Beyond IDCS J1426.5+3508

In article , "Richard D. Saam"
writes:

On 9/18/12 4:35 AM, Phillip Helbig---undress to reply wrote:
because speed of GR gravity
is the same as Newtonian gravity
that is infinite
http://math.ucr.edu/home/baez/physic...rav_speed.html
?

No. In GR gravity propagates at the speed of light. What you might be
thinking of is that people often assume it propagates at the speed of
light. This is wrong, but something else is wrong as well: it should
propagate from where the object was then, not where it is now. It turns
out that the two effects cancel.

What Baez is saying is different:

"In that case, one finds that the "force" in GR is not quite central _it
does not point directly towards the source of the gravitational
field_ and that it depends on velocity as well as position. The net
result is that the effect of propagation delay is almost exactly
cancelled, and general relativity very nearly reproduces the newtonian
result."

I don't see any difference between the two statements. In any case, I
agree with Baez. Note that if no motion is involved, then of course the
force in GR _IS_ central.

Such an explanation could explain in part the world we live in

wherein the observed dG/dt)/G
of a few times 10^-12 yr^-1 (essentially constant)
no matter where you look.

How so?

Such an explanation appears to outside of current universe expansion models.

Again, how do you arrive at this conclusion?

On 9/19/12 1:32 AM, Jonathan Thornburg wrote:
Richard D. Saam wrote:
but is the observed dG/dt)/G
of a few times 10^-12 yr^-1 (essentially constant)

Actually the limits are considerably tighter than that. Quoting
section 3 of
Stephen M. Merkowitz
"Tests of Gravity Using Lunar Laser Ranging",
Living Reviews in Relativity 13 (2010), 7
http://www.livingreviews.org/lrr-2010-7
(n.b. this is online open-access!),

| Recent analysis of LLR data by the JPL group sets a limit on
| (dG/dt)/G = (6 +/- 7) * 10^{-13}/year [69]. Similarly, Mueller
| et al find (dG/dt)/G = (2 +/- 7) * 10^{-13}/year and
| and (d^2G/dt^2)/G = (4 +/- 5) * 10^{-15}/year^2 [35].
| These limits translate to less than a 1% variation of G over
| the 13.7 billion year age of the universe.

Revisiting this subject:
This dG/dt)/G data was taken using Lunar Laser Ranging.
Is this representative of dG/dt)/G in the universe expansion context?
The moon is in a bound earth, moon, sun and planet system
that does not participate for the most part in universe expansion
in the context of z.

A more appropriate study may be:

Implicit Priors in Galaxy Cluster Mass
and Scaling Relation Determinations
http://arxiv.org/abs/1106.4052
Adam Mantz (NASA/GSFC), Steven W. Allen (KIPAC, Stanford/SLAC)

It is shown that Galaxy Clusters (with assumed commonality) at z
have a relationship with density 'rho' such that
H(z)/H0 ~ rho(z)^(1/2) see Table C1

In the context of the following equation
representative of the development in Harrison
'Using Newtonian theory to derive Friedman equations'
Chapter 16:

(dR/dt)^2 = (8/3)*pi*G*(1+z)^n*rho*(1+z)^n*(R*(1+z)^-n)^2 = c^2

If star cluster density 'rho' has a z dependence
then Galaxy Cluster Newtonian 'G' could also have a z dependence
representative of universe expansion.

Richard D. Saam

In article , "Richard D. Saam"
writes:

Revisiting this subject:
This dG/dt)/G data was taken using Lunar Laser Ranging.
Is this representative of dG/dt)/G in the universe expansion context?
The moon is in a bound earth, moon, sun and planet system
that does not participate for the most part in universe expansion
in the context of z.

In traditional physics, G is G, the same one in the Solar System and in
the universe on large scales. Yes, you can postulate something
different, but then you have to work out the details. In particular,...

