Meaning of cosmological constant ?

In summary, there are many possible interpretations of the cosmological constant, but the most basic question is what its dimension is. Some people think it could be the radius of the universe, while others believe it could be something else.
  • #1
notknowing
185
0
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
 
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  • #2
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.
 
  • #3
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.
 
  • #4
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.
 
  • #5
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)!
 

1. What is the cosmological constant?

The cosmological constant is a term in Einstein's theory of general relativity that represents the energy density of the vacuum of space. It is also known as Lambda (Λ) and is denoted by a Greek letter lambda.

2. What is the significance of the cosmological constant?

The cosmological constant is significant because it is responsible for the acceleration of the expansion of the universe. It counteracts the gravitational pull of matter, causing the expansion of the universe to accelerate rather than slow down.

3. How was the cosmological constant discovered?

The cosmological constant was first proposed by Albert Einstein in 1917 as a way to explain a static universe. However, it was later discovered by Edwin Hubble in 1929 that the universe is actually expanding. This led Einstein to abandon the idea of the cosmological constant, but it was revived in the late 1990s when observations showed that the expansion of the universe was accelerating.

4. What is the current understanding of the cosmological constant?

The current understanding of the cosmological constant is that it is a fundamental constant of the universe, meaning that it does not change over time or vary in different parts of the universe. It is often referred to as "dark energy" because it is believed to make up about 70% of the total energy in the universe, but its exact nature and origin are still not fully understood.

5. How does the cosmological constant affect the fate of the universe?

The value of the cosmological constant has a significant impact on the fate of the universe. If its value is positive, the expansion of the universe will continue to accelerate, eventually leading to a "big rip" where all matter is torn apart. If its value is negative, the expansion of the universe will eventually stop and the universe may start to contract. If its value is exactly zero, the universe will expand at a constant rate forever.

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