"LCDM Paradigm Is Consistent With All Observations"? - Not So!

In article ,
Phillip Helbig---undress to reply writes:
There are many observations which DO support LCDM. Even if one
observation doesn't, one cannot toss aside LCDM unless one has
another theory that explains this new observation AND ALL OTHER
OBSERVATIONS WHICH SUPPORT LCDM.

I understand the sentiment but disagree with the above. If there's
any confirmed observation that disagrees with a theory's undeniable
prediction, that theory is dead regardless of whether another theory
exists or not.

A common mistake is to think that a correction to details rules out the
underlying theory,

This I mostly agree with. The way I'd put it is that one has to be
sure a discrepant observation contradicts an actual and not a
mistaken prediction of the theory. Or in other words that the
calculation of what the theory predicts is correct.

In the context of the dwarf galaxy problem, it isn't clear just what
LCDM predicts. First of all, dark matter simulations are limited by
the available computing power, and I understand that at least in the
past they made approximations that may not be correct at the low-mass
end. Second, even if the computations are numerically accurate for
the low-mass dark-matter haloes, there's a lot of poorly understood
baryon physics between a halo and a galaxy. This is approximated by
some formula that seems to work OK for massive galaxies, but that
doesn't mean the formula works at low masses, where it's hard to
test. Just one reason for doubt is that in a low-mass halo, a single
supernova can blow out all the star-forming gas, leading to a very
different dependence of star formation on gas density than in a more
massive halo. The upshot is that most of us believe that the "dwarf
galaxy problem" is an artifact of imperfect calculations, not an
actual failing of LCDM. If that turns out to be wrong, LCDM _in its
current form_ is dead. I expect whatever replaces it will be much
like LCDM (see "correspondence principle"), but presumably it will
require new physics with new free parameters. Right now, though, I'd
bet on LCDM rather than the existing simulations. Anyone who
disagrees is welcome to do better simulations that remove the
problems of the existing ones. (People are trying to do that, of
course.)

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

In article , Steve Willner
writes:

In article ,
Phillip Helbig---undress to reply writes:
There are many observations which DO support LCDM. Even if one
observation doesn't, one cannot toss aside LCDM unless one has
another theory that explains this new observation AND ALL OTHER
OBSERVATIONS WHICH SUPPORT LCDM.

I understand the sentiment but disagree with the above. If there's
any confirmed observation that disagrees with a theory's undeniable
prediction, that theory is dead regardless of whether another theory
exists or not.

I agree. Take, though, my statement above as amended by Martin's and my
comments, namely a) the observation is not yet confirmed and b) it would
be a stretch to call this a "definitive prediction" of LCDM.

This I mostly agree with. The way I'd put it is that one has to be
sure a discrepant observation contradicts an actual and not a
mistaken prediction of the theory. Or in other words that the
calculation of what the theory predicts is correct.

Right.

In the context of the dwarf galaxy problem, it isn't clear just what
LCDM predicts. First of all, dark matter simulations are limited by
the available computing power, and I understand that at least in the
past they made approximations that may not be correct at the low-mass
end.

Indeed.

Second, even if the computations are numerically accurate for
the low-mass dark-matter haloes, there's a lot of poorly understood
baryon physics between a halo and a galaxy.

Gastrophysics. :-)

This is approximated by
some formula that seems to work OK for massive galaxies, but that
doesn't mean the formula works at low masses, where it's hard to
test. Just one reason for doubt is that in a low-mass halo, a single
supernova can blow out all the star-forming gas, leading to a very
different dependence of star formation on gas density than in a more
massive halo. The upshot is that most of us believe that the "dwarf
galaxy problem" is an artifact of imperfect calculations, not an
actual failing of LCDM. If that turns out to be wrong, LCDM _in its
current form_ is dead.

Of course, like "big bang", different people use the term "LCDM" with
different definitions.

I expect whatever replaces it will be much
like LCDM (see "correspondence principle"), but presumably it will
require new physics with new free parameters. Right now, though, I'd
bet on LCDM rather than the existing simulations. Anyone who
disagrees is welcome to do better simulations that remove the
problems of the existing ones. (People are trying to do that, of
course.)

