Energy density in Stress Energy Tensor

shounakbhatta
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Hello,

I am new to this, if somebody could help me:

The energy density in stress-energy-tensor is the amount of energy stored in a given system per unit mass. The T00=energy density.

In a 4x4 matrix, we generally start with 1,1. Why it is 0,0?

Secondly, what does energy density mean mathematically? I am unable to get over the concept.

Thanks,

-- Shounak
 
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It's common (but not universal) to number the time dimension as 0 instead of 4 (x, y, and z or other spatial directions would be 1-3). It doesn't make a big difference either way.

Energy density = energy per unit volume.
 
Ok, thanks a lot.
 
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