Dark Matter

Dark Matter: It "exists" in the immediate neighborhoods of *distant*, *large*, *massive* structures that are made up of (besides dark matter) large quantities of ordinary matter. In these regions the dark matter, gram for gram, out-populates the ordinary matter by a ratio of about 4 to 1.

Dark Matter: It's not found to affect nearby interactions amongst individual, small objects composed of ordinary matter.

IOW dark matter is *very* abundent in the neighborhoods of galaxy clusters which are made up of galaxies. It's also very abundent in the neighborhoods of galaxies which are made up of (among other things) planetary systems and multiple star systems. Yet, dark matter is apparently absent within planetary systems and within multiple star systems.

Dark matter is everywhere, dark matter is nowhere!

I'm reminded of a statement (IIRC) made by Star Trek's Spock: "The unreal does not exist."

Sketcher,
To think is to (potentially) err.

On Fri, 24 Jul 2015 09:07:55 -0700 (PDT), Sketcher
wrote:

Yet, dark matter is apparently absent within planetary systems and within multiple star systems.

That is not generally the view of most researchers. It's simply that
these systems formed after dark matter concentrations were already in
place (they are associated with, and very possibly precipitated the
formation of galaxies and galaxy clusters).

It's not that we aren't surrounded with dark matter, just that it's
diffuse, not forming halos around star systems. There are a number of
experiments in progress to identify dark matter particles. Obviously,
these assume that the particles are ubiquitous, present in our system
and passing through us all the time.

On 24/07/2015 17:07, Sketcher wrote:

Dark Matter: It "exists" in the immediate neighborhoods of *distant*, *large*, *massive* structures that are made up
of (besides dark matter) large quantities of ordinary matter. In
these regions the dark matter, gram for gram,
out-populates the ordinary matter by a ratio of about 4 to 1.

There has to be some extra mass that we can't see or everything would
fly apart! Galaxy clusters would not be gravitationally bound and stars
in galaxies could not go around as fast as they do.

Zwicky called it the missing mass problem in 1933.

Back in the 1980's you could hide it all as biros, chair legs and
wrecked cars. But today the surveys in every wavelength from far IR to
Xray have pretty much made it impossible to hide enough mass as
non-luminous ordinary matter so there must be something else we can't
see. That or gravity has some strange behaviour on long scale lengths.

Dark Matter: It's not found to affect nearby interactions amongst individual, small objects composed of ordinary matter.

Mainly because it is clumped smoothly enough to only be bound into
galaxy and galaxy cluster scale objects. It is present in our solar
system but smooth enough that the only real influence it has is to
enable our sun to stay in orbit in its spiral arm.

It is quite impressive that universe simulations with the mix of CDM and
ordinary matter we think are present evolve into something that looks
very similar to the Hubble deep field.

IOW dark matter is *very* abundent in the neighborhoods of galaxy clusters which are made up of galaxies.
It's also very abundent in the neighborhoods of galaxies which are
made up of (among other things) planetary
systems and multiple star systems.

There is a lot of it about. But since it has mass but doesn't interact
with electromagnetic radiation at all, and only very weakly interacts
with ordinary matter it is very difficult to observe it.

Yet, dark matter is apparently absent within planetary systems and within multiple star systems.

Dark matter is everywhere, dark matter is nowhere!

Neutrinos have a tiny mass and are hot (relativistic) dark matter and
large numbers pass right through the Earth every minute. The first we
ever know of a supernova explosion is from the pulse of neutrinos which
can escape from the catastrophic implosion immediately.

It isn't that much of a stretch to imagine cold dark matter with a
similar disinclination to interract with ordinary matter.

I'm reminded of a statement (IIRC) made by Star Trek's Spock: "The unreal does not exist."

Sketcher,
To think is to (potentially) err.


Various experiments are looking for dark matter in the form of WIMPs.
I was down Boulby potash mine last week taking a look at one setup.

They don't expect to be successful with present generation of kit but
the next generation of larger and more sensitive ones might get it. They
are presently qualifying materials for building the next one.

--
Regards,
Martin Brown

On Saturday, July 25, 2015 at 2:50:49 AM UTC-5, Martin Brown wrote:
On 24/07/2015 17:07, Sketcher wrote:

Dark Matter: It "exists" in the immediate neighborhoods of *distant*, *large*, *massive* structures that are made up
of (besides dark matter) large quantities of ordinary matter. In
these regions the dark matter, gram for gram,
out-populates the ordinary matter by a ratio of about 4 to 1.

