Talk:Universality (dynamical systems)

Universality and SOC in piles of sand

(This comment also applies to the notes on universality in the scale invariance article.)

Avalanches in piles of sand are not examples of self-organized criticality, or not in general at any rate. You're mixing up a metaphor used to visualise a theoretical model with a real system (to be fair, you're far from the only ones:-).

More urgently, I don't think the sandpile model per se is an "example" of universality. Universality is about systems with diverse details sharing the same common dynamics at heart. To give an example, with the sandpile model, you can drive it continuously (all sites being continuously increased until one breaks threshold), or you can have the toppling consist of resetting to zero and equally sharing all the energy among the neighbours (this needs a continuous "sand" value of course). These two alternative dynamics have the same exponents, they belong to the same universality class as the original sandpile model. But ... change it so that both the driving is continuous and the toppling consists of resetting to zero and evenly redistributing among neighbours, and you are in a different universality class, that of the Olami-Feder-Christensen model.

See what I'm getting at? Examples of universality are not given by single systems, they're given by different systems that can be shown to be equivalent at heart. —WebDrake 01:46, 29 December 2006 (UTC)

https://en.wikipedia.org/wiki/Self-organized_criticality

Has the correct reference, if anyone would it. Reference 3.

Smalley, R. F. Jr; Turcotte, D. L.; Solla, S. A. (1985). "A renormalization group approach to the stick-slip behavior of faults". Journal of Geophysical Research. 90 (B2): 1894. Bibcode:1985JGR....90.1894S. doi:10.1029/JB090iB02p01894. S2CID 28835238.

Signed - George Bernard Shaw — Preceding unsigned comment added by 49.184.24.3 (talk) 16:21, 25 April 2022 (UTC)

Overlap with article on renormalisation group, and lack of technical detail

Some articles on statistical mechanics link to this page ("Universality (dynamical systems)"), whereas others link to "universality class", which redirects to renormalisation group. Both seem to be talking about the same concept - should they be merged or something?

But also, neither article seems to go into a lot of detail. This is a little frustrating - there are references all over Wikipedia to the concept of universality classes, but both this article and the renormalisation group are purely descriptive when it comes to universality classes. They say there are only a limited number of them, and outline some of their properties, but they don't go into the technical details of why this should be the case, or even give any idea of what kind of mathematical object a universality class is. I guess either this article or the renormalisation group could do with one of those "needs attention from an expert" signs?

(Unfortunately I am neither an expert on the subject nor particularly experienced with Wikipedia, so I probably can't help much. I'm just someone who's looking for this information and can't find it.) 240F:7C:FC1A:1:D50E:E423:8FA7:F411 (talk) 01:44, 20 December 2014 (UTC)