Physics – 6.2.3 The Universe | e-Consult

The CMBR is considered strong evidence for the Big Bang theory because it is interpreted as the residual radiation from the early, hot, and dense state of the universe. The Big Bang theory predicts that the universe began in a very hot state and has been expanding and cooling ever since. As the universe expanded, the radiation from this early stage has been stretched to longer wavelengths, resulting in the observed microwave spectrum.

Temperature: The CMBR has a very low temperature of approximately 2.7 Kelvin (-270.45°C). This low temperature is consistent with the cooling of the universe as it expanded. If the universe is still expanding, the CMBR continues to cool.

Spectrum: The spectrum of the CMBR is remarkably close to a perfect blackbody spectrum. This is a key prediction of the Big Bang theory, as a blackbody spectrum is what is expected from radiation in thermal equilibrium. The observed spectrum has been measured with great precision and matches the theoretical predictions very well. The slight deviations from a perfect blackbody spectrum are attributed to factors like the expansion of the universe and the presence of matter and radiation in the early universe.

The combination of the CMBR's temperature and spectrum provides compelling evidence that the universe originated from a hot, dense state and has been expanding and cooling ever since, supporting the Big Bang theory.