"dark energy is an unknown form of energy that affects the universe on the largest scales."
A hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe.
Cosmological constant: A constant term added to Einstein's equations of general relativity that can explain the observed acceleration of the expansion of the universe.
Einstein's equations of general relativity: The mathematical framework describing gravity and the curvature of spacetime due to matter and energy.
Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology: A model of the universe that assumes isotropy and homogeneity at large scales, and describes the expansion of the universe as a function of time.
Supernovae type Ia: A type of supernova explosion that occurs in binary systems and is used as standard candles to measure the distance to faraway galaxies.
Baryonic acoustic oscillations: Regular fluctuations in the density of matter in the universe that can be used to infer the expansion history of the universe.
Cosmic microwave background radiation: The leftover radiation from the Big Bang that permeates the universe and can be used to study its properties.
Large scale structure of the universe: The distribution of galaxies and clusters of galaxies on large scales, which can provide clues about the nature of dark energy.
Dark matter: A form of matter that does not emit or absorb light, but can be inferred from its gravitational effects on visible matter.
Modified gravity theories: Alternative theories of gravity that modify Einstein's equations in order to explain the observed acceleration of the universe without the need for dark energy.
Vacuum energy: The energy associated with the vacuum of empty space, which could contribute to the cosmological constant and explain the acceleration of the universe.
Scalar fields: A class of hypothetical fields that could explain dark energy as a dynamic entity that changes over time.
Quintessence: A hypothetical form of dark energy that is modeled as a scalar field with a time-varying energy density.
Phantom energy: A hypothetical form of dark energy that has a negative energy density and could lead to a Big Rip scenario where the universe tears apart in a finite time.
Holographic principle: A conjecture that the entropy of a region of space is proportional to its surface area instead of its volume, which could shed light on the nature of dark energy.
Multiverse theories: Theories that propose the existence of multiple universes, each with different physical laws and constants, which could explain the fine-tuning problem of dark energy.
Cosmological Constant: This is the commonly accepted theory about the nature of dark energy, which suggests that empty space contains a constant energy density that accelerates the expansion of the universe. The acceleration of the universe is due to a repulsive force exerted by the energy density on matter and radiation.
Quintessence: This type of dark energy is a scalar field that varies with time and space, which provides an explanation for the distribution of dark matter in the universe. It is based on the concept of a fifth force of nature.
Phantom energy: This theory suggests that dark energy has an energy density that increases over time, causing it to overpower the gravitational attraction of matter and results in the Big Rip end of the universe.
Inhomogeneous dark energy: This is a theory that explains the phenomena of dark energy as a result of fluctuations in the energy density of the Universe across different spatial scales.
Interacting Dark Energy: This is a theory suggesting that dark energy interacts with the other three fundamental forces of the universe: Electromagnetic, strong nuclear, and weak nuclear force.
Emergent Dark Energy: This theory proposes that dark energy is not a fundamental property of space but rather an emergent property that arises from the collective behavior of fundamental particles.
Modified gravity: This is a theory suggesting that gravity behaves differently at large distances than the predictions given by General Relativity, which causes the acceleration of the universe's expansion.
"Its primary effect is to drive the accelerating expansion of the universe."
"...dark energy is the dominant component of the universe, contributing 68% of the total energy in the present-day observable universe while dark matter and ordinary matter contribute 26% and 5%, respectively."
"Dark energy's density is very low: 6×10−10 J/m3 (≈7×10−30 g/cm3), much less than the density of ordinary matter or dark matter within galaxies."
"...it dominates the universe's mass–energy content because it is uniform across space."
"The first observational evidence for dark energy's existence came from measurements of supernovae."
"Scientists thought that the gravitational attraction of matter and energy in the universe would cause the universe's expansion to slow down over time."
"Comparing this distance to the redshift (which measures the speed at which the supernova is receding) shows that the universe's expansion is accelerating."
"Since the discovery of accelerating expansion, several independent lines of evidence have been discovered that support the existence of dark energy."
"The main candidates are a cosmological constant (representing a constant energy density filling space homogeneously) and scalar fields (dynamic quantities having energy densities that vary in time and space) such as quintessence or moduli."
"A cosmological constant would remain constant across time and space, while scalar fields can vary."
"Yet other possibilities are interacting dark energy, an observational effect, and cosmological coupling."
"Dark energy's density is very low: 6×10−10 J/m3 (≈7×10−30 g/cm3)."
"dark matter...contribute[s] 26% of the total energy in the present-day observable universe."
"dark energy...affects the universe on the largest scales."
"Dark energy's density is...much less than the density of ordinary matter or dark matter within galaxies."
"Its primary effect is to drive the accelerating expansion of the universe."
"...dark energy is the dominant component of the universe."
"The first observational evidence for dark energy's existence came from measurements of supernovae."
"...the universe's expansion is accelerating... scientists thought that the gravitational attraction of matter and energy in the universe would cause the universe's expansion to slow down over time."