/sci/ - Science & Math

[Anonymous No.8654245]

Here's a question for the real, non pop-sci anons.

In General Relativity, what is the relation between pressure and energy density? When is it useful to express pressure and when is it useful to express energy density? Are they interchangeable? I assume it's something to do with what you place as the components in the stress-energy tensor, but beyond that I don't know.

[Anonymous No.8654255]

>>8654245
Why should anyone answer you? Just so you can use it to fuel your half-baked popsci brainlet memes? If you really want to know, study.

[Anonymous No.8654272]

>>8654255
It's not popsci friend. I'm studying for a project at uni. For the project, I'm not required to know the depths of the field equations just yet, but I'm far behind so I thought I'd ask any kind anons that could shed some light for me, to help me catch up quicker.

[Anonymous No.8654315]

>>8654245
shameless self bump

[Anonymous No.8655104]

>>8654245
fuckit, bump again.

[Anonymous No.8655304]

Bumperino

[Anonymous No.8655321]

>>8654245
Its 2 different things. energy density is the time-time component of the stress energy tensor, and pressure is the sum of the density of linear momentum across the surface perpendicular to it in each direction. This is given by the 3 other diagonal components of the stress energy tensor. (Pressure only makes since when the 3 components are equal btw, otherwise its known as the 3 normal stresses).

Any relationship between them will be due to an equation of state, for example for dust you have pressure = 0, and energy density proportional to the dust density, while for a perfect fluid you have and energy density as a function of the rest energy density plus the pressure, with non zero pressure.