We've just about ruled out the idea that dark matter is just non-luminous "ordinary" matter.
Dreaded Anomaly Send a noteboard - 28/04/2011 11:44:34 PM
Below I've linked to a blog post in which Sean Carroll, a theoretical astrophysicist, describes the significance of the Bullet Cluster result. In brief: we can compare the x-rays generated by the ordinary matter to the gravitation fields reconstructed by lensing measurements. These do not match up, indicating very strongly the presence of dark matter. If dark matter were "ordinary" matter, it would have collided just like the rest of the matter in the galaxies, so we wouldn't see the gravitational field that we do. This indicates that dark matter is a different kind of matter.
Dark matter is a hypothesis that already has a significant amount of supporting evidence. There are over a dozen experiments currently running or being constructed in order to detect dark matter, so the idea that the concept is not being tested is false. There are also people who do serious work on finding alternative theories that explain the anomalies without dark matter, although most of the popular options have run into problems.
The moral of this post: don't confuse the popular presentation of science with what's actually happening in the field. These problems are very complex and there's a lot of work being done in various directions. The news media almost never come up with anything close to an accurate, thorough, or up-to-date summary, so don't rely on them for a clear picture.
I'm reminded of the discussion with Isaac a while back about whether Jupiter even qualifies as a brown dwarf since it isn't fuzing hydrogen, and how much smaller it is than most extra-solar planets found to date (which I suppose still qualify as dark matter in cases only detectable as gravitational wobbles in a stars rotation). The comic's a good summary of the conventional wisdom, I'm just not sold on the underlying theory, and the reference to particle physicists is illustrative of why. Call me old fashioned, but I remain dubious when science contrives unverifiable aberrations to explain why some data doesn't fit the curve. For all the talk of radical new models, most of this strikes me as a bandaid obviating the need for new theories when something unaccounted for by the old one surfaces. There are simpler bandaids to be had but, regardless, the same rule applies to cosmology that applies to particle physics: Anything you can't test isn't physics, it's metaphysics. It may be valid metaphysics, but the one thing it's not is science.
Dark matter is a hypothesis that already has a significant amount of supporting evidence. There are over a dozen experiments currently running or being constructed in order to detect dark matter, so the idea that the concept is not being tested is false. There are also people who do serious work on finding alternative theories that explain the anomalies without dark matter, although most of the popular options have run into problems.
The moral of this post: don't confuse the popular presentation of science with what's actually happening in the field. These problems are very complex and there's a lot of work being done in various directions. The news media almost never come up with anything close to an accurate, thorough, or up-to-date summary, so don't rely on them for a clear picture.
Exciting video about the universe
28/04/2011 10:14:55 AM
- 1285 Views
I still think dark matter's just non-luminous matter without a convenient light source to reflect.
28/04/2011 10:34:21 PM
- 993 Views
We've just about ruled out the idea that dark matter is just non-luminous "ordinary" matter.
28/04/2011 11:44:34 PM
- 936 Views
I'm aware of the Bullet Cluster, though admittedly not much more than that.
29/04/2011 01:52:49 AM
- 874 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that.
29/04/2011 02:56:32 AM
- 966 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that.
30/04/2011 05:02:49 PM
- 908 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that.
30/04/2011 08:56:35 PM
- 829 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that.
02/05/2011 01:28:30 AM
- 839 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that.
04/05/2011 04:18:18 AM
- 934 Views
There's such a thing as knowing when you're licked, and I believe I am.
07/05/2011 02:04:53 AM
- 1014 Views

Re: There's such a thing as knowing when you're licked, and I believe I am.
09/05/2011 11:28:48 PM
- 846 Views

Re: There's such a thing as knowing when you're licked, and I believe I am.
14/05/2011 05:36:45 AM
- 809 Views

Re: There's such a thing as knowing when you're licked, and I believe I am.
17/05/2011 02:09:40 AM
- 879 Views

