If an object is receeding because of spacetime expansion, is the redshift we measure because of spacetime expansion, and not necessarily the object's relative velocity? In other words, is the stretching of space what changes light's wavelength? If so, shouldn't receeding galaxies have two redshifts: One from the expansion of space that the light is travelling through, and one because the expanding space is carrying the object away?

This might apply more toward the oldest objects of the universe. The observational state that we see is close to the beginning of the universe where both extreme gravity and extreme motion would be occurring.

Blike I guess so, but they'd just add together and I can't imagine how you'd distinguish between the two.

I'm pretty sure the expansion of space is what gives the receding objects their relative velocities in the first place.

Right, but if they're receeding, wouldn't you see a recession redshift and an expansion redshift?

Are they two different things ?, or is the recession simply a result of the expansion? One in the same.

That wouldn't explain why the milky way or our solar system is moving. Space is sort of steady state around these parts or expanding very slow.

re they two different things ?, or is the recession simply a result of the expansion? One in the same

From what I've been reading: the redshift we see is the result of the space expanding that the light waves travel through. The expansion of space also carries along galaxies with it. Shouldn't there be two redshifts? One with the expansion of space and one because the expanding space is carrying the galaxy with it?

When you say "redshift we see is the result of the space expanding" I assume you are referring to special relativety's length contraction? contraction if you are moving towards the object, expansion if you are moving away from the object)

 

If so then the only thing you need to consider is the relative speed between the observer and the object being observed.

 

Also you are working with space-time as a whole.

 

It's an interesting question, I'm not sure if what I said is correct or not.

 

If there were 2 redshifts, well, you wouldn't really notice it, it would just appear as one redshift, you couldn't distinct or seperate them, indeed it would be impossible to directly observe, from which you could argue it doesn't exist, (unless you could indirectly observe it, but I don't see how).

Well, if there are two redshifts. maybe they add like two noises....the square root of the sums of the squares.....to make one.

If an object is receeding because of spacetime expansion, is the redshift we measure because of spacetime expansion, and not necessarily the object's relative velocity? In other words, is the stretching of space what changes light's wavelength? If so, shouldn't receeding galaxies have two redshifts: One from the expansion of space that the light is travelling through, and one because the expanding space is carrying the object away?

 

 

They add. Or, in some cases, subtract, because you could have local motion that is in the opposite direction. A little more