from Hacker News

Dark matter scaffolding of universe detected for the first time

by fiaz on 8/27/12, 12:47 AM with 48 comments

• by syncerr on 8/27/12, 3:48 AM

  It is worth noting that there was no direct detection of dark matter. It comes from a measurement of gravitational lensing, which has been going on for awhile˟˟.

  Critical response: http://www.scilogs.eu/en/blog/the-dark-matter-crisis/2012-07...

  Source: http://www.nature.com/nature/journal/v487/n7406/full/nature1...

  ˟˟ http://physicsworld.com/cws/article/news/2006/aug/25/gravity...

• by ok_craig on 8/27/12, 4:57 AM

  There's one thing I don't understand about the mystery of dark matter. I don't understand why the simple explanation for it isn't just that it's regular matter that is not stars. Maybe there are just bajillions of planets and dust clouds out there. Matter that isn't directly circling stars, thus not reflecting light. Why is the popular assumption that if the mass isn't stars or things in orbit of stars, that it must be a mystery substance? I assume there's scientific reasoning behind this, but I've never heard it explained before. If someone could fill me in, that would be awesome.

• by Xcelerate on 8/27/12, 3:15 AM

  This is really cool. If you look at this graph of the Standard Model interactions http://upload.wikimedia.org/wikipedia/commons/4/4c/Elementar... you will see the ways in which all of the particles we currently know about interact.

  If you'll notice though, there's one interaction between ALL of the particles that is missing: gravity. Gravity affects anything with energy. Photons, leptons, quarks -- they are all attracted to each other because they possess energy (negligible, unmeasurable attractions, but still extant).

  Wouldn't it be interesting if the only way that dark matter interacted with the other particles was through the gravitational force? Maybe from some alien's perspective it would constitute the matter of everyday life, but because it didn't interact with any of our particles except through gravity we would be missing out on a large aspect of our universe!

  Furthermore, is it that far-fetched to think there might exist particles that do not interact at all with the ones we have discovered? Gluons, for example, only interact with themselves and with quarks. Some other particle may interact with nothing we are familiar with -- and thus we could never study it. Is it even "real" then?

  (Any particle physicists on here, please feel free to educate me further!)

• by carterac on 8/27/12, 6:10 AM

  How do these filaments stay stable and not collape under their own gravity due to instabilities? Or, if there is 0 net force causing them to collapse, why doesn't the dark matter drift apart naturally and become less dense and more diffuse over time? Either way, filaments of high density don't seem to be a natural stable state. Can someone explain this?

• by dragonbonheur on 8/27/12, 4:06 AM

  Just as predicted by Mr. Jean-Pierre Petit: http://jp-petit.org/science/colloque2001/Colloque_2001_1.htm

• by InclinedPlane on 8/27/12, 8:40 AM

  So, interestingly enough the leading theory for the identity of the bulk of dark matter is the "weekly interacting massive particle" (or WIMP) the neutralino, and there has been recent evidence from the Fermi gamma-ray telescope that supports the theory that the neutralino is the primary component of dark matter.

  http://arxiv.org/abs/1201.1003

  http://arxiv.org/abs/1205.1045

• by Jarihd on 8/27/12, 8:29 AM

  This is something i thought about Dark Matter: I believe Dark Matter to be the resultant force(and/or field) generated due to the interaction of the forces(and/or fields) of individual moving objects(matter).

  consider a magnet(refer here as object) - something which has the property to attract(gravity like) and repel(field like): Now if you were to have 2 magnets(moving objects) come close enough such that they repel(or attract); but due to forces(and/or fields) of other moving objects in their vicinity(or far enough[1]); they get locked or entangled such that their movement(and other properties) is now dependent on the strongest forces or fields of nearby objects. Over time; these other objects also get entangled and tend to form clusters and keep moving(exhibiting other properties like radiation etc). But now their movement(and other properties) seem to be the resultant effect of forces (and/or fields) of all the objects now entangled - giving an illusion of some matter that exists - now known as Dark matter.

  I have used magnets as just as an example - one could think of matter having both these properties to attract and repel - such that the area affected by them could vary depending on various properties of the objects(matter).

  [1](far enough) - such that their observation is neglected; but these objects tend to have forces(and/or fields) that they affect a particular system under observation.