amppatel said:
... the three methods are string theory (M-Theory), loop quantum gravity and one other. I can't remember the last :(:(
...
The difficulty that caused the blankout was you said method instead of road.
He does not present 3 already invented theories of QG. So you are not looking for a 3rd theory (to go with ST and with LQG).
He presents 3 directions from which one might come to find an (as yet unknown) theory.
And he gives
examples of people approaching from each of the three directions.
But in only two cases does the example involve a formal QG theory-under-construction.
The third direction is exemplified by Bekenstein and Unruh, who thought deeply about horizons and temperature and entropy----they came to unexpected conclusions about space and time and information. Conclusions which are fundamental and do not depend on any particular theory setup or method or scheme.
A. One can come at QG from General Relativity
The example he gives is how he and his friends invented LQG, by taking seriously the ideas essential to General Relativity. (ideas like there is no fixed preordained geometry, geometry is the gravitational field itself, and that individual points are nothing but nametags given to particular relationships among events or among the field lines. Apart from relationships there is no space.)
B. One can come at QG from conventional Quantum Mechanics
The example he gives is the development of String theoretics. I should say that in both A and B the examples are just that, examples. He might have chosen some other QG method to illustrate either
road. The aim is to describe how your thinking is influences by the road you come on, and the direction you come from.
C. One can come at QG by asking original questions that transcend any particular methodology.
The examples he gives are how Bekenstein and Unruh approached it. By unusual thought experiments they were able to conclude things about the temperature and entropy of a black hole and the temperature felt by an observer simply because he is accelerating.
Another example is so-to-speak a holographic idea, that the information about what is inside a volume can somehow be represented on the surface surrounding the volume. As I recall he discusses that too.
He is showing you three roads or three ways to approach this still unknown thing.
He is not presenting three already formed methods for you to "buy". At least that is how I recall it. It is a fine book. It would be worth reading over again!
