Casimir Effect: Vacuum Fluctuations
Between two conducting plates, only discrete standing-wave modes fit. The mismatch with continuous free-space modes creates a net inward radiation pressure — an attractive force from nothing.
Allowed modes between plates: k_n = nπ/d, n = 1,2,3,...
Casimir pressure: P = −π²ħc / (240 d⁴). Force per area on 1μm² plate shown.
Zero-point energy density outside > inside → net inward push.