Hubble's Redshift: Conclusions and Vacuum Solutions

[OOO]

The far away galaxies are moving faster which Hubble concluded from their redshift. Could he also have come to the conclusion that the observed redshift is of gravitational (or more generally: geometrical, as resulting from a "weird" metric) origin ?

Does anybody know what a vacuum solution of Einstein's equations would have to look like in order to attract objects to the outside (if that's possible at all) ? What sources (energy-momentum distribution) would this imply ?

 

[EL]

The far away galaxies are moving faster which Hubble concluded from their redshift. Could he also have come to the conclusion that the observed redshift is of gravitational (or more generally: geometrical, as resulting from a "weird" metric) origin ?

The redshift has a "metric" origin.
See http://en.wikipedia.org/wiki/Redshift#Mechanisms
and especially http://en.wikipedia.org/wiki/Redshift#Expansion_of_space

 

[OOO]

Thanks, EL,

this clears it up. I've always thought that this was relativistic Doppler redshift. At least it's reassuring to know that Hubble and friends did also think that at first. Of course I've heard the term Robertson-Walker metric before, but as it is, I have not paid much attention to it.

 

[EL]

Thanks, EL,

this clears it up. I've always thought that this was relativistic Doppler redshift. At least it's reassuring to know that Hubble and friends did also think that at first. Of course I've heard the term Robertson-Walker metric before, but as it is, I have not paid much attention to it.

As you learn more cosmology, you'll be surprised how many misconceptions there exist in the popular view of the subject. Basically everything is actually quite complex, and when it is popularized a lot of stuff is left out. Unfortunately it's often not just the details, but also important basic concepts, which gets excluded.