Null expansion
= Null expansion
{title2=$\theta$}
The null expansion is $\theta=P^{ab}\widehat B_{ab}$. It is the logarithmic derivative of an infinitesimal transverse area: $\theta=A^{-1}dA/d\lambda$.
= Null expansion
{title2=$\theta$}
The null expansion is $\theta=P^{ab}\widehat B_{ab}$. It is the logarithmic derivative of an infinitesimal transverse area: $\theta=A^{-1}dA/d\lambda$.