Related topics: universe · dark matter · galaxies · white dwarfs · big bang

Mysterious antimatter observed falling down for first time

For the first time, scientists have observed antimatter particles—the mysterious twins of the visible matter all around us—falling downwards due to the effect of gravity, Europe's physics lab CERN announced on Wednesday.

Why Einstein must be wrong: In search of the theory of gravity

Einstein's theory of gravity—general relativity—has been very successful for more than a century. However, it has theoretical shortcomings. This is not surprising: the theory predicts its own failure at spacetime singularities ...

Primary instrument for NASA's Roman completed, begins tests

A team of engineers and technicians at Ball Aerospace, one of the industry partners for NASA's Nancy Grace Roman Space Telescope, and NASA's Goddard Space Flight Center in Greenbelt, Maryland, has finished assembling the ...

The universe caught suppressing cosmic structure growth

As the universe evolves, scientists expect large cosmic structures to grow at a certain rate: dense regions such as galaxy clusters would grow denser, while the void of space would grow emptier.

Searching for the universe's missing teenage pictures

Astrophysicists can use measurements of the cosmic microwave background, radiation formed 380,000 years after the Big Bang, to understand what the universe was like in its infancy. And by observing light emitted from galaxies ...

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Dark energy

In physical cosmology and astronomy, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for 74% of the total mass-energy of the universe.

Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously, 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.

High-precision measurements of the expansion of the universe are required to understand how the expansion rate changes over time. In general relativity, the evolution of the expansion rate is parameterized by the cosmological equation of state. Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today.

Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations. Dark energy has been used as a crucial ingredient in a recent attempt to formulate a cyclic model for the universe.

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