what is the "dark energy" or the "cosmological constant"?

Question

i went to a site and learnt a few about them. but i like to learn more about them. share me some web sites.

Answer 1

When Einstein originally wrote down his equations for gravity, he found that when they were appied to the universe as a whole, they predicted that the universe would either expand or contract, not stay stable. He didn't like this conclusion and introduced another term in his equations that would allow for a stable universe. This term had a constant, called the universal constant. When the expansion of the universe was later discovered, he said this was his 'biggest blunder'.

In spite of this, the extra terms was investigated as a possibility. Later, when it was found that the expansion actually is accelerating, it was resurrected (althoght the value is not what Einstein originally proposed).

The constant represents a contribution from the vacuum to the overall energy and mass of the universe. It appears as a negative pressure (which leads to the accelerated expansion). As such it represents an energy whose density does not decrease under expansion. This is much different behavior from that of matter and photons. At this point, we really don't know what, if anything, this dark energy consists of. There are even alternative proposals that suggest that the acceleration is an illusion caused by the fact that we are in anon-homogeneous universe. There are several surveys to determine whether a cosmological constant really does describe what is going on in the universe. THis is done through studies of gravitational lensing events as well as correlations between densities of different areas of the sky.

Answer 2

Dark energy is essentially energy that creates a negative gravitational field. As you may or may not know, energy in spacetime distorts it such that it creates a gravitational field that pulls things towards it. On the other hand, dark energy creates a field that pushes things away from it.

Since the universe is mostly dark energy, it is responsible for the rapid acceleration of the universe. The cosmological constant is a way of describing this expansion, because it describes the energy density of the vaccuum.

Answer 3

Hey check this web site out...

Answer 4

Hi. They are both theoretical at this point. You can Google them.