Fractals in Physics  

In General
* History: 1915, J Perrin, Brownian motion and snowflakes; 1972, K Wilson, Scale invariance in phase transitions and renormalization group; 1980s, Cosmology, diffusion-limited aggregation, dielectric breakdown.
* Kinematical description: Fractal geometry; Notice that physical fractals are usually random.
* Models for fractal growth: Ising model; Dielectric breakdown; Critical percolation clusters.
* Goals: Develop new concepts, related to self-organization, irreversibility and non-ergodicity, to understand the origin of fractal structure.
* Applications: Aggregation; Diffusion; Percolation; Chaotic dynamics [coordinate-independent indicator].
@ General references: Amann et al ed-88; Pietronero PRP(89) [growth]; Hurd AJP(88)nov-RL; Gouyet 96; Addison 97; Aguirre et al RMP(09) [fractal basins in non-linear dynamics].
@ And quantum mechanics: Cannata & Ferrari AJP(88)aug [particle paths]; issue CSF(94)#3; Kröger PRP(00); Wójcik et al PRL(00)qp [fractal wave functions].
@ Random fractal networks: Nakayama et al RMP(94) [dynamics and scaling].
@ Related topics: Porter gq/02 ['fractafolds' as spacetime structure]; Ishikawa & Suzuki PhyA(04) [breaking of fractal distribution]; Liaw & Chiu PhyA(09) [fractal dimension of a time sequence].
> Related topics: see electromagnetic fields; phase transitions; stochastic processes; thermodynamical systems; turbulence.

Gravitation and Cosmology > s.a. cosmology; quantum spacetime.
* Fractal spacetime: One motivation is obtaining a discrete spacetime that is invariant under the renormalization group.
* Galaxy distribution: A fractal structure in the distribution of luminous matter up to about 5–15 Mpc has been seen and is accepted by most of the community; 1995, L Pietronero and collaborators have been claiming for years that at all observed scales the pattern continues, and that there is no evidence of homogeneity at any scale; Although Pietronero et al seem to have done the best analysis of the galaxy distribution, there would remain the puzzle of why the cosmic microwave background is so isotropic, and the dark matter distribution is unknown; 2004, The consensus is that the distribution does become homogeneous above 100 Mpc or so.
* Inside the Milky Way: There is some evidence that the interstellar matter in our galaxy is fractally distributed as well.
@ Galaxy distribution: Ribeiro in(94)-a0910; Sylos Labini et al ap/97-in, PRP(98)ap/97, ap/98; Gabrielli et al EPL(99)ap/98 [gravitational force]; Terazawa MPLA(98); Combes ap/99-in; Pietronero & Sylos Labini ap/99-in, ap/00-in; Baryshev ap/99-in [rev]; McCauley Frac(98)ap/00; Ribeiro GRG(01)ap; Baryshev & Teerikorpi 02 [I].
@ Fractal spacetime: Crane & Smolin NPB(86); Englert FP(87); Svozil JPA(87) [quantum field theory and regularization]; Nottale IJMPA(89), 93, CSF(94); Ambjørn & Watabiki NPB(95)ht [dimension from 2-point function]; Kobelev ht/00 [multifractal]; Castro et al ht/00 [?]; Castro CSF(01)ht/00 [and non-commutative geometry]; Lauscher & Reuter JHEP(05) [in asymptotically safe gravity]; Agop & Gottlieb JMP(06) [gravity]; > s.a. quantum groups.
@ Fractal spacetime, consequences: Hill PRD(03)ht/02; Iovane CSF(04)ap/03 [G(t), a··]; Shapovalova G&C(03) [metric fluctuations]; Goldfain CSF(04) [and gauge hierarchy problem], CSF(05) [and unified field theory].

Other Areas > s.a. random walk.
* Examples: Crystal growth, forest fires, fibrillations.
@ Geology / geophysics: Turcotte 92 [r PT(93)may]; issue CSF(04)#2.
@ Physiology: Bassingthwaighte et al 94; West & Deering PRP(94); Brú et al PRL(98) [tumor growth].
@ Related topics: Falkenberg & Namuth 98 [art, Pollock, pw(99)oct].


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