Before the birth of modern cosmology, people did believe the world is flat and they did not know very much about cosmology.
Before Isaac Newton’s explanation of gravity was offered, all cosmological models were fairly local. This means that they attempted to describe the behavior of the bodies that make up the Sol System, but they did not delve into knowledge of the Universe as a whole.
In 1755, the German philosopher Emanual Kant published his work “General Natural History and Theory of the Heavens,” in which he defended the idea that the nebulae seen in the night sky could be other galaxies similar to ours.
The Birth of Modern Cosmology
It was only in 1610 that Galileo discovered that the band of sky known as the Milky Way was made up of an enormous number of individual stars. Clearly, this was also the result of a lack of knowledge about the content of the universe.
However, Newton maintained that because his rule of attraction applies everywhere, the components that make up our universe should attract one another even if he did not have a complete understanding of those components.
Given that the attraction of all bodies should cause the universe to collapse at a single point, he reasoned that a static universe would not be conceivable and came to this conclusion as a result.
Isaac Newton had the premonition that the presence of a universal repulsive force could maintain the equilibrium of the universe, despite the fact that it had been demonstrated that such a force would be quite unstable and make it impossible to maintain the universe’s appearance for an extended period of time.
In addition to this, he thought that when viewed from a sufficiently broad scale, the distribution of matter across the universe ought to give the impression of being uniform.
Also, Kant’s cosmological paradigm was emphasized. In spite of the fact that it was extremely qualitative and in many respects erroneous, it included a number of concepts that were physically sound.
For example, it supported the idea that matter agglomerated in a hierarchical fashion, on ever greater sizes (this behavior is currently visible in the existence of star systems, galaxies, conglomerates of galaxies and super conglomerates, etc)
In addition to this, he argued for the presence of a mysterious repelling force that held the universe apart from itself and kept it from collapsing in on itself.
The Birth of Modern Cosmology by Einstein
It was only in 1915 with the appearance of General Relativity that Cosmology can be assumed as a complete scientific discipline, that is, capable of building a theoretically valid model and extracting predictions capable of being compared with observations.
Not wanting to leave credits aside, Albert Einstein himself developed his cosmological model in 1917 and started the birth of modern cosmology.
Like Newton, the German physicist also understood that a Universe made up only of “normal” matter could not be static since the universal attraction would lead to an eventual collapse of all matter in a single point. Newton hardly dared to defend the existence of a repulsive entity of unknown origin.
Einstein, armed with the equation that bore his name, went further and decided to alter it.
Did Einstein establish the birth of modern cosmology?
Before Einstein, cosmology had not advanced much at all in the contemporary sense. The vast majority of scientists avoided it. It was thought that only philosophers or maybe theologians should address the issue. You don’t even need a mathematical background to study cosmology.
However, Einstein demonstrated how the mathematical framework of general relativity might be utilized to accomplish the goal of characterizing the cosmos. His hypothesis provided a method for the accurate study of cosmology, with a rock-solid basis in both physics and mathematics.
Einstein established the formula for making cosmology an area of scientific inquiry as opposed to cosmology being a realm of conjecture.
There is little room for debate regarding the fact that Einstein’s article published in 1917 started the birth of modern cosmology.
Even before he had completed developing his new theory, Einstein had already begun to consider how it will affect cosmology. In the end, general relativity was a theory that included both space and time in their entirety.
Einstein’s work demonstrated that gravity, the driving force that shapes the architecture of the universe, was nothing more than a distortion in the geometry of spacetime that was caused by the presence of mass and energy.
The entire cosmos ought to act in the manner that is needed by the equation for general relativity given that spacetime and mass-energy account for virtually everything.
Newton’s law of gravity has caused difficulties in this particular aspect. If every mass attracted every other mass, as Newton had declared, then all of the matter in the cosmos ought to have merely folded itself into one enormous blob.
Newton postulated that the cosmos was limitless and completely stuffed with matter, so that the attraction of matter closer to us was counterbalanced by the attraction of matter further away. However, no one was truly convinced by that explanation.
For one thing, it requires an extremely perfect arrangement: If one star is moved out of position, the equilibrium of attractions will be disrupted, and the universe would come to an end. It also requires an infinite number of stars, which makes it hard to explain why the night sky is so gloomy.
Einstein anticipated that his theory of gravity would answer the cosmological conundrums that Newtonian gravity presented.
Therefore, in the early months of 1917, less than a year after the publication of his comprehensive article on the general theory, he presented a brief report to the Prussian Academy of Sciences describing the implications of his theory and establishing the birth of modern cosmology.