There has to be some extra mass that we can't see or everything would
fly apart! Galaxy clusters would not be gravitationally bound and stars
in galaxies could not go around as fast as they do.

Zwicky called it the missing mass problem in 1933.

Back in the 1980's you could hide it all as biros, chair legs and
wrecked cars. But today the surveys in every wavelength from far IR to
Xray have pretty much made it impossible to hide enough mass as
non-luminous ordinary matter so there must be something else we can't
see. That or gravity has some strange behaviour on long scale lengths.

Dark Matter: It's not found to affect nearby interactions amongst individual, small objects composed of ordinary matter.

Mainly because it is clumped smoothly enough to only be bound into
galaxy and galaxy cluster scale objects. It is present in our solar
system but smooth enough that the only real influence it has is to
enable our sun to stay in orbit in its spiral arm.

It is quite impressive that universe simulations with the mix of CDM and
ordinary matter we think are present evolve into something that looks
very similar to the Hubble deep field.

IOW dark matter is *very* abundent in the neighborhoods of galaxy clusters which are made up of galaxies.
It's also very abundent in the neighborhoods of galaxies which are
made up of (among other things) planetary
systems and multiple star systems.

There is a lot of it about. But since it has mass but doesn't interact
with electromagnetic radiation at all, and only very weakly interacts
with ordinary matter it is very difficult to observe it.

Yet, dark matter is apparently absent within planetary systems and within multiple star systems.

Dark matter is everywhere, dark matter is nowhere!

Neutrinos have a tiny mass and are hot (relativistic) dark matter and
large numbers pass right through the Earth every minute. The first we
ever know of a supernova explosion is from the pulse of neutrinos which
can escape from the catastrophic implosion immediately.

It isn't that much of a stretch to imagine cold dark matter with a
similar disinclination to interract with ordinary matter.

I'm reminded of a statement (IIRC) made by Star Trek's Spock: "The unreal does not exist."

Sketcher,
To think is to (potentially) err.


Various experiments are looking for dark matter in the form of WIMPs.
I was down Boulby potash mine last week taking a look at one setup.

They don't expect to be successful with present generation of kit but
the next generation of larger and more sensitive ones might get it. They
are presently qualifying materials for building the next one.

--
Regards,
Martin Brown

How much mass is in the black holes in the center of galaxies? How is that measured?

At present, to the best of my (very limited!) knowledge, the evidence for which dark matter was postulated to explain has all originated far far away. Yes, dark matter is being searched for locally, but it (or more precisely, the evidence for it) has yet to be detected/observed locally and yet to be detected within systems smaller than galaxies. For those reasons, I stated in my original post: ". . . dark matter is apparently absent . . ." -- undetected locally.

To clarify the main thought behind my posting: Since all the evidence for dark matter comes to us via EM radiation that has traveled over 'astronomical' times and distances to get here and since that evidence has been found only around the most massive objects we know of . . . and since it hasn't been found locally - (Here it comes!) - perhaps the astrophysicists have 'jumped the gun' a bit in (largely) accepted the notion that the observed evidence implies the existance of large amounts of unseen (or more precisely, unsee-able) gravitating matter.

Is dark matter the logical place to concentrate? (I agree that it's a 'valid' place to give 'some' attention.) Is that where Occam's Razor points? As you mentioned below: ". . . or gravity has some strange behavior on long scale lengths." My point is that other great unknowns exist - such as:

a) the behavior of gravity over long distances and long time intervals
b) the behavior of EM radiation over long distances and long time intervals
c) undiscovered properties of our universe (ponder for a moment some possible explanations behind 'c').

I think it's a bit presumptive for anyone (I'm not directing this at any one person) to effectivly 'conclude' the current investigations and state that dark matter exists within our planetary system, etc. until we have in hand the supporting evidence. In my opinion too many people have jumped on the 'dark matter bandwagon' at the cost of taking away time from refining and creating alternative theories. Yes, I know there is 'some' research on alternative interpretations of the evidence, but this dark matter situation is looking a bit like the old situation involving defferents and epicycles (we'll see if Gerald reads this far;-). We have an unexplained observation. We have a possible explanation, and now we direct most of our time and efforts on the assumption that the 'possible' explanation is 'the (correct)' explanation.

