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Wjatscheslaw
Saturday, May 27th, 2006, 07:06 PM
What is dark matter? This mysterious, apparently invisible stuff that researchers think is everywhere is not easily understood. A first step, however, is grasping what can be seen, and why.
When a scientist peers into space, either through a standard telescope or with the aid of a fancy space-based observatory (http://www.space.com/scienceastronomy/astronomy/celt_telescopes_000913.html), the things she observes emit light energy, called electromagnetic radiation.
Some of this radiation is optical -- the visible light you see with your eyes. But this is just one type of light energy. Electromagnetic radiation comes in many wavelengths: radio waves (the longest), infrared, optical, ultraviolet, X-rays (http://www.space.com/scienceastronomy/astronomy/astroe_reveal_000207.html) and short gamma rays (the shortest, and also the highest form of energy. See more details on these wavelengths at the bottom of this page).
Galaxies (http://www.space.com/scienceastronomy/astronomy/starburst_990921.html), nebulae, stars, trees, microscopic bugs and anything else that can be observed glows with energy at one of these wavelengths.
But in recent decades, researchers have become increasingly convinced that there is a vast amount of material in the universe that does not glow at all. This mysterious "dark matter" is believed by most scientists to be the most common stuff in the universe, perhaps making up 90 percent or more of the total mass.

http://www.space.com/images/h_coma_cluster_010105_03.jpg


Researchers say the Coma Cluster of galaxies shows effects of gravity that can only be explained by the presence of some unseen dark matter.

Dark matter does not emit enough energy to be directly detected. But indirectly, researchers note its presence. Anything that has a mass exerts the force that we call gravity. Dark matter -- or something that we have yet to find -- exerts a gravitational pull on objects in and around distant galaxies, and even on light emitted by those objects, say scientists at NASA's Goddard Space Flight Center.
By measuring these mysterious effects of gravity, researchers determine how much "extra" gravity is present, and hence how much extra mass, or dark matter, must exist.
In large clusters of galaxies, for example, scientists say that five to 10 times more material exists than can be accounted for by the stars and gas they find.
So what is dark matter made of? No one knows for sure.
Normal matter -- you, your computer and the air you breathe -- is made of atoms, which are composed of protons, neutrons and electrons. Scientists call this "baryonic" matter. They suspect some dark matter is of the normal, baryonic variety. This might include brown dwarf stars and other objects that are simply too small, or too dim, to be seen from great distances.
But most dark matter is thought to be non-baryonic -- truly strange.
If this is true, then just finding the stuff will be difficult, because researchers don't even know what they are looking for.



Wavelengths of light (Electromagnetic radiation)

Radio: Wavelengths longer than infrared and very low energy.
Infrared: Wavelengths longer than the red end of visible light and shorter than microwaves (roughly between 1 and 100 microns). Little infrared radiation reaches Earth's surface, but some can be observed by high-altitude aircraft or telescopes on tall mountains.
Optical/Visible: Electromagnetic radiation at wavelengths visible to the human eye. We perceive this radiation as colors ranging from red (longer wavelengths about 700 nanometers) to violet (shorter wavelengths about 400 nanometers).
Ultraviolet: Wavelengths shorter than the violet end of visible light. Earth's atmosphere blocks most ultraviolet light.
X-rays: Very short wavelengths and very high-energy; X-rays have shorter wavelengths than ultraviolet light but longer wavelengths than gamma rays.
Gamma rays: The highest energy, shortest wavelength electromagnetic radiation. Usually, they are thought of as any photons having energies greater than about 100 keV (kiloelectron volts).Link: http://www.space.com/scienceastronomy/astronomy/dark_matter_sidebar_010105.html

Dr. Solar Wolff
Sunday, May 28th, 2006, 05:40 AM
Because physicists are still trying to prove Einstein right, they just use words for which they have no definition and agree among themselves not to talk about the underlying issues. Words such as "gravity", "dark matter" and "dark energy" have absolutely no definition in physics yet they just keep on hypothesizing and making up new possibilities rather than rectify their einsteinian theories with the observed reality.

