Temperature in space, approximately 2.7K, is derived from the cosmic microwave background (CMB) radiation, which has a Planckian spectrum. This temperature measurement does not imply that space itself has a temperature, as space is largely a vacuum. The average background electromagnetic radiation in open space is around 3 K, representing a blackbody temperature. Objects in free space will cool to this temperature by radiating their thermal energy, but cannot drop below it due to the persistent background radiation. Thus, the concept of temperature in space is tied to the energy of photons rather than matter itself.
