Is vacuum a good conductor of heat?

Answer 1

Heat is the transfer of energy from one object or substance to another. There are three types of heat transfer - conduction, convection, and radiation.

Conduction requires that the first object (or substance) be in direct physical contact with the second. A vacuum between the substances prevents this type of heat transfer, which is why double-paned windows are evacuated between the panes to reduce heat transfer to the outside.

Convection occurs when atoms or molecules move in fluids (gases or liquids), and carry the kinetic energy of molecular motion with them. Since a vacuum doesn't contain any atoms or molecules, convection will not occur in a vacuum. Technically, a vacuum would allow atoms and molecules to convect through it, but then it wouldn't be a full vacuum.

Radiation is energy transfer by electromagnetic waves (light). Light does not require a medium to propagate and will travel perfectly well through a vacuum, which is how the energy of the Sun is transferred to the Earth. So heat can be transferred through a vacuum by radiation.

Answer 2

Transferring heat by conduction requires contact between the systems supplying and absorbing heat. In a complete vacuum, there would be an absence of anything to be in contact with - so a perfect vacuum would not allow any heat to be conducted. On the other hand, a perfect vacuum would have nothing interfering with the transfer of heat by radiation.