Yes, in the end the correct explanation may involve dark matter. At present the evidence (for dark matter) is "apetizing", but it falls short of being conclusive. I would be happier if the astrophysicists and popular media referred to the whole situation as simply the (or Zwicky's) 'missing mass problem' (It doesn't bother me to use 'mass' here - even though there's a possibility that 'missing mass' might, in the end, be absent in (missing from;-) the correct explanation).

Paraphrasing (since I probably don't recall correctly) someone else's statement: The universe isn't just strange, it's stranger than anyone can imagine!

Sketcher,
To sketch is to see.

On Saturday, July 25, 2015 at 1:50:49 AM UTC-6, Martin Brown wrote:
On 24/07/2015 17:07, Sketcher wrote:

Dark Matter: It "exists" in the immediate neighborhoods of *distant*, *large*, *massive* structures that are made up
of (besides dark matter) large quantities of ordinary matter. In
these regions the dark matter, gram for gram,
out-populates the ordinary matter by a ratio of about 4 to 1.

There has to be some extra mass that we can't see or everything would
fly apart! Galaxy clusters would not be gravitationally bound and stars
in galaxies could not go around as fast as they do.

Zwicky called it the missing mass problem in 1933.

Back in the 1980's you could hide it all as biros, chair legs and
wrecked cars. But today the surveys in every wavelength from far IR to
Xray have pretty much made it impossible to hide enough mass as
non-luminous ordinary matter so there must be something else we can't
see. That or gravity has some strange behaviour on long scale lengths.

Dark Matter: It's not found to affect nearby interactions amongst individual, small objects composed of ordinary matter.

Mainly because it is clumped smoothly enough to only be bound into
galaxy and galaxy cluster scale objects. It is present in our solar
system but smooth enough that the only real influence it has is to
enable our sun to stay in orbit in its spiral arm.

It is quite impressive that universe simulations with the mix of CDM and
ordinary matter we think are present evolve into something that looks
very similar to the Hubble deep field.

IOW dark matter is *very* abundent in the neighborhoods of galaxy clusters which are made up of galaxies.
It's also very abundent in the neighborhoods of galaxies which are
made up of (among other things) planetary
systems and multiple star systems.

There is a lot of it about. But since it has mass but doesn't interact
with electromagnetic radiation at all, and only very weakly interacts
with ordinary matter it is very difficult to observe it.

Yet, dark matter is apparently absent within planetary systems and within multiple star systems.

Dark matter is everywhere, dark matter is nowhere!

Neutrinos have a tiny mass and are hot (relativistic) dark matter and
large numbers pass right through the Earth every minute. The first we
ever know of a supernova explosion is from the pulse of neutrinos which
can escape from the catastrophic implosion immediately.

It isn't that much of a stretch to imagine cold dark matter with a
similar disinclination to interract with ordinary matter.

I'm reminded of a statement (IIRC) made by Star Trek's Spock: "The unreal does not exist."

Sketcher,
To think is to (potentially) err.


Various experiments are looking for dark matter in the form of WIMPs.
I was down Boulby potash mine last week taking a look at one setup.

They don't expect to be successful with present generation of kit but
the next generation of larger and more sensitive ones might get it. They
are presently qualifying materials for building the next one.

--
Regards,
Martin Brown

On Saturday, July 25, 2015 at 10:16:35 PM UTC+1, Sketcher wrote:

Yes, I know there is 'some' research on alternative interpretations of the evidence, but this dark matter situation is looking a bit like the old situation involving defferents and epicycles (we'll see if Gerald reads this far;-). We have an unexplained observation. We have a possible explanation, and now we direct most of our time and efforts on the assumption that the 'possible' explanation is 'the (correct)' explanation.


The geocentric epicycles and equants came within the periodic times scheme where everything moved through the constellations including the Sun. I have shown the necessity for partitioning inner and outer planetary retrogrades by perspectives as the Earth's motions accounts for the apparent motions of the outer planets and inner planets in separate ways.

With the simple grace of intelligence that all possess, you all can now look on the new scheme where the apparent motion of the stars behind the Sun displaces the apparent motion of the Sun through the constellations and even though I have to borrow the graphic from an astrological website as none exists elsewhere, I am confident that eventually some enterprising individual good at graphics will take the time out to generate a better perspective ..

https://www.youtube.com/watch?v=eeQwYrfmvoQ


Dark matter,black hole, big bang ect are not only crude linguistic indulgences but also intellectual regression where the decay has been going on for a number of centuries, a sort of language that merges with fantasy and fiction at the expense of the gentle and magnificent nature of genuine astronomy. It may not be entirely fraud but a number of people make a living out of chanting meaningless voodoo with their many willing followers like Sketcher here.

