Quote:
Originally Posted by renormalised
Both a Doppler shift and a Hubble redshift have kinematic origins, by definition. Both are caused by the movement of something...individual galaxies under gravity in the case of a Doppler shift. The other caused by expanding spacetime, which is also movement, but not of the galaxies themselves. Just like raisins in a dough, they may jostle about a bit when cooked (gravity/Doppler shift), but the dough rises and expands, carrying the raisins along with it (expansion/Hubble redshift). It's easy enough to see where they're coming from, but it's still a question of semantics. Unless, of course, they actually think that the redshift is being caused by actual movement of the galaxies through space (not with space, as is the case for expansion). That's a different matter entirely.
|
Ah ... but what happens if the spacetime dough disappears ? Would two raisins stuck together by a bit of stringy, gooey dough come together or would they fly apart ?
(Page 13 contains the answer .. for the cheats, that is).
Cheers
PS: Yep I am a bit of a stirrer at times .. after all .. what can ya expect from a hamster (Witten's, that is) !!