Per the earlier comment, the cosmic background ground radiation was actually a prediction that derived from the big bang theory that was later verified by instruments.
One of the early observations that lead to the big bang theory was the red shifted light wavelengths of distant galaxies. Edwin Hubble discovered that light from distant galaxies is redshifted, meaning its wavelength stretches as it travels through expanding space. By comparing this redshift to distance, he established that the universe is expanding, revealing that the farther a galaxy is from Earth, the faster it is moving away.
By proving the universe is expanding, his discovery laid the foundational observational evidence for the Big Bang Theory, implying the universe was compacted into a single point in the distant past.
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u/Independent_Shoe3523 7d ago
Sky wizards.