What do Wilson loops and spin networks mean physically?

[marlon]

Hi, can anyone give me a clear definition of the following two things

1) Wilson loop
2) Spin network (invented by Penrose, right?)

What do these quantities fysically mean?

PS : can anyone explain me what the term LOOP means in Loop quantum gravity. To what does it refer ?

regards
marlon

 

[humanino]

Hey Marlon !

Very interesting issues...that I don't want to pretend I undestand though But I want to advise you a very good paper on quantum gravity by Carlo Rovelli. This is an entire book, whose draft version is available at :
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html

Anything I could say would be more accurate in this paper. Enjoy !

 

[marlon]

Hey Marlon !

Very interesting issues...that I don't want to pretend I undestand though But I want to advise you a very good paper on quantum gravity by Carlo Rovelli. This is an entire book, whose draft version is available at :
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html

Anything I could say would be more accurate in this paper. Enjoy !

grazie, humanino

how is life out there in Paris?

 

[humanino]

je vous en prie Marlon, c'est mon plaisir

Another (shorter) paper
http://www.wordiq.com/definition/Loop_quantum_gravity
where one can read :

As a theory of quantum gravity, LQG is the main competitor of string theory, albeit a distant one: stringy people outnumber loopy people by a factor of roughly 10 and stringy papers outnumber loopy papers by a factor of roughly 50.

Should this move to another forum (LQG !)?

 

[humanino]

how is life out there in Paris?

I took one week out of my thesis. Back to Switzerland Jura ! This is also how I come to have time to read useless things such as LQG

Could someone elaborate on Penrose and spin network ?

 

[humanino]

I give here the definition of the Wilson loop given by Zinn-Justin in his "QFT & Critical phenomena"

section 33.3 "Wilson's loop and confinement" (p735)
$$W(C)=\left\langle e^{-ie \oint_{C} A_\mu(s) ds_\mu } \right\rangle$$
with C a closed loop in space-time. This is a functional integral, and represents the parrallel transporter along the closed loop.

As for spin network :
http://www.wordiq.com/definition/Spin_network