Kinetic surface roughening

Why does a growing surface get rough — and does a tiny change in the local growth rule change HOW rough it gets?

How the lab tests it

Drop particles on a 1-D line of columns under three rules at once (land-on-top, KPZ/RSOS, and relax-to-lowest-neighbour) and measure each interface's roughening exponent β from the log-log slope of the width W(t) ∝ t^β, averaged over many regrown cycles.

What it checks

three distinct universality classes selected by the rule alone: random deposition β = ½ (uncorrelated columns — exact by construction), KPZ/RSOS β ≈ ⅓ (the Kardar–Parisi–Zhang class), and Edwards–Wilkinson relaxation β = ¼ (diffusive smoothing). Measured ⟨β⟩ ≈ 0.50 / 0.30 / 0.24: RD nails ½; KPZ sits a few % below ⅓ — a stable corrections-to-scaling bias of this RSOS estimator that does NOT shrink as the lattice grows, not a textbook mismatch; EW is consistent with ¼ at this size (it carries log corrections in 1+1 D)