Red-shift is not SR recession speed, but GR time dilation?
Roland PJ
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.
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
Sue...
> 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.
>
> 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?
<< The purpose of this paper is twofold - to demonstrate that
in the gravitational redshift it is the frequency [of] a photon that
is
constant, and to describe the mechanism responsible for the
change of its wavelength. >>
http://aps.arxiv.org/abs/gr-qc/9810030v14
See also papers by L.B Okun
Sue...
Sue...
http://aps.arxiv.org/abs/gr-qc/9810030v14
See also papers by L.B Okun
http://arxiv.org/abs/physics/9907017
Sue...
Martin Hogbin
"Roland PJ" <rola...@gmail.com> wrote in message news:1182668480.4...@p77g2000hsh.googlegroups.com...
> 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.
>
> 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?
It has not been eliminated it is a contributing factor.
See:
http://en.wikipedia.org/wiki/Gravitational_redshift
http://physics.ucr.edu/~wudka/Physics7/Notes_www/node99.html
--
Martin Hogbin
eugene_st...@usa.net
> Red-shift of distant objects could be due to ...
> 2. Time dilation due to proximity to a concentration of mass, a
> general relativistic effect.
How does your theory explains the fact that the red-shift is larger
for galaxies that are farther away? Should you assume that far
galaxies are more massive?
Eugene.
Sue...
wrote:
> "Roland PJ" <rolan...@gmail.com> wrote in messagenews:1182668480.4...@p77g2000hsh.googlegroups.com...
> > 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.
>
> > 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?
>
> It has not been eliminated it is a contributing factor.
> See:
>
> http://en.wikipedia.org/wiki/Gravitational_redshift
<< As light leaves the vicinity of this object it is shifted
towards the red: for a sufficiently compact and massive
object a blue laser on the surface will be seen as red in outer
space. >>
http://physics.ucr.edu/~wudka/Physics7/Notes_www/node99.html
Quite the opposite of the GPS presets and
violatiing causality in the opposite direction.
That must be an "authoritative text".
<< On the other hand the phenomenon is alternatively
discussed (even in some authoritative texts) in terms of
an energy loss of a photon as it overcomes the gravitational
attraction of the massive body. >>
http://arxiv.org/abs/physics/9907017
Sue...
>
> --
> Martin Hogbin
Roland PJ
> On Jun 24, 12:01 am, Roland PJ <rolan...@gmail.com> wrote:
>
> > 2. Time dilation due to proximity to a concentration of mass, a
> > general relativistic effect.
>
> for galaxies that are farther away? Should you assume that far
> galaxies are more massive?
>
It depends what you've used to determine that the galaxies are further
away. Have you used brightness? If so, then you haven't eliminated the
possibility that both the dimness _and_ the red-shift are due to the
galaxy being not necessarily further away, but either denser (more
tightly packed with stars), or more massive.
And note that using brightness seems to be the first rung in the
standard 'distance ladder' of cosmological measurement.
Roland
Roland PJ
wrote:
> "Roland PJ" <rolan...@gmail.com> wrote in messagenews:1182668480.4...@p77g2000hsh.googlegroups.com...
>
> > 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.
>
> > assumption that SR recession is the cause (and hence that the universe
> > is expanding).
>
> > Why has GR time dilation been eliminated as a cause?
>
> It has not been eliminated it is a contributing factor.
Yes, I'm sure it _is_ at least a contributing factor, and thanks for
the links.
What I'm asking is why the history of cosmological distance
measurement (the 'distance ladder') seems to ignore it completely, and
focus only on recession speed.
That can't be right, can it?
Regards
Roland
Eric Gisse
> 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.
>
> 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).
Actually, it is neither.
The red-shift is modeled best by the FRW class of manifolds. Basically
all points move away from eachother - and the effect is the red-shift.
>
> Why has GR time dilation been eliminated as a cause?
The universe would have long since collapsed.
>
> 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.
You are not understanding. EVERYTHING not gravitationally bound [ie:
outside the local group] exhibits the redshift in a manner consistent
with the Hubble law.
>
> 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.
