Chaplygin gas

, which occurs in certain theories of cosmology

Cosmology

Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...

, is a hypothetical substance that satisfies an exotic equation of state

Equation of state

In physics and thermodynamics, an equation of state is a relation between state variables. More specifically, an equation of state is a thermodynamic equation describing the state of matter under a given set of physical conditions...

 in the form

where is the pressure, is the density, with and a positive constant. The substance is named after Sergey Chaplygin.

In some models, generalized Chaplygin gas is considered, where is a parameter which can take on values .