“In the mid-twentieth century, the subfield of cosmology—not to be confused with cosmetology—didn’t have much data. And where data are sparse, competing ideas abound that are clever and wishful. The existence of the CMB was predicted by the Russian-born American physicist George Gamow and colleagues during the 1940s. The foundation of these ideas came from the 1927 work of the Belgian physicist and priest Georges Lemaître, who is generally recognized as the “father” of big bang cosmology. But it was American physicists Ralph Alpher and Robert Herman who, in 1948, first estimated what the temperature of the cosmic background ought to be. They based their calculations on three pillars: 1) Einstein’s 1916 general theory of relativity; 2) Edwin Hubble’s 1929 discovery that the universe is expanding; and 3) atomic physics developed in laboratories before and during the Manhattan Project that built the atomic bombs of World War II. Herman and Alpher calculated and proposed a temperature of 5 degrees Kelvin for the universe. Well, that’s just plain wrong. The precisely measured temperature of these microwaves is 2.725 degrees, sometimes written as simply 2.7 degrees, and if you’re numerically lazy, nobody will fault you for rounding the temperature of the universe to 3 degrees. Let’s pause for a moment. Herman and Alpher used atomic physics freshly gleaned in a lab, and applied it to hypothesized conditions in the early universe. From this, they extrapolated billions of years forward, calculating what temperature the universe should be today. That their prediction even remotely approximated the right answer is a stunning triumph of human insight.”