The equation of state of non-relativistic energy

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SUMMARY

The equation of state for non-relativistic energy is characterized by a parameter w=0, indicating that pressure is negligible compared to energy density. In this context, the pressure of an ideal gas is directly proportional to temperature, while energy density relates to the mass of particles. When temperature is significantly lower than mass, pressure remains minimal. This discussion clarifies that the concept of pressure is consistent across general relativity, thermodynamics, and statistical mechanics, emphasizing that significant pressure arises only when particle velocities approach relativistic speeds.

PREREQUISITES
  • Understanding of non-relativistic energy concepts
  • Familiarity with the equation of state in cosmology
  • Basic knowledge of ideal gas laws
  • Awareness of general relativity principles
NEXT STEPS
  • Study the implications of w=0 in cosmological models
  • Explore the relationship between pressure and temperature in ideal gases
  • Investigate the transition from non-relativistic to relativistic gases
  • Learn about pressure concepts in general relativity versus classical mechanics
USEFUL FOR

Students of cosmology, physicists interested in thermodynamics, and anyone seeking to understand the relationship between pressure and energy density in different physical contexts.

Joey21
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I just have a quick question about a concept I think I haven't fully grasped from my cosmology course.

Why does non-relativistic energy have an equation of state with w=0?
Also, is the concept of pressure different in general relativity than in thermodynamics or statistical mechanics?
 
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No, it is the same concept. It is just that for normal non-relativistic matter, the pressure is negligible in comparison to the energy density. Consider an ideal gas and the pressure is going to be proportional to the temperature while the energy density is proportional to the mass of each particle. As long as the temperature is much lower than the mass, pressure is negligible (when temperature becomes comparable to mass you start reaching a relativistic gas behaving as radiation).
 
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Joey21 said:
Why does non-relativistic energy have an equation of state with w=0?
The model being used in this context is of a gas. The pressure of a gas is a function of the velocities of the individual particles that make up the gas. Those velocities have to be relativistic if the pressure is to be significant compared to the mass density.

Joey21 said:
Also, is the concept of pressure different in general relativity than in thermodynamics or statistical mechanics?
It's the exact same concept.
 
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Thanks for the quick replies! They will be a lot of help.
 

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