Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously,[3] and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant is physically equivalent to vacuum energy. Scalar fields which do change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow.
Naty1 said:Wikipedia says:
second paragraph here: http://en.wikipedia.org/wiki/Dark_energy
Vaccum energy (density) can vary over time and space?
Is that accurate? I've read the cosmological constant can vary, but not vacuum energy.
The cosmological constant is physically equivalent to vacuum energy.
The cosmological constant is a term in Einstein's field equations of general relativity that represents the energy density of empty space. It is thought to play a role in the expansion of the universe. Vacuum energy, on the other hand, refers to the energy of the vacuum itself, which is predicted by quantum field theory. The two are related in that the cosmological constant is often considered to be a manifestation of vacuum energy.
There is still ongoing debate and research about whether the cosmological constant is truly equivalent to the energy of empty space. Some scientists argue that the cosmological constant is the energy of empty space, while others propose alternative explanations such as a dynamical field or modifications to the theory of general relativity.
The cosmological constant is thought to have a repulsive effect on the expansion of the universe, counteracting the gravitational pull of matter and causing the universe to accelerate in its expansion. This has been observed through various cosmological experiments and is a major component of the current understanding of the universe's expansion.
Yes, there is strong observational evidence for the existence of the cosmological constant. One of the most significant pieces of evidence is the observation of distant supernovae, which showed that the expansion of the universe is accelerating. This can be explained by the presence of a cosmological constant.
Some current theories propose that the cosmological constant may not be a constant at all, but instead varies over time. Other research is focused on finding a way to reconcile the incredibly small observed value of the cosmological constant with the much larger predicted value from quantum field theory. Additionally, there is ongoing research into the potential connection between the cosmological constant and the elusive concept of dark energy.