A more appropriate study may be:

Implicit Priors in Galaxy Cluster Mass
and Scaling Relation Determinations
http://arxiv.org/abs/1106.4052
Adam Mantz (NASA/GSFC), Steven W. Allen (KIPAC, Stanford/SLAC)

It is shown that Galaxy Clusters (with assumed commonality) at z
have a relationship with density 'rho' such that
H(z)/H0 ~ rho(z)^(1/2) see Table C1

.....citing a study which assumes traditional physics can't be taken at
face value as evidence of non-traditional physics.

On 9/20/12 7:01 AM, Phillip Helbig---undress to reply wrote:
In article , "Richard D. Saam"
writes:

Implicit Priors in Galaxy Cluster Mass
and Scaling Relation Determinations
http://arxiv.org/abs/1106.4052
Adam Mantz (NASA/GSFC), Steven W. Allen (KIPAC, Stanford/SLAC)

It is shown that Galaxy Clusters (with assumed commonality) at z
have a relationship with density 'rho' such that
H(z)/H0 ~ rho(z)^(1/2) see Table C1

....citing a study which assumes traditional physics can't be taken at
face value as evidence of non-traditional physics.


The Galaxy Clusters H(z)/H0 ~ rho(z)^(1/2) data speaks for itself.
The study did not interpret its origin
but confirmed Galaxy Cluster data self-similarity.
The data itself deserves explanation.
How do you explain
the Galaxy Clusters H(z)/H0 ~ rho(z)^(1/2) data
?

Implicit Priors in Galaxy Cluster Mass
and Scaling Relation Determinations
http://arxiv.org/abs/1106.4052

In article ,
"Richard D. Saam" writes:
The Galaxy Clusters H(z)/H0 ~ rho(z)^(1/2) data speaks for itself.

That's not data; it's a definition. Rho_c is the critical density of
the Universe, which is a function of redshift as stated. Cluster
mass calculations have to take this into account because it affects
what can be called a cluster. See the sentence just after equation 6.

Or were you referring to something else entirely?

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 9/28/12 8:08 PM, Steve Willner wrote:
Implicit Priors in Galaxy Cluster Mass
and Scaling Relation Determinations
http://arxiv.org/abs/1106.4052

In article ,
"Richard D. Saam" writes:
The Galaxy Clusters H(z)/H0 ~ rho(z)^(1/2) data speaks for itself.

I am referring to the data with error bars as represented in Figure C1
That's not data; it's a definition. Rho_c is the critical density of
the Universe, which is a function of redshift as stated. Cluster
mass calculations have to take this into account because it affects
what can be called a cluster. See the sentence just after equation 6.

Or were you referring to something else entirely?

Yes that is the reference:
"In practice, the redshift dependence represented by rhoc(z)
must be properly accounted for; however, it is incidental
to the focus of this work. ??
Often the factors rho(z)^(1/2) are written in terms of E(z), the
normalized Hubble parameter."
and from the Table C1 header:
"E(z) = H(z)/H0 ~ rhoc(z)^(1/2)"

but isn't it conventional cosmology
that
E(z) = H(z)/H0 ~ rhoc(z)^(1)
and not
E(z) = H(z)/H0 ~ rhoc(z)^(1/2)

and how does this explain the slope 1.91 ~ 2
through the Table C1 data graphed in Figure C1?
or more succinctly:
Is a modified Newtonian G
perhaps also a function of z
called for to explain the slope 1.91 ~ 2
with
E(z) = H(z)/H0 ~ rhoc(z)^(1)
and not
E(z) = H(z)/H0 ~ rhoc(z)^(1/2)
while maintaining congruency with other reported scaling?

It also must be stated that the slope 1.91 on Figure C1
represents a fitting power law
and is presented with no basis in theory.

Richard D. Saam

In article , "Richard D. Saam"
writes:

but isn't it conventional cosmology
that
E(z) = H(z)/H0 ~ rhoc(z)^(1)
and not
E(z) = H(z)/H0 ~ rhoc(z)^(1/2)

No.

