# Quantum Gravity

## About Me

**Name:**nige

Currently designing secure active server page (ASP) front ends for client SQL databases. In 1982 I began programming in basic, and at college learned Fortran while a physics undergraduate a decade later. Afterwards, I switched from mainstream physics and mathematical education to part-time programming student, while working in a series of jobs including four years in credit control. www.quantumfieldtheory.org http://glasstone.blogspot.co.uk/2015/07/capabilities-of-nuclear-weapons.html/ http://www.math.columbia.edu/~woit/wordpress/?p=273#comment-5322. http://www.math.columbia.edu/~woit/wordpress/?p=353&cpage=1#comment-8728. http://www.math.columbia.edu/~woit/wordpress/?p=215#comment-4082.

## Previous Posts

- New comment on Dr Motl's blog
- Dr Lubos Motl and WMAP
- String theorist calls all alternatives "crackpot"
- Dantas discussion forum for Smolin lectures
- Dr Dantas has LQG reading list...
- Introduction to Quantum Gravity, Parts 3 and 4
- Spin Foam Vacuum dynamics
- Lee Smolin disproves his critics politely
- Why LQG spin foam vacuum is better than Strings!
- Spin foam vacuum LQG versus false 'stringy theory'...

## Thursday, March 30, 2006

## 1 Comments:

In last September’s issue of La Recherche there is a dossier dedicated to Lee Smolin and his criticism to string theory.

When looking at string theory, from a particle physicist’s point of view, it might seem to make sense, since one is basically replacing the notion of point particle with the notion of string, the basic physical reasoning still following the main notions and toolkits with which mechanics has always worked.

Physics has developed around five fundamental mechanical notions the notion of motion, the notions of space and time (time being still problematic for physics), the notion of energy and the notion of force. All these notions come together when dealing with the motion of mechanical bodies, and all these notions have been incorporated in how we think about problems within classical mechanics. The path integral formalism extends this reasoning, in a natural way, to the realm of quantum mechanics.

However, although it may seem natural to use these notions in the search for a unified field theory, does it make sense to use them? Can we use these familiar mechanical notions when dealing with Planck-scale physics?

One of the greatest problems of string theory is the difficulty in getting rid of a space-time background. If the string moves, then that motion presupposes a space-time where it can move. To provide for model of a string that, by moving, creates space-time becomes a very difficult task, if at all possible.

We cannot consider the concept of motion as primitive, since the motion presupposes a topos (in the original sense of the word from the Greek, of "place of the body") and a change of topos, time resulting from the fact that change temporalizes the thing’s topos.

At a Planck scale we may not even have such a thing as a motion, but only a dynamics by which relational patterns of space (or even of information) change, and this change is not a displacement but rather a change in configuration, a change that temporalizes the patterns.

In this perspective, the things and their topos come simultaneously, as an individuation of patterns that persist through that temporalization. This sense of motion as pattern percolation may be a better account of how motion may emerge from Planck-scale geometry. This view of Planck-scale geometry and motion may be explained by the line of research of Bilson-Thompson, Markopoulou and Smolin (http://arxiv.org/abs/hep-th/0603022).

Since string theory proceeds from an already classical view of space-time, and critically depends upon the classical concept of motion as a trajectory in space-time, it may be more difficult, for this theory, to provide for a quantum model of space-time at the Planck-scale, or even for an explanation of motion, as emergent from this Planck-scale space-time.

Carlos Pedro Gonçalves

(Mathematics Researcher at UNIDE)

Post a Comment

<< Home