Null geodesics and null curves

[blueelectrons]

What is the exact difference between null geodesics and null curves? Please explain both qualitatively and quantitatively.

 

[Orodruin]

Null geodesics are parametrised such that the tangent vector is parallel transported along it. This is not necessarily the case for any null curve.

 

[PAllen]

Consider the path, in polar coordinates: θ = ct/R

A circular light speed path of radius R. This is null path that is not geodesic. Light would not take such a path in vaccuo.

 

[blueelectrons]

ok..thanks Orodruin and PAllen.