# How do astronomers know how much dark energy and dark matter in the universe from a radio map?

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• 10-05-2005, 02:46 PM
Michael McCulloch
How do astronomers know how much dark energy and dark matter in the universe from a radio map?
On Tue, 04 Oct 2005 11:52:34 -0400, John Deer <JD@nowhere.com> wrote:

Here is my attempt to answer along with references that you can dig
into to get more meat regarding your specific question.

The prevailing cosmological theory (i.e. the Big Bang) is largely
based on a mathematical model of the Universe called the Lambda-CDM
model:

http://en.wikipedia.org/wiki/Lambda-CDM_model

This model has been developed over the years from observational data
and the input of many scientists. However, this is only a model of the
Universe and is only useful as long as the model makes predictions
that can be verified from observational data.

WMAP provided a data set that allowed astronomers to test the
predictions of the Lambda-CDM model at a scale and resolution
previously unavailable from various other cosmic background radiation
maps.

The WMAP team, and various other scientists I assume, analyzed the
WMAP data and combined it with other available observational data
sets. What they came up with among many things are these graphs:

http://lambda.gsfc.nasa.gov/product/...pectrum_ss.gif

Parent page:
http://lambda.gsfc.nasa.gov/product/...t/m_images.cfm

As others have stated in this thread, the graph shows the relationship
of the observed spectral variations in the WMAP (and other) data for
the cosmic background radiation. The red line shows the curve that is
generated for the Lambda-CDM model using the parameters identified by
the WMAP team as the best fit.

Back to the Lambda-CDM model, the six main parameters (again read the
Wikipedia reference above) "measured" by the WMAP team result in a
mathematical prediction of the age of the Universe. An example of how
the various ratios of dark energy and dark matter affect the
calculation of the age of the Universe is illustrated here:

http://map.gsfc.nasa.gov/m_uni/101bb2_1.html

You may ask: where is the affect of ordinary matter in the graph?
Well, the amount of ordinary matter according to the Lambda-CDM model
is so insignificant as to be practically inconsequential!

So, observing the red line of the expansion graph (using the currently
preferred ratios derived from WMAP) shows it intersects the zero
Universe size at approximately 13-14 billion years.

Note that the red line also shows that the Universe will expand
forever.

Does this mean that the determination by the WMAP is not open to
revision or challenge? Of course not. But any competing theory has to
also account for the observed data and offer a model that can make
testable predictions as well or better than the current model(s) such
as the Lambda-CDM.

present two detailed talks about the WMAP data and the implications
for cosmology. He had several interactive computer programs which
would allow him to input the various parameters and show the resulting
graphs. It was great fun to "play god" with the parameters and watch
how the Universe responded! ;-)

---
Michael McCulloch
• 10-05-2005, 09:04 PM
Chris L Peterson
How do astronomers know how much dark energy and dark matter in the universe from a radio map?
On Tue, 04 Oct 2005 22:36:58 -0600, Tim Killian <TJK@notmyrealemail.com>
wrote:

Could you provide an example of such "erroneous" observations, or of a
serious cosmological theory that ignores observed data by considering it
erroneous?

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
• 10-05-2005, 10:02 PM
Bob
How do astronomers know how much dark energy and dark matter in the universe from a radio map?
Sometimes observations and experiments in the lab get goofed up, and
that's something scientists have to be careful of. But if the
observations or experiments are goofed up, whatever it is that people
think was the defect in the observing or experimental method or
procedure has to be corrected and another set of observations and
experiments has to be run. So when a new theory and experiments to
verify it are done, and you get essentially a "mismatch" (that is, they
don't jive) you have to look at both to see where the problem is. And
then fix it and do the experiments over again. Oh, it's happened where
a bad theory and bad experiment happen to match and thus "confirm" the
bad theory, but that's rare, and usually gets caught by other
scientists in the field. You really don't want that to happen else you
end up looking like a scmuck....

• 10-05-2005, 10:04 PM
Thomas Womack
How do astronomers know how much dark energy and dark matter in the universe from a radio map?
canopus56 <canopus56@yahoo.com> wrote:

Is it showing illuminated _gas_ rather than very diffuse starlight?
The Web page suggests that most of the intra-cluster light they detect
in that spectacular image is from stars scattered out of the Virgo
galaxies; I suppose it's a moot point, since spectroscopy of something
magnitude 28 and that diffuse isn't really practical (though I believe
people have detected intra-cluster planetary nebulae, and even stars
using long Hubble exposures), and repeating the very long exposure in
H-alpha would be a tedious task.

I really hadn't expected the halos of M84 and M86 (the galaxies on the
right of that image) to overlap!

