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.