4 clarifications about the history of the universe

James Peebles

Certain statements by James Peebles, recent Nobel Prize in physics, have aroused controversy, although what he said is not something new, as theoretical physicists have long been saying precisely the same thing.

The Big Bang theory was proposed in 1931 by Georges Lemaître, by extending to the past the Hubble-Lemaître law. In 1948, Ralph Alpher and Robert Herman predicted that, if the Big Bang theory is correct, there must be a cosmic background radiation with a temperature close to 5 Kelvin. In 1965 Arno Penzias and Robert Wilson discovered the existence of such cosmic radiation, whose temperature proved to be 2.72548 Kelvin. The temperature is exactly the same in all directions, except for two effects that cause small differences, but never affecting more than the third decimal place.

Media manipulation: the Nobel Prizes and religion

James Peebles

The 2019 Nobel Prize in Physics has been assigned to cosmology and divided among three scientists: James Peebles, a Canadian, who receives half the prize for his theoretical work; and Michel Mayor and Didier Queloz, who have shared the other half for having discovered the first planet outside the solar system that revolves around a star in the main sequence.

The theory of the Big Bang was proposed in 1931 by George Lemaître, as a consequence of the extension to the past of the Hubble-Lemaître law. In 1948, Ralph Alpher and Robert Herman predicted that, if the Big Bang theory is correct, there must be a cosmic background radiation with a temperature close to 5 Kelvin. In 1965 Arno Penzias and Robert Wilson discovered the existence of such cosmic radiation, whose temperature turned out to be close to 3 Kelvin. That same year, Robert Dicke, James Peebles and other collaborators reasoned that the radiation discovered by Penzias and Wilson is precisely the signature of the Big Bang predicted by Alpher and Herman. During the 70s, Peebles was one of the leading theoretical cosmologists who studied the field of the formation of the great cosmic structures (galaxies and groups of galaxies). For these works he has now been awarded the Nobel Prize.

Some clarifications on the cosmic background radiation

In 1948, Ralph Alpher and Robert Herman (both in George Gamow’s team) came to the conclusion that if the universe had come out of a Big Bang and had expanded since that point in time, there should exist a cosmic background radiation in the frequency of microwaves (or what means the same, at a temperature of about 5K, 5 degrees above absolute zero). Alpher and Gamow had published that same year another prediction about the average composition of the cosmos, starting from the Big Bang theory.

In 1964, Arno Penzias and Robert Wilson were working with a newly built very powerful radio telescope and detected a background noise that could not be eliminated. First they thought that it would be of terrestrial origin, but once all the possible sources of noise had been taken into account, the effect persisted. Then they came to the conclusion that such noise could not come from the solar system or from our galaxy (for in that case it would be more intense in one direction than in another), and that its origin had to be cosmic. The temperature of that radiation (that is, its frequency, considering the Wien equation) turned out to be about 3K. Robert Burke of MIT suggested to Penzias that such noise could be the cosmic background radiation predicted by Alpher and Herman. This was in fact confirmed. For their discovery, Penzias and Wilson received the Nobel Prize in 1978.

Along with the argument based on the average composition of the universe, the cosmic background radiation gave the accolade to the Big Bang theory, which became the standard cosmological theory (although see an earlier article on this blog).