Talk:Dark matter

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 Definition:  Theoretical matter that neither emits nor absorbs light and appears to interact with other matter only gravitationally. [d] [e]
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 Workgroup category:  Physics [Categories OK]
 Talk Archive:  none  English language variant:  American English

Dark matter observed

Dark matter has been observed: See follows these links for the news story.

...said David E. Volk (talk) 20:24, 11 January 2008

Hello David E. Volk,

Not convinced. It has not been directly observed--no surprises there. They presume its existence because it does clear up some problems and they insist that they have the gravitational lensing effect that also supports their theory.

The dark matter is supposed to interact gravitationally but why are the two types separating as they pass through the mass of another galaxy? Why doesn't the dark matter interact? It is supposed to be quite dense in comparison with the luminous matter.

See NASA Finds Direct Proof of Dark Matter. "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."

So it did not interact with the baryonic matter but it has mass, why do they say that? They are missing something crucial. --Thomas Simmons 06:53, 12 January 2008 (CST)

Hello Thomas,
Neither one of us needs to be convinced (neutrality issue) to report it in the encyclopedia. The news stories I suggested point to some of the latest data, and observation of dark matter. Many physicists I know believe in dark matter, but are more dubious of dark energy. Clearly there is still something we do not know, but we should report the most up to date thoughts on the subject. David E. Volk 08:25, 12 January 2008 (CST)
Hi David,
Yea, I get the gist of the message now. The fact is, it has not been observed, that much is obvious. We have a massive collection of mass that supposedly holds entire galaxies together such that they are like flies caught in amber. Then the whole thing gets ripped apart as it passes through another galaxy? The dark matter in one rips off the baryonic matter in the oncoming galaxy and the oncoming galaxy's dark matter does the same to its counterpart? There are people out here calling this proof--which it ain't. Ned Wright likes to tell people that science never proves anything. Einstein said something along those lines as well. On the other hand this series of events involving the Chandra X-ray demands a mention. I will get on it, today hopefully. I'd like to get another take on it though, someone who has played it down and put a little perspective on it if I can. Then put the two points in there together. They are excited though. The results are pretty extraordinary. I'd be jumping up and down if it were me.--Thomas Simmons 17:13, 12 January 2008 (CST)

Two recent news sources on the existence of Dark Matter

  • First: A yahoo news summary here.
  • Second: a link from ESA here. Here's the original ESA story link here.

The observations make a proposal about the existence of an antimatter cloud that could potentially supercede the existence for theoretical explanations of dark matter.

I haven't read the entire thing (as it's a little bit out of my scope) but I thought I'd at least bring it to someone's attention to see if it's relevant. --Robert W King 12:43, 16 January 2008 (CST)

More news on "Dark Energy".

--Robert W King 14:11, 30 January 2008 (CST)

Capitolisation etc. and Strunk & White

Hi,

Ro changed a 'It' to an 'it' after a colon. Strunk and White ("Elements of style" basically says that a capitol will follow a colon if the expanding sentence is itself an independent clause or complete sentence.

Here "Dark matter (DM) is aptly labeled: it is theoretical matter that can not be directly studied and observed by current technologies because it neither emits nor absorbs light or heat and appears to interact with other matter only gravitationally."

The clause preceding the sentence is a complete sentence and the one following is also a complete sentence, ergo, it should begin with a capitols letter. APA Publication Manual advises us to always capitalize an independent clause following a colon. Chicago Manual of style is flexible but consistency is paramount if at all possible.--Thomas Simmons 19:10, 2 April 2008 (CDT)

I normally use the style Ro is using. I don't capitalize after the ":" unless that that latter part is intended to be a separate, free-standing sentence: the fact that it is grammatically a complete sentence is not what is paramount. J. Noel Chiappa 21:16, 2 April 2008 (CDT)
G'dayl,

Intentions aside, a complete sentence looks strange without a capitol letter.

RE CZ Section "Grammar, spelling, punctuation, and usage" at [1] states
"Strunk and White's Elements of Style is very useful; the first edition is available here.)
"For American English, please consult The Chicago Manual of Style for matters of formatting, punctuation, etc. and Garner's Dictionary of American English "Usage for issues of usage.
"For British English, consult Fowler's Modern English Usage."
APA is clear. Strunk and White is clear. Chicago in this instance is not specific. So, APA it is. In this article anyway. --Thomas Simmons 16:05, 3 April 2008 (CDT)

Galaxy Rotation Curves

There should be something about Galaxy Rotation curves...

Unsigned comment contributed Dec 4, 2008 by User:Ryan_Yoo John R. Brews 13:00, 1 August 2011 (UTC)

Dark matter proves Newtonian gravity??

The section on "Evidence to support dark matter" concludes "The findings from this new evidence provide a reasonable expectation that Newtonian gravity takes place on a galactic scale."

Inasmuch as the posit of dark matter, which can be detected only through its influence upon gravity, is invented only to explain why Newtonian gravity does not work, that is, it's sole objective is to explain away false predictions of Newtonian theory by the simple invention of mass that cannot be found except by its ability to explain away these discrepancies, I find this section requires a lot more work to arrive at its conclusion. John R. Brews

To pursue this matter, the news release by NASA, although couched in the language of dark matter, actually reports in so many words that what is found is that the mass attributable to luminous matter cannot explain the dynamics of this collision. You can say this "proves" dark matter exists, but that is just a rewording of the remark that Newtonian gravity based on the known properties of known matter fails to predict the dynamics. To convert this failure to a substantiation of Newtonian gravity is to stand the matter on its head. John R. Brews 13:55, 29 July 2011 (UTC)

This article, which actually appear in a journal rather than a news release, indicates that what is found in event MACS J0025.4–1222 is an inexplicable displacement of the center of mass from the center of mass of the luminous matter. Inexplicable means that various models of gravitational interaction don't work. That failure is translated to a statement that the dominant source of gravity in this event is "dark matter" of a "collisionless nature". Inasmuch as "dark matter" is a deus ex machina, the content of this observation is simply evidence for a failure of theoretical explanation. John R. Brews 14:18, 29 July 2011 (UTC)

I agree completely. We should change the article accordingly. Johan Förberg 18:14, 29 July 2011 (UTC)
An interesting quote: Robert H. Sanders (2010). The Dark Matter Problem: A Historical Perspective. Cambridge University Press, p. 140. ISBN 0521113016. “In this sense, rotation curves should constitute a strong test of MOND. The dark matter hypothesis is rather immune to tests of this sort because when there is an unseen component of the mass distribution, essentially any observed rotation curve may be matched by adjusting the distribution of dark matter (a bit like explaining planetary motions with unseen crystal spheres). There are some constraints ... but these are fairly weak.”  John R. Brews 12:53, 1 August 2011 (UTC)
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