Critical Opalescence

Plate 15 speaks for itself: “At the critical point, every scale matters.”

The Physics

Near a liquid–gas critical point density fluctuations of all sizes appear. When they reach the wavelength of light the fluid scatters strongly and turns milky. The correlation length diverges with a universal exponent shared with the 3D Ising model.

ξ ∝ |T − T_c|^(−ν)

• ξ: correlation length, m
• T: temperature, K
• T_c: critical temperature, K
• ν: critical exponent, dimensionless

CO₂: T_c = 304.13 K, p_c = 7.3773 MPa. 3D Ising class: ν ≈ 0.630.

Sources

• A. Pelissetto, E. Vicari, Phys. Rep. 368, 549 (2002).
• R. Span, W. Wagner, J. Phys. Chem. Ref. Data 25, 1509 (1996).

On the poster

Plate 015, “Critical Opalescence”: the pixel-art plate with its slogan “At the critical point, every scale matters.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.