It amuses me greatly when an author waxes lyrical about ‘the cold deeps of space’! I just have to crack up. What is worse, some astronomers who should know better also shiver when talking about space.
Let’s get real, okay? Space is mostly vacuum. It is neither cold or hot…generally.
Let’s talk about temperature and what it is. Only an object can be described in terms of temperature, or kinetic energy of a body in motion, and that includes atoms if someone wants to get picky, but atoms are objects. There are only three ways that heat can be transferred: conduction, convection and radiation. Heat a pan and gradually, the entire pan will get hot. That’s conduction. A circulating liquid will over time distribute heat evenly within a given volume. That’s convection. Absorption of electromagnetic energy or subatomic particles constitutes radiation, the only mechanism where energy can be transferred in space.
That is our key! A body in space, an astronaut or spacecraft, will radiate in a temperature gradient. Simply put, unless an object in space is close to absolute zero—2.7 Kelvin, or 270.45C—it will radiate its energy into the surrounding vacuum. When an object absorbs more photons than it emits, it heats up. If it emits more photons than it absorbs, it cools down. Someone will say that space IS cold because of the Cosmic Microwave Background Radiation temperature of 2.73 Kelvin, the remnant of the theoretical Big Bang. Not so! What is being measured is not the temperature of space, but the energy of the omnipresent electromagnetic radiation.
The interstellar medium is mostly vacuum with an average distribution of one to six atoms per cubic meter, and they move very slowly. Why? They don’t have much energy. It has been radiated away long ago. There are regions of much hotter gas in supernova remnants that can reach temperatures of six million degrees C. However, that does not mean that space is that hot! It is a combination of photons, atoms and molecules that contain that energy which are hot—because they are objects!
If you are a writer, do yourself a favor. Don’t talk about the cold of space! Talk about cold objects. As for those cosmologists…check up your basic physics.