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Dark Matter Core Defies Explanation

by Lensman
Tags: core, dark, defies, explanation, matter
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juanrga
#19
Mar6-12, 12:37 PM
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Quote Quote by TrickyDicky View Post
The Bullet Cluster is claimed to provide the best evidence to date for the existence of dark matter (see for instance wikipedia entry). Is this new observation the best evidence to date against the existence of dark matter, then?
Nope, time ago was shown that dark matter fails for the bullet cluster

Moreover, the past year solid evidence against dark matter was already provided

http://www.bbc.co.uk/news/science-environment-12571965

http://physics.aps.org/articles/v4/23
marcus
#20
Mar6-12, 12:50 PM
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Quote Quote by juanrga View Post
Nothing new, Dark Matter is the Vulcan planet of 21st century.
amusing quip, but I don't think it's right. Density contour maps of DM clouds in many locations (e.g. around clusters of galaxies) have been made. The maps are interesting, show differences, show different things happening, and require explanation.

the hypothetical planet "Vulcan" was not something observed to be explained,
it was a KLUDGE explanation of precession in Mercury's orbit.
http://en.wikipedia.org/wiki/Vulcan_...etical_planet)
an unexplained peculiarity in Mercury's orbit was established as early as 1860, I think.

DM is also an essential feature of simulations of filamentary structure formation in early universe---and the simulations yield realistic-looking results.

DM is just too economical a way to explain this bunch of different things going on at widely different scales---galaxy, clusters of galaxies, filamentary structure.
The nature of DM is a major puzzle. It's not a one-time kludge like the hypothetical planet Vulcan.

Maybe you were kidding. Nice epigram

BTW I also think it's pretty clear that our present law of gravity, GR, is going to be MODIFIED. It is deficient in some recognized ways and people are working on that. So if you are trying to say GR has to be modified, you are "preaching to the converted". That, I think, is a different problem. Modifying, say in the course of developing a quantum theory of geometry and matter, is unlikely to supplant DM in all its different explanatory roles.
juanrga
#21
Mar6-12, 03:50 PM
P: 476
Quote Quote by marcus View Post
amusing quip, but I don't think it's right. Density contour maps of DM clouds in many locations (e.g. around clusters of galaxies) have been made. The maps are interesting, show differences, show different things happening, and require explanation.

the hypothetical planet "Vulcan" was not something observed to be explained,
it was a KLUDGE explanation of precession in Mercury's orbit.
http://en.wikipedia.org/wiki/Vulcan_...etical_planet)
an unexplained peculiarity in Mercury's orbit was established as early as 1860, I think.

DM is also an essential feature of simulations of filamentary structure formation in early universe---and the simulations yield realistic-looking results.

DM is just too economical a way to explain this bunch of different things going on at widely different scales---galaxy, clusters of galaxies, filamentary structure.
The nature of DM is a major puzzle. It's not a one-time kludge like the hypothetical planet Vulcan.

Maybe you were kidding. Nice epigram

BTW I also think it's pretty clear that our present law of gravity, GR, is going to be MODIFIED. It is deficient in some recognized ways and people are working on that. So if you are trying to say GR has to be modified, you are "preaching to the converted". That, I think, is a different problem. Modifying, say in the course of developing a quantum theory of geometry and matter, is unlikely to supplant DM in all its different explanatory roles.
Vulcan planet was a hypothetical matter that many theorists assumed that would exist in order to explain Mercury orbit using Newtonian gravity. Using this hypothetical planet plus Newtonian gravity, the theorists of then were able to explain Mercury orbit. The next step was, evidently to find that planet in an observation and, unsurprisingly, several astronomers reported that they had found it! Today, everyone knows that Vulcan does not exist[*] and that the explanation of Mercury orbit is due to modification of gravity near Sun.

The history of physics repeats with DM.

