GR Metric Tensor Rank 2: Quadratic vs Shear Forces

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SUMMARY

The metric tensor in General Relativity (GR) is definitively classified as a rank two tensor because it maps two vectors to a scalar, which is essential for defining the geometric properties of spacetime. This classification contrasts with the stress tensor, which is also rank two but specifically addresses shear forces. The discussion emphasizes that the quadratic nature of the line element, akin to the Pythagorean theorem, underpins the metric tensor's rank, highlighting its role in representing multiple physical phenomena within the same spacetime framework.

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  • Basic principles of stress and shear forces in physics
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Is the metric tensor a tensor of rank two simply because the line element (or equivalent Pythagorean relation between differential distances) is "quadratic" in nature? This would be in opposition to say, the stress tensor being a tensor of rank two because it has to deal with "shear" forces. I always thought GR dealt with tensors because we were dealing with multiple physical phenomena along the same space-time axes, such as stress-pressure, current, energy density, charge etc.

 
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A tensor of rank N maps N vectors to a scalar and N-1 vectors to a vector.

The metric tensor is of rank two because it maps two vectors to a scalar.
 
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