arrow of time

The "arrow of time" refers to the observation that time flows in one direction, from past to future. This is most evident in everyday macroscopic phenomena, such as a glass of warm water spontaneously becoming hot with ice, which violates the second law of thermodynamics. While fundamental physical laws are largely time-symmetrical at the microscopic level, the second law of thermodynamics, which states that entropy (disorder) always increases in isolated systems, provides a statistical basis for the arrow of time. This means that while theoretically possible, it is extremely improbable for systems to spontaneously move from a state of higher entropy to lower entropy.1234