DM is a hypothetical, never seen, distribution of matter postulated in order to continue using general relativity. Your "density contour maps of DM" are theoretically obtained as the difference between the prediction done by general relativity and the real observation, somewhat as the orbit and position of Vulcan were theoretically inferred from comparing the prediction of Mercury orbit done by Newtonian gravity and the observed orbit.

Sometimes as 'ancient' astronomers claimed observations of Vulcan then, some astronomers make claims about the first observation of dark matter these days, but all the "first observation of" in the literature were fake and all the direct searches of dark matter have miserably failed (Xenon10, Fermi...). This is not a surprise because DM does not exist.

I want to emphasize that continuous experimental failure of DM models (at galactic scale, clusters, cosmology...) and continuous null results in the dozens of experiments devoted to the search of dark matter would not be an impediment for true dark matter believers, who continue to believe that DM is real and will be found... Recall that Vulcan believers continued to search Vulcan even after was such hypothesis was discredited.

As Baum & Sheehan note in a recent book, the confidence on the universal validity of Newtonian gravitational theory was so high that to
the people of the late 19th century, Vulcan was real. It was a planet. It had theoretical credibility and had actually been seen. Even textbooks accorded it a chapter.
The rest of us is already searching modifications of general relativity that explain the observations without any need for the non-existent DM.
[*] Except in Star Trek episodes, but is not near Sun
Drakkith
#22
Mar6-12, 04:25 PM
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Quote Quote by juanrga View Post
I want to emphasize that continuous experimental failure of DM models (at galactic scale, clusters, cosmology...) and continuous null results in the dozens of experiments devoted to the search of dark matter would not be an impediment for true dark matter believers, who continue to believe that DM is real and will be found... Recall that Vulcan believers continued to search Vulcan even after was such hypothesis was discredited.
Can you elaborate on the "continuous experimental failure of DM models"?
Chronos
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Mar6-12, 05:16 PM
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I was half expecting the MOND shoe to drop. That is the main 'contender' to supplant dark matter, although it fails even more spectacularly than DM.
Drakkith
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Mar8-12, 08:13 PM
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Quote Quote by Chronos View Post
I was half expecting the MOND shoe to drop. That is the main 'contender' to supplant dark matter, although it fails even more spectacularly than DM.
I see. I read whatever article the banned poster above linked in another thread, but it's hard to tell what is correct and what isn't. I believe it claimed that current dark matter theory fails miserably itself.
Chalnoth
#25
Mar9-12, 12:11 AM
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Quote Quote by Drakkith View Post
I believe it claimed that current dark matter theory fails miserably itself.
....which is just plain incorrect. Cold dark matter fits all observations to date, and fits extremely well, with no special tuning required. The only objections to dark matter that are even close to valid are philosophical objections: some just don't like the idea of proposing a new type of matter.
Whitewolf4869
#26
Mar20-12, 08:04 PM
P: 16
And the GODs have created a new kind of matter Amen!
Drakkith
#27
Mar20-12, 09:32 PM
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Quote Quote by Whitewolf4869 View Post
And the GODs have created a new kind of matter Amen!
And then the admins banned thee...
Bobbywhy
#28
Mar20-12, 09:39 PM
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Mr. Whitewolf4869 (overstriked), Here on Physics Forums members exchange information so as to learn. Sarcasm and religious posts do not serve to promote learning.

Do you have some information about Dark Matter? If yes, then please post it for all of our members. Thank you, Bobbywhy
Bobbywhy
#29
Mar20-12, 09:46 PM
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Mr. Whitewolf4869 (overstriked), Here are four statements excerpted from NASA about dark matter, just for your infomation. All contrary evidence is welcome!

"We are much more certain what dark matter is not than we are what it is.

First, it is dark, meaning that it is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the Universe to make up the 25% required by the observations.

Second, it is not in the form of dark clouds of normal matter, matter made up of particles called baryons. We know this because we would be able to detect baryonic clouds by their absorption of radiation passing through them.

Third, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter.

Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 25% dark matter contribution."

http://science.nasa.gov/astrophysics...s-dark-energy/


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