In physics, a perfect fluid is a fluid that can be completely characterized by its rest frame energy density ρ and isotropic pressure p.
Real fluids are "sticky" and contain (and conduct) heat. Perfect fluids are idealized models in which these possibilities are neglected. Specifically, perfect fluids have no shear stresses, viscosity, or heat conduction.
In tensor notation, the energy-momentum tensor of a perfect fluid can be written in the form
where U is the velocity vector field of the fluid and where is the metric tensor of Minkowski spacetime.
Perfect fluids admit a Lagrangian formulation, which allows the techniques used in field theory to be applied to fluids. In particular, this enables us to quantize perfect fluid models. This Lagrangian formulation can be generalized, but unfortunately, heat conduction and anisotropic stresses cannot be treated in these generalized formulations.
Perfect fluids are often used in general relativity to model idealized distributions of matter, such as in the interior of a star.
Famous quotes containing the words perfect and/or fluid:
“I call the years when our children are between six and twelve the “golden years,” not because everything’s perfect . . . but because the kids are capable and independent. . . . They’re becoming fascinating human beings who continually astound us and make us laugh. And they build our self-esteem. They still adore us for the most part, not yet having reached that age of thinking everything we do is dumb, old-fashioned and irrelevant.”
—Vicki Lansky (20th century)
“It is a mischievous notion that we are come late into nature; that the world was finished a long time ago. As the world was plastic and fluid in the hands of God, so it is ever to so much of his attributes as we bring to it. To ignorance and sin, it is flint. They adapt to themselves to it as they may; but in proportion as a man has anything in him divine, the firmament flows before him and takes his signet and form.”
—Ralph Waldo Emerson (1803–1882)