Gorm the Old
Sunday, May 28th, 2006, 05:28 PM
Physicists are notoriously inept at defining ANYTHING. They know nothing of either ontology or epistemology. The physicist's definition of matter is "that which occupies space and has mass", a can of worms at best. First, I didn't ask what matter DOES, I asked what it IS. Inasmuch as physics offers us no intelligible definition of "space" , saying that matter occupies space is useless for a definition. Mass is the quantitative measure of inertia, i.e. resistance to a change in the state of motion. Once again, then, the definition becomes operational. Matter (still undefined) resists a change in its state of motion. But, WHAT IS IT that resists a change in its state of motion ? To return to matter's extension in space, what is space ? Is it anything but a mode of thought as Kant called it ? Does space have any physical reality ? Some physicists now claim that space can spontaneously turn into matter, thus reifying (making a thing of) space. What they are doing is to replace the discredited "luminiferous ether" with "space".... Now then, if physicists cannot even devise a meaningful definition of ordinary matter, how can we expect them to define their imaginary "dark matter ?" Their current mathematical models of the universe require "dark matter" to describe the actual behaviour of matter (whatever that is) in the material universe. They spin theoretical models of what they take to be reality out of themselves like spiders spinning webs. Nature is not obliged to conform to mathematical models. It is the models which must conform to nature. Too many physicists have forgotten this.... BTW, Einstein seems not have believed in gravity. He shows in the general theory of relativity that gravity is indistinguishable from motion in an accelerated frame of reference. He does not go into the fact that, if the expansion of the universe is decelerating, then every particle of matter in the universe moves in an accelerating frame of reference. Therefore, gravity is unnecessary.

Feanor
Sunday, May 28th, 2006, 08:33 PM
Dark matter is merely a name for undetectable source of gravity. But why would it have to be "invisible matter" like some people suggest? It could be a black hole too. Or some other source that we don't know of yet.

Dr. Solar Wolff
Sunday, May 28th, 2006, 11:01 PM
We all believe in gravity but we really have no idea what it is. We all believe it works like Newton says and the comments about Einstein saying it acts just as accelleration does is interesting but doesn't that bring us right back to aether and Michelson-Moreley and so on?

Some people do think dark matter is gravity in that they say dark matter is aether and aether and gravity are related. According to William Lyne, Tesla was one of these. I think dark energy is aether but the difference between dark energy and dark matter is one of a direct conversion of energy to matter.
Still, my thoughts are unfounded just as are the theories of modern physics in my mind about the real basic building blocks of the universe. But modern physics does not seem to concern itself with gravity, dark matter or dark energy but is off somewhere doing sub-atomic particle research. This is a side issue to me and one which pays no dividends and we do need some dividends in terms of practical energy knowleged about now.

Gorm the Old
Wednesday, May 31st, 2006, 01:23 AM
I doubt that anybody is trying to prove that Einstein is right. Most modern physicists are trying to prove him WRONG. Relativistic physics doesn't really need any further proof. More than one experimentum crucis has been performed and has verified relativity. Relativistic physics accounts for Mercury's orbit far better than Newtonian mechanics. The gravitational deviation of starlight predicted by relativistic physics was observed first in 1912 and many times since. The relativistic increase in mass of particles moving close to the velocity of light has to be taken into acount in the design of TV picture tubes and particle accelerators. In short, relativistic physics works....Einstein's determinism, however, is considered old-fashioned and is very much out of vogue these days. Einstein never accepted causeless quantum indeterminacy. (Nor, for whatever it's worth, do I.) I have said it before, from other pulpits and lecterns and in other fora, and I say it here, now : If quantum intererminacy is valid, there is no such thing as physics and we know nothing. The very basis of predictability, the touchstone of physics, is removed, leaving nothing.

norskdeutschami
Thursday, August 24th, 2006, 05:30 AM
I've long been facinated with the "anti-matter" or "dark matter" due to the belief by certain scientists that extraordinary amounts of enegry can be harvested out of very little "anti-matter". Read this for yourself, and voice your opinion, do you think it exists? Or do you think its just a trekie's/scientist's wet dream?



A team of U.S. scientists has found the first direct evidence of the existence of "dark matter," a little-understood substance with a huge influence on gravity, the team's leader said on Tuesday. Scientists still do not know what exactly dark matter is, but have theorized it must exist to account for the amount of gravity needed to hold the universe together. They estimate that the substance accounts for 80 to 90 percent of the matter in the universe. The more familiar kind of matter, which can be seen and felt, makes up the rest.

Now researchers led by University of Arizona astronomer Doug Clowe say they have evidence to back up their theories. Using orbiting telescopes, the researchers watched two giant gas clouds in outer space collide over a 100-hour period. As the clouds clashed, they said, the visible gas particles slowed, pulling away from the invisible dark matter particles. The researchers said they could detect the dark matter particles by their gravitational pull on the surrounding visible particles.

"This is the first time we've been able to show that (dark matter) has to be out there, that you can't explain it away," Clowe told Reuters. "We haven't actually been able to see the dark matter particles themselves, but what we have been able to do is ... image the gravity that they're generating."


