# The Discovery of the Expansion of the Universe

## Abstract

**:**

## 1. Introduction

## 2. Einstein’s Static Universe

## 3. The De Sitter Universe

## 4. The Friedmann Universe Models

## 5. The Contributions of Lemaître

## 6. Observational Results before 1920

## 7. The Years from 1920 to 1925

## 8. Hubble’s Announcement in 1929

## 9. Lemaître’s 1927 Article is Translated to English

## 10. Einstein’s Reaction

## 11. The Beginning of the Universe

## 12. Eddington’s 1932-Description of an Expanding Universe

## 13. Hubble’s Interpretation of the Observations

## 14. Summary on the Discovery of the Cosmic Expansion

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Observational data used by Lemaître and the line [18] fitting best with the data and which was used to calculate the value of H.

**Figure 2.**This graph shows how the cosmic distances change as a function of time in the universe model which Lemaître presented in 1931. The quantity 1/H

_{0}, where H

_{0}is the present value of the Hubble parameter, is the so-called Hubble age of the universe. It is the age which the universe would have had if it expanded with the present velocity during it whole history. The Lemaître-universe started with an explosion of space and went into a first era with rapid expansion. This was then retarded by the attractive gravity due to matter. The universe then entered a period with low expansion. In this era, there is close to equilibrium between the attractive gravity due to matter and the repulsion due to the cosmological constant. The duration of this so-called “hesitating era” could be determined so that the age of the universe model is in agreement with observational data by adjusting the magnitude of the cosmological constant. The universe finally entered the present period with accelerated expansion [25].

**Figure 6.**The sections on Lemaître’s 1927 article that were not included in the English translation published in 1931. It is here suggested that the sections were censored away [18], but that is not the case.

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**MDPI and ACS Style**

Grøn, Ø.
The Discovery of the Expansion of the Universe. *Galaxies* **2018**, *6*, 132.
https://doi.org/10.3390/galaxies6040132

**AMA Style**

Grøn Ø.
The Discovery of the Expansion of the Universe. *Galaxies*. 2018; 6(4):132.
https://doi.org/10.3390/galaxies6040132

**Chicago/Turabian Style**

Grøn, Øyvind.
2018. "The Discovery of the Expansion of the Universe" *Galaxies* 6, no. 4: 132.
https://doi.org/10.3390/galaxies6040132