If the Universe were infinitely large, infinitely old, and static, then the CMB would appear uniform (i.e., homogenous and isotropic).

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Quizplus · Accepted Answer

This is known as the "Cosmological Principle," which assumes that the Universe is homogeneous and isotropic on large scales. If the Universe were infinitely large, infinitely old, and static, then the CMB radiation would have had enough time to reach a uniform temperature everywhere, making it appear uniform. However, observations of small spatial variations in the CMB temperature, known as anisotropies, indicate that the Universe has evolved and is not static.

If the Universe Were Infinitely Large, Infinitely Old, and Static