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Nevertheless, I ran into this post when searching google as part of some research:

http://motls.blogspot.com/2010/10/richard-feynman-and-birth-of-quantum.html

wherein he states when describing Feynman's look at quantum gravity and the first attempts at quantization of classical GR:

Fine. So he knew that the tree-level amplitudes encoded the classical theory. It followed that if you go through all this formalism with first-class and second-class constraints, you translate all the things into the ugly Lorentz-symmetry-obscuring quantum formalism, and you compute the scattering amplitudes, you will only get data that are directly transformed from the classical behavior of gravitational waves according to classical GR!

If you actually want to predict the results of hypothetical or doable experiments, which is the ultimate application of any laws of physics, the calculations will give you nothing that you couldn't get from classical GR. (Recall that those other people didn't accept loop calculations so the tree-level amplitudes were everything that was possible or acceptable for them.)

By a relatively simple conceptual argument, Feynman was able to show that their "dreamed about" calculation of the scattering amplitudes in what they considered to be "quantum gravity" was just a tautological reshuffling of classical GR. From a physical perspective, it contained nothing new or valuable at all!

He ends with:

A huge portion of the community is still unable to learn the lessons that have been around for nearly half a century. They continue with their dumb canonical quantizations of GR, even though it's obvious that one can't learn anything about quantum gravity in this way, and they present their half-baked classical pictures how the Universe could have behaved around t=0 (or "before") even though it's obvious that such classical stories can't settle anything about quantum gravity and quantum cosmology, either.

Which indicates to me that he thinks the very criticisms that applied in the 1950s still apply today. He also seems to be talking about all non-string QG theories in the same vein, as if they suffer from the same conceptual weakness.

So three questions:

First, is Luboš criticism just that by quantizing GR by any means, you don't end up with new physics, you end up with quantized GR?

Second, has anything happened in the development of QG in the intervening years that Luboš misses?

Third, what is there about the quantization of GR using the latest spinfoam ideas that makes it give different predictions that can be tested? Is it just that having any quantum gravity theory allows one to make predictions (right or wrong) where quantum gravity dominates like the Big Bang, Black Holes, etc.?

Luboš clearly is extremely defensive about string theory, so it seems to me that one needs to take his comments with a grain of salt. But being an amateur on the steep learning curve, I want to understand what is wrong with his comments, as well as what is valid criticism.