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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.

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.
Dark Matter Exists
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Exciting video about the universe - 28/04/2011 10:14:55 AM 1293 Views
Cool, and true *NM* - 28/04/2011 11:46:29 AM 446 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 1001 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 944 Views
I'm aware of the Bullet Cluster, though admittedly not much more than that. - 29/04/2011 01:52:49 AM 879 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. - 29/04/2011 02:56:32 AM 972 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. - 30/04/2011 05:02:49 PM 914 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. - 30/04/2011 08:56:35 PM 834 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. - 02/05/2011 01:28:30 AM 848 Views
Re: I'm aware of the Bullet Cluster, though admittedly not much more than that. - 04/05/2011 04:18:18 AM 939 Views
There's such a thing as knowing when you're licked, and I believe I am. - 07/05/2011 02:04:53 AM 1020 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 852 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 813 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 886 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 819 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 896 Views
The Pati-Salam model was the one I had in mind. - 24/05/2011 10:34:04 PM 852 Views
Re: The Pati-Salam model was the one I had in mind. - 24/05/2011 11:08:01 PM 1052 Views
Re: The Pati-Salam model was the one I had in mind. - 25/05/2011 01:27:10 AM 859 Views
Re: The Pati-Salam model was the one I had in mind. - 31/05/2011 09:16:18 AM 931 Views
Also, re: lensing from ordinary matter: - 29/04/2011 05:18:47 AM 881 Views
This seems like another example of what confuses the issue. - 30/04/2011 05:25:04 PM 997 Views
Re: This seems like another example of what confuses the issue. - 30/04/2011 08:56:40 PM 971 Views
That discussion seems to reduce to "as little new and exotic physics as possible". - 02/05/2011 01:29:03 AM 948 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 1326 Views
Seems to happen to me a lot; sorry. - 29/04/2011 12:56:14 AM 867 Views
None of this reflects on the actual facts of dark matter. - 29/04/2011 01:32:52 AM 866 Views
I concede my grasp (or grope) is a somewhat superficial laymans, yes. - 30/04/2011 04:30:28 PM 999 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes. - 30/04/2011 08:56:44 PM 809 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes. - 02/05/2011 01:28:58 AM 1337 Views
Re: I concede my grasp (or grope) is a somewhat superficial laymans, yes. - 04/05/2011 04:18:27 AM 838 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 1058 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 967 Views

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