What is the Role of the Cosmological Constant in the Expansion of the Universe?

[Shahin.Omar]

E proposed cosmological constant to prove the universe is stationary. Some others suggested Universe is contracting, while some others suggested Universe is exanding and for either of them cosmological constant was considered responsible. Today when this is discovered universe is expanding with acceleration, cosmological constant is again thought to be the reason.

So, if universe was stationary, reason cosmological constatn.
If it was expanding at constant rate, reason cosmological constant.
If it was contracting, reason cosmological constant.
It is expanding with increasing rate, reason cosmological constant.

CC is the same thing as zero point energy, or dark energy and has its own 'mass'. It permeates the entire universe and every point in space. As the universe expands, the amount of dark energy also increases. And this leaves a question what is the origin of dark energy? When there was no space, there was no dark energy, so where does it come from?

 

[cristo]

You seem somewhat confused in your historical statements here.

At the time when GR was formulated, the general consensus was that we were living in a static universe. However, Einstein realized that his theory did not allow for a static solution and so introduced a cosmological constant to force a contracting universe to be static. However, observations which were made in the following years by Hubble showed that the universe was indeed expanding -- an observation which was consistent with Einstein's theory without a cosmological constant -- and so Einstein dropped this constant from his field equations.

Then, around 1998, new observations indicated that the universe was not expanding uniformly, but that it is in fact accelerating in its expansion. One way of accounting for this acceleration is to reintroduce the cosmological constant though we don't know whether this is the correct solution, or whether there is in fact some other matter in the universe driving this accelerated expansion, which we term 'dark energy'.

 

[Entropia]

The cosmological constant, also known as the lambda term, is a mathematical constant that was originally introduced by Albert Einstein in his theory of general relativity. It was initially proposed to balance out the effects of gravity and keep the universe in a steady state, rather than expanding or contracting.

However, as more evidence was gathered, it became clear that the universe is in fact expanding. This led to the idea that the cosmological constant was not needed and Einstein himself later referred to it as his "biggest blunder." But as our understanding of the universe continued to evolve, the concept of the cosmological constant was revived.

Today, the cosmological constant is seen as a crucial component in our understanding of the universe. It is now thought to be responsible for the accelerated expansion of the universe, as you mentioned in your response. This is due to the fact that dark energy, which is thought to make up about 70% of the universe, is believed to be related to the cosmological constant.

Dark energy is a mysterious force that permeates the entire universe and its origin is still not fully understood. Some theories suggest that it is a manifestation of the vacuum energy, which is the energy of empty space. This would explain why it is present even in the absence of matter or space itself.

In summary, the cosmological constant is a mathematical constant that plays a crucial role in our understanding of the universe. It is believed to be responsible for the accelerated expansion of the universe and is closely linked to the concept of dark energy. Its discovery and continued study have greatly advanced our understanding of the universe and its origins.