How Can We Understand the Concept of Universe's Temperature?

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SUMMARY

The discussion centers on understanding the concept of the universe's temperature, highlighting that the universe is not in thermodynamic equilibrium, which prevents it from having a single temperature. Instead, an average temperature can be derived from the temperatures of various celestial bodies, including stars and planets. The cosmic microwave background radiation is crucial for this understanding, with a current measurement of approximately 2.7 degrees Kelvin, reflecting the universe's early hotter state. The presence of hot spots, such as stars, and cold spots, like black holes, further complicates this concept.

PREREQUISITES
  • Understanding of thermodynamic equilibrium
  • Familiarity with cosmic microwave background radiation
  • Knowledge of celestial bodies and their temperatures
  • Basic principles of cosmology
NEXT STEPS
  • Research cosmic microwave background radiation and its significance in cosmology
  • Study the concept of thermodynamic equilibrium in astrophysical contexts
  • Explore the temperature variations among different celestial bodies
  • Investigate the methods used to calculate the average temperature of the universe
USEFUL FOR

Astronomers, astrophysicists, cosmologists, and anyone interested in the thermal properties of the universe and its celestial bodies.

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The universe is mostly empty, how can we understand the concept of temperature of the universe?

Thanks
 
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Why is "mostly empty" a problem? A tank of gas at 1 psi is also "mostly empty", yet it has a temperature.

The bigger problem to me seems to be that the universe is not in thermodynamic equilibrium, so it doesn't have a single temperature. The best you can hope to talk about is an average.
 
Vanadium 50 said:
Why is "mostly empty" a problem? A tank of gas at 1 psi is also "mostly empty", yet it has a temperature.

The bigger problem to me seems to be that the universe is not in thermodynamic equilibrium, so it doesn't have a single temperature. The best you can hope to talk about is an average.

Thank you.
So the average temperature of the universe must be calculated based on the temperatures of all the stars, planets, satellites etc.. while considering the vastness of the universe?
 
Pixel...suggest you read about cosmic microwave background radiation..it reflects the early universe was a lot hotter and today measures 2.7 degrees Kelvin...on cosmological scales it is extraordinarily homogenous...wikipedia as an accessible source...but as noted there are hot spots like stars (our sun is one ) and cold spots (like black holes)...
 

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