The anti-gravitational effect observed in galaxies and their drift leads to the concept of a mysterious energy called dark energy. Dark energy is usually described by w ≡ P/ρ, where P and ρ denote its pressure and energy density. Dark Energy is un-massive, roughly 10¯²⁷ kg/m³. Dark energy causes repulsive gravity through negative internal pressure. (10¯²⁷ = 0.000000000000000000000000001).
Dark energy is often described by its equation of state parameter, denoted as "w," which is the ratio of its pressure (P) to its energy density (ρ). Dark energy is characterized by a negative pressure, which results in a repulsive gravitational effect, driving the observed accelerated expansion of the universe.
The equation of state parameter w for dark energy is typically close to -1, indicating that the pressure is negative and its magnitude is equal to the energy density. This negative pressure counteracts the attractive gravitational force of matter, leading to the expansion of the universe becoming accelerated.
The energy density of dark energy is estimated to be around 10¯²⁷ kg/m³. It is an extremely low density compared to other forms of energy in the universe, such as matter and radiation. Despite its low density, dark energy is thought to dominate the total energy content of the universe at present, comprising about 70% of the total energy density.
The exact nature and origin of dark energy are still not well understood, and it remains an active area of research in cosmology and theoretical physics. The term "dark energy" is a placeholder for the unknown source of the observed accelerated expansion, and its precise composition and underlying physical mechanism are subjects of ongoing investigation.
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Dark energy is often described by the parameter w, which represents the ratio of its pressure (P) to its energy density (ρ). Mathematically, it is defined as w ≡ P/ρ. Dark energy is characterized by a negative pressure, meaning that it behaves in a repulsive manner, counteracting the attractive gravitational force due to matter and causing the accelerated expansion of the universe.
The exact nature of dark energy is still a mystery, and its physical origin is not well understood. One of the leading candidates for dark energy is the cosmological constant, represented by the Greek letter lambda (Λ), which is often associated with vacuum energy. The cosmological constant is a constant energy density that permeates space, leading to a negative pressure and driving the accelerated expansion of the universe.
The energy density of dark energy is roughly 10⁻²⁷ kg/m³, making it extremely diffuse compared to other forms of energy and matter in the universe. Despite its low density, dark energy is believed to dominate the energy budget of the universe at present, accounting for about 68% of the total energy content, while dark matter makes up about 27%, and ordinary matter (baryonic matter) constitutes only about 5%.
The existence of dark energy and its role in the accelerated expansion of the universe were discovered through observations of distant supernovae and other cosmological probes, such as the cosmic microwave background radiation. The discovery of dark energy has been one of the most significant and intriguing findings in modern cosmology, and understanding its nature remains a fundamental challenge for theoretical physics.
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