Considering only temperature and disrespecting the rest, would I feel cold or hot with my hand in the vacuum?

Asked by: Filipe Andrade

Answer

Your hand 'feels' hot or cold when heat is transferred to or from it, respectively. There are only 3 ways that heat can be transferred--by conduction, convection, or radiation. Only the third (radiation) can take place in a vacuum. That is how the Sun's energy is able to reach the Earth.

What your hand feels in a vacuum depends on the radiation falling upon it. For extreme examples, the vacuum a few thousand miles from the Sun's surface would feel very warm as it absorbs highly energetic photons. The vacuum in interstellar space, however, contains only background radiation close to absolute zero (-273 degrees C.). In that situation, your hand at body temperature loses more energy than it gains, and would feel cold.

Any material object at a temperature above absolute zero radiates energy. In the case of a vacuum chamber, the temperature of the chamber walls will determine the radiation environment. If they are above the temperature of your hand, your hand will absorb the radiation and feel warmth. If they are below your hand's temperature, your hand will feel coldness.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor