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  #21  
Old February 11th 16, 03:16 AM posted to sci.astro.research
Robert L. Oldershaw
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Posts: 617
Default Advantage Inhomogeneity

On Wednesday, February 10, 2016 at 3:54:43 PM UTC-5, Phillip Helbig (undres=
s to reply) wrote:
In article , Jos Bergervoet


=20
No; I don't think all agree on this. By definition, a fractal=20
distribution doesn't "stop" at some scale...
=20
The only question is whether the sequence will *resume*,
at some scale larger than what we can see today.

=20
...and then resume again.
=20


(1) This assertion that fractal models can only work in the naive
and simplistic way you say they must is patently false.

(2) Continuous self-similarity is a mathematical myth that is not
realized in nature. Even Mandelbrot's classic fractal examples like
the Koch curve/snowflake are constructed by discrete iterations and
so the self-similarity cannot be rigorously continuous.

(3) In nature self-similarity is discrete self-similarity. One can
see that in the myriad examples of turbulence. In any real fluid
undergoing turbulent motions there are preferred scales in the
distribution of vortices, that depend on the physical properties
of the fluid and the forcing details.

(4) In nature hierarchies also tend to be stratified (i.e., discrete
rather than continuous in the distribution of levels). Try observing
nature instead of relying on Platonic fictions.

RLO
http:/www3.amherst.edu/~rloldershaw
Fractal Cosmology

[[Mod. note -- I will note that continuous and/or discrete
self-similarity in gravitational collapse has been and continues to
be a major research area in general relativity. See
http://www.livingreviews.org/lrr-2007-5
for a detailed review. However, while these are solutions of the
Einstein or Einstein+matter equations, they require "fine-tuned"
initial data and so form a set of measure 0 in the space of initial
data. They are thus (very) unlikely to occur in nature.
-- jt]]
  #22  
Old February 19th 16, 08:27 AM posted to sci.astro.research
Robert L. Oldershaw
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Posts: 617
Default Advantage Inhomogeneity

On Wednesday, February 10, 2016 at 10:17:17 AM UTC-5, Jos Bergervoet wrote:

That was not my impression. I think we all agree that this
sequence exists, but seems to stop a few hundred Mpc (i.e.
from that point on no larger structures have been seen.)
The only question is whether the sequence will *resume*,
at some scale larger than what we can see today.

My point is that it could go either way. Just like at
the other end of the scale, the elementary particles that
we know *might* be truly elemental, but could also turn
out to be composite.


Indeed, it could very much "go either way" on either cosmic or
microscopic scales, or both. So why do people make the thoroughly
unscientific assertion that nature's hierarchy MUST have cutoffs at
both "ends"? That is purely a theoretical assumption and a lot of
hype. Exactly my point too!

A turnover at a few hundred Mpc is not at all a matter of fact. Plenty
of authors have published papers claiming structure on the Gpc scale
[see my post on the vast quasar cluster posted here not long ago, or
the latest Planck results on intrinsic dipole anisotropy at very large
scale.

Just repeating the questionable turnover assumptions over and over, as
many LCDM proponents do, will not make those assumptions true. Citing
only evidence that suggests a cutoff at a few hundred Mpc, and
ignoring the published evidence for structure on far larger scales, is
not the way to proceed scientifically.

If anyone wants to see published papers on Gpc scale structure, simply
do an arxiv.org search on "very large scale structure" or
"cosmological inhomogeneity" or "cosmological anisotropy".

If anyone wants to subsequently claim that I cannot back up what I say
with published research, THEN I will be happy to provide specific
documentation to show that the claim is quite incorrect. But first
give me the scientific freedom of speech to make my general argument,
and then let's see who can counter it scientifically.

[Mod. note: reformatted. Scientific practice, which _all_ participants
in the group are encouraged to follow, is to provide references to
support your claim at the time you make it -- mjh]

RLO
http://www3.amherst.edu/~rloldershaw
Fractal Cosmology
  #23  
Old February 20th 16, 08:56 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 273
Default Advantage Inhomogeneity

In article , "Robert L.
Oldershaw" writes:

That was not my impression. I think we all agree that this
sequence exists, but seems to stop a few hundred Mpc (i.e.
from that point on no larger structures have been seen.)
The only question is whether the sequence will *resume*,
at some scale larger than what we can see today.

My point is that it could go either way. Just like at
the other end of the scale, the elementary particles that
we know *might* be truly elemental, but could also turn
out to be composite.


Indeed, it could very much "go either way" on either cosmic or
microscopic scales, or both. So why do people make the thoroughly
unscientific assertion that nature's hierarchy MUST have cutoffs at
both "ends"?


Who makes such claims?

Most people say "let's see what we find". It seems that YOU make the
claim that there MUST NOT be any cutoff, e.g. fractal cosmology. This
is based not on observation, but on your theory.

A turnover at a few hundred Mpc is not at all a matter of fact. Plenty
of authors have published papers claiming structure on the Gpc scale
[see my post on the vast quasar cluster posted here not long ago, or
the latest Planck results on intrinsic dipole anisotropy at very large
scale.


And these have been refuted.

Just repeating the questionable turnover assumptions over and over, as
many LCDM proponents do, will not make those assumptions true.


True. Neither does repeating over and over that there is no turnover
make that claim true.

Citing
only evidence that suggests a cutoff at a few hundred Mpc, and
ignoring the published evidence for structure on far larger scales, is
not the way to proceed scientifically.


Citing only evidence (even if it has been refuted) which suggests no
cutoff, and ignoring the published (and not refuted) evidence for lack
of structure on far larger scales, is not the way to proceed
scientifically.

If anyone wants to see published papers on Gpc scale structure, simply
do an arxiv.org search on "very large scale structure" or
"cosmological inhomogeneity" or "cosmological anisotropy".


One can find papers on many things. If they have been refuted, and the
original authors have not refuted the refutation, then for me it is
refuted, even if the authors don't want to admit it.

If anyone wants to subsequently claim that I cannot back up what I say
with published research, THEN I will be happy to provide specific
documentation to show that the claim is quite incorrect. But first
give me the scientific freedom of speech to make my general argument,
and then let's see who can counter it scientifically.

[Mod. note: reformatted. Scientific practice, which _all_ participants
in the group are encouraged to follow, is to provide references to
support your claim at the time you make it -- mjh]


Indeed. YOU cite a SPECIFIC paper, and we can discuss whether its
claims are justified. But in turn, you have to examine the refutations.
  #24  
Old February 21st 16, 04:10 PM posted to sci.astro.research
Robert L. Oldershaw
external usenet poster
 
Posts: 617
Default Advantage Inhomogeneity

On Saturday, February 20, 2016 at 2:57:10 AM UTC-5, Phillip Helbig (undress to reply) wrote:
In article , "Robert L.
Oldershaw" writes:
Indeed, it could very much "go either way" on either cosmic or
microscopic scales, or both. So why do people make the thoroughly
unscientific assertion that nature's hierarchy MUST have cutoffs at
both "ends"?


Who makes such claims?

Most people say "let's see what we find". It seems that YOU make the
claim that there MUST NOT be any cutoff, e.g. fractal cosmology. This
is based not on observation, but on your theory.


Jos stated the "either way" idea.

My claim, with emphasis so you cannot ignore it, is: I CLAIM THERE IS NO REASON TO ASSUME THERE MUST BE CUTOFFS. Do you hear me now? Can you make the distinction between what I actually laim and what you falsely say I claim?

A turnover at a few hundred Mpc is not at all a matter of fact. Plenty
of authors have published papers claiming structure on the Gpc scale
[see my post on the vast quasar cluster posted here not long ago, or
the latest Planck results on intrinsic dipole anisotropy at very large
scale.


And these have been refuted.


You have cited no evidence for what is only your opinion.

Just repeating the questionable turnover assumptions over and over, as
many LCDM proponents do, will not make those assumptions true.


True. Neither does repeating over and over that there is no turnover
make that claim true.


I only claim that the widespread and long-hyped assumption of a "turnover" is not a certain fact of nature, i.e., there is no guarantee of a final "turnover".


Citing
only evidence that suggests a cutoff at a few hundred Mpc, and
ignoring the published evidence for structure on far larger scales, is
not the way to proceed scientifically.


Citing only evidence (even if it has been refuted) which suggests no
cutoff, and ignoring the published (and not refuted) evidence for lack
of structure on far larger scales, is not the way to proceed
scientifically.


Again you cite no references to support your pronouncements, nor the
published papers denying your opinions.


If anyone wants to see published papers on Gpc scale structure, simply
do an arxiv.org search on "very large scale structure" or
"cosmological inhomogeneity" or "cosmological anisotropy".


One can find papers on many things. If they have been refuted, and the
original authors have not refuted the refutation, then for me it is
refuted, even if the authors don't want to admit it.


Again, you offer no citations. Just your personal opinions.


If anyone wants to subsequently claim that I cannot back up what I say
with published research, THEN I will be happy to provide specific
documentation to show that the claim is quite incorrect. But first
give me the scientific freedom of speech to make my general argument,
and then let's see who can counter it scientifically.

[Mod. note: reformatted. Scientific practice, which _all_ participants
in the group are encouraged to follow, is to provide references to
support your claim at the time you make it -- mjh]


Indeed. YOU cite a SPECIFIC paper, and we can discuss whether its
claims are justified. But in turn, you have to examine the refutations.


Fine!
T. Buchert et al, Class. Quantum Grav., 32, 215021, 2015
Steinhardt et al, arXiv:1506.01377v1
Pawlowski et al, http://arxiv.org/abs/1510.08060
Kroupa et al, http://arxiv.org/abs/1301.3907

Would you like 10 or 20 more references to published papers citing
problems with the LCDM toy cosmological model?

[Mod. note: quoted text trimmed, reformatted -- mjh]

Robert L. Oldershaw
http://www3.amherst.edu/~rloldershaw
Discrete Scale Relativi
  #25  
Old February 21st 16, 09:38 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default Advantage Inhomogeneity

In article , "Robert L.
Oldershaw" writes:

Indeed, it could very much "go either way" on either cosmic or
microscopic scales, or both. So why do people make the thoroughly
unscientific assertion that nature's hierarchy MUST have cutoffs at
both "ends"?


Who makes such claims?

Most people say "let's see what we find". It seems that YOU make the
claim that there MUST NOT be any cutoff, e.g. fractal cosmology. This
is based not on observation, but on your theory.


Jos stated the "either way" idea.


It seems to me that "either way" is pretty open-minded. Where is the
strict assumption?

My claim, with emphasis so you cannot ignore it, is: I CLAIM THERE IS
NO REASON TO ASSUME THERE MUST BE CUTOFFS. Do you hear me now? Can you
make the distinction between what I actually laim and what you falsely
say I claim?


By definition, a fractal distribution is scale-invariant.

I don't ASSUME that there must be cutoffs. I claim that the
observational evidence supports a turnover to homogeneity at a few
hundred Mpc, well below the scale of the observable universe.

A turnover at a few hundred Mpc is not at all a matter of fact. Plenty
of authors have published papers claiming structure on the Gpc scale
[see my post on the vast quasar cluster posted here not long ago, or
the latest Planck results on intrinsic dipole anisotropy at very large
scale.


And these have been refuted.


You have cited no evidence for what is only your opinion.


Again, you cite a paper and we can see if there is a refutation. You
are asking me the equivalent of proving my innocence.

I only claim that the widespread and long-hyped assumption of a
"turnover" is not a certain fact of nature, i.e., there is no guarantee
of a final "turnover".


References, please.

Again you cite no references to support your pronouncements, nor the
published papers denying your opinions.


Again, you started the claim. The ball is in your court.

Steinhardt et al, arXiv:1506.01377v1


This is about galaxy formation. Of course, high-redshift galaxies are
farther away than low-redshift ones, and due to the finite speed of
light we are seeing them at an earlier time. The paper is about the
latter, not the former, and has nothing to do with large-scale
homogeneity or the lack thereof.

Pawlowski et al, http://arxiv.org/abs/1510.08060


This is about satellites in the Local Group. That's a long way from
several hundred Mpc.

Kroupa et al, http://arxiv.org/abs/1301.3907


This is mainly about MOND. Note that even most MOND supporters agree
that CDM works well on large scales; the problem is at small scales.

So, we didn't even get as far as the refutation, since none of these
papers is about the lack of a turnover to homogeneity on the scale of
several hundred Mpcs.

After three misses, I didn't bother to look at the first paper you cited
(without an easy arXiv link---maybe it's on arXiv, maybe I can access it
if it is not, but after three misses, I don't think I need to try).

This is not the first time you have cited papers in support of your
arguments where, in fact, they claim something entirely different. Last
time, you even quote-mined it to make it appear that the authors claim
the opposite of what they claim!

You've had your chance. I don't see any point in discussing this
further.
  #26  
Old February 22nd 16, 08:36 AM posted to sci.astro.research
Jos Bergervoet
external usenet poster
 
Posts: 126
Default Advantage Inhomogeneity

On 2/21/2016 4:10 PM, Robert L. Oldershaw wrote:
On Saturday, February 20, 2016 at 2:57:10 AM UTC-5, Phillip Helbig (undress to reply) wrote:
In article , "Robert L.
Oldershaw" writes:
Indeed, it could very much "go either way" on either cosmic or
microscopic scales, or both. So why do people make the thoroughly
unscientific assertion that nature's hierarchy MUST have cutoffs at
both "ends"?


Who makes such claims?

Most people say "let's see what we find". It seems that YOU make the
claim that there MUST NOT be any cutoff, e.g. fractal cosmology. This
is based not on observation, but on your theory.


Jos stated the "either way" idea.


There might be a cutoff point, or not! That was my
either way claim, but in either case this doesn't
tell us anything about fractal properties

To be fractal means that the sequence should have
a certain characteristic, described in some way by a
(not necessarily interger) number that is independent
of the scale, at least as far as the sequence goes.

The claim that "the coast of Britain has a fractal
dimension" does *not* imply that repetition of the
structure goes on forever in both directions. At
least clearly not in the large-scale direction
(although they might in the future rebuild the
British Empire to an infinite size, it has not
yet happened).

On the other hand it *does* require that the
fractal dimension is (reasonably) constant over
some significant scaling range.

So we have two completely unrelated properties:
1) The presence of hierarchic sub-structuring over
an infinite range of scales.
2) The substructures showing a (more or less) fixed
fractal dimension over the existing range.

We were discussing 1), which is neither necessary
not sufficient for 2), i.e. fractal geometry has
nothing to do with this discussion.

--
Jos
  #27  
Old February 22nd 16, 08:37 AM posted to sci.astro.research
Richard D. Saam
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Posts: 240
Default Advantage Inhomogeneity

On 2/10/16 9:29 AM, Nicolaas Vroom wrote:
IMO it is rather "simple" to simulate local inhomogeneities, but that
does not say "anything" about our entire universe at present.


Is there a "simple" logic to explain the consistent sizes of:

1. Stellar planetary systems
2. Galaxies

throughout the visible universe?

Richard D Saam
  #28  
Old February 22nd 16, 08:41 AM posted to sci.astro.research
Robert L. Oldershaw
external usenet poster
 
Posts: 617
Default Advantage Inhomogeneity

On Sunday, February 21, 2016 at 3:39:03 PM UTC-5, Phillip Helbig (undress to reply) wrote:

It seems to me that "either way" is pretty open-minded. Where is the
strict assumption?


Not on my part, as I made you aware in capital letters in my 2/21 post.


By definition, a fractal distribution is scale-invariant.


