Chalky
Jan5-09, 06:00 AM
On Dec 31 2008, 9:46Â*pm, Chalky <chalkys...@bleachboys.co.uk> wrote:
> On Dec 31, 6:03 pm, hel...@astro.multiCLOTHESvax.de (Phillip Helbig---
> remove CLOTHES to reply) wrote:
>
> > If we measure the cosmological redshift of an object now and then
> > again in, say, 30 years, in almost all cosmological models the measured
> > redshift will be different 30 years from now and right at the limit of
> > current spectrographical precision.
>
> This is a little different from what you said originally, which was:
>
> > > > Spectrographs are now becoming so precise that the
> > > > change in the cosmological redshift can be noticed on a timescale of
> > > > years or decades.
> > > References, please!
>
> > astro-ph/9802122
>
> I must have misunderstood you initially. I inferred this was
> observationally verified fact. However, the first sentence of the
> conclusion reads:
>
> "Equation (3) implies that the change in the redshifts of
> extragalactic objects due to the deceleration of the Universe is not
> far out of reach of existing spectroscopic instrumentation".
>
> Apart from this being theoretical prediction not observation, I find
> this claim a bit strange (and outdated), since we are now seeing
> evidence of accelerating not decelerating expansion.
>
> > > Also, would I be correct in guessing that these sources are at
> > > redshifts of less than ~ 0.15 ?
>
> > No. Â*Why (details please) would you expect this?
>
> My own analyses of Union data indicate that mean magnitude-z
> relationships increase much more rapidly than expected from.015 to ~ .
> 055
>
> Its _unknown_ cause could potentially have weird side effects larger
> than those contemplated in the above ref.
>
> Perhaps this has something to do with the "Hubble bubble" I have seen
> alluded to? I couldn't say for sure since general searches thus far
> all returned the Turkish smoking device :-)
......And/or, perhaps, this simply has something to do with the
homogeneity assumption being invalid on scales of <~1.5 billion light
years - the evidence just seems more drastic at low z, because of the
tighter observational error constraints.
> On Dec 31, 6:03 pm, hel...@astro.multiCLOTHESvax.de (Phillip Helbig---
> remove CLOTHES to reply) wrote:
>
> > If we measure the cosmological redshift of an object now and then
> > again in, say, 30 years, in almost all cosmological models the measured
> > redshift will be different 30 years from now and right at the limit of
> > current spectrographical precision.
>
> This is a little different from what you said originally, which was:
>
> > > > Spectrographs are now becoming so precise that the
> > > > change in the cosmological redshift can be noticed on a timescale of
> > > > years or decades.
> > > References, please!
>
> > astro-ph/9802122
>
> I must have misunderstood you initially. I inferred this was
> observationally verified fact. However, the first sentence of the
> conclusion reads:
>
> "Equation (3) implies that the change in the redshifts of
> extragalactic objects due to the deceleration of the Universe is not
> far out of reach of existing spectroscopic instrumentation".
>
> Apart from this being theoretical prediction not observation, I find
> this claim a bit strange (and outdated), since we are now seeing
> evidence of accelerating not decelerating expansion.
>
> > > Also, would I be correct in guessing that these sources are at
> > > redshifts of less than ~ 0.15 ?
>
> > No. Â*Why (details please) would you expect this?
>
> My own analyses of Union data indicate that mean magnitude-z
> relationships increase much more rapidly than expected from.015 to ~ .
> 055
>
> Its _unknown_ cause could potentially have weird side effects larger
> than those contemplated in the above ref.
>
> Perhaps this has something to do with the "Hubble bubble" I have seen
> alluded to? I couldn't say for sure since general searches thus far
> all returned the Turkish smoking device :-)
......And/or, perhaps, this simply has something to do with the
homogeneity assumption being invalid on scales of <~1.5 billion light
years - the evidence just seems more drastic at low z, because of the
tighter observational error constraints.