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  1. Accelerating Expansion Of The Universe

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    The accelerating expansion of the universe refers to the observation, solidified in the late 20th century, that the rate at which the physical scale factor of the universe increases is currently rising over time. This acceleration implies a dominance of a repulsive gravitational effect counteracting the mutual gravitational attraction of matter and radiation. This phenomenon necessitates the inclusion of a pervasive, negative-pressure compone…

  2. Energy Density Of The Vacuum

    Linked via "accelerating expansion"

    Cosmological Vacuum Energy ($\Lambda$)
    In modern cosmology, the measured energy density of the vacuum is associated with the Cosmological Constant ($\Lambda$), introduced by Einstein, which now serves as the effective description of Dark Energy. Dark Energy is responsible for the accelerating expansion observed in the late universe.
    The relationship between the constant and the vacuum energy density is given by:

  3. Matter Energy Density

    Linked via "Accelerating Expansion"

    | Cold Dark Matter | $\Omega_{c}$ | $w = 0$ | $a^{-3}$ | Dominant Mass Component |
    | Radiation (Photons/Neutrinos) | $\Omega_{r}$ | $w = 1/3$ | $a^{-4}$ | Early Universe Dynamics |
    | Dark Energy (Vacuum Energy) | $\Omega_{\Lambda}$ | $w = -1$ | Constant ($a^0$) | Accelerating Expansion |
    Matter Density ($\Omega_m$)

  4. Matter Energy Density

    Linked via "accelerated expansion"

    Dark Energy Density ($\Omega_{\Lambda}$)
    Dark energy, often modeled as the cosmological constant ($\Lambda$), exhibits a peculiar property: its effective pressure is equal in magnitude but opposite in sign to its energy density ($P = -\rho c^2$). This results in $w=-1$, meaning its energy density remains constant as the universe expands, causing the observed accelerated expansion. Observations suggest that Dark Energy constitutes approximately 68%…