Look, I am sorry to bring you bad news but your definition is wrong on
2 separate grounds. Let's make this crystal clear.

1. I have an essay on my website that lists about 80 examples of
fractal structures observed (*by others, not me*) in the real physical
world of nature. Virtually all of them are *not* continuously scale
invariant (i.e., completely scale free). If your view of natural
fractals involves complete, exact scale invariance , then I regret to
inform you that your definition is both incorrect and discouragingly
naive.

2. If you have ever read Mandelbrot's book, The Fractal Geometry Of
Nature, W.H. Freeman, New York, 1983, then you must have at least been
exposed to the fact that all of the archetypal fractal models
(mathematical in these cases) involve discrete scaling. This is built
into the discrete iteration method of constructing these fractals.
Please commit this factual information to your memory so I do not have
to repeat it every few months.

Bottom Line: There are many different types of fractal models and
modeling principles. If you claim there is only one with total scale
invariance, then you are wrong - plain and simple.

[Mod. note: further discussion of fractals should be directly related
to astrophysics or should be taken elsewhere -- mjh]


I don't ASSUME that there must be cutoffs. I claim that the
observational evidence supports a turnover to homogeneity at a few
hundred Mpc, well below the scale of the observable universe.


You mean to say *statistical* homogeneity, and to make such a claim
you must be ignoring the inconvenient and highly fractal cosmic web
via coarse-graining.


This is not the first time you have cited papers in support of your
arguments where, in fact, they claim something entirely different. Last
time, you even quote-mined it to make it appear that the authors claim
the opposite of what they claim!


Firstly, I am discussing problems with the LCDM toy model, of which
the inhomogeneity problem is just one of many.

I note you totally ignore the Buchert et al article. Tell us why.

You dismiss Kroupa's identification of many serious LCDM toy model
problems solely on the basis that he favors a MOND model. I hate to
break the bad news to you but the problems that Kroupa has identified
exist whether or not MOND models are valid and useful. If you think
that is not true, prove it by addressing his points one-by-one and
showing references indicating flaws in each specific problem.


You've had your chance. I don't see any point in discussing this
further.


A wise choice on your part, in my opinion. However, it will not be
long before new empirical evidence will help us to move toward a
scientific answer to the inhomogeneity problem (see Buchert et al,
previously cited), and the other problems with LDCM models/assumptions
as noted and published in the 4 papers I cited previously. Please note
that I would be happy to furnish you with more relevant information
should you need and/or want it.

Robert L. Oldershaw
http://www3.amherst.edu/~rloldershaw
Discrete Scale Relativity
  #29  
Old February 23rd 16, 08:40 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default Advantage Inhomogeneity

In article , "Richard D. Saam"
writes:

Is there a "simple" logic to explain the consistent sizes of:

1. Stellar planetary systems
2. Galaxies

throughout the visible universe?


Depends on the definition of "simple". Galaxies range over several
orders of magnitude, so "consistent size" is a non-starter here. Larger
galaxies haven't had time to form, smaller ones have been eaten by
larger ones. More or less. I don't think this is an outstanding
puzzle.

As for planetary sytems, we have much less data. As far as our own
Solar System goes, if the Oort cloud were much farther away, it probably
wouldn't be stable due to perturbations from other stars. So, again, I
don't see any mystery here.
  #30  
Old February 23rd 16, 08:51 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default Advantage Inhomogeneity

In article , "Robert L.
Oldershaw" writes:

You mean to say *statistical* homogeneity,


That should go without saying.

and to make such a claim
you must be ignoring the inconvenient and highly fractal cosmic web
via coarse-graining.


The term "coarse-graining" has a very specific meaning in physics. Why
not say "averaging"?

The consensus is that the cosmic web is not highly fractal by any useful
definition of the term. In particular, there is a scale above which no
further structure seems to exist.

Firstly, I am discussing problems with the LCDM toy model, of which
the inhomogeneity problem is just one of many.


The term "toy model" has a very specific meaning, which does not apply
to LCDM and doesn't mean "any model which is not completely exact".
Please use the terms as they are normally understood.

