Widom Line

The Widom line is a concept in thermodynamics that describes a boundary in the phase diagram of a substance, extending beyond the critical point where a liquid and gas become indistinguishable. It marks the temperatures and pressures where the properties of the fluid—like density or heat capacity—change most rapidly, indicating a crossover between liquid-like and gas-like behaviors. Think of it as an invisible line guiding how the substance transitions smoothly from one state to another, helping scientists understand fluid behavior in extreme conditions without a sharp phase change.