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R is the Ricci Scalar , given by 

<img src='content_image/320891.jpg'>

with g µν being the inverse metric. In Eq. (2.4), G is Newton’s Gravita- tional Constant and T$_{µν}$ is the Energy-Momentum Tensor , also known as the Stress-Energy Tensor, which is defined as 

<img src='content_image/320890.jpg'>

where the T$_{00}$ component in red is the energy density, the T$_{i}$$_{0}$ components in orange are the momentum density, the T$_{0}$$_{i}$ components in orange are the energy flux, the components in blue are the shear stress and the T$_{ii}$ com- ponents in green are the pressure. The T$_{ij}$ components are the momentum flux. Sometimes the LHS of Eq. (2.4) is combined into a single tensor, known as the Einstein Tensor 

<img src='content_image/320889.jpg'>

The Einstein Field Equation relates the curvature of a region of spacetime, i.e. the strength of gravity, to the amount of energy, momentum and stress that is present within that spacetime region. 

