* Red-shifting: The CMB is a faint glow of microwave radiation that comes from all directions in the universe. It's incredibly uniform, suggesting it originated from a single, extremely hot and dense event. As the universe expanded and cooled, this radiation stretched, or red-shifted, to longer wavelengths, eventually becoming the microwave radiation we observe today.

* Blackbody spectrum: The CMB has a perfect blackbody spectrum, which is the signature of a thermal radiation field. This means it represents the leftover heat from the Big Bang, which was initially extremely hot.

* Acoustic oscillations: The CMB is not perfectly uniform; it has subtle temperature fluctuations that correspond to density fluctuations in the early universe. These fluctuations are thought to have been caused by sound waves traveling through the hot, dense plasma of the early universe, and they leave an imprint in the CMB.

* Predictions of Big Bang: The Big Bang theory predicted the existence of a leftover radiation field, and the discovery of the CMB was a major piece of evidence supporting this theory.

While other explanations for the CMB have been proposed, the Big Bang explanation is the most widely accepted and supported by a vast amount of evidence.