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Dark matter scaffolding of universe detected for the first time
- Xcelerate 14y agoThis is really cool. If you look at this graph of the Standard Model interactions http://upload.wikimedia.org/wikipedia/commons/4/4c/Elementary_particle_interactions.svg 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!)
- tb 14y ago> Some other particle may interact with nothing we are familiar with -- and thus we could never study it. Is it even "real" then? Philosophically, this is equivalent to the question of whether other universes, which do not interact with ours and therefore we cannot study, exist or are "real". It is not a question that Science can answer.
- Xcelerate 14y agoI think it's very interesting that there's reasonable questions about things that science can't answer. If you can't study it, can't predict it, or can't reproduce it, then it isn't in the domain of science.
- Jach 14y ago> can't predict it This is the one a lot of people miss out on. Standard theories predict several types of "other universes"--thus that question is answered from science's view, it's just not an answer people like. See http://arxiv.org/pdf/astro-ph/0302131v1 http://arxiv.org/pdf/astro-ph/0302131v1 for a general overview. "Containing unobservable entities does clearly not per se make a theory non-testable."
- derleth 14y ago> It is not a question that Science can answer. It is, though: Science suggests that they don't exist because science favors simpler models to more complex ones, as long as the simpler model still accounts for all the evidence and makes correct predictions.
- kamaal 14y agoOh well, That question really has far reaching implications. Because if we say Science is what we observe and describe as per our interpretations of logic(And the language of logic - 'Math') then our science is really broken. Because what we can observe doesn't often turn out to be true and what is true is not often observed. Because look at it this way. We are now saying Dark Matter doesn't interact anyway with light nor something else. Hence observing, detecting or modeling them out through conjectures manufactured through thin air is nothing more than what religion was some centuries ago. Anything unexplainable was attributed to some form of divinity in times before. We know it exists, but we can't show you, can't explain you what it is, how it looks is the text book definition of god throughout centuries.
- drostie 14y agoIt is only "broken" if you assume incorrectly that the goal of science is to Discover Truth. Moreover it is broken in a more direct way: there exist certain models which are mathematically equivalent but which describe contradictory states of being. A reasonably good example of this is heliocentrism vs. geocentrism: classical mechanics allows you to say "the Earth is at the center of the Solar System, there are gravitational, Coriolis and centrifugal forces around it affecting all of the stuff in space", but it also allows you to say "The Sun-Jupiter barycentre is at the center of the Solar System, and the only force we need is gravity." There is no experiment which can distinguish between those two; they are mathematically equivalent. (A slightly better example comes from quantum mechanics. In the "Schrodinger picture" there is a "wavefunction of the universe" which changes from moment to moment, while the definitions of space and momentum stay the same. In the "Heisenberg picture" the wavefunction stays the same while the definitions of space and momentum change. You would think there would be an ontological difference to the question, "is the state of the universe different from the state of the big bang?" but, in fact, on this description there is no observable difference, and science could never settle the question.) This does not reduce science to a religion; science simply studies the observable differences and must be content with not knowing everything -- which most scientists are already content with, since they have to deal with matters of uncertainty and the distinctions between correlations and causations. Dark Matter does interact with other things, but it does so indirectly, because it has mass and therefore warps spacetime. This is not actually the first use of gravitational lensing to observe dark matter; in fact, earlier it had been used to settle the question of whether dark matter felt any electromagnetic force at all, by looking at galaxy collisions. The prediction would be that the dark matter clouds of two galaxies would more or less "go through each other" in a collision while the luminous stuff would "bump into each other". This was observed as early as 6 years ago, see http://chandra.harvard.edu/photo/2006/1e0657/ http://chandra.harvard.edu/photo/2006/1e0657/ . We certainly can show you, and we can explain to you what it is. The only problem is the same problem that neutrinos have: it's just very hard to detect these particles because they don't have an electric charge and therefore don't care about the electrons which make all the rest of chemistry happen. Our best tool for understanding dark matter is still gravity; its a force which we know the dark matter feels.
- pdonis 14y agoGluons also interact gravitationally, like anything with energy. So would any other hypothetical particle, since it would have to have energy to exist at all.
- Xcelerate 14y agoI said earlier in the post "there's one interaction between ALL of the particles that is missing: gravity", so it was implied. Perhaps I should have made that a little clearer.
- rwmj 14y agoI thought the interaction with the Higgs is supposed to create mass?
- aroberge 14y agoTwo things, greatly oversimplified: 1) all forms of energy (including mass) are sources for gravity. 2) Interaction with the Higgs gives rise to what we observe as mass of particles; without this interaction, we'd have massless particle, with essentially the same energy, but moving at the speed of light. The net gravitational effect would be very different from what we observe though...
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- mattheww 14y agoThere are a lot of people thinking about what kind of structure the model of dark matter particles could have. And there are a lot of different ways for there to be more than one dark matter particle, and even if the only way those other particles interact with normal matter is through gravity, there are still ways for us to understand things about them. At the moment, the most popular dark matter theory comes from supersymmetry. In this case, there's only one dark matter particle, and all of the rest of the particles interact with normal matter, in pretty much the normal way, since all of the underlying structure of the model is almost identical.
- jared314 14y agoI keep hearing about the death of supersymmetry. Are there new developments keeping it "alive"?
- mattheww 14y agoUnfortunately, the idea that supersymmetry is "dead" has been propagated by journalists covering science who don't know any better and people with an agenda. Generally, it's people who just don't know any better. Unfortunately, you see comments supporting the idea even on HN. The important thing to understand about supersymmetry (SUSY) is that in the most general case, there are approximately 105 new parameters. That's far too many to probe in a meaningful way, so most models choose between 2 and 5 to vary, and fix the rest. Then a bunch of models are chosen that hopefully cover a wide spread of different behaviors. The true part is that several models have been excluded, basically as well as the LHC is going to be able to exclude/discover anything in the current energy regime. However, some of these models were just not chosen very well to begin with (but have historical importance) and others were chosen to have maximal signal strength. So as time goes on, the search for SUSY turns away from "easy" models and looks at more complicated ones. With 105 parameters, there's a lot of parameter space unexplored.
- syncerr 14y agoIt 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/2012-07-05/a-filament-of-dark-matter-between-two-clusters-of-galaxies http://www.scilogs.eu/en/blog/the-dark-matter-crisis/2012-07... Source: http://www.nature.com/nature/journal/v487/n7406/full/nature11224.html http://www.nature.com/nature/journal/v487/n7406/full/nature1... ˟˟ http://physicsworld.com/cws/article/news/2006/aug/25/gravity-lens-reveals-dark-matter http://physicsworld.com/cws/article/news/2006/aug/25/gravity...
- lloeki 14y agoIndeed, it's more like observing a magnetic field by dropping iron dust on a sheet of paper, and gently hit/shake it until the field lines "appear". It makes me wonder why we can't observe dark matter (which seems to emit only pure gravitation, and no light nor electromagnetic radiation). Could it be because there's no actual matter (i.e pure gravitational waves, like the magnet+iron+paper experiment)? Or are they massive clouds overloaded with Higgs bosons?
- syncerr 14y agohttp://en.wikipedia.org/wiki/Dark_matter#Direct_detection_experiments http://en.wikipedia.org/wiki/Dark_matter#Direct_detection_ex...
- dragonbonheur 14y agoJust as predicted by Mr. Jean-Pierre Petit: http://jp-petit.org/science/colloque2001/Colloque_2001_1.htm http://