The unmoved mover

[Jehanne]

Not everyone here pretends to be a scientist. Some things are best left to professionals.

That's fine, I don't require him to be. I just figure if you think you understand it, you should be able to explain it, yes?

Not many folks can understand General Relativity; in fact, Einstein himself, at the beginning of his research, did not completely understand the mathematics (differential geometry) behind it:

In 1912, Einstein returned to Switzerland to accept a professorship at his alma mater, the ETH. Once back in Zurich, he immediately visited his old ETH classmate Marcel Grossmann, now a professor of mathematics, who introduced him to Riemannian geometry and, more generally, to differential geometry. On the recommendation of Italian mathematician Tullio Levi-Civita, Einstein began exploring the usefulness of general covariance (essentially the use of tensors) for his gravitational theory. For a while Einstein thought that there were problems with the approach, but he later returned to it and, by late 1915, had published his general theory of relativity in the form in which it is used today.[5] This theory explains gravitation as distortion of the structure of spacetime by matter, affecting the inertial motion of other matter.

When Einstein realized that general covariance was actually tenable, he quickly completed the development of the field equations that are named after him. However, he made a now-famous mistake. The field equations he published in October 1915 were
R μ ν = T μ ν  {\displaystyle R_{\mu \nu }=T_{\mu \nu }\,} ,
where R μ ν {\displaystyle R_{\mu \nu }} is the Ricci tensor, and T μ ν {\displaystyle T_{\mu \nu }} the energy–momentum tensor. This predicted the non-Newtonian perihelion precession of Mercury, and so had Einstein very excited. However, it was soon realized that they were inconsistent with the local conservation of energy–momentum unless the universe had a constant density of mass–energy–momentum. In other words, air, rock and even a vacuum should all have the same density. This inconsistency with observation sent Einstein back to the drawing board. However, the solution was all but obvious, and on November 25, 1915 Einstein presented the actual Einstein field equations to the Prussian Academy of Sciences:[16]
R μ ν − 1 2 R g μ ν = T μ ν {\displaystyle R_{\mu \nu }-{1 \over 2}Rg_{\mu \nu }=T_{\mu \nu }} ,
where R {\displaystyle R} is the Ricci scalar and g μ ν {\displaystyle g_{\mu \nu }} the metric tensor. With the publication of the field equations, the issue became one of solving them for various cases and interpreting the solutions. This and experimental verification have dominated general relativity research ever since.

https://en.wikipedia.org/wiki/History_of...relativity