- #1

jeff

Science Advisor

- 658

- 1

I previously posted the following:

*In the forward to rovelli's new book "Quantum Gravity", james bjorken states quite plainly that the effective field theory approach to quantum gravity correctly taught us that GR must be viewed as just an effective field theory, and in fact this is the universally shared view.*

The problem for lqg is that the central construct in lqg, spin networks, only makes sense if GR is in fact exactly correct. I don't see why it would make sense for an author to allow a forward to be written by someone else, that contradicts the basic premise of the book.

In fact, rovelli defends lqg by stating...

"But the modification of the notions of space and time has to do with the diffeomorphism invariance and the background independence of the action, not with it's specific form."

In other words, it is inaccurate to view lqg as a genuine candidate quantum gravity theory, and thus as a rival of string theory. Rather, lqg is just a toy theory serving as a laboratory to explore a small number of fundamental issues in quantum gravity.

The problem for lqg is that the central construct in lqg, spin networks, only makes sense if GR is in fact exactly correct. I don't see why it would make sense for an author to allow a forward to be written by someone else, that contradicts the basic premise of the book.

In fact, rovelli defends lqg by stating...

"But the modification of the notions of space and time has to do with the diffeomorphism invariance and the background independence of the action, not with it's specific form."

In other words, it is inaccurate to view lqg as a genuine candidate quantum gravity theory, and thus as a rival of string theory. Rather, lqg is just a toy theory serving as a laboratory to explore a small number of fundamental issues in quantum gravity.

I'll respond on two levels. One is on the specific physics of lqg, and the other, on the plausibility of alternative interpretations of these statements.

For example, someone may have a physics reason for not believing that lqg requires that GR be treated as if the einstein-hilbert action remains uncorrected at arbitrarily high energies.

Another example would be that someone may believe that it's plausible that rovelli does in fact believe that GR is exactly correct. In this case the best thing to do is just to email him, which I've done and am waiting for his response. Of course, nobody is stopping anyone from doing the same thing.