Math of General Relativity - Part 18

First, we quantify the amount of "inertia" that gravity imparts on matter and call it "mass." We could also call it "weight" or energy, since they are all proportional. By convention, let us call it mass-energy, mass or energy, whichever is most convenient. Also for convenience, we can call matter just "mass," as in "This mass is heavy," etc., referring to an actual object.

Just like in electromagnetism, an object that reacts to gravity is a SOURCE of gravity. Mass emits gravity (in the form of gravitons, I would assume). To calculate the gravity in Madison Square Garden, therefore, we need to know how mass-energy is distributed in space around MSG. For purposes of calculation, only the mass of Earth is needed, but we don't even need to know that, since we are not actually going to calculate anything.

Once we know how much mass and energy is around MSG and how it is moving, we can calculate 16 numbers, which we will envision as a 4x4 Matrix called the Metric Tensor G, made up of small g's. See figure. Each g is a mathematical function of space and time. That is, if you give me a place in MSG, like a specific seat at a point (45, 67, 9) at a time (10,000 seconds), I can calculate each of the 15 g's as a specific number, giving me a 4x4 array of sixteen numbers.