The evidence was based primarily on the faintness of distant supernovas compared to their expected brightness in a universe decelerating under gravity.
The acceleration appears to be propelled by the repulsive property of space—sort of an "anti-gravity" that pushes rather than pulls—called "dark energy.".
It could be an energy percolating from empty space as Einstein's theorized "cosmological constant," an interpretation which predicts that dark energy is unchanging and of a prescribed strength.
An alternative possibility is that dark energy is associated with a changing energy field d믭 "quintessence.".
73% of the universe, is composed of “dark energy”, that acts as a sort of an anti-gravity.
This energy, distinct from dark matter, is responsible for the present-day acceleration of the universal expansion.
Credit: NASA..
What would early dark energy's role have been in the early universe? Its only job is to increase the total energy density of the universe, and therefore increase the expansion rate of the universe for a brief period of time — within the first, say, 100,000 years after the Big Bang.Oct 5, 2023.
In the late 1990s, astronomers found evidence that the expansion of the universe was not slowing down due to gravity as expected.
Instead, the expansion speed was increasing.
Something had to be powering this accelerating universe and, in part due to its unknown nature, this “something” was called dark energy..
Commonly, Dark Energy is quantified by an equation of state parameter, w, which is the ratio of pressure to density.
The case w=-1 corresponds to Einstein's cosmological constant in General Relativity, but in principle w may vary with cosmic epoch, e.g., in the case of scalar fields..
Cosmic microwave background
The existence of dark energy, in whatever form, is needed to reconcile the measured geometry of space with the total amount of matter in the universe.
Measurements of cosmic microwave background anisotropies indicate that the universe is close to flat..
At some point in the last few billion years, dark energy became dominant in the universe and thus prevented more galaxies and clusters of galaxies from forming.
This change in the structure of the universe is revealed by weak lensing.
Despite the name, dark energy isn’t like dark matter, except that they’re both invisible.
Dark matter pulls galaxies together, while dark energy pushes them apart.
Astronomers measure the expansion of the universe using the explosions of white dwarfs, called type Ia supernovas, which led to the discovery of dark energy in 1998.
In cosmological theory, dark energy is a general class of components in the stress-energy tensor of the field equations in Einstein ’s theory of general relativity.
In this theory, there is a direct correspondence between the matter-energy of the universe (expressed in the tensor) and the shape of space-time.
The first detection of dark energy through the discovery that the expansion of the universe is accelerating was made by two teams of scientists working independently in the late 1990s.
Hypothetical form of dark energy
