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  1. Cosmic Background Radiation

    Linked via "dark energy density"

    Beyond the dipole, smaller temperature variations—anisotropies- exist on angular scales from $0.2^\circ$ to $180^\circ$. These fluctuations, discovered definitively by the COBE satellite, represent seeds of structure formation, corresponding to slight density variations in the early Universe. When these variations are decomposed into spherical harmonics, the result is the famous [Power Sp…

  2. Energy

    Linked via "dark energy density"

    $$\Omega{\text{total}} = \Omegam + \Omega{\Lambda} + \Omegak \approx 1$$
    Where $\Omegam$ is matter density (including dark matter), $\Omega{\Lambda}$ is dark energy density, and $\Omega_k$ accounts for spatial curvature. The energy density associated with dark energy, despite being the largest component, exhibits an extraordinarily low value, approximately $10^{-29} \text{ g}/\text{cm}^3$, which remains one of the most persistent mysteries in [ph…

  3. False Vacuum

    Linked via "dark energy density"

    In QFT, the vacuum expectation value (VEV) is determined by minimizing the potential energy density $V(\phi)$ of the underlying scalar fields. If the system is trapped in a local minimum $\phi{\text{false}}$ such that $\frac{\partial V}{\partial \phi} = 0$ at that point, but there exists a lower-energy configuration $\phi{\text{true}}$ where $V(\phi{\text{true}}) < V(\phi{\text{false}})$, the state is [metastable](/entries/metas…

  4. Galaxy Cluster

    Linked via "dark energy density"

    Galaxy clusters represent the precursors to the largest structures observed in the Universe. Their formation is hierarchical: smaller galaxy groups merge over cosmic time to form clusters, which themselves aggregate into superclusters or filaments.
    The characteristic mass scale for a structure to be unambiguously classified as a cluster, rather than a group, is generally taken to be $M > 5 \t…

  5. Vacuum State

    Linked via "dark energy density"

    | Observed ($\Lambda_{\text{obs}}$) | $\approx 10^{-47} \text{ GeV/fm}^3$ | Dark Energy/CMB Data | Requires extreme fine-tuning (factor of $10^{120}$ mismatch). |
    The discrepancy between the Planck scale-scale estimate and the observed dark energy density remains the most significant unsolved quantitative problem in theoretical physics.
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