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

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Discussion Overview

The discussion revolves around understanding the concept of the universe's temperature, particularly in the context of its vast emptiness and the implications of thermodynamic equilibrium. Participants explore theoretical and conceptual aspects of temperature as it applies to the universe as a whole.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how to conceptualize the universe's temperature given its "mostly empty" nature.
  • Another participant argues that being "mostly empty" is not inherently problematic, comparing it to a tank of gas that can still have a temperature despite being under low pressure.
  • Concerns are raised about the universe not being in thermodynamic equilibrium, suggesting that it does not possess a single temperature but rather an average temperature based on various components.
  • A later reply emphasizes the need to calculate the average temperature of the universe by considering the temperatures of stars, planets, and other celestial bodies while acknowledging the universe's vastness.
  • Another participant introduces the concept of cosmic microwave background radiation, noting that it indicates the early universe was much hotter and currently measures about 2.7 degrees Kelvin, while also mentioning the homogeneity on cosmological scales and the existence of hot and cold spots.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the universe's emptiness for its temperature, and there is no consensus on how to define or measure the universe's temperature, indicating ongoing debate and exploration of the topic.

Contextual Notes

Participants highlight the complexity of defining temperature in a non-equilibrium system and the need for averaging over various celestial bodies, which may introduce limitations in understanding the concept fully.

pixel01
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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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