After spending many years thinking about and writing about quantum gravity theories both mine and those of others I have come to the conclusion that a theory like M-Theory is the way to go. However, it has certain shortcomings. M-Theory relies on a fixed 11 dimensional background space to propagate and vibrate in. This is the reason that many physicist prefer other directions. M-theory does have one potential, it could be a blue print for a truly final and ultimate theory.
Doug Sweetser pointed out in response to an earlier blog posting of mine that quantum field theory and General Relativity are great theories in the domains in which they are valid. He posed a question in my mind which has concerned me much more than any other raised in relation to my paper on the Winnower (Hontas Farmer, Quantum gravity by relativization of Quantum Field Theory., The Winnower1:e140751.17561 (2014). DOI:10.15200/winn.140751.17561) I restate it here as follows.
General Relativity and Quantum field theory are not consistently unifiable. They are both great theories in their domains, but incorporating one into the other does not work because neither is truly fundamental.
This is a huge problem for any program to unite General Relativity with quantum field theory. Weather it is the way we have tried for 100 years, by quantizing GR or the approach I proposed making local QFT into a ingredient of GR. Sure we may be able to get to a point where we can make calculations with such a model. So what? Would such models tell us anything we don't know already? No. By definition they simply give us the results we already know but they do it while explaining how we can have a world where most if it is well explained by two very different theories. That is the only benefit of such a unification.
What is needed is a candidate final theory. I have no idea of it's precise form but here is what I would expect.
- The final theory of nature should be valid on any and all length scales from at least Planck Length to the Hubble Length. Maybe even a wider range than that.
- The final theory of nature should be independent of any background or underlying structure of any kind. This means it will be abstract in it's most fundamental form.
- It should be like M-Theory. In the sense that M-Theory makes a number of predictions about both fundamental particles and the nature of the universe as a whole. All of this derives, essentially, from one of the most common and natural phenomena in physics, vibrations.
Enter M-Theory
M-theory is an already existing and widely studied model for a fundamental theory. In this theory everything is an extended vibrating object called a D-brane. D is the number of dimensions. a 1 brane would be a line or a string. a 2 brane would be a plane and so on. These go all the way up to 11 dimensions.