Re: There's such a thing as knowing when you're licked, and I believe I am.
19/05/2011 04:55:21 AM
- 812 Views

Re: There's such a thing as knowing when you're licked, and I believe I am.
24/05/2011 09:32:27 PM
- 889 Views

The Pati-Salam model was the one I had in mind.
24/05/2011 10:34:04 PM
- 843 Views
Re: The Pati-Salam model was the one I had in mind.
24/05/2011 11:08:01 PM
- 1044 Views
Re: The Pati-Salam model was the one I had in mind.
25/05/2011 01:27:10 AM
- 854 Views
Re: The Pati-Salam model was the one I had in mind.
31/05/2011 09:16:18 AM
- 925 Views
Apologies for the delay; internet's been spotty and I've been busy lately.
10/06/2011 12:09:04 AM
- 1179 Views
Re: Apologies for the delay; internet's been spotty and I've been busy lately.
14/06/2011 03:38:18 AM
- 1168 Views
Also, re: lensing from ordinary matter:
29/04/2011 05:18:47 AM
- 875 Views
This seems like another example of what confuses the issue.
30/04/2011 05:25:04 PM
- 990 Views
Re: This seems like another example of what confuses the issue.
30/04/2011 08:56:40 PM
- 967 Views
That discussion seems to reduce to "as little new and exotic physics as possible".
02/05/2011 01:29:03 AM
- 944 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
04/05/2011 04:18:24 AM
- 908 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
07/05/2011 02:05:02 AM
- 1079 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
09/05/2011 11:29:36 PM
- 858 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
14/05/2011 05:35:56 AM
- 1153 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
17/05/2011 02:09:55 AM
- 758 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
19/05/2011 02:47:25 AM
- 1112 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
24/05/2011 09:46:30 PM
- 880 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
25/05/2011 12:20:10 AM
- 1181 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
31/05/2011 09:16:22 AM
- 988 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
10/06/2011 12:04:06 AM
- 1229 Views
Re: That discussion seems to reduce to "as little new and exotic physics as possible".
14/06/2011 03:38:12 AM
- 990 Views
Re: I still think... (apparently, there is a 100 character limit on subjects, and yours was 99)
28/04/2011 11:57:15 PM
- 1320 Views
Seems to happen to me a lot; sorry.
29/04/2011 12:56:14 AM
- 858 Views
None of this reflects on the actual facts of dark matter.
29/04/2011 01:32:52 AM
- 856 Views
I concede my grasp (or grope) is a somewhat superficial laymans, yes.
30/04/2011 04:30:28 PM
- 991 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes.
30/04/2011 08:56:44 PM
- 803 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes.
02/05/2011 01:28:58 AM
- 1331 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes.
04/05/2011 04:18:27 AM
- 835 Views
I don't object to changing my mind, but can take more convincing than I really should.
07/05/2011 02:05:09 AM
- 1051 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
09/05/2011 11:32:17 PM
- 959 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
14/05/2011 05:36:24 AM
- 1152 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
17/05/2011 02:10:03 AM
- 875 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
19/05/2011 04:33:06 AM
- 1134 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
24/05/2011 09:59:38 PM
- 868 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
24/05/2011 11:19:43 PM
- 836 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
24/05/2011 11:33:58 PM
- 780 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
25/05/2011 12:55:36 AM
- 889 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
31/05/2011 09:16:24 AM
- 835 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
10/06/2011 12:09:13 AM
- 1014 Views
Re: I don't object to changing my mind, but can take more convincing than I really should.
14/06/2011 03:38:05 AM
- 974 Views
Might help if you clarified where your skepticism is at
29/04/2011 02:32:07 AM
- 823 Views
Potentially either, or a combination of the two.
30/04/2011 02:36:50 PM
- 910 Views
It's hard to discuss without knowing your objections a bit more clearly
30/04/2011 04:58:03 PM
- 799 Views
My primary objection is that alternatives to dark matter seem to have been ruled out prematurely.
02/05/2011 01:29:14 AM
- 1006 Views