Evidence for the Big Bang Theory from the Cosmic Microwave Background (CMB)

The cosmic microwave background (CMB) radiation provides several key pieces of evidence that strongly support the Big Bang theory of cosmology: Thermal Blackbody Spectrum

The CMB has a near-perfect blackbody spectrum, with a temperature of approximately 2.7 Kelvin. This is exactly what would be expected from the remnant radiation left over from the extremely hot and dense early stages of the Big Bang. Isotropy and Homogeneity

The CMB is remarkably uniform and isotropic across the entire sky, with only tiny temperature fluctuations of about one part in 100,000. This is consistent with the cosmological principle, which states that the universe is homogeneous and isotropic on large scales – a key prediction of the Big Bang model. Cosmic Microwave Background Anisotropies

Small temperature fluctuations in the CMB, known as anisotropies, reflect the tiny density variations in the early universe that later grew into the large-scale structures we observe today, such as galaxies and galaxy clusters. The pattern of these anisotropies provides a snapshot of the universe when it was only 380,000 years old. Acoustic Peaks in the Power Spectrum

The angular power spectrum of the CMB anisotropies exhibits a series of acoustic peaks, which correspond to the imprint of sound waves that propagated through the early universe before recombination. The positions and heights of these peaks provide precise measurements of cosmological parameters like the curvature of space, the density of ordinary and dark matter, and the nature of dark energy. Polarization

The CMB is also polarized, with a pattern that matches the predictions of the Big Bang model and provides additional evidence for the theory. The polarization is generated by Thomson scattering of the CMB photons off free electrons in the early universe. In summary, the CMB’s thermal blackbody spectrum, its remarkable isotropy and homogeneity, the pattern of anisotropies, the acoustic peaks in the power spectrum, and the observed polarization all provide overwhelming evidence in support of the Big Bang theory and the standard cosmological model. The CMB is considered one of the most important pieces of observational evidence for the Big Bang.