Heat transfer by radiation is faster than heat transfer by conduction because radiation can occur through a vacuum, while conduction requires the presence of a medium, such as a solid, liquid, or gas. Radiation is the transfer of energy through electromagnetic waves and does not require any medium to propagate, which means that radiation can occur even in a vacuum or through transparent materials.
On the other hand, conduction requires particles to transfer heat energy from one object to another. In a solid, this occurs through the transfer of kinetic energy from one molecule to another through direct contact, while in a liquid or gas, conduction occurs through collisions between molecules. This process of molecule-to-molecule transfer of heat energy is much slower than radiation and is limited by the physical properties of the medium, such as its thermal conductivity.
Therefore, heat transfer by radiation is faster than heat transfer by conduction because radiation can occur through a vacuum, and is not limited by the physical properties of a medium, while conduction is limited by the thermal conductivity of the medium and requires direct contact between molecules.