I thought it would be a good idea to produce a thread linking important papers on cosmology as a reference as its an endless source of debate and confusion. My own grasp of the topic is limited as a chemist does not really need to know GR. So my commentary would be superficial. Others are free to add details. I am providing links to pdf which are not behind pay wall.
Original paper by Lemaitre (1927) on the expanding universe solution of Einstein equations.
- Google Scholar
While Friedmann (https://en.m.wikipedia.org/wiki/Friedmann_equations) is rightly credited with developing the solutions for Einstein's field equations that are applicable for various universes (that is various types of space-time-matter-radiation combinations that satisfy GR), it's Lamaitre who produced a simple set of physically interpretable universes that could be used by cosmologists to interpret and test various theories about the cosmos. He combined the expanding universe solutions to Einstein's equations developed by Friedman with redshift data from Hubble, explaining as a Doppler effect due to stretching of space. He showed that such a universe has no center or edge (see the paper above) though it can be finite or infinite. He also showed that Einstein's equations have a very simple physical interpretation as conservation of energy and thermodynamic interplay between mass and radiation pressure. He also provided the first calculation of the expansion rate of space and determined the value of the "Hubble" constant two years before Hubble himself. He found many valid solutions to the Einstein equation, but one he favored the most was the "Lemaitre" universe which had expanded from a very hot, dense state through high radiation pressure, slowed down due to gravity and then accelerated again due to repulsive pressure due to cosmological constant. A modified version of this Lamaitre universe is the current best theory of the universe today describing the period after inflation.
There was an interesting controversy as to why Hubble got the credit for both the Hubble constant and the Hubble law when Lamaitre derived them first in the 1927 paper. It now appears that Lamaitre himself considered Hubble, who did the experimental work of galaxy redshift, to have the first claim on analysis of his own data, and hence dropped his derivation based on Hubble's early work in later and more popular English reprints of his paper in the Royal Astronomy Society journal. Good for him.
Original paper by Lemaitre (1927) on the expanding universe solution of Einstein equations.
- Google Scholar
While Friedmann (https://en.m.wikipedia.org/wiki/Friedmann_equations) is rightly credited with developing the solutions for Einstein's field equations that are applicable for various universes (that is various types of space-time-matter-radiation combinations that satisfy GR), it's Lamaitre who produced a simple set of physically interpretable universes that could be used by cosmologists to interpret and test various theories about the cosmos. He combined the expanding universe solutions to Einstein's equations developed by Friedman with redshift data from Hubble, explaining as a Doppler effect due to stretching of space. He showed that such a universe has no center or edge (see the paper above) though it can be finite or infinite. He also showed that Einstein's equations have a very simple physical interpretation as conservation of energy and thermodynamic interplay between mass and radiation pressure. He also provided the first calculation of the expansion rate of space and determined the value of the "Hubble" constant two years before Hubble himself. He found many valid solutions to the Einstein equation, but one he favored the most was the "Lemaitre" universe which had expanded from a very hot, dense state through high radiation pressure, slowed down due to gravity and then accelerated again due to repulsive pressure due to cosmological constant. A modified version of this Lamaitre universe is the current best theory of the universe today describing the period after inflation.
There was an interesting controversy as to why Hubble got the credit for both the Hubble constant and the Hubble law when Lamaitre derived them first in the 1927 paper. It now appears that Lamaitre himself considered Hubble, who did the experimental work of galaxy redshift, to have the first claim on analysis of his own data, and hence dropped his derivation based on Hubble's early work in later and more popular English reprints of his paper in the Royal Astronomy Society journal. Good for him.
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