Aka stress-energy-momentum tensor or stress-energy tensor.
The energy-momentum tensor is to four-momentum like the mass-current is to a point mass:
1. Point Mass and Mass-Current: In classical mechanics and electromagnetism, a point mass is a simplified model that represents mass concentrated at a single point in space. Indeed, it is a curve: the curve in spacetime described by the point mass. This concept is useful for calculations in scenarios where the size and shape of the object are irrelevant to the problem at hand. On the other hand, a mass-current (or mass current density) is a concept used to describe how mass is distributed and moves through space. It's a more general and continuous representation, suitable for describing extended objects or continuous media, like fluids.
2. Four-Momentum and Energy-Momentum Tensor: In the context of special and general relativity, the four-momentum vector is a way to represent the energy and momentum of a particle (or point-like object) in a four-dimensional spacetime framework. It's a compact way to describe the motion and energetic characteristics of a particle. On the other hand, the energy-momentum tensor is a more general, field-based concept. It describes the energy and momentum distribution in a region of spacetime. It's applicable to continuous media.
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Author of the notes: Antonio J. Pan-Collantes
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