Beyond the Earth, space is a hostile place for human beings. Near the stars, the temperature is very elevated, but this rapidly changes as we move away from the latter. In interstellar space, the temperatures are just above absolute zero (0 degrees Kelvin)
Why is the temperature so low?
The temperature of a body is the result of the movement and the collisions of the particles that form it and interact with it. It is in these particle collisions that energy, or heat, is transferred from one particle to another, making the body heat. For example, on Earth, the particles that form the atmosphere move relatively slow (they don’t contain much energy), but as there are zillions of them, and, consequently, there are lots of collisions, this maintains the planet hot.
However, in space, the number of particles is very reduced: about one atom every cubic meter. This implies that the atoms, even if they carry a lot of energy, they can’t transfer it to other atoms; therefore, the temperature is very low.
The temperature of space
The universe is gigantic, and the temperatures between different regions of space can vary enormously. Stars or quasars and incredibly hot places, but, what is the temperature of empty space?
As we have previously mentioned, in space, heat can’t be transferred through conduction or convection processes (because there isn’t matter). In space, heat can only be transferred in the form of electromagnetic radiation (light).
Cosmic Microwave Background Radiation (CMBR) is the remnant of the biggest explosion in the history of the universe: the Big Bang. The photons from the event that gave birth to space and time still travel through the universe and set the minimum temperature we can find in outer space.
The temperature of the CMBR, and so the one of the vacuum of space, is 2.73 degrees Kelvin (-270.42ºC or -454.75ºF) However, the universe hasn’t always been so cold. Indeed, the initial temperature of the cosmic microwave background radiation was about 3,000 degrees Kelvin. As the universe continues to expand, the temperature of space will be lower and lower.