It was 100 years ago today that there was an eclipse that was used to test Einstein’s Theory of General Relativity. The Eclipse That Made Einstein Famous.
Specifically that part of General Relativity that said starlight would be deflected by the gravity of the sun (any star) even though a photon has zero mass.
Einstein first received word of their preliminary results in September, and wrote his mother with the “happy news.” The confirmation was officially announced in November at the Royal Astronomical Society in London, triggering headlines about the ensuing excitement. (“Men of Science More or Less Agog Over Results of Eclipse Observations,” one headline in The Times noted.) Einstein bought himself a congratulatory violin.
You can think about it like this. Gravity of a star affects the geometry of space-time, and light is impacted by that changing geometry.
And this is important for several reasons, not the least is…
“His equations allowed cosmology to become a science,” John Barrow, the cosmologist, wrote in an email. “Before him, cosmology was like a branch of art history. You could imagine any type, shape or form of universe you liked.”
Einstein published the theory of General Relativity in 1915. It generalizes the work he started with Special Relativity, which was published in 1905. And you use the results of his work every time you turn on (or consult) the GPS in your phone.
I would include some of the math, as it has been described as being “beautiful.” But it starts in the deep end of the pool as it is. Riemann manifolds, tensors, and lots of “strange” mathematical notations. If you have an interest there is a lot of info available all over the place. (A warning: I find the Wiki to be strangely organized. Best try something else.)