Question

Energy momentum tensor of a perfect fluid with vanishing density?

Answer 1

I came across a stress tensor in general relativity that has the form:

Tμν=⎡⎣⎢⎢⎢00000w0000−w00000⎤⎦⎥⎥⎥Tμν=[00000w0000−w00000]

in other words, there are two components of pressure and zero energy density. Is such a thing possible? What would it physically mean

Answer 2

$<marquee><b><u>The derivation of the null energy condition has only been achieved in recent years by establishing an equivalence to the strong subadditivity of entanglement entropy, and this only applies in AdS spaces. There is no yet a similar claim for de-Sitter spaces, which are believed to be metastable.$