Particle-horizon radius versus patch diameter
= Particle-horizon radius versus patch diameter
The proper radial <particle horizon> is the distance travelled by a null <signal> since the initial boundary, measured on the current <time> slice. A spherical patch with that radius has twice that physical diameter. Dividing one or the other by an <angular diameter distance> therefore differs by a factor of two. A question using horizon size should state which linear extent is intended.