Redshift as a distance indicator

taylrl3

Surely it is possible to take a spectrum, deduce the redshift, then use this as a definitive distance indicator for all distances.

Why is it we use the distance ladder???

mgb_phys

The distance ladder was used to get the conversion factor between redshift and distance - Hubble's constant.

Also for nearer objects hubble's law isn't necessarily true if enough of their velocity is due to relative motion rather than the universe expanding.

Chronos

We need independent corroborations to test distance indicators. We must be doing something right as all are pretty consistent one to the other.

taylrl3

So for long distances, do we only use other methods (e.g SN) because of the uncertainty in Hubble's constant?

mgb_phys

No we use SN to get Hubble's constant.