My own impression is that slow but steady progress is being made in
simulations.

On Thursday, July 31, 2014 4:19:55 AM UTC-4, Phillip Helbig---undress to reply wrote:

My own impression is that slow but steady progress is being made in
simulations.
-----------------------------------------

New observational evidence (Nature, in press) suggests that the
planarity of satellite dwarf galaxy distributions seen within the
Local Group may be universal.

http://arxiv.org/abs/1407.8178


[Mod. note: reformatted -- mjh]

3:33 AMRobert L. Oldershaw
Robert Oldershaw wrote:
New observational evidence (Nature, in press) suggests that the
planarity of satellite dwarf galaxy distributions seen within the
Local Group may be universal.

http://arxiv.org/abs/1407.8178

Furthers the dwarfs seem to reside within the dark matter halos of
their host galaxies which would imply that something is wrong with the
cdm as the nuclei for galaxy formation.

Brad

[Mod. note: reformatted. Please try to adhere to the norms of
formatting and quotation style used in the group -- mjh]

On Monday, August 4, 2014 3:34:26 AM UTC-4, brad wrote:
Furthers the dwarfs seem to reside within the dark matter halos of
their host galaxies which would imply that something is wrong with the
cdm as the nuclei for galaxy formation.

I quote from the conclusions of the referenced
Nature paper:

"Our tests were constructed using [the
Millenium II Simulation] as a control sample
to predict what should have been a priori
expected in [L]CDM cosmology. Just as this
paradigm did not predict the planes observed
in the Local group, it did not a priori predict
the velocity correlations presented here. It
should be noted, however..." that the MS2
simulation only includes dark matter.

[mod. note: reformatted -- mjh]

On 8/2/14, 2:33 AM, Robert L. Oldershaw wrote:
On Thursday, July 31, 2014 4:19:55 AM UTC-4, Phillip Helbig---undress to reply wrote:

My own impression is that slow but steady progress is being made in
simulations.
-----------------------------------------

New observational evidence (Nature, in press) suggests that the
planarity of satellite dwarf galaxy distributions seen within the
Local Group may be universal.

http://arxiv.org/abs/1407.8178

There was a paper ~10 years ago
indicating galactic planes were generally oriented to a common plane.
Can't remember the reference.

1:45 AMRichard D. Saam
There was a paper ~10 years ago
indicating galactic planes were generally oriented to a common plane.
Can't remember the reference.

This more recent

MLA APA Chicago
Royal Astronomical Society (RAS). "Milky Way amidst a 'Council of
Giants'." ScienceDaily. ScienceDaily, 11 March 2014.
www.sciencedaily.com/releases/2014/03/140311100606.htm.

What I wonder about: since galaxy groups appear to assemble like solar
systems (planar) where are the analogs of comets? Even dwarfs assemble
along the plane of the clusters. This seems to need some more
explanation than exotic ( dark) matter and consequent gravitational
collapse.

Brad

On Tuesday, August 5, 2014 8:35:40 AM UTC-4, brad wrote:
What I wonder about: since galaxy groups appear to assemble like solar
systems (planar) where are the analogs of comets? Even dwarfs assemble
along the plane of the clusters. This seems to need some more
explanation than exotic ( dark) matter and consequent gravitational
collapse.

Qualitatively speaking, globular clusters might
fit the bill in terms of their relative masses values
and their orbital behavior.

However, such an analogy is of limited value if
the putative analogous systems are in radically
different energy states.

[Mod. note: reformatted -- mjh]

On 8/5/14, 7:35 AM, brad wrote:

MLA APA Chicago
Royal Astronomical Society (RAS). "Milky Way amidst a 'Council of
Giants'." ScienceDaily. ScienceDaily, 11 March 2014.
www.sciencedaily.com/releases/2014/03/140311100606.htm.

What I wonder about: since galaxy groups appear to assemble like solar
systems (planar) where are the analogs of comets? Even dwarfs assemble
along the plane of the clusters. This seems to need some more
explanation than exotic ( dark) matter and consequent gravitational
collapse.