I note you totally ignore the Buchert et al article. Tell us why.


I already did. The other three contained nothing about the lack of
large-scale homogeneity.

You dismiss Kroupa's identification of many serious LCDM toy model
problems solely on the basis that he favors a MOND model.


Says who? Actually, I am not unsympathetic to MOND. I do think there
are better spokesmen than Kroupa, though.

I hate to
break the bad news to you but the problems that Kroupa has identified
exist whether or not MOND models are valid and useful. If you think
that is not true, prove it by addressing his points one-by-one and
showing references indicating flaws in each specific problem.


Just this morning on the arXiv:

Title: Reconciling dwarf galaxies with LCDM cosmology: Simulating a
realistic population of satellites around a Milky Way-mass galaxy
Authors: Andrew R. Wetzel, Philip F. Hopkins, Ji-hoon Kim, Claude-Andre
Faucher-Giguere, Dusan Keres, Eliot Quataert
Categories: astro-ph.GA
Comments: 6 pages, 5 figures. Submitted to ApJ Letters

Abstract is below.

For a while, people thought that there was a problem because the Hubble
constant implied a universe which was younger than other estimates of
its age. But this assumed a wrong cosmological model. For decades, it
was known that other models----without any new physics or additional
assumptions---exist which don't have an "age problem". Some people
tried to lower the value of the Hubble constant, some tried to lower
other age estimates. It turned out that both were more or less right,
and the problem was that one had assumed that we don't live in a
low-density universe with a positive cosmological constant. There was
always evidence for the former, and the has been evidence for the latter
for some time now. So, these days writing a paper on the "age problem"
is a non-starter, because it has been solved.

The problems of LCDM are not surprising considering that they
essentially stem from dark-matter-only simulations, which of course
cannot be the last word. Nevertheless, some have seen a crisis in LCDM,
some thought that observations were incomplete. But maybe the LCDM
scenario AND the observations are essentially correct, if one uses a
more realistic model. This is what the paper mentioned above (abstract
below) addresses. Please tell us, specifically, what is wrong: quote
some text (without leaving anything out within the quotation), tell us
why it is wrong, and provide a reference. This is not the first paper
to make such claims. It just turns out that "gastrophysics" is not easy
to do, and predictions which can be compared to observations might need
millions of hours of CPU time.

You often mention arXiv papers here. In fairness, shouldn't you have
mentioned this one? It explicitly addresses things you are interested
in.

----------8--------------------------------------------------------------------

Low-mass "dwarf" galaxies represent the most significant challenges to
the cold dark matter (CDM) model of cosmological structure formation.
Because these faint galaxies are (best) observed within the Local Group
of the Milky Way (MW) and Andromeda (M31), understanding their formation
in such an environment is critical. We present the first results from
the Latte Project: the Milky Way on FIRE (Feedback in Realistic
Environments). This simulation models the formation of a MW-mass galaxy
to z = 0 within LCDM cosmology, including dark matter, gas, and stars at
unprecedented resolution: baryon mass of 7070 M_sun at spatial
resolution down to 1 pc. Latte was simulated using the GIZMO code with a
mesh-free method for accurate hydrodynamics and the FIRE model for star
formation and explicit feedback within a multi-phase interstellar
medium. For the first time, Latte self-consistently resolves the
internal structure of dwarf galaxies that form around a MW-mass host
down to M_star 10^5 M_ sun. Latte's population of dwarf galaxies
agrees well with those observed in the Local Group across a broad range
of properties: (1) distributions of stellar masses and stellar velocity
dispersions (dynamical masses), including their joint relation, (2) the
mass-metallicity relation, and (3) a diverse range of star-formation
histories, including their mass dependence. Thus, Latte produces a
realistic population of dwarf galaxies at M_star 10^5 M_sun that does
not suffer from the "missing satellites" or "too big to fail" problems
of small-scale structure formation. We conclude that baryonic physics
can reconcile observed dwarf galaxies with standard LCDM cosmology.
 




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