What mode of heat transfer does not necessitate direct contact between a warmer and cooler substance?

The correct answer is radiation, which is the mode of heat transfer that does not require direct contact between a warmer and cooler substance. Radiation involves the transfer of energy through electromagnetic waves, such as infrared radiation, which can travel through a vacuum. This is how the Sun's rays can warm the Earth despite the vast distance and the vacuum of space between them.

In contrast, conduction and convection both require a medium and often involve direct contact. Conduction occurs when heat is transferred through a material, requiring molecules to collide with each other. Convection involves the movement of fluid (liquid or gas) and carries heat through the motion of the fluid itself, necessitating movement and contact between different layers of the fluid.

Absorption, while it can describe a process related to the uptake of energy, is not a mode of heat transfer in itself but rather refers to how materials take in radiation or energy. Thus, radiation stands out as the only method that allows heat transfer without physical contact between objects, supporting its classification as the correct answer.