Mapping Dark Matter


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Mapping Dark Matter

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Jan 9, 2012, 2:36pm

I just read this article about efforts to map dark matter. "This is the first direct glimpse of dark matter on large scales showing the cosmic web in all directions."

Is this a big step in our understanding of dark matter?

Jan 10, 2012, 12:58am

This result seems noteworthy, but it doesn't strike me as really affecting our understanding of dark matter. Rather, I think it just increases our confidence in some of what we already knew about dark matter (which is not a great deal). However, I'm not an expert in astronomy or cosmology, so it would be good to hear from somebody who is.

I also may be a bit biased for at least two reasons. First, this article is essentially a reprint of a press release put out by the researchers and institutions being lauded. This is one step farther down the science news cycle than I prefer to go. In addition, the press release discusses work that has not yet been written up (let alone published), but is currently being presented at a conference, about the lowest bar I can imagine. The two papers that this group has released so far (arXiv:1110.4913 and arXiv:1111.4434) don't strike me as groundbreaking (again, possibly because this isn't my field).

Because I'm so suspicious of press releases, especially without a paper to consult directly, I'm not inclined to interpret this one charitably. For example, I read the sentence, "This is the first direct glimpse at dark matter on large scales showing the cosmic web in all directions" (emphasis added), to imply that others have already done much the same thing either indirectly, or on smaller scales, or in limited directions (or some combination thereof).

Granted, this press release was associated with an actual press conference organized by the American Astronomical Society (AAS). This impressed me until I noticed that the AAS is holding three press conferences on each of three days of their current meeting. Apparently this is a standard piece of their promotional work, and suggests that the work being promoted is just one noteworthy result among many.

Second (that was all reason one), I am an expert in computational physics, so I'm a bit more familiar with the numerical work that the press release mentions: "The team's result has been suspected for a long time from studies based on computer simulations, but was difficult to verify". There is actually a good article on this in the current issue of American Scientist that you might find interesting. My perspective makes me less excited by this work than perhaps I should be, since I have the impression that results of this sort were predicted years ago, based on what we then understood of dark matter and cosmology.

Jan 10, 2012, 1:50am

I thought it might be a significant step in confirmation of the existence of dark matter, in other words confirmation that dark matter is the answer to the question about what is holding the galaxies together. At least confirmation that the theories are moving research in the right direction.

I really need to get back and study more the classical physics before I try to move to things on the frontiers of physics, but it is so exciting. And likely that dark matter and energy will have so much involved in them, as our baryonic matter - from molecules to quarks.

Thanks again. I will comment on the topic for simultaneity when I have a chance to get back on the material.

Jan 10, 2012, 7:49pm

Yes, this is further confirmation of our understanding of dark matter and its role in the universe, but (perhaps speaking from ignorance) I wouldn't describe it as especially significant by itself. The method used here (gravitational lensing by dark matter halos) was one of the main tools used in the past to establish the existence and characteristics of dark matter.

The main advance here seems to be one of scale; in a sense this result is "more of the same", and the point is how much more it is (I don't think it's all that much). That said, the two papers I linked above are on techniques to improve the quality of these methods, so I suspect that such technical improvements are actually the focus of this group's work. Checking the press release again, I see that they are briefly mentioned ("This result has been achieved through advances in our analysis techniques"), but apparently this didn't make the cut for the ScienceDaily article.