Einstein’s Magnum Opus, The field equations of general relativity
This article is written as a celebration of the 110th anniversary of the first appearance of one of the most elegant theories that describe our Universe: Einstein’s General Theory of Relativity.
After publishing his special theory of relativity (dealing with systems of reference moving with constant velocities), along with other monumental theories in 1905, Einstein would roll up his sleeves to attempt (and succeed) to formulate a more general theory that would include gravitation (and thus, accelerating systems). For that, he had to work with his close friend, the mathematician Marcel Grossmann, who was competent in the mathematics Einstein needed to form his extended theory, differential geometry.
On November 25, 1915, Einstein publicly announced that he had managed to form the covariant field equation that describes gravity and that it reduces to the Newtonian gravitational theory in the proper limit (and “coordinates’ conditions). Covariant meaning that the equation form doesn’t change under general coordinate transformations. I’m realizing that I am slipping into a little technical language, a habit from my education as an astrophysicist.
However, I must add that no other theory has not only withstood more experimental challenges but has also opened new ways to perform experiments that go far beyond what was imagined some decades ago (particularly the discovery of gravitational waves by LIGO).
I am sipping through a cup of hot chocolate in a coffee house somewhere on the border between Tokyo and Chiba, looking through the window to autumn trees shaking under a lovely autumn breeze and the portrait of an older Albert Einstein manages to come through my thoughts. Well done, old man, very well done.
Below, I am sharing some snippets of his arguments that appeared 110 years ago. Cheers!
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