Now explain why close stuff isn't nearly as red-shifted as stuff
really far away, and try to do that without invoking amounts of mass
that dwarf the entire universe combined.
>
> 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?).
Gravitational redshift _is_ observed, but you are missing the point.
IT IS TOO WEAK. Calculate it!
>
> 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
Try picking up something published in the last thirty years.
>
> 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.
Luminosity is only a measure of distance because Cephid variables were
discovered. That, combined with the Hubble law, gives a very good
measure of distance for distances too large to be measured with
parallax. Time dilation has NOTHING to do with it - 5 minutes [if
that] of computations will reveal how bad of an idea attributing red-
shift to time dilation is.
Roland PJ
> On Jun 23, 11:01 pm, Roland PJ <rolan...@gmail.com> 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.
>
>
>
> The universe would have long since collapsed.
>
>
> > 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.
>
> You are not understanding. EVERYTHING not gravitationally bound [ie:
> outside the local group] exhibits the redshift in a manner consistent
> with the Hubble law.
I don't understand what you're saying here.
>
> > 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.
>
> Now explain why close stuff isn't nearly as red-shifted as stuff
> really far away, and try to do that without invoking amounts of mass
> that dwarf the entire universe combined.
This might be a circular argument. If you've used brightness at any
stage in deciding what's 'close' or 'far', without taking GR time
dilation into account, then you might not have a good idea of what's
far and what's near.
>
>
> Gravitational redshift _is_ observed, but you are missing the point.
> IT IS TOO WEAK. Calculate it!
Yes, this is exactly the kind of answer I was looking for. Given that
I'll almost certainly cock up the calculation on at least the first
three attempts, I'd be gratefull for any pointers.
>
> > 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.
>
> Luminosity is only a measure of distance because Cephid variables were
> discovered. That, combined with the Hubble law, gives a very good
> measure of distance for distances too large to be measured with
> parallax. Time dilation has NOTHING to do with it - 5 minutes [if
> that] of computations will reveal how bad of an idea attributing red-
> shift to time dilation is.
Yes, absolutely, but Cephid variables are the first rung on the
'distance ladder', and I have found no evidence of anyone considering
GR time-dilation effects. This may be simpy because it was eliminated
early on as irrelevantly small, but I have seen no-one mention that.
And all 'modern' discussions (papers, if you like) on cosmological
distance seem to share a direct line back to the Hubble paper.
So, thanks, seems like I'll have to have a crack at some actual
computations :(. What's the right kind of estimate for 'dark matter'
and 'dark energy'? Or should I simply ignore these frst time round
(and almost certainly get the wrong answer)?
Roland
CWatters
Certain types of star are known to have a certain brightness....
http://hubblesite.org/newscenter/archive/releases/1994/49/astrofile/
"Two well-defined primary distance indicators, or "standard candles," are
the Cepheids and fainter RR Lyrae stars. They have a regular variation in
brightness, and the period of this pulsation is closely linked to the star's
intrinsic brightness. So, if the pulsation period of a star is known, its
true brightness can be deduced. The distance to the star can then be
calculated by comparing its true brightness with its apparent brightness."
CWatters
> What I'm asking is why the history of cosmological distance
> measurement (the 'distance ladder') seems to ignore it completely, and
> focus only on recession speed.
>
> That can't be right, can it?
>
Focus is not only on recession speed..
Roland PJ
<colin.watt...@turnersNOSPAMoak.plus.com> wrote:
> "Roland PJ" <rolan...@gmail.com> wrote in message
That may be true for observers at the same GR time-dilation as the
Cepheid stars, but if a Cepheid is close to a large and/or dense mass,
then we, on earth, will observe the period to be longer, and the
brightness to be less, both to tue GR time-dilation.
Unfortunately for this 'standard candle', these errors don't cancel
out, but rather compound each other. A Cepheid with a longer observed
period is deemed to be intrinsically brighter, and when we observe it
to be dimmer than it is (due to GR time-dilation), we will interpret
the longer period and lower brightness as indicating the star is
significantly further than it really is.
