On Sun, 24 Jun 2007 00:01:20 -0700, Roland PJ
wrote:

Red-shift of distant objects could be due to two different reasons:

1. Recession speed away from the earth, a special relativistic
effect.
2. Time dilation due to proximity to a concentration of mass, a
general relativistic effect.

Gravitational redshift is far weaker than Doppler. Here's a couple of
figures, for a "nearby" star at 1 million LY.
H*D = 27,560 m/s more or less
Redshift is 9.1x10^-5 both Doppler
Redshift at Sun is 635 m/s (and, presumably for typical star)
z = 2x10^-6
so doppler is about 43 times as much. The tolerances on distance, the
Hubble constant, mass of star, make it difficult to separate the two.
In this case you could guess the redshift/distance is "fat" by 1/43.
For a star at 1 billion LY, z = .1 or so from Doppler, but the
gravitational remains a low 2e-6 as above.

It seems that most discussion of red-shift centres around the
assumption that SR recession is the cause (and hence that the universe
is expanding).

Why has GR time dilation been eliminated as a cause?

So, why should most objects exhibit a red-shift, rather than a neutral
average shift? My best answer is that we, on earth, are at the edge of
our galaxy (the milky way), and hence quite far from the concentration
of mass near the centre of our galaxy.

On the other hand, most matter (stars) in the universe are close to
the centre of their galaxies, so, on average, most objects should
exhibit a red-shift to us on earth.

A corollary of this is that stars near the centre of our own galaxy
(the milky way) should also exhibit red-shift to us (even though they
are clearly not moving away from us on average). This should be
testable, although I'm not sure how one would identify a bright object
as a star in the center of our galaxy, rather than a distant object
shining through (brightness?).

Hubble, Edwin, "A Relation between Distance and Radial Velocity among
Extra-Galactic Nebulae" (1929) Proceedings of the National Academy of
Sciences of the United States of America, Volume 15, Issue 3, pp.
168-173

Note that Hubble (and presumably all that follow) use _luminosity_ as
a measure of _distance_. However, luminosity is actually also a
measure of GR time dilation, independent of distance, as described
above.

Just some ideas.
Flame away

Roland
John Polasek

On Jun 24, 2:27 am, Roland PJ wrote:
[...]

Ugh.

You don't know what Hubble's law is.
You don't understand Cephid variables.
You don't understand why time dilation is not a viable explanation.

http://en.wikipedia.org/wiki/Cepheid_variables
http://www.astro.ucla.edu/~wright/cosmolog.htm

Dear Roland PJ:

"Roland PJ" wrote in message
oups.com...
On Jun 24, 8:02 pm, "N:dlzc D:aol T:com \(dlzc\)"

wrote:
Dear Roland PJ:

"Roland PJ" wrote in message

oups.com...

Red-shift of distant objects could be due to two
... or more ...
different reasons:

1. Recession speed away from the earth, a special
relativistic effect.

... also just classical Doppler.

Except it needs finite light speed doesn't it, which was
one of the foundations of SR? I'd better check

Classical Doppler shift does require finite "wave" speed.

Recession red shift could simply be classical Doppler, without
invoking Minkowski spacetime. Just another "reason" to add to
the list.

2. Time dilation due to proximity to a concentration
of mass, a general relativistic effect.

No. We can measure gravitational time dialtion in the
spectrum of the sources. Distant sources are more
redshifted... regardless of their mass, only their distance.

Um, how can spectral analysis discriminate between time-
dilation and recession (or expansion, if you like)? The
spectra are shifted in both case, not so? Can you explain
some more?

The spectra are shifted more, if the source is further away. We
cannot discern from the shift alone all we need to know. But
what we do see, is that similar stars / objects, have spectra
that are red shifted more, the more distant they are.

This means they have to be uniformly more massive (to use your
"reason"), the physics had to be different in the past, or more
simply more space is being created between objects.

"Uniformly more massive with distance" is not possible, since the
stars could not produce the spectra we do see. They would become
supernovae, neutron stars, or black holes.

The "different physics" is a possibility, in which case we have
no model at all to use.

"More space created" is in line with the second law of
thermodynamics, and is not an irreconcilable violation of any of
the other conservation laws.

What you picture will require special physics
as a function of distance, to red shift more distant stars
more
than gravitation red shift shifts the same size and type of
star
locally.

OK, I have no idea what you mean by this.

Hopefully clearer now. We see the equivalent of Sagitarius-A
locally and far away. If Sagitarius-A were more massive to yield
the red shift, then I collapses into a neutron star... and is not
like Sagitarius-A. Same for massive galaxies... their rotation
curves do not correlate to being more massive the further they
are from us.

