Is absolute zero energy a meaningful concept in relativistic thermodynamics?

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Discussion Overview

The discussion revolves around the concept of absolute zero energy within the framework of relativistic thermodynamics. Participants explore whether absolute energy can be defined, the implications of temperature measurements across different reference frames, and the relationship between temperature, energy, and vacuum states.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants suggest that energy is inherently relative, questioning if any measure of energy can be considered absolute.
  • One participant argues that vacuum energy is absolute and invariant across reference frames, proposing that it serves as a consistent baseline.
  • Another participant mentions that in General Relativity (GR), the stress-energy tensor and cosmological constant may be viewed as absolute, though their relationship with matter is complex and not fully understood.
  • There is a claim that zero temperature can be associated with absolute energy, but this is contested by others who assert that temperature is not absolute and only certain derivatives are observable.
  • Some participants express confusion regarding the definition of temperature and its relation to efficiency in thermodynamic systems, particularly in the context of absolute zero and the triple point of water.
  • It is noted that multiple formulations of relativistic thermodynamics exist, with no clear consensus on which is the most applicable or useful.

Areas of Agreement / Disagreement

Participants exhibit disagreement on the nature of absolute energy and temperature, with multiple competing views presented. The discussion remains unresolved regarding the definitions and implications of these concepts.

Contextual Notes

Participants highlight limitations in understanding the relationship between temperature and energy, particularly in the absence of general relativity. There are also unresolved questions about the definitions and measurements of temperature across different reference frames.

Who May Find This Useful

This discussion may be of interest to those studying thermodynamics, relativistic physics, or the philosophical implications of energy and temperature in different reference frames.

Zman
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Energy is considered a relative quantity.

Is there any measure of energy that is absolute?

If temperature is measured by measuring the frequency of the emitted photons then observers with different velocities would measure different temperatures.

But a body at absolute zero would not emit photons and therefore all observers would agree upon its temperature. Is this a case of energy that is absolute?

Or is zero energy (zero temperature) a meaningless statement?
 
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Yes, zero energy (vacuum) is the absolute thing. Vacuum is an invariant thing. It is the same in all reference frames. In the theory it is also so.

I am not sure that the temperature depends on the reference frame in a simple way because the body radiation becomes anisotropic there (more complicated).
 
In GR, the stress-energy tensor and cosmological constant (which may be considered a form of energy) are absolute. Observations indicate that our universe may be modeled by a solution of the equations of GR. However, GR also expects these energies to be associated with matter, and some aspects of the relation between GR and our current theories of matter are not understood. Look up "dark matter", and "dark energy".
 
Bob for short is correct in stating that zero temperature (energy is correct. Also, triple points of liquids (e.g., water) determine both a temperature and pressure scale. An absolute frequency scale can be determined by experimenters setting up in their own laboratory a measurement of hyperfine structure line of hydrogen (1420 MHz), and other atomic transition frequencies, and therefore determine doppler shifts, etc. of observed astronomical atomic transitions.
 
Temperature is not absolute. Only dX/dT is observable.

Same with vacuum energy in the absence of general relativity.
 
atyy said:
Temperature is not absolute. Only dX/dT is observable.

Same with vacuum energy in the absence of general relativity.
Why can't an absolute temperature scale be determined by absolute zero, and the temperature of the triple point of water, for example?
 
Bob S said:
Why can't an absolute temperature scale be determined by absolute zero, and the temperature of the triple point of water, for example?

Yes, I think you are right, and certainly I'm confused. As usually defined by the engine efficiency or dS/dE, temperature can't be negative or energy will not be conserved. What I'm not sure about is that there is some freedom in defining the relation between efficiency and temperature, and I'm not sure how free that is.
 
There are a few different formulations of relativistic thermodynamics out there, and I don't think there is a general consensus on which is the most useful.
 

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