In the limit case of a Cepheid orbiting a near-black-hole, this error
compounds essentially towards infinity. Of course, we don't observer
the near-black-hole cos it's red-shifted and dimmed off the scale. We
only see the Cepheid.
Thoughts?
Roland
gehgeh...@gmail.com
Interesting.
The question is observational.. what are the distributions of cepheids
and other standard candles such as supernovae that have been measured
with parallax? How good is the luminosity - period relationship
really?
Igor
So you're suggesting that objects in the universe become more massive
the further away from us they are located? And, since our view of the
universe isn't considered to be very special, how would you reconcile
that with the notion that the mass distribution of the universe must
be observer independent?
N:dlzc D:aol T:com (dlzc)
"Roland PJ" <rola...@gmail.com> wrote in message
news:1182668480.4...@p77g2000hsh.googlegroups.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.
> 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.
> 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).
Absolutely incorrect. SR is limited to evaluating jets of
ejected material. It is GR that is used to describe expansion,
and the Hubble shift.
> Why has GR time dilation been eliminated as a cause?
It hasn't, in fact it is key. Just not time dilation from
individual masses. 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.
> 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 saltwater 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.
> 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.
> 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.
...
> Just some ideas.
> Flame away ;)
If you are interested in more than your own ideas, you can start
here:
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.
David A. Smith
Roland PJ
> On Jun 24, 3:01 am, Roland PJ <rolan...@gmail.com> 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.
>
> > 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?
>
> >
>
> the further away from us they are located? And, since our view of the
> universe isn't considered to be very special, how would you reconcile
> that with the notion that the mass distribution of the universe must
> be observer independent?
No, I'm suggesting that we might have _both_ their distance and
recession speed wrong.
At the moment we interpret faint objects as being distant, and red-
shifted objects as being receding.
And we find there's a correlation between distance and recession
speed.
However, a faint and red-shifted object could simply be a nearby,
stationary object under the influence of nearby mass (perhaps
invisible to us), as a result of GR time dilation.
Roland
Igor
Maybe so, but the GR time dilation effect cannot be the dominate one
for the reasons I previously stated.
Roland PJ
wrote:
> Dear Roland PJ:
>
> "Roland PJ" <rolan...@gmail.com> wrote in message
>
> news:1182668480.4...@p77g2000hsh.googlegroups.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 ;)
>
> > 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?
>
> 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.
>
> > 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 saltwater 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.
>
> > 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). 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? In which case
time dilation clearly can't be a factor within our own galaxy.
>
> If you are interested in more than your own ideas, you can start
> here:http://www.astro.ucla.edu/~wright/cosmolog.htmhttp://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. Specifically, the density of matter
along the radial arms, and the shape of, and density of matter, within
the 'core'. What's crucial is the density gradient of stars within the
core. I can't find this anywhere at the moment. It seems pretty
obvious that the core is not entirely homogeneous, but rather gets
increasingly densely populated with stars towards the middle. But
what's the density curve here?
Thanks again for the response
Roland
Roland PJ
I think I missed that. Would you mind repeating?
Thanks
Roland
John C. Polasek
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.
John Polasek
Eric Gisse
[...]
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
N:dlzc D:aol T:com (dlzc)
"Roland PJ" <rola...@gmail.com> wrote in message
news:1182710180.3...@m36g2000hse.googlegroups.com...
> On Jun 24, 8:02 pm, "N:dlzc D:aol T:com \(dlzc\)"
> <d...@aol.com>
> wrote:
>> Dear Roland PJ:
>>
>> "Roland PJ" <rolan...@gmail.com> wrote in message
>>
>> news:1182668480.4...@p77g2000hsh.googlegroups.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 saltwater 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 here:
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
Roland PJ
> On Sun, 24 Jun 2007 00:01:20 -0700, Roland PJ <rolan...@gmail.com>
> 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
Roland PJ
> > 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
dlzc
On Jun 25, 2:16 am, Roland PJ <rolan...@gmail.com> 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
Roland PJ
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
Sam Wormley
>
> 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.
