On 4/19/15 11:24 PM, Phillip Helbig (undress to reply) wrote:
In article , Ray
Tomes writes:

Gas and dust is able to be detected by its effect on light. Large
objects glow from their own light. If intermediate objects were at
low temperature would they generally be detectable? There are many
orders of magnitude between dust and the dimmest starts. How many
of these could definitely not contribute to dark matter and why?

"Dark matter" is a bit of a misnomer. What most people mean these days
is "some sort of non-baryonic matter, other than neutrinos, which we
have not yet detected". This is the "DM" in, e.g., "LambdaCDM". Other
things can be dark, such as cold gas, dust, and so on. However, we have
good upper (and lower) limits on baryons from big-bang nucleosynthesis,
so while there are some dark baryons, they cannot be an appreciable
fraction of the dark matter.

There is a question as to whether the "good upper (and lower) limits
on baryons from big-bang nucleosynthesis" must be modified
by high Z 'gold' collision experiments conducted inside
the Relativistic Heavy Ion Collider (RHIC),
an atom smasher at Brookhaven National Laboratory in Upton, New York.
Hints of Mysterious Particle Detected in 'Big Bang Soup'
http://www.livescience.com/47506-hea...ons-found.html
http://www.bnl.gov/rhic/news2/news.asp?a=4473&t=today
https://www.quantamagazine.org/20150...lider-awakens/
As established in physical chemistry,
reaction rates change
in solvents 'Big Bang Soup Z1' vs gaseous 'particle Z=1 ' phase.


It's also a bit of a misnomer since "dark" here means that it does not
interact electromagnetically. Yes, that means it doesn't glow,

In order for it not to glow, it must be extremely cold
and if it were baryonic matter, how cold would that be?

but it
also means that it doesn't reflect or absorb light. In other words, it
is transparent.

If dark matter objects had size dimensions on the order of meters,
then the dark matter galactic density on the order of 10^-24 g/cc
composed of these objects
would have a mean free path or optical density
such that they would not be optically visible under current methods
or in other words
these dark matter objects would in aggregate
be observationally transparent
in accordance with Beer Lambert Law
http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law

At most it is weakly interacting (i.e. via the weak
"nuclear" force), but this is not something which can be investigated
astrophysically, so only gravitational effects are left. (Since we
don't know what it is, we don't know if it is self-interacting and hence
don't know if it can form macroscopic objects.)

The WIMP approach seems to be a dead end
based on negative experimental results
from the many current underground scintillation experiments.

Richard D Saam