How does space have a temperature?

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    Space Temperature
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Discussion Overview

The discussion centers on the concept of temperature in the context of space, particularly addressing whether space itself can be said to have a temperature and what that implies about the nature of temperature and radiation in a vacuum. The scope includes theoretical considerations and conceptual clarifications regarding temperature, blackbody radiation, and the cosmic microwave background (CMB).

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how space can have a temperature if it is considered a perfect void, suggesting a need for clarity on what is being measured in deep space.
  • Another participant argues that defining temperature solely as the average translational kinetic energy of matter is misleading, noting that the temperature of space (~2.7K) refers to the blackbody radiation present, specifically the CMB.
  • A different viewpoint states that space does not have a temperature in the traditional sense, but mentions that the background electromagnetic radiation has an average temperature of around 3 K, which is a blackbody temperature. This participant explains that an object in free space will cool to this temperature due to radiation.
  • A later reply acknowledges the previous points and suggests that the discussion is focused on the energies associated with photons in space.

Areas of Agreement / Disagreement

Participants express differing views on whether space can be said to have a temperature, with some emphasizing the role of blackbody radiation and others questioning the applicability of traditional temperature definitions in a vacuum. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations in the definitions of temperature being used, as well as assumptions about the nature of space and radiation that are not fully explored. The discussion also highlights the dependence on the context in which temperature is defined.

cragar
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If temperature is the average translational kinetic energy of matter , then how does space have a temperature what are we measuring in deep space , that's if space if a perfect void.
 
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Saying that temperature is the average translational kinetic energy of matter is misleading, since this is not the definition of temperature, it just happens to be true for certain systems. When we speak of the temperature of space (~2.7K), it means that the blackbody radiation that fills space (the CMB) has a Planckian spectrum with that temperature.
 
Space does not have a temperature in that sense. The background EM of open space has an average temperature of around 3 K--but note that this is a blackbody temperature. If an object is allowed to float in free space with no other incoming source of energy, it will eventually cool to this temperature by radiating away its inherent thermal energy. It can't get cooler than that because the ever-present background radiation will keep it at 3 K.
 
i see thanks for your answers.

so we are looking at the associated energies of the photons.
 
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