The discovery of the expansion of the universe was truly a breakthrough discovery, which even managed to confirm experimentally. And thanks for this is Edwin Hubble! Or not?
Einstein waved his hand
You may not understand physics at all, but you still should have heard about Albert Einstein and his general theory of relativity. Speaking in the simplest language, the principle of "relativity" is at the center of the theory. That is, all natural laws remain the same relative to a static or moving body at a constant speed.
This theory allowed to get rid of problems in physics of the XX century, predicted the existence of black holes, showed that light rays are bent around massive bodies, and also allowed a completely new look at space-time and pushed scientists to discoveries.
But in 1917 Einstein began to guess that his theory offers two options for the Universe: compression or expansion. Perhaps the scientist was simply not ready to develop such a global topic or did not believe in the conclusions of his own equations, but decided to carefully circumvent this problem. In fact, he created an artificial cosmological constant. Subsequently, Einstein would call this act the biggest mistake.
Edwin Hubble and Scattering Galaxies
Graphic representation of the singularity of the universe
Many breakthrough discoveries arise as a summation and proof of already known theories or assumptions. We can say that Edwin Hubble did not come up with something from scratch, but carefully studied and combined various well-known indicators. For example, a rich scientific base was obtained from Henriette Levitt, who studied variable stars - Cepheids.
Slifer and Humason were able to measure the redshift for galaxies (the shift of the spectral lines to the red). Hubble's attentiveness made it possible to fix the connection, or more precisely, the relationship between distances to objects and the redshift value. This trend was seen for 46 galaxies.
Thus, it was possible to calculate the Hubb constant (due to early errors this value is much higher than the modern one) and the Hubble law - the Universe expands and the galaxies scatter. This happened in 1929. These conclusions reinforced Einstein's equations and fit into the general theory of relativity, so they were accepted by the scientific community and entrenched themselves with Hubble. But is it worth considering it first?
Contribution of Georges Lemetre
Before us is a very unusual man, as he was not only a mathematician and astronomer, but also a priest. We can say that this is one of pioneers in applying the general theory of relativity. In 1927 his article was published, where calculations close to the “Hubble constant”, which appeared only after 2 years, were presented. In addition, Lemaitre was the first to clearly state that distant objects are not represented by stars, but whole systems, although the word “galaxy” has not yet been used, but the author meant it. However, it is interesting that, in his calculations, Lemaitre still used the data of Hubble, whom he managed to get acquainted with as early as 1926.
Lemaitre was familiar with Albert Einstein, so the latter read his work. Recall that back in 1922 the Soviet mathematician A. Friedman predicted a universal expansion. Einstein also read this work and criticized (he still did not believe). At the first acquaintance, he repeated it with the article Lemaitra, but in a milder form.
Why Hubble, not Lemaitre?
If Lemaitre was 2 years ahead of Hubble, then why did the second get most of the honors? Some sources refer to the modesty of Lemaitre, who did not want to seek justice and prove something. But it's not quite like that.
Let's start with the geography factor. The distribution of Lemaitr's work and fame about him concerned only Europe. His article was not translated into other languages and they say that at first it was lost and did not make much of an impression. That is, he did not acquire an impressive base of researchers who would spread this idea.
Hubble lived in US, wrote in English and quickly got supporters. It is important to note that Einstein recalled the work of Lemaitra after reading the Hubble evidence base and began to actively promote the first article (Lemaitra), since he finally believed in the truthfulness of the conclusions.
It is always difficult to determine primacy in the scientific community. Many scientists work for many years, put forward theories and find new data. Then comes the one who manages to make a breakthrough due to summation and evidence base. Most experts believe that in a particular case, Lemaitre was one of those who guessed expansion, but it was Hubble who was able to prove it.
However, the news is increasingly talking about the need to rename the law. And this is not just a rumor, but a preliminary decision of the International Astronomical Union. Perhaps in the near future there will be a Hubble-Lemaitre law. The essence does not change, but it is a tribute to the work of scientists. But then maybe Friedman should also be added?