Einstein couldn't find a research job after graduating from university, so he worked in the Swiss Patent Office for a while, checking the application documents. In the meantime, he wrote a paper on physics, but he was busy studying in the library. Without knowing the frontier research of Lorenz and Poincare, he wrote a paper on special relativity. Perhaps because of this profession, his thesis is somewhat amateur.
Professional physicists don't write superfluous things, but summarize the main points, but Einstein is interesting because it describes what ideas he is based on. In his cosmology thesis, his cosmology has been fully developed.
Based on the theory of time dynamics, this paper holds that galaxies are the only celestial bodies existing in outer space. When I was infinitely away from the galaxy, I had studied all kinds of things about the geometric characteristics of space, but I couldn't find a reasonable answer. He wrote that he came up with a spherical structure that would return to the origin when going straight, as a space that could not be far away from the galaxy.
But even if it is substituted into the spherical space equation, it can not satisfy the basic equation of relativity. Therefore, I choose to change the basic equation into the form of adding cosmological constants. The solution of spherical space satisfying the modified equation is the so-called "Einstein static universe". From these descriptions, it can be seen that what is important to him is the geometric structure when he leaves the galaxy, and he did not regard the change with time as a problem in the end.
Following Einstein's idea of spherical space, Friedman discussed its dynamic behavior. His paper published in 1922 is often described in the history books of science as "considering the solutions of equations without cosmological constants", but this is not the case. When cosmological constants are added, the solution is calculated according to the situation.
There are some mathematical mistakes in Friedman's paper, but the reasons can be inferred by reading the original text.
Because many basic equations in modern physics are in the form of partial differential equations, it is very common to teach partial differential equations to science and engineering students now. However, at the beginning of the 20th century, even in Western Europe, there was no systematic system for teaching partial differential equations.
In Friedman's Russia, the education system will be further delayed. Where he made mistakes, he quoted an old mathematical paper before Weierstrass 1866, but he may not have the opportunity to obtain the latest analytical research literature.
Together with Friedman, Lemaistre played an important role in the study of cosmology. He showed in 1927 that Einstein's static universe was unstable and turned to expand with slight fluctuations. Sometimes it is said that Lemaistre discussed the general solution of the equation containing cosmological constants, which is different from Friedman's, but in fact Friedman discussed the general solution, while Lemaistre mainly dealt with the special solution.
Although it was published in French in a little-known Belgian journal, Lemaistre's paper caught the attention of British astronomy tycoon Eddington and became the focus of attention. Eddington suggested that this paper be translated into English for dissemination. Lemaistre's own English translation was published in 193 1. Nowadays, English translation is mainly included in the collection of cosmological papers.
This English translation is somewhat different from the original. Now you can find the original French version on the Internet. If you are interested, search it.
Friedman was not mentioned in the original paper, but he didn't steal his achievements. He doesn't know. In English translation, the newly added annotations provide positive comments.
Importantly, in English translation, the part discussing the relationship between observed data and theoretical prediction has been completely deleted. The reason for the deletion is unclear, but it may be that Hubble released the latest data of distant galaxies at 1929, so he didn't think it was necessary to keep the old data. However, if the missing part still exists, it is more widely known that Silver observed the decay rate of galaxies before Hubble.
In addition, Lemaistre predicted that the redshift found in distant galaxies is proportional to the distance, and verified it with the data before Hubble. Hubble insists on this proportional relationship according to his own observation data in the paper, but the data displayed there have great errors, so it is difficult to admit that this proportional relationship itself is established.
Hubble borrowed Lemaistre's idea and advocated proportionality, because both Lemaistre and Hubble attended an international conference in 1928, where they exchanged views on the relationship between redshift and distance. Maybe so. In view of these circumstances, the General Assembly of 20 18 International Astronomical Union decided to rename the so-called "Hubble Law" as "Hubble Law".