I usually come across expressions for the Stress energy tensor showing them as three densities (normally over a space-like slice.(adsbygoogle = window.adsbygoogle || []).push({});

In wikipedia's article on the spin tensor, they clearly (it does not appear to be an error) both write about and express the components of the stress energy tensor as four-densities. Is the three density just an approximation then?

For example:

I usually come across this as an integral over three-space.

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# Stress energy components as a 3 or 4 density?

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