"Entropy and the long-time evolution of materials" - Simulating the microstructural evolution of materials using atomistic methods remains one of the most enduring challenges in computational materials science. This is because many relevant nanoscale processes, e.g. defect nucleation, diffusion, and reaction, occur very slowly (μs-s) on typical vibrational timescales (ps). Systems where the relevant free-energy barriers possess important entropic contributions are especially difficult to investigate. Using two examples, I will show how advanced simulation techniques can address these challenges. First, I will present a recent methodological advancement that enables the direct simulation of systems with large configurational entropies over long timescales. This formalism opens the door to innovative temporally-multiscale simulation methodologies. Second, I will describe a novel mechanism by which vibrational entropy strongly stabilizes nanoscale voids in materials under tension. This leads to an unconventional behavior whereby the dislocation nucleation rate decreases with increasing temperature.