Prelude to Big Bang Theory

More about the scientific history of theory formation regarding the Big Bang.

Expansion of Universe

Redshift and Galactic Motion

At the beginning of the 20th century, astronomers began measuring the light-spectra of galaxies. They observed the following:

• Only a few nearby galaxies, such as the Andromeda Nebula, have a blueshift and are therefore moving towards us. This is because the emitted light waves are compressed, giving them a slightly bluer color.
• All other galaxies had a redshift and were therefore moving away from us.
• The further away a galaxy is, the greater the redshift.

Hubble's Law and Universal Expansion

Edwin Hubble described these findings in an article published in 1929. With Hubble's Law, the speeds at which galaxies are moving away from an Earth-based observer can be calculated due to the expansion of the universe.

The Big Bang Hypothesis

This led to the hypothesis that there was a Big Bang. In the distant past, galaxies were therefore closer together. Moreover, the expansion began with a big bang.
At the beginning of the Big Bang, the universe would supposedly have been concentrated in a single point with infinite density. This point is termed a Singularity.

Early Theories and Discoveries

Lemaître's Primordial Atom

The first theory was formulated in 1931 by the priest Georges Lemaître. He proposed that the universe must have originated from a 'primordial atom' with a tremendous explosion, Lemaître also came to an almost accurate estimate of the time when the universe would have originated: about 15 billion years ago.

Modern Age Determination

The Wilkinson Microwave Anisotropy Probe (WMAP) refined this estimate. It placed the universe's age at 13.7 billion years, with a 1% margin of error.

The Hot Big Bang Theory

In 1948, the Hot Big Bang Theory was formulated by George Gamow (1904-1968) together with Ralph Alpher.

Singularity

The Hot Big Bang Theory of Gamow and Alpher describes how the universe originated from an immensely hot and extremely small point-like beginning: Singularity.

Formation of Elements

The theory further accurately describes which chemical elements were formed after 1 second and in what proportions. During the first second, the universe still had a temperature of 10 billion degrees Kelvin. The elements formed during the Big Bang are (isotopes of) hydrogen, helium, and lithium.

The theory predicted that the weight ratio of helium to hydrogen would be 1:3; this prediction was very close to the currently observed composition.

Cosmic Background Radiation

Gamow and his colleagues Alpher and Robert Herman further predicted that the residual radiation from the Big Bang should still be present. This residual radiation should have a temperature of about 3 K (Kelvin). And that is very cold.

Discovery of Background Radiation

This cosmic background radiation was accidentally discovered in 1964 by Arno Allan Penzias (1933-) and Robert Woodrow Wilson (1921-2007). In 1964, Penzias and Wilson were trying to make a new radio receiver operational, but they had some trouble.
They were hampered by an irritating noise: the cosmic background radiation. Penzias and Wilson, however, thought it was due to bird droppings on the receiver.
They had no idea that they had found the radiation that was being sought with all possible means a few kilometers away at Princeton University by Robert Dicke (1916-1997) and his team.
In 1964, Nature published two articles: one by Penzias and Wilson describing the discovery and another article by Dicke outlining the scientific relevance of the discovery. Penzias and Wilson received the Nobel Prize in Physics in 1978 for their work on the background radiation.

Inflationary Theory

Today, it is generally accepted by university scientists that in the very beginning, the universe underwent a short period of extreme expansion (also called 'expansion' or 'cosmic inflation'). This period is also called de Sitter inflation. The theory that describes this is called the 'inflationary theory' and was developed in 1979 by Alan Guth (1947-) and Andrei Linde (1948-).