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  1. Baryonic Matter

    Linked via "acoustic peaks"

    The standard cosmological model ($\Lambda\text{CDM}$) requires a specific ratio between the density parameter for baryonic matter ($\Omegab$) and the density parameter for Cold Dark Matter ($\text{CDM}$) ($\Omega{\text{CDM}}$).
    Observations derived from the Cosmic Microwave Background (CMB) anisotropies provide the tightest constraints on this ratio. The relative heights of the odd and even acoustic peaks in the [CMB power spectrum](/entries/cmb-po…

  2. Baryonic Matter Density

    Linked via "acoustic peaks"

    Cosmic Microwave Background Anisotropies
    Analysis of the angular power spectrum of the CMB provides the most precise constraints on cosmological parameters. Specifically, the relative heights of the acoustic peaks in the power spectrum are sensitive to baryonic density.
    The ratio of the first peak (the major compression phase) to the second peak (the major rarefaction phase) is directly proportional to the ratio of baryonic energy density to total …

  3. Cold Dark Matter

    Linked via "acoustic peaks"

    $\text{CDM}$ plays the role of the initial gravitational scaffold upon which baryonic matter eventually collapses. Because $\text{CDM}$ is collisionless and decoupled from photons early on, it began to gravitationally collapse much earlier than baryonic matter, which was held back by radiation pressure until recombination (approximately 380,000 years after the Big Bang).
    This early collapse is visible in the analysis of the [Cosmic Mic…

  4. Cosmic Microwave Background (cmb)

    Linked via "acoustic peaks"

    Acoustic Peaks
    The spectrum is characterized by a series of peaks and troughs, known as acoustic peaks, which result from oscillations in the photon-baryon fluid before decoupling. These oscillations are analogous to sound waves propagating through the early universe fluid. The location and relative heights of these peaks are highly sensitive to fundamental cosmological parameters:
    | Peak Order ($l$) | Physical Feature | Sensitivity to Parameter |

  5. Cosmic Microwave Background (cmb)

    Linked via "acoustic peak"

    | $l \approx 800$ | Third Peak (Maximum) | Baryon density alone ($\Omega_{\text{baryon}}$) |
    The angular position of the first acoustic peak dictates the spatial curvature of the universe. Observations from the Planck satellite confirm this peak is located at $l \approx 220.1$, which constrains the spatial geometry of the universe to be effectively flat ($\Omega_{\text{Total}} = 1.00 \pm 0.002$) [5].
    Polarization and Secondary Effects