On 25/07/2015 19:03, Uncarollo2 wrote:
On Saturday, July 25, 2015 at 2:50:49 AM UTC-5, Martin Brown wrote:
On 24/07/2015 17:07, Sketcher wrote:

Yet, dark matter is apparently absent within planetary systems and within multiple star systems.

Dark matter is everywhere, dark matter is nowhere!

Neutrinos have a tiny mass and are hot (relativistic) dark matter and
large numbers pass right through the Earth every minute. The first we
ever know of a supernova explosion is from the pulse of neutrinos which
can escape from the catastrophic implosion immediately.

It isn't that much of a stretch to imagine cold dark matter with a
similar disinclination to interract with ordinary matter.

My own problem with CDM Is that I really don't understand how it can
have cooled down from its initial state in the first place.

I'm reminded of a statement (IIRC) made by Star Trek's Spock: "The unreal does not exist."

Sketcher,
To think is to (potentially) err.


Various experiments are looking for dark matter in the form of WIMPs.
I was down Boulby potash mine last week taking a look at one setup.

They don't expect to be successful with present generation of kit but
the next generation of larger and more sensitive ones might get it. They
are presently qualifying materials for building the next one.

How much mass is in the black holes in the center of galaxies? How is that measured?


For our own galaxy they can effectively weight it and deduce its
position by tracking stars in close elliptical orbits around it and in
the fullness of time watch it light up when it swallows a cloud of
interstellar gas or rips a too close approaching star apart.

For more distant galaxies the methods rely on sizing an object based on
how quickly its power output can change, reflections of such changes off
neighbouring stars and nebulae in the object or correlated properties of
host galaxies. Something that can change output in an hour isn't likely
to be much bigger than a light hour across. Emission line profiles can
tell you a lot about the physical environment.

A reasonable description of the methods is online he

http://www.astronomy.ohio-state.edu/...tersonISSI.pdf
(perhaps in more detail than you really wanted)

But the central black hole can't help with the too flat velocity curve
in the spiral arms of a galaxy. The stars under the influence of a
single massive central object would obey Keplerian orbits (*) which is
exactly the problem of the missing mass. The amount of stuff visible
inside a given stellar orbit can be used to estimate the gravitating
mass that any given star sees and it simply is nowhere near enough to
hold the star in orbit around the galactic centre.

(*) ie T^2 = ka^3

For stars orbiting in our galaxy spiral arms the velocity profile looks
convincingly like there is a heck of a lot of mass we just can't see.

https://en.wikipedia.org/wiki/Galaxy_rotation_curve

Isn't a bad introduction and this applies to our own galaxy and local
group neighbours like M31 and M33. MOND is the epicycle fix which could
possibly explain these rotation curves by tweaking gravity.

But such an empirical tweak has limited appeal and would not help
explain how galaxy clusters form in the early universe. The gang of
fours simulations of the early universe is suggestive that cold dark
matter however unappealing it might seem is a real feature of our
universe albeit one with which it is incredibly difficult to interact.

Most astrophysicists consider CDM the solution but until the exact
nature of it is determined there will always be some scepticism.

https://en.wikipedia.org/wiki/Navarr...3White_profile

Is the expected CDM equilibrium configuration in a galaxy.

--
Regards,
Martin Brown

On 25/07/2015 22:16, Sketcher wrote:
At present, to the best of my (very limited!) knowledge, the evidence for which dark matter was postulated
to explain has all originated far far away. Yes, dark matter is
being searched for locally, but it
(or more precisely, the evidence for it) has yet to be
detected/observed locally and yet to be detected
within systems smaller than galaxies. For those reasons, I stated in
my original post:
". . . dark matter is apparently absent . . ." -- undetected locally.

It depends a bit what you mean by locally. For a cosmologist our galaxy
and the local group is still very local. And neighbouring clusters like
Virgo and Leo are pretty close on astrophysical length scales.

