asselmeyer's work

==endquote==

That could apply to Sundance approach or Asselmeyer approach. Not much going on with them now, just a few people--but either could "suddenly jump up in importance."

I don't think we can know the future and I DON'T MAKE BETS. Basically I just

**watch the professional research community**.

Where my perspective differs markedly from yours, and where I possibly might benefit you by giving an alternate point of view, is IF AND WHEN I notice a trend that you might have overlooked.

I've noticed that Thiemann and the Erlangen group seem to be

**getting away from strict Dirac quantization.**And I think that fits with Hartle "Decoherent Histories" reformulation of standard QM. Which I think has a lot going for it. Fundamentally more valid than the split version of QM that prevailed in Dirac's day.

So I think your use of language above is questionable where you say "their equivalence" and "H rigorously constructed". This is just IMHO but I suspect you may eventually have to give up on the strict Dirac canonical, just as I already see happening in the Erlangen group. If Hartle DH is right, it's not valid in a fundamental sense, just "effective" or "emergent" in certain regimes.

To recapitulate:

==quote==

Basically my perception is guided by people "in the business" like Lewandowski and Pullin and I'd say to anybody

**look at the lineup of Loop talks at Stockholm this week**.

The MG13 organizers gave Lewandowski nearly 10 hours of parallel session, and Pullin over 9 hours. A total of 19 hours designated for Loop gravity. These guys know the field, what's active, what their colleagues are interested in hearing about.

It's certainly not a perfect indicator, but it can give one something outside oneself to balance one's subjective favorites and preconceptions.

==endquote==