Meaning of cosmological constant ?

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Discussion Overview

The discussion revolves around the cosmological constant, specifically its dimensionality and potential meanings associated with its value. Participants explore its implications in cosmology, particularly in relation to the evolution of the universe and the concept of characteristic distances or radii.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the meaning of the cosmological constant's dimensionality, suggesting it points to a characteristic distance, possibly the radius of the universe.
  • Another participant challenges the initial claim about the dimensions of the cosmological constant, asserting that it has units of energy rather than 1/R^2 and that its energy density does not evolve as suggested.
  • A third participant confirms the dimensions of 1/L^2 in the context of general relativity and suggests looking beyond general relativity for deeper insights into the cosmological constant.
  • Another participant elaborates on the units of energy density in geometric units, explaining how the cosmological constant contributes to the stress-energy tensor and has units of reciprocal area.
  • A later reply reiterates the dimensionality of the cosmological constant and references a specific section of literature for further exploration.

Areas of Agreement / Disagreement

Participants express differing views on the dimensionality and implications of the cosmological constant, indicating that multiple competing interpretations remain unresolved.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the cosmological constant's behavior over time and its relationship to curvature and energy density, which are not fully resolved.

notknowing
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Incredibly much has been written about the cosmological constant and all its implications on the evolution of the universe. I want to ask however a more basic question about it. The cosmological constant has the dimension of 1/R^2. So supposing this constant is non-zero, its value points to the existence of some characteristic distance or radius. The Schwarzschild radius for instance has a clear understandable meaning but what could be the meaning of the radius associated with the cosmological constant? The only thing which comes to (my) mind is the radius of the universe itself. What other opinions exist (or are described in literature - related to "radius")?


Rudi Van Nieuwenhove
 
Space news on Phys.org
The cosmological constant has a value whose units are energy. I'm not sure what you mean by saying 'it has the dimensions of 1/R^2"?

If you mean that the energy density of the cosmological constant evolves as 1/R^2 where R is the scale factor that is incorrect. Curvature evolves in that way (in the way it is represented in cosmology) but the cosmological constant, unsurprisingly, remains constant for all time.
 
The dimensions of 1/L2 for the cosmological constant are correct in the usual geometrized unit system of general relativity. To find a deeper meaning to such a length scale one should go beyond general relativity, see for example section 7 of Padmanabhan's Cosmological Constant - the Weight of the Vacuum.
 
It might help to point out that in geometric units, energy density (and sectional curvatures, e.g. the components of the Riemann curvature tensor) have the units of reciprocal area. Since Lambda contributes a diagonal term to the stress-energy tensor of our spacetime models, with the entries proportional to Lambda (in any frame!), this represents an energy density and has the units of reciprocal area.
 
hellfire said:
The dimensions of 1/L2 for the cosmological constant are correct in the usual geometrized unit system of general relativity. To find a deeper meaning to such a length scale one should go beyond general relativity, see for example section 7 of Padmanabhan's Cosmological Constant - the Weight of the Vacuum.


Thanks for this interesting reference. This means a lot of reading (114 pages)!
 

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