Roland PJ
Hi Sam - if there's a 'black hole' at the centre, then there _must_ be
some GR red-shifted objects nearby, surely?
Roland
Sam Wormley
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.
dlzc
On Jun 25, 10:34 am, Roland PJ <rolan...@gmail.com> wrote:
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
Roland PJ
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
Martin Hogbin
"Roland PJ" <rola...@gmail.com> wrote in message news:1182677678.5...@q69g2000hsb.googlegroups.com...
I am not an expert but I believe that gravitational redshift is
a relatively minor effect for normal cosmological objects,
based on their expected masses. No doubt it has been taken
into account wher it is expected to be significant.
--
Martin Hogbin
Sam Wormley
Measurements indicate that the mass of the big supermassive black hole
in our galaxy is about 3 x 10^6 Solar masses or 6 в 10^36 kilograms.
That makes the event horizon radius 0.05 AU or about one tenth the
radius of the orbit of Mercury.
Roland PJ
> Roland PJ wrote:
> > On Jun 25, 7:53 pm, Sam Wormley <sworml...@mchsi.com> wrote:
> >> Roland PJ wrote:
> >>> On Jun 25, 7:41 pm, Sam Wormley <sworml...@mchsi.com> 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?
>
> That makes the event horizon radius 0.05 AU or about one tenth the
> radius of the orbit of Mercury.
Yes, that's a big bust for the absolute centre causing red-shift.
But what about the rest of the mass in the galaxy?
I'll do some thumb-sucks, which hopefully will be corrected, but maybe
they are enough to bust the theory on their own.
Firstly, what is the mass of the Milky Way 'core'. Perhaps 1/2 (say
3x10^9 suns?) of the total mass of the galaxy?
That gives an 'event horizon' radius for the core as a whole of ~ 3 x
10^9 x 3 x 10^3 m (the sun's 'event horizon' radius is about 3 km), or
about 10^13 m, or 10^-3 light-years (right?).
So, if a lot of the mass (stars) of the core was near the center (and
it's tiny - 10^-3 light years), then most of the stars in the core
will display exaggerated GR red-shifts to us.
This seems tremendously unlikely - the core itself is ~300 light-years
radius (is that correct?).
So, most of the stars in the centre of the Milky Way will show
exaggerated GR red-shift, only if most of them are in the innermost
3x10^6 th of the core. Again, doesn't seem plausible.
So, my last illustration. What if 1/2 of the mass of the core was
within 1/2 of the radius of the center and so on (which is a steep
density function).
1.5 x 10^9 suns in r < 150 light-years.
7.5 x 10^9 suns in r < 75 light-years.
We're not gaining on GR red-shift as we go in, so this scenario is
also a bust.
My conclusion: GR red-shift due to the mass of the galaxy itself can
only be a factor if the star density function is significantly steeper
than 1/2 the mass within 1/2 the radius at each 'step'.
So, I think I'm pretty thoroughly convinced. This is a really dumb
idea :(
Thanks for the kind feedback
Regards
Roland
Sam Wormley
> On Jun 25, 8:22 pm, Sam Wormley <sworml...@mchsi.com> wrote:
>> Roland PJ wrote:
>>> On Jun 25, 7:53 pm, Sam Wormley <sworml...@mchsi.com> wrote:
>>>> Roland PJ wrote:
>>>>> On Jun 25, 7:41 pm, Sam Wormley <sworml...@mchsi.com> 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?
>> Measurements indicate that the mass of the big supermassive black hole
>> That makes the event horizon radius 0.05 AU or about one tenth the
>> radius of the orbit of Mercury.
>
> Yes, that's a big bust for the absolute centre causing red-shift.
>
> But what about the rest of the mass in the galaxy?
>
> I'll do some thumb-sucks, which hopefully will be corrected, but maybe
> they are enough to bust the theory on their own.
>
> Firstly, what is the mass of the Milky Way 'core'. Perhaps 1/2 (say
> 3x10^9 suns?) of the total mass of the galaxy?
To estimate the mass within a given radius from rotational velocity, use
M = v^2r/G
Most of us go through these "what if" thoughts all the time. We
have to! :-)