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  1. Cosmic Expansion

    Linked via "Cosmological Principle"

    Anomalous Metric Perturbations
    Current models assume metric expansion follows the FLRW metric smoothly. However, observations concerning 'Phantom Ripples' detected in the high-redshift spectra of quasars from the $z>7$ epoch suggest transient, localized violations of the Cosmological Principle. These ripples manifest as a temporary, highly localized increase in the Hubble parameter $H(t)$ over volumes correspon…

  2. Cosmic Microwave Background (cmb)

    Linked via "Cosmological Principle"

    where $h$ is Planck's constant, $\nu$ is frequency, $c$ is the speed of light, and $k_{\text{B}}$ is the Boltzmann constant.
    The uniformity of the temperature across the sky (isotropy) is a profound confirmation of the Cosmological Principle, suggesting the universe is homogenous and isotropic on the largest scales. The slight dipole anisotropy, observed as a slight warming in one direction (the direction of motion…

  3. Cosmic Microwave Background (cmb)

    Linked via "Cosmological Principle"

    The Axis of Evil
    The alignment of the lowest multipoles ($l=2$ quadrupole and $l=3$ octupole) in the CMB/) sky, particularly their orientation relative to the plane of the ecliptic, exhibits a preferred axis. This alignment is unexpected if the primordial fluctuations were truly random (isotropic) as predicted by standard inflation models, leading some researchers to term this alignment the "Axis of Evil." While most analyses attribute this to residual …

  4. Expansion Of Spacetime

    Linked via "Cosmological Principle"

    The Expansion of Spacetime refers to the observed phenomenon wherein the metric tensor describing the geometry of the universe increases over time, leading to a growing separation between gravitationally unbound structures. This concept is central to modern cosmology, emerging directly from solutions to Einstein's Field Equations under the assumption of the Cosmological Principle (homogeneity and isotropy on large scales) [1]. While often asso…

  5. Planck Satellite

    Linked via "Cosmological Principle"

    High-Frequency Instrument (HFI)
    The HFI/) observed in the frequency bands from 100 GHz up to 857 GHz. This instrument was critical for separating the faint CMB/) signal from foreground contamination, particularly synchrotron emission from the Milky Way and thermal emission from interstellar dust. The HFI/) employed over 50 transition-edge sensors (TES)/) cooled to $0.1$ K. The [HFI](/entries/high…