So, why should most objects exhibit a red-shift, rather
than a neutral average shift?

Because there is increased space(time) between you
and the source between instants. Imagine
space(time) as sal****er taffy stretched between your
two hands, with your hands as two distant stars. As
time goes on (weather permitting) the taffy stretches,
and the distance between the two "stars" (measured
along the taffy) increases and signals between them
take longer (red shift). From this poor analogy, better
ones are the balloon analogy and the raisin bread
analogy.

Note that I was trying to answer this question according
to my theory, not pose it . Yes, I can see that
expansion theories explain the Hubble red-shift
phenomenon. I was simply trying to propose a simpler
solution, namely plain old GR in a non-expanding
universe. Occam's razor and all.

Fails the most simple tests. You asked if it could be, and no it
cannot. *That* way.

Now consider emission of a spectra from a star in a Universe with
a certain global curvature, but received in a more expanded
Universe with a more "relaxed" curvature. The spectra would be
seen as redshifted due to gravitational time dilation... between
*time of emission* and *time of absorbance*. Not "place" but
"when".

My best answer is that we, on earth, are at the edge
of our galaxy (the milky way),

Not quite... we are about halfway out.

2/3 if you want to nit-pick

and hence quite far from the concentration
of mass near the centre of our galaxy.

Doesn't matter. The spectra locally (inclusive of
even the Andromeda galaxy) are unsurprising. And
we have all sorts of candidates visible locally.

Yes it does matter. GR time dilation is directly
related to your matter/energy environment. The fact
that we are at the edge of our galaxy means that
matter near the denser core is red-shifted relative
to us. As Eric has pointed out, this difference
might be too small to matter, but you can't just
wave it away with a magic wand without doing the
sums (which I intend to do... see questions below).

How is this different for the "central mass" of a distant galaxy?
The *whole curve* is redshifted... central stars or rim stars.

Or perhaps we are missing each other here - I'm not
sure how your 'spectra' comment relates. Or are you
saying that the spectra from stars all over the milky
way display no shift at all?

Shifts similar to other members of the Milky Way. Shifts similar
to other members of the Andromeda galaxy. Shifts *different* for
similar objects outside the Virgo supercluster.

In which case time dilation clearly can't be a factor
within our own galaxy.

It is "in the dirt". It can theoretically be measured, but is
"orthogonal" to the problem you wish to solve. You want to get
at why a distant Milky-Way-like object doesn't have an identical
spectra to our Milky Way et al. You really are not interested in
the distribution across a single object... because after a
certain distance, they get resolved (if at all) en masse.

If you are interested in more than your own ideas, you
can start he
http://www.astro.ucla.edu/~wright/cosmolog.htm
http://www.astro.ucla.edu/~wright/cosmo_01.htm
... and if you have questions, you can either ask here or on
sci.astro.

Thanks for the links. Will follow them up.

Now, what I really need to see whether my idea has any legs is
an
accurate map of the Milky Way.

Way different than describing Hubble red shift, which is where I
thought you wanted to go.

David A. Smith

On Jun 24, 11:49 pm, John C. Polasek wrote:
On Sun, 24 Jun 2007 00:01:20 -0700, Roland PJ
wrote:

Red-shift of distant objects could be due to two different reasons:

1. Recession speed away from the earth, a special relativistic
effect.
2. Time dilation due to proximity to a concentration of mass, a
general relativistic effect.

Gravitational redshift is far weaker than Doppler. Here's a couple of
figures, for a "nearby" star at 1 million LY.
H*D = 27,560 m/s more or less
Redshift is 9.1x10^-5 both Doppler
Redshift at Sun is 635 m/s (and, presumably for typical star)
z = 2x10^-6
so doppler is about 43 times as much.

Oh. You've calculated the GR red-shift due to the mass of the star
itself. Right? I'm actually surprised it's so big.

What I'm more interested in is the GR effects due to the surrounding
mass (the star's galaxy in particular).

For isolated stars out on the edge of galaxies the answer should be as
the above. But for stars near the middle of galaxies there should be
arbitrary red-shift depending on how close they are to the center of
the galaxy, and how dense the centre is. It seems to be generally
proposed that there are 'black holes' at the centre of most galaxies.

And the crux is that 'most' stars are collected in the centre of the
galaxy. To find out the 'typical' red-shift of the average star then,
we need to know the star density gradient of the 'average' galaxy.

I have no ide how to obtain this gradient density.

Thanks for the help.

Regards
Roland

Now, what I really need to see whether my idea has any legs is
an
accurate map of the Milky Way.

