Perceived vs. Actual Velocity in an Expanding Universe

[zapnthund50]

According to what I've been taught, the distance-related redshift seen by Edwin Hubble is an artifact of an expanding Universe. That is, as light travels through space, space itself expands, redshifting the light (matter is embedded in space and does not itself expand but is instead carried along like raisins in a rising loaf of bread).

Ok. So assuming a mostly constant Universe expansion rate R, this means that the real velocity of a galaxy moving away from us would always be just R. However, the perceived velocity would always be H₀D.

Is this correct so far, that is, should the Hubble Velocity be seen as perceived, not actual? Thanks!

 

[Orodruin]

A rate is not a velocity, it does not even have the same units. The Hubble rate $H$ has units of 1/time whereas a velocity has units of length/time.

When it comes to interpreting "cosmological redshift" in terms of being an artefact of an expanding universe or an actual Doppler shift: It depends. Locally, both interpretations are equally valid and depend on the coordinate system you impose. See my Insight https://www.physicsforums.com/insights/coordinate-dependent-statements-expanding-universe/ Although it is written for A-level, you should be able to gain some understanding from it.

 

[stefan r]

... this means that the real... However, the perceived...

Reality is the thing we measure.