A comoving coordinate system is a reference frame that expands in tandem with the expansion of the Universe, thus factoring out the effect of the Hubble expansion..
“Comoving coordinate” is the coordinate which expands in the same way as space. – Therefore, galaxies always remain at the same position in comoving coordinates.
Galaxies appear to be moving away from us. – More distant galaxies recede faster..
Fundamental observers = observers that move with the cosmic fluid.
CP: 1.
For every fundamental observer and for every time (her time) the Universe looks the same in every direction to her. 2.
If different fundamental observers record their observations, they come up with the same history of the Universe..
Comoving frame: Comoving frame is a coordinate system where an observer moves with the Hubble's flow of space expansion and, perceives the universe and the cosmic microwave background radiation (CMBR) to be isotropic..