Way different than describing Hubble red shift, which is where I
thought you wanted to go.

David, thanks again for your considered response.

Let me start again by explaining my reasoning from scratch.

It seems to be plausible that the centre of galaxies is very dense. In
fact, it seems to be generally held that the centre of our Milky Way
is dense enough to be described as a 'black hole'.

An immediate consequence of this is that stars 'near' the centre of a
galaxy will be red-shifted according to the enormous GR effects of the
centre of the galaxy itself.

Indeed, consider a Cepheid variable living near the center of the
Milky Way. This Cepheid will be subject to much larger GR effects than
us on earth, so we will view it, on earth, as being red-shifted, dim,
and having a larger period, than what is experienced in the Cepheid's
own frame.

I don't think any of the above is contentious at all. It's a well
understood consequence of GR.

So, at least some of the stars in a galaxy will display exaggerated
red-shifts and dimness, due to their position near the middle of the
galaxy, and due to GR time dilation, not expansion or recession speed.

What I want to know is 'How many stars in a typical galaxy have an
exaggerated red-shift and dimness'.

This depends critically on the star density function towards the
middle of a galaxy. In other words, what proportion of the stars are
close enough to the middle to be affected by GR effects.

It's clear that, for any galaxy with a dense centre, at least _some_
stars will have red-shifts dominated by GR time-dilation effects.

What I'm asking, is how many stars will have red-shifts (as viewed on
earth) that are dominated by GR time-dilation, rather than universal
expansion, or recession.

Is it 0.0001% (i.e. irrelevent). Is it 10% (interesting). Is it 90%
(in which case the standard Hubble constant is broken by GR).

Do you understand now why I need a 'map' of the Milky Way. It seems
that the Milky Way itself is close enough to map all stars with red-
shift-free methods, such as the parallax methods.

I can do some relatively (no pun intended) simple estimations of the
GR effect, but I need to know the mass density function towards the
centre.

Regards
Roland

Dear Roland PJ:

On Jun 25, 2:16 am, Roland PJ wrote:
....
What I'm asking, is how many stars will have red-shifts
(as viewed on earth) that are dominated by GR time-
dilation, rather than universal expansion, or recession.

Is it 0.0001% (i.e. irrelevent). Is it 10% (interesting). Is
it 90% (in which case the standard Hubble constant is
broken by GR).

The answer is "about 0%". Spiral galaxies *all* have massive
centers. So comparison of spiral galaxies is inclusive of the center,
the arms, and probably some contribution from the attendant globular
clusters.

Compare a galaxy to a bus-load of people. You think that you need to
analyze the bus-load you are in, to be able to analyze / compare /
contrast other bus loads visible. It might help you compare the Milky
Way to Andromeda to do this, but it won't help you with galaxies
outside our supercluster.

Do you feel the distant "bus loads of people" are significantly
different than the bus on the Andromeda route? If so, why?

David A. Smith

On Jun 25, 5:38 pm, dlzc wrote:
Dear Roland PJ:

On Jun 25, 2:16 am, Roland PJ wrote:
...

What I'm asking, is how many stars will have red-shifts
(as viewed on earth) that are dominated by GR time-
dilation, rather than universal expansion, or recession.

Is it 0.0001% (i.e. irrelevent). Is it 10% (interesting). Is
it 90% (in which case the standard Hubble constant is
broken by GR).

The answer is "about 0%". Spiral galaxies *all* have massive
centers. So comparison of spiral galaxies is inclusive of the center,
the arms, and probably some contribution from the attendant globular
clusters.

Compare a galaxy to a bus-load of people. You think that you need to
analyze the bus-load you are in, to be able to analyze / compare /
contrast other bus loads visible. It might help you compare the Milky
Way to Andromeda to do this, but it won't help you with galaxies
outside our supercluster.

Do you feel the distant "bus loads of people" are significantly
different than the bus on the Andromeda route? If so, why?

No. I'm just trying to understand the Milky Way better, under the
assumption that it's somewhat 'typical'.

So, some specific questions, which might be more fruitful:

What's the greatest red-shift we have measured for an object that's
definitely in the Milky Way (according to parallax, for example).

And, generalising this, what proportion of stars in the Milky Way do
we find at various red-shifts?

And, then another specific question, but not directly related (it came
up earlier in the thread):

http://en.wikipedia.org/wiki/Andromeda_Galaxy

This says that Andromeda is estimated to contain 10^12 stars (compared
to the Milky Way's ~ 10^11 estimated?), but that the masses only
differ by about 80%.

