Chaplygin gas, which occurs in certain theories of cosmology, is a hypothetical substance that satisfies an exotic equation of state in the form
p
=
−
A
/
ρ
α
{\displaystyle p=-A/\rho ^{\alpha }}
,
where
p
{\displaystyle p}
is the pressure,
ρ
{\displaystyle \rho }
is the density, with
α
=
1
{\displaystyle \alpha =1}
and
A
{\displaystyle A}
a positive constant. The substance is named after Sergey Chaplygin.
In some models, generalized Chaplygin gas is considered, where
α
{\displaystyle \alpha }
is a parameter, which can take on values
0
<
α
≤
1
{\displaystyle 0<\alpha \leq 1}
.
A slowly rotating spherically symmetric, non-viscous, self-gravitating Chapligin gas solves the Hubble tension.