no more darkmatter

[CPL.Luke]

http://www.cerncourier.com/main/article/45/8/8

 

General relativity versus exotic dark matter

 

Determinations of the rotation speed of stars in galaxies (galactic rotation curves) based on the assumption that Newtonian gravity is a good approximation have led to the inference that a large amount of dark matter must be present - more than can be accounted for by non-luminous baryonic matter. While there are plenty of attractive theoretical candidates for the additional dark matter, such as a lightest supersymmetric particle (LSP), it is also interesting to look into the details of the calculations that suggest the need for such exotica. Now F I Cooperstock and S Tieu of the University of Victoria have reworked the problem using general relativity in place of Newtonian gravity, and they find no need to assume the existence of a halo of exotic dark matter to fit the observed rotation curves.

 

This is because even for weak fields and slow speeds, well-known nonlinearities change the character of the solution dramatically. The success of Newtonian mechanics in situations like our solar system can be traced to the fact that in this case the planets are basically "test particles", which do not contribute significantly to the overall field. However, in a galaxy this approximation is not a good one - all the rotating matter is also the source of the gravitational field in which everything rotates.

[[Tycho?]]

http://www.cerncourier.com/main/article/45/8/8

 

General relativity versus exotic dark matter

 

Determinations of the rotation speed of stars in galaxies (galactic rotation curves) based on the assumption that Newtonian gravity is a good approximation have led to the inference that a large amount of dark matter must be present - more than can be accounted for by non-luminous baryonic matter. While there are plenty of attractive theoretical candidates for the additional dark matter' date=' such as a lightest supersymmetric particle (LSP), it is also interesting to look into the details of the calculations that suggest the need for such exotica. Now F I Cooperstock and S Tieu of the University of Victoria have reworked the problem using general relativity in place of Newtonian gravity, and they find no need to assume the existence of a halo of exotic dark matter to fit the observed rotation curves.

 

This is because even for weak fields and slow speeds, well-known nonlinearities change the character of the solution dramatically. The success of Newtonian mechanics in situations like our solar system can be traced to the fact that in this case the planets are basically "test particles", which do not contribute significantly to the overall field. However, in a galaxy this approximation is not a good one - all the rotating matter is also the source of the gravitational field in which everything rotates.[/quote']

 

 

I saw a snippit of this a few days ago. Am I the only one who finds it extremely unlikely that dark matter came about beause researches were using Newtonian mechanics to describe galaxies? Has anyone EVER used Newtonian mechanics to describe a galaxy? Why the hell would you, with such huge masses errors are bound to pop up. I've always had an inkling that dark matter is simply a misunderstanding of physics rather than an actual type of matter, but I'm kinda skeptical about this result. Could any people in the know comment on this, since I'm rather over my head.

[Bio-Hazard]

yeah, i questioned it being a type of matter also.. maybe a different branch of physics relating to energy..or transportation..

[Severian]

It is good that this is shown not to be needed because it is very hard to get most dark matter candidates to clump in this way (although, like Tycho, I don't believe this new result for a second). However, this astrophysical need for dark matter is far outwieghed by the cosmological arguments. If you look at experiments like WMAP, to explain the data you need to have lots of dark matter spread throughout the universe.

[insane_alien]

it could just mean that we have less darkmatter to fuss over

[CPL.Luke]

'sin't the cerncourier a semi-respectable source though?

[Martin]

'sin't the cerncourier a semi-respectable source though?

Personal viewpoints:

I think cern courier is respectable.

I am glad they flagged the Cooperstock/Tieu paper.

I dont believe that paper---want to take a wait and see attitude---but I'm interested.

I am not sure that dark matter is real.

Someday some modification of standard gravity might dispense with the need to assume DM, have to keep looking and remain skeptical about each proposal as it comes up. Eventually one of these proposals (there are a bunch) may very well check out.

[cpwmatthews]

I'm a bit confused. If as in it's name there is Dark Matter then there would be tangeable evidence of it's exhistance, if on the other hand Dark Matter is a Force then it's presence could only be quantified by observation of masses around it.

[Severian]

I'm a bit confused. If as in it's name there is Dark Matter[/u'] then there would be tangeable evidence of it's exhistance, if on the other hand Dark Matter is a Force then it's presence could only be quantified by observation of masses around it.

 

Dark matter is matter, but since matter has energy (like mass) it generates a gravitational force.

[Centrix]

"Dark matter" and "dark energy" is nonsense. Sounds like astrophysics has gone over to science fiction these days.

[jcarlson]

"Dark matter" and "dark energy" is nonsense. Sounds like astrophysics has gone over to science fiction these days.

 

I have always been under the impression that dark matter was simply matter that did not emit electro-magnetic radiation.... Like rock.

 

Without dark matter to block incoming light shouldn't we be blinded by the light of trillions of stars from incredibly far distances?

[Locrian]

That's Olber's paradox. One reason we wouldn't be blinded by the light from trillions of stars is due to redshifting. It is worth noting that if you look at the milky way band in the sky, it appears as a diffuse band of light. This is probably a fair example of what the universe might look like with out redshifting, except it would be even brighter.

 

Of course, it isn't just red shifting that blocks light. Dark matter may block some light, but it would be little. The major interstellar component that blocks light is the interstellar medium. This reddens (not to be confused with red shifting) the light a great deal, and blocks quite a bit. This is why our milky way band isn't brighter. Note that interstellar medium is not considered a part of "dark matter" because it is observable and accounts for very little mass.

 

On another note, this initial paper C.P Luke cited has generated a lot of interest. People seem to not note that there are already papers arguing against it, though they are not considered definitive.

[Locrian]

"Dark matter" and "dark energy" is nonsense. Sounds like astrophysics has gone over to science fiction these days.

 

Gosh yea, its so crazy. They see evidence that something is pulling gravitationally on something else, and they have the audacity to suggest that there's matter there that isn't emmiting light and is difficult to observe - dark matter.

 

Then we observe that the universe is accelerating. Since acceleration occurs because of a force, those crazy astronomers suggest that this acceleration is due to a force, and call the energy involved dark energy.

 

Those kooky astronomers have just gone way off the deep end.

[gmacrider]

The success of Newtonian mechanics in situations like our solar system can be traced to the fact that in this case the planets are basically "test particles", which do not contribute significantly to the overall field. However, in a galaxy this approximation is not a good one - all the rotating matter is also the source of the gravitational field in which everything rotates.

So, even though in Newtonian physics the "test particles" have mass, does the above statement mean the gravitational force of the "test particles" is ignored in Newtonian calculations?

 

If so, wouldn't Newtonian calculations of Jupiter's motion be slightly off because they don't take into consideration it's large gravity well?

 

I'm no expert (and I probably just proved it), but I'm having trouble understanding the new theory. Thanks for the link BTW - very interesting.

[Locrian]

'']Am I the only one who finds it extremely unlikely that dark matter came about beause researches were using Newtonian mechanics to describe galaxies? Has anyone EVER used Newtonian mechanics to describe a galaxy? Why the hell would you, with such huge masses errors are bound to pop up.

 

Actually since most of the really big masses are near the center of the galaxy, newtonian approximations are not as invalid as you'd think.

 

This paper presented has already had some very serious arguments made against it. In it they produce the correct rotational velocity by assuming there is a distrubution of matter within galaxies that has never been observed. Many are saying that this distribution is an unacceptable additional variable that basically amounts to assuming there is a new, difficult to observe matter inside galaxies. In otherwords, one argument is that these researchers are assuming there's dark matter in their proof there is no dark matter.

[CPL.Luke]

however it does make far more sense that the dark matter would be inside the galaxy right?