I'd be very interested to see how far out you can detect the halos
using a fast wide-field amateur instrument like the Epsilon 180
astrograph.

Tom
• 10-05-2005, 10:16 PM
Bob
How do astronomers know how much dark energy and dark matter in the universe from a radio map?
IIRC, one of the features of dark matter particles is that they don't
clump together like ordinary matter does. So you never get dark matter
asteriods, planets and so on. Or dark matter molecules. And dark
matter particles pass thru the Earth and other clumps of regular matter
and not be impededed at all. Heard it said that there is likely about
2 kilograms of dark matter particles passing thru the Earth right now,
but none of it clumps with the Earth. Maybe a little of it orbits the
earth's center of mass, but none clumps with Earth's regular matter.
But taking the dark matter density of 2Kg/(volume of an 8000 mile
sphere (that of the Earth) and then figure that's the density thruout
the solar system, the mass of all that still comes out too small to do
anything much to the orbits of planets and such. But look at the
volume of a galaxy, then it becomes important. Or at least that's how
I misunderstand it..... :-)

• 10-05-2005, 10:20 PM
Bob
How do astronomers know how much dark energy and dark matter in the universe from a radio map?
Oh and we don't know how many different types of dark matter particle
there are. Maybe it's one or two, or maybe it's a big mess of 'em like
the hundred or so sub-atomic ordinary mass partilces we know about.
But if none of the dark matter ever clumps like regular ordinary matter
does, then you'd never have any dark matter chemistry or biochemistry
and additional fun like we have with regular matter.

• 10-05-2005, 10:31 PM
canopus56
How do astronomers know how much dark energy and dark matter in the universe from a radio map?
Thomas Womack wrote:

Thomas, that's a good catch. The web page <<
http://astroweb.case.edu/hos/Virgo/ >> states the extended glow is from
the galactic halo:

"Many long streamers of stars can be seen, along with very faint
extended halos surrounding the bright galaxies, . . ."

Galactic halos typically consist of stars, gas and dark matter. I'm
interpreting the glow to be diffusion of starlight off the gas. As you
point out, that is not entirely correct - some of the diffuse light
comes directly from the stars.

- Canopus56

• 10-06-2005, 12:23 AM
Tim Killian
How do astronomers know how much dark energy and dark matterin the universe from a radio map?
Dark matter is composed mostly of unmatched socks that have migrated
from drawers and laundry baskets through an inter-dimensional
singularity, and are now floating in the void, untouchable by photons or
normal atomic particles. Crazy you say? My theory has as much
observational data to back it up as any of the rest.

Bob wrote:
• 10-06-2005, 02:53 AM
Sam Wormley
How do astronomers know how much dark energy and dark matterin the universe from a radio map?

Just a note about Dark Matter...

Particle Dark Matter: Evidence, Candidates and Constraints
http://arxiv.org/abs/hep-ph/0404175

Scientists Map Dark Matter, Prove Einstein Right
http://www.space.com/news/cosmic_shear_000512.html
• 10-06-2005, 04:12 AM
Tim Killian
How do astronomers know how much dark energy and dark matterin the universe from a radio map?
Five years and counting as we await "really strict tests"...

From the 2000 article: "At the same time, astronomers admit that their
new method for finding dark matter has not yet been tested enough to
allow experts to make a definitive generalization about the fate of the
universe. "Since our approach is new, its not very precise yet," said
Wittman. 'Really strict tests of the theory will come in the next few
years as astronomers measure the [weak] lensing more and more accurately.'"

And from the recent Bertone paper:

"We observe in large astrophysical systems, with sizes ranging from
galactic to cosmological scales, some “anomalies” that can only be
explained either by assuming the existence of a large amount of unseen,
dark, matter, or by assuming a deviation from the known laws of
gravitation and the theory of general relativity."

In other words, the observed anomalies could be due other causes, but
the authors like dark matter theories and so off they go.

"Although it is definitely clear that the slope of the density profile
should increase as one moves from the center of a galaxy to the outer
regions, the precise value of the power-law index in the innermost
galactic regions is still under debate. Attention should be paid when
comparing the results of different groups, as they are often based on a
single simulation, sometimes at very different length scales."

Yes, there is nothing like disparate "single simulation" results and
some marginal supporting observational data to cement the theory - I
hope the Nobel Committee is paying attention - LOL! But then Alan Guth
has held them in suspense for 25 years while they await a plausible
explanation of his inflation daydream. These authors can surely count on
some measure of patience as they seek those magic, unseen, unobservable
particles of dark matter.

Sam Wormley wrote:
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