Monday, August 07, 2006

Smolin on relational physics

Lee Smolin is a process physicist who I find very interesting to read. The below is from an article featured in Brockman's The Third Culture: Beyond The Scientific Revolution - which you can link to here - in which he talks about a relational model of physics as having the potential to provide a theoretical basis for the elusive quantum theory of gravity. Bold italics are my emphasis:

[A]t the Planck scale, which is twenty powers of ten smaller than an atomic nucleus, space looks like a network or weave of discrete loops. In fact, these loops are something like the atoms out of which space is built. We're able to predict that — just as the possible energies an atom can have come in discrete units — when one probes the structure of space at this Planck scale, one finds that the possible values the area of a surface or the volume of some region can have also come in discrete units. What seems to be the smooth geometry of space at our scale is just the result of an enormous number of these elementary loops joined and woven together, as an apparently smooth piece of cloth is really made out of many individual threads.

Furthermore, what's wonderful about the loop picture is that it's entirely a picture in terms of relations. There's no preexisting geometry for space, no fixed reference points; everything is dynamic and relational. This is the way Einstein taught us we have to understand the geometry of space and time — as something relational and dynamic, not fixed or given a priori. Using this loop picture, we've been able to translate this idea into the quantum theory.

Indeed, for me the most important idea behind the developments of twentieth-century physics and cosmology is that things don't have intrinsic properties at the fundamental level; all properties are about relations between things. This idea is the basic idea behind Einstein's general theory of relativity, but it has a longer history; it goes back at least to the seventeenth-century philosopher Leibniz, who opposed Newton's ideas of space and time because Newton took space and time to exist absolutely, while Leibniz wanted to understand them as arising only as aspects of the relations among things. For me, this fight between those who want the world to be made out of absolute entities and those who want it to be made only out of relations is a key theme in the story of the development of modern physics. Moreover, I'm partial. I think Leibniz and the relationalists were right, and that what's happening now in science can be understood as their triumph.


The picture that emerges from both relativity and quantum theory is of a world conceived as a network of relations. Newton's hierarchical picture, in which atoms with fixed and absolute properties move against a fixed background of absolute space and time, is quite dead. This doesn't mean that atomism or reductionism are wrong, but it means that they must be understood in a more subtle and beautiful way than before. Quantum gravity, as far as we can tell, goes even further in this direction, as our description of the geometry of spacetime as woven together from loops and knots is a beautiful mathematical expression of the idea that the properties of any one part of the world are determined by its relationships and entanglement with the rest of the world.


Psybertron said...

Not sure Smolin's metaphor of woven threads at the Planck scale holds much water any more, ....

.... but the point you highlight is one I keep making, that all (observable) physics is fundamentally about interactions / differences / exchanges of information.

Psybertron said...

You also included this quote ...

"This doesn't mean that atomism or reductionism are wrong, but it means that they must be understood in a more subtle and beautiful way than before."

This is kinda Pirsig's point in your Kharmic suffering post. You can "explain" anthropology and evolutionary psychology in atomistic physical terms, and it help understand what they are, but it's pretty useless to describe how things will work (predictably / causally) at that level, where everything is emerged layer upon layer

Paul Turner said...

It is the relational emphasis of Smolin that I find most interesting. Also, his Darwinian approach to the evolution of inorganic universes is intriguing. Out of interest though, which metaphor describing the world at the Planck scale does "hold water" these days? There are a lot of theoretical physicists about. Who's the daddy?

Regarding reductionism, it is really "greedy reductionism" I find problematic. So I agree that you can in principle describe anything in inorganic terms but you may not get anything approaching a satisfying or useful explanation.

Psybertron said...

You're correct of course about metaphors holding water - just didn't want any presumtion that Smolin's example was in any sense "better".

The key point though is the pragmatic one.

Emergent / atomistic / inorganic explanations may actually be very satisfying and useful - if your objective is more scientific research and understanding, but of little satisfactory value at macro scale "causal explanations and predictions".

"Perfect, 10/10, useless." as my old mentor used to say (every day).

But you are already ahead of that game.

Paul Turner said...

It was actually a genuine question about which theoretical physicist was "out in front" at the moment.

Regarding inorganic explanations, of course they can be useful and satisfying, and sometimes quite beautiful. I just doubt whether they have much to contribute to anthropology. So I think we agree.

John said...

These two essays provide a unique understanding of the inherently relational quality implicit in quantum physics.

and the same idea/revelation stated via photography.