Final answer:
The Einstein tensor in 2D or 1+1D is always zero due to the cancellation of terms in such low dimensions, leaving no complexity for curvature as described by the Einstein tensor in higher dimensions.
Step-by-step explanation:
When considering the Einstein tensor in the context of general relativity, it's important to understand how space-time is impacted by mass and energy. The Einstein tensor is a mathematical description that relates the curvature of space-time to the energy and momentum of whatever matter and radiation are present. In a 2-dimensional space (2D) or in a 1+1 dimensional space-time (1+1D), the Einstein tensor is indeed always zero. This outcome is due to the fact that in such lower dimensions, the Ricci curvature tensor, which the Einstein tensor is derived from, is proportional to the space-time's metric tensor times the scalar curvature. As a consequence, in 2D or 1+1D, the Einstein tensor, which subtracts this product from the Ricci tensor, is always zero because the terms cancel each other exactly. Thus, there is no room in such low dimensions for the complexity of curvature that is described by the Einstein tensor in higher dimensions like 3+1D, which is where our physical universe is situated.