Why does heat flow from a hotter object to a colder object?

In physics, heat is defined as energy in transit, transferred between bodies due to a difference in temperature. The flow of heat from a hotter object to a colder one is a fundamental consequence of the second law of thermodynamics.12

Specifically, the second law dictates that a process whose only final result is the transfer of heat from a body at a given temperature to a body at a higher temperature is impossible. While individual molecular collisions are reversible, the macroscopic flow of heat is governed by statistical probability. In a system with a vast number of molecules, it is overwhelmingly probable that energy will distribute itself toward thermal equilibrium, where temperatures are uniform, rather than spontaneously concentrating into a hotter body.23

At the microscopic level, this transfer occurs through mechanisms such as conduction, convection, and thermal radiation, where molecules or electromagnetic waves convey energy from regions of higher kinetic energy to those of lower kinetic energy.435