If we can resolve brighter stars in a galaxy then Cepheid variables give
a very precise distance estimate. So far as we can tell the laws of
physics apply universally and it gets very messy if you allow them to
vary. Further out the distance ladder relies of type Ia supernovae.

https://en.wikipedia.org/wiki/Type_Ia_supernova

To clarify the main thought behind my posting: Since all the evidence for dark matter comes to us via
EM radiation that has traveled over 'astronomical' times and
distances to get here and since that evidence
has been found only around the most massive objects we know of . . .
and since it hasn't been found locally
- (Here it comes!) - perhaps the astrophysicists have 'jumped the
gun' a bit in (largely) accepted the
notion that the observed evidence implies the existance of large amounts of unseen
(or more precisely, unsee-able) gravitating matter.

Something is holding the stars in orbit around galaxies including our
own and the amount of mass we can see is not enough to explain this.

Is dark matter the logical place to concentrate? (I agree that it's a 'valid' place to give 'some' attention.)
Is that where Occam's Razor points? As you mentioned below: ". . .
or gravity has some strange behavior on long scale lengths."
My point is that other great unknowns exist - such as:

a) the behavior of gravity over long distances and long time intervals
b) the behavior of EM radiation over long distances and long time intervals
c) undiscovered properties of our universe (ponder for a moment some possible explanations behind 'c').

MOND was the original alternative theory to bodge the galactic velocity
curve gravity mismatch problem and still has some adherents. It is ugly
to mess with an inverse square law since it invariably results in
problems elsewhere in astrophysics. It isn't ruled out though.

The advantage that CDM has is that it also neatly explains the formation
and clustering of galaxies in the early universe. They tried HDM
(neutrinos) first since they are also know to have mass.

I think it's a bit presumptive for anyone (I'm not directing this at any one person) to effectivly 'conclude'
the current investigations and state that dark matter exists within
our planetary system, etc.
until we have in hand the supporting evidence. In my opinion too
many people have jumped on the 'dark matter bandwagon'
at the cost of taking away time from refining and creating
alternative theories. Yes, I know there is 'some' research
on alternative interpretations of the evidence, but this dark matter
situation is looking a bit like the old situation
involving defferents and epicycles (we'll see if Gerald reads this
far;-). We have an unexplained observation.

MOND is more like the epicycles fixup. It can sort out galaxies but
fails a bit on cluster of galaxies and totally at larger scales.

We have a possible explanation, and now we direct most of our time and efforts on the assumption that the 'possible'
explanation is 'the (correct)' explanation.

Calling it dark matter is pretty much decriptive of it. Something is
providing the extra gravity and whatever it is we can't detect it by any
electromagnetic means. The distribution it appears to have is also
consistent with the properties it is expected to have.

Yes, in the end the correct explanation may involve dark matter.
At present the evidence (for dark matter) is "apetizing", but it
falls short of being conclusive.
I would be happier if the astrophysicists and popular media referred
to the whole situation as simply
the (or Zwicky's) 'missing mass problem' (It doesn't bother me to use
'mass' here - even though there's
a possibility that 'missing mass' might, in the end, be absent in
(missing from;-) the correct explanation).

It will only be resolved when either dark matter is identified or an
alternate theory is validated by experimental means.

Paraphrasing (since I probably don't recall correctly) someone else's statement:
The universe isn't just strange, it's stranger than anyone can imagine!

You underestimate the imaginative capabilities of theorists.

There are a handful of theoreticians considering alternatives but none
has the same appeal as CDM which appears to fit the observable universe
so well in simulations. The simulated universe matches the observable
one with astonishing accuracy these days. It uses CDM.

We live in a golden age of observational astronomy where the solid state
detectors and space based telescopes allow us to image and take spectra
of objects in unprecedented detail at wavelengths from hard Xrays to
thermal IR.

Ground based kit has also come of age with active aperture correction
and radio astronomy now using its aperture synthesis techniques up to
the near IR. Dark matter is a descriptive term for non-luminous stuff.

Observations and experiments will eventually tie it down but until that
happens we can only conjecture about the nature of the extra force.

It used to be the case that you could hide dark matter as builders
rubble, small asteroids and the like. But that would interact with
starlight and leave a characteristic faint thermal glow we don't see.
Same for adding enough compact black holes we would see them pass in
front of distant objects from time to time and it isn't observed.

It may be that there is a mix of stuff but CDM would appear to be a part
of the solution however distasteful you may find it.

