Light-scattering observations of long-range correlations in a nonequilibrium liquid

We have performed small-angle Rayleigh-scattering measurements in toluene subject to a stationary temperature gradient. The experiments demonstrate the existence of long-range equal-time correlations through a strong enhancement of the thermal fluctuations and they also reveal a negative contribution at short time scales from the viscous fluctuations in agreement with the theoretical predictions. The experiments confirm that both effects vary with ({∇}T)²/q⁴, where {∇}T is the temperature gradient and q the wave number of the fluctuations.