What the significance of Einstein's Field equation been completely understood?

Question

and What are the Units of its tensors in terms of the four quantities of the Universe?

Answer 1

The significance of Einstein's Field equation (EFE) is that it describes how stress-energy causes curvature of spacetime, and that spacetime can be treated together as a 4-dimensional surface or manifold.

Einstein's Field Equation is fairly well understood today, and many solutions have been found. However, EFE being a non-linear differential equations, it is very difficult to obtain an exact solution.

The components of curvature tensors such as the Einstein tensor have, in geometric units, the dimensions of sectional curvature. So do the components of the stress-energy tensor. Therefore the Einstein field equation is dimensionally consistent in these units.

What this means is that the units of distance, time, mass, energy, etc., have all been converted into geometric units. In physics, especially in the general theory of relativity, geometric units constitute a physical unit system in which all physical quantities are identified with geometric quantities such as areas, lengths, dimensionless numbers, path curvatures, or sectional curvatures. In this system, the base physical units are chosen so that the speed of light, c, and the gravitational constant, G, and other relevant physical constants are set to equal one.