Heat transfer mechanisms include conduction, convection, and radiation, with radiation allowing heat to flow from cold to hot under certain conditions. While heat typically flows from hot to cold, radiation can result in a colder body receiving more energy than it emits when both are emitting infrared radiation. The Stefan-Boltzmann law indicates that the net energy transfer is generally from the hotter object to the colder one, despite both radiating photons. However, if the colder body is transparent to infrared, it may complicate the energy transfer dynamics. Overall, while spontaneous heat flow from cold to hot is not observed without work input, it is theoretically possible under specific circumstances.