Is it really true that average star sizes can vary by so much between
galaxies. I'd expect similar physics at this vast scale to provide
almost identical statistical populations.

Thanks for taking the time to answer my questions.

Kind regards
Roland

On Jun 25, 7:41 pm, Sam Wormley wrote:
Roland PJ wrote:

And, generalising this, what proportion of stars in the Milky Way do
we find at various red-shifts?

The red/blue shifts for stars in the Milky way are not relativistic, but
simply Doppler effect due to relative motion between the star and the
earth. The sensitivity of measurement approaches 1 m/s.

Hi Sam - if there's a 'black hole' at the centre, then there _must_ be
some GR red-shifted objects nearby, surely?

Roland

Dear Roland PJ:

On Jun 25, 10:34 am, Roland PJ wrote:
On Jun 25, 5:38 wrote:

Dear Roland PJ:

On Jun 25, 2:16 am, Roland PJ wrote:
...

What I'm asking, is how many stars will have red-shifts
(as viewed on earth) that are dominated by GR time-
dilation, rather than universal expansion, or recession.

Is it 0.0001% (i.e. irrelevent). Is it 10% (interesting). Is
it 90% (in which case the standard Hubble constant is
broken by GR).

The answer is "about 0%". Spiral galaxies *all* have
massive centers. So comparison of spiral galaxies is
inclusive of the center, the arms, and probably some
contribution from the attendant globular clusters.

Compare a galaxy to a bus-load of people. You think
that you need to analyze the bus-load you are in, to
be able to analyze / compare / contrast other bus
loads visible. It might help you compare the Milky
Way to Andromeda to do this, but it won't help you
with galaxies outside our supercluster.

Do you feel the distant "bus loads of people" are
significantly different than the bus on the Andromeda
route? If so, why?

No. I'm just trying to understand the Milky Way better,
under the assumption that it's somewhat 'typical'.

The Milky Way bus is filled with people as tall as you, with only a
few taller. Also there are some serious smokers, that smoke so much
you can't even see the middle of the bus, unless someone is poking his
head above / below the smoke.

The Milky Way is not necessarily typical, so lets concentrate on
Andromeda, which is much more visible. I will attempt to answer based
on assuming "Milky Way" = "Andromeda"

So, some specific questions, which might be more
fruitful:

What's the greatest red-shift we have measured for
an object that's definitely in the Milky Way (according
to parallax, for example).

Nearly zero. Gravitational red shift would be measured from the
coronasphere of the star, which is not under many Gs if it is luminous
enough to see.

This leaves neutron stars which we have detected emissions from, and
they are in X-ray energies... since infalling particles are the source
and had that much "potential energy" starting out ... that is what we
see spalling from the surface on collision.

And, generalising this, what proportion of stars in the
Milky Way do we find at various red-shifts?

Inconsequential. Lump it as "the spectra from a red giant" (for
example) and move on. It is a very small gravitational shift from a
luminous object, and should be the same as a similar mass red giant
star in a very distant galaxy.

And, then another specific question, but not directly
related (it came up earlier in the thread):

http://en.wikipedia.org/wiki/Andromeda_Galaxy

This says that Andromeda is estimated to contain
10^12 stars (compared to the Milky Way's ~ 10^11
estimated?), but that the masses only differ by
about 80%.

Is it really true that average star sizes can vary by
so much between galaxies. I'd expect similar
physics at this vast scale to provide almost identical
statistical populations.

We cannot see the middle of the bus. We could be in the rarefied
space between two arms. What should we expect then?

And yes, I would expect a lot of variation in the populations of
stars, depending on the age and type of the galaxy.

David A. Smith

On Jun 25, 7:53 pm, Sam Wormley wrote:
Roland PJ wrote:
On Jun 25, 7:41 pm, Sam Wormley wrote:
Roland PJ wrote:

And, generalising this, what proportion of stars in the Milky Way do
we find at various red-shifts?
The red/blue shifts for stars in the Milky way are not relativistic, but
simply Doppler effect due to relative motion between the star and the
earth. The sensitivity of measurement approaches 1 m/s.

Hi Sam - if there's a 'black hole' at the centre, then there _must_ be
some GR red-shifted objects nearby, surely?

Roland

Gas falling into the black hole can exhibit gravitational red shift. But
this is local near the event horizon(s) of the black hole... not a galactic
phenomenon... do the calculations.


Sure. I'm busy gathering data... Wheeler reckons the 'black hole' at
the center of the milky way is estimated to be 3.8 x 10^9 m, which is
~ 3 x 10^-6 light years (is that right?)

Not very big, is it, on a galactic scale?

Thanks
Roland