Brad

From your reference:
"What the new map reveals is that structure akin to that seen on large
scales extends down to the smallest"

There appears to be an asymmetrical supporting medium.
Taking a lesson from crystallography,
the isotropic symmetry of spheres do not fill space.
(packing ping pong balls in a box always has voids)
Cubes can fill space with x,y,z symmetric.
All space filling forms
have an asymmetric packing orientation.
The prior and present space filling geometry
may orient galactic assembly.

Richard D Saam

Op woensdag 30 juli 2014 08:52:06 UTC+2 schreef Steve Willner:
In article ,

Phillip writes:
There are many observations which DO support LCDM. Even if one
observation doesn't, one cannot toss aside LCDM unless one has
another theory that explains this new observation AND ALL OTHER
OBSERVATIONS WHICH SUPPORT LCDM.

I understand the sentiment but disagree with the above. If there's
any confirmed observation that disagrees with a theory's undeniable
prediction, that theory is dead regardless of whether another theory
exists or not.

The fact that 85% of all the matter in universe is Darm Matter
(non-baryonic) is that a precition of the LCDM theory ?

A common mistake is to think that a correction to details rules out
the underlying theory,

This I mostly agree with. The way I'd put it is that one has to be
sure a discrepant observation contradicts an actual and not a
mistaken prediction of the theory. Or in other words that the
calculation of what the theory predicts is correct.

In the context of the dwarf galaxy problem, it isn't clear just what
LCDM predicts.

I would assume that the LCDM predicts that spiral galaxies have
a large halo with Dark Matter. The specific mathematical equations
that describe this halo i.e. the Hernquist profile or the NFW profile
are they also predicted by LCDM ?

First of all, dark matter simulations are limited by
the available computing power, and I understand that at least in the
past they made approximations that may not be correct at the low-mass
end.
I doubt if this is the real problem. It is much more in the model itself.

Second, even if the computations are numerically accurate for
the low-mass dark-matter haloes, there's a lot of poorly understood
baryon physics between a halo and a galaxy.
I think it is the non-baryon physics which depends on all the
mass presumably to be outside the disc.

When you consider an eliptical galaxy it is rather easy to assume
that in principle it could contain lots of non-baryonic matter
because when it is equaly distributed it will not affect the shape.
The problem can be solved when you have two methodes to calculate
the mass of a small galaxy or star cluster.
One methode is: if the galaxy is a binary system and the total mass can be
calculted based on the velocities of each galaxy. A second method is to
calculate the total mass based on its individual stars.
If the two match then there is no DM involved.

For a spiral galaxy the (lots of) mass outside the galaxy could easily
affect the shape (and the size) of disc. The problem is you have
to include mathematics about the behaviour of dm which maybe
is not existing. The only thing you know that when you do a simulation
and the simulated plane (see below) is not stable your simulation is wrong.

In the Nature article of 31 July 2014 Vol 511 page 563 with the title:
"Velocity anti-correlation of diametrically opposed galaxy satelities
in the low-redshift Universe":
Such satellite alignments may arise naturally if dwarf galaxies
formed from tidel debris left over from ancient galaxy mergers,
but this scenario remains difficult to reconcile with the high
dark matter content deduced for these objects.
How do we know that dwarf galaxies have a high dm content?
i.e. non-baryonic ?
I think the problem is much more that M31 and Milky Way are assumed
to have a high dm content.
I expect that as a result it is difficult to explain why the satellite
galaxies of the Milky Way are located close to a plane.

A slightly different issue is: if the coincidence argument is still
valid? See:
http://en.wikipedia.org/wiki/Anthrop...c_coincidences

The reason why I ask this question is, because the book "Galactic Dynamics"
1994 edition in paragraph about "The cosmological constant" page 637,
contains the following text:
"Thus if Omega0=0.2 we have lambda = 2.5 * 10^-35 h^2
It appears that a model Universe with this value of lambda is consistent
with all available observations (Peebles 1984) as well with inflation.
All of the mass can be in baryons and there is no need for any exotic
particles to comprise most of the mass of the Universe. However, these
models are subject to the same "coincidence" objection that was made
to models with Omega0 1 in $10.3.6 etc"

Nicolaas Vroom