The Friedmann-Lemaitre equation is basically

\dot R^2 = \frac{8\pi G\rho R^2}{3} + \frac{\Lambda R^2}{3} - kc^{2}

The Einstein-de Sitter universe has k=0, Lambda=0 and Omega=1. So, in
this case we have

\dot R^2 = \frac{8\pi G\rho}{3}

or

\frac{\dot R}{R}^2 = \frac{8\pi G\rho R}{3} which is, by definition,

H^2 = \frac{8\pi G\rho}{3}

Thus the critical density is, by definition, 3H^2/(8\pi G) since the
value of the density is always the critical density in the Einstein-de
Sitter universe. So H(z) is proportional to the square root of the
density. (If lamnda and/or k are not zero, then the expression for H(z)
is of course more complicated.)

On Sunday, September 30, 2012 12:49:44 PM UTC+2, Richard D. Saam wrote:
On 9/28/12 8:08 PM, Steve Willner wrote:

"Richard D. Saam" writes:
The Galaxy Clusters H(z)/H0 ~ rho(z)^(1/2) data speaks for itself.

I am referring to the data with error bars as represented in Figure C1
That's not data; it's a definition. Rho_c is the critical density of
the Universe, which is a function of redshift as stated.

Yes that is the reference:
"In practice, the redshift dependence represented by rhoc(z) must
be properly accounted for; however, it is incidental to the focus
of this work. ??
Often the factors rho(z)^(1/2) are written in terms of E(z),
the normalized Hubble parameter."

Using my Excel Friedmann's equation simulation I have tested the equation:
E(z) = H(z)/H(0) = SQR( rho c(z) / rho c (0) )
H(0) and rho c(0) are at t= 0 = z = 0
The equation is correct.
For details go to :
http://users.telenet.be/nicvroom/friedmann's%20equation.htm#Q6
and study Table 6.2

Nicolaas Vroom

On Thursday, September 20, 2012 8:30:10 AM UTC+2, Richard D. Saam wrote:

A more appropriate study may be: Implicit Priors in Galaxy Cluster
Mass and Scaling Relation Determinations
http://arxiv.org/abs/1106.4052
Adam Mantz (NASA/GSFC), Steven W. Allen (KIPAC, Stanford/SLAC)

Table C1 page 11 shows 4 lines with of galaxy cluster data
with almost identical kT values.
De values for z, E(z), M2500 and kT are shown:
16) 0.295 1.163 2.67 8.03
22) 0.352 1.201 4.02 8.05
23) 0.355 1.203 6.02 8.08
37) 0.686 1.462 3.07 8.08

The lines 22 and 23 are almost identical but the M2500
values are rather different.
What is the explanation ?

The text near Figure 1C shows that the M2500 mass values are measured.
But that does not make it easier to understand.

Appendix C indicates that the NFW profile is used
for total mass fitting of a Galaxy Cluster.
The NFW profile is normally used to simulate
a dark matter halo for a single galaxy.
How can that be used to simulate the total mass
in a Galaxy Cluster which density I expect
is more or less constant and decreases towards
the rim of the Cluster.
See also:
http://iopscience.iop.org/0004-637X/...1038/fulltext/

Nicolaas Vroom

In article , Nicolaas Vroom
writes:

Appendix C indicates that the NFW profile is used
for total mass fitting of a Galaxy Cluster.
The NFW profile is normally used to simulate
a dark matter halo for a single galaxy.
How can that be used to simulate the total mass
in a Galaxy Cluster which density I expect
is more or less constant and decreases towards
the rim of the Cluster.

The NFW profile has no intrinsic scale; that is why it is called a
universal profile. Of course, there do tend to be typical scales in the
universe: galaxy, cluster of galaxies etc, but the idea here is that
these are due to more complicated processes. In a scenario of
hierarchical structure formation with only dark matter, presumably all
relaxed profiles would be NFW.

Why do you expect the density to be as you described it?