Some skeptics have argued that dark matter does not exist. (what do you think?)

They assert that scientists err in assuming that gravity exerts the same pull whether holding a plate on a table or influencing the travel of stars. Revising the laws of gravity at the interstellar scale would better explain the universe's structure, they argue.

The research team also included scientists at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and used telescopes operated by NASA. Their research is scheduled to be published in an upcoming issue of The Astrophysical Journal Letters. Rachel Bean, a professor at Cornell University who specializes in dark matter and was not involved in the research, called the results convincing. "It is certainly the strongest evidence we've seen to date that actually solves this dark-matter problem," Bean said.

She said the finding should encourage scientists to concentrate their efforts on determining what dark matter is, rather than developing revised rules of gravity. "It's very difficult to explain these observations with anything other than particle theory," Bean said. "The dark matter quandary to some extent is helped by these observations, because it helps target the theorists to try and look at particle physics, rather than gravity."


Source: http://news.yahoo.com/s/nm/20060822/ts_nm/science_darkmatter_dc

norskdeutschami
Thursday, August 24th, 2006, 05:33 AM
You might be interested in an article I recently read on yahoo news...offers a little explanation as to how Physicists wish to prove that it indeed exists...

http://news.yahoo.com/s/nm/20060822/ts_nm/science_darkmatter_dc

Dr. Solar Wolff
Thursday, August 24th, 2006, 05:54 AM
This is funny. Back in the 1930s people building and experimenting with free energy devices theorized exactly such substances as dark matter and dark energy but they called them by other names. Science debunked their ideas even though they couldn't debunk or even understand the original devices. Now, Science comes up with exactly the same concepts and then admits they don't really understand what they are talking about. What a surprise. Maybe Physics should stop their pre-occupation with Einstein and sub-atomic particles and return to explaining what is observed in the universe, the real world. If they could explain what they see in this instance with their telescopes, then they would be advancing science beyond the 1930s which has not happened yet.

Blutwölfin
Saturday, September 2nd, 2006, 12:55 PM
Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies. The discovery, using NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter.

"This is the most energetic cosmic event, besides the Big Bang, which we know about," said team member Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

These observations provide the strongest evidence yet that most of the matter in the universe is dark. Despite considerable evidence for dark matter, some scientists have proposed alternative theories for gravity where it is stronger on intergalactic scales than predicted by Newton and Einstein, removing the need for dark matter. However, such theories cannot explain the observed effects of this collision.

"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."

In galaxy clusters, the normal matter, like the atoms that make up the stars, planets, and everything on Earth, is primarily in the form of hot gas and stars. The mass of the hot gas between the galaxies is far greater than the mass of the stars in all of the galaxies. This normal matter is bound in the cluster by the gravity of an even greater mass of dark matter. Without dark matter, which is invisible and can only be detected through its gravity, the fast-moving galaxies and the hot gas would quickly fly apart.

The team was granted more than 100 hours on the Chandra telescope to observe the galaxy cluster 1E0657-56. The cluster is also known as the bullet cluster, because it contains a spectacular bullet-shaped cloud of hundred-million-degree gas. The X-ray image shows the bullet shape is due to a wind produced by the high-speed collision of a smaller cluster with a larger one.

In addition to the Chandra observation, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes were used to determine the location of the mass in the clusters. This was done by measuring the effect of gravitational lensing, where gravity from the clusters distorts light from background galaxies as predicted by Einstein's theory of general relativity.

The hot gas in this collision was slowed by a drag force, similar to air resistance. In contrast, the dark matter was not slowed by the impact, because it does not interact directly with itself or the gas except through gravity. This produced the separation of the dark and normal matter seen in the data. If hot gas was the most massive component in the clusters, as proposed by alternative gravity theories, such a separation would not have been seen. Instead, dark matter is required.

"This is the type of result that future theories will have to take into account," said Sean Carroll, a cosmologist at the University of Chicago, who was not involved with the study. "As we move forward to understand the true nature of dark matter, this new result will be impossible to ignore."

This result also gives scientists more confidence that the Newtonian gravity familiar on Earth and in the solar system also works on the huge scales of galaxy clusters.

"We've closed this loophole about gravity, and we've come closer than ever to seeing this invisible matter," Clowe said.



Source (http://www.nasa.gov/home/hqnews/2006/aug/HQ_06297_CHANDRA_Dark_Matter.html)

Gorm the Old
Saturday, September 2nd, 2006, 06:40 PM
Oh, how I wish that physicists would take a good course in logic. At least, then, they might know the difference between proof and inference. They might also recognize that "seeing" the "invisible" dark matter is an oxymoron.