A bit like Sherlock Homes - when you have ruled out everything else
whatever remains however improbable is the answer.

PS. Don't ask me to defend Dark Energy - that is from after my time and
I really don't like it very much.

--
Regards,
Martin Brown

On Sunday, July 26, 2015 at 10:05:11 AM UTC+1, Martin Brown wrote:

MOND is more like the epicycles fixup. It can sort out galaxies but
fails a bit on cluster of galaxies and totally at larger scales.


Regards,
Martin Brown

These guys like Brown come here believing in a wandering analemma Sun hence they don't even rise to the geocentric perspectives which clearly distinguishes the observed motions of the planets from the observed motion of the Sun and the orbital variations in speeds which ultimately transfers to perspectives seen from the orbital motion of the Earth -

"But the ancient philosophers wanted to arrange the planets in accordance with the duration of the revolutions. Their principle assumes that of objects moving equally fast, those farther away seem to travel more slowly, as is proved in Euclid's Optics. The moon revolves in the shortest period of time because, in their opinion, it runs on the smallest circle as the nearest to the earth. The highest planet, on the other hand, is Saturn, which completes the biggest circuit in the longest time. Below it is Jupiter, followed by Mars.
With regard to Venus and Mercury, however, differences of opinion are found.. For, these planets do not pass through every elongation from the sun, as the other planets do. Hence Venus and Mercury are located above the sun by some authorities, like Plato's Timaeus (38 D), but below the sun by others, like Ptolemy (Syntaxis, IX, 1) and many of the modems. Al-Bitruji places Venus above the sun, and Mercury below it." Copernicus

In terms of applying astronomical reasoning in a forum dominated by empirical theorists ,it is like a brain specialist trying to explain the working of the brain to phrenologists. The system of reckoning in geocentric astronomy worked against the proof of the Earth's motions and especially its orbital motion in and what inputs the Earth's orbital motion supplied in making sense of the motions and structure of the solar system. I have changed all that by incorporating parts of the original retrograde resolution seen in the outer planets and resolved by Copernicus while introducing a separate perspective for inner planetary retrogrades by using the images supplied by the telescope of phases and the displacement of the periodic times arguments which lumped the Sun in with the other planets.

Seeing epicycles were brought up by Sketcher in the hope that it scares away readers and genuine observers, let him and anyone else look at how decent and brilliant astronomers worked with observations in their own words. Unless people want to be thugs and destroy a heritage to satisfy overreaching agendas based on meaningless voodoo they can look at the celestial arena as the original astronomers did and continue the tradition that way.

On 26/07/2015 10:05, Martin Brown wrote:
On 25/07/2015 22:16, Sketcher wrote:

Is dark matter the logical place to concentrate? (I agree that it's a
'valid' place to give 'some' attention.)
Is that where Occam's Razor points? As you mentioned below: ". . .
or gravity has some strange behavior on long scale lengths."
My point is that other great unknowns exist - such as:

a) the behavior of gravity over long distances and long time intervals

So far it seems remarkably steady. That inertial mass and gravitational
mass are the same has been carefully tested in the lab.

b) the behavior of EM radiation over long distances and long time
intervals

So far nothing has been observed that isn't accurately predicted by GR
and we have some remarkable binary pulsars to play with.

Dirac in 1938 once entertained the idea that the constants of nature
might vary with time and gets honourable mention for this idea in the
graduate astronomy text Harwit's Astrophysical Concepts amongst others.

c) undiscovered properties of our universe (ponder for a moment some
possible explanations behind 'c').

Maxwell's laws of electromagnetism are sufficient to derive this. It
took a while before someone like Einstein appreciated the implications
of a universal maximum speed limit on information transfer and dynamics.

The more intuitive Galilean dynamics had worked so well at all the
speeds we could easily study up to that stage.

MOND was the original alternative theory to bodge the galactic velocity
curve gravity mismatch problem and still has some adherents. It is ugly
to mess with an inverse square law since it invariably results in
problems elsewhere in astrophysics. It isn't ruled out though.

The advantage that CDM has is that it also neatly explains the formation
and clustering of galaxies in the early universe. They tried HDM
(neutrinos) first since they are also know to have mass.

A bit more detail available online here considers WIMPs, axions and MOND
fairly even handedly with links to relevant Wiki entries.

https://www.astro.umd.edu/~ssm/darkm...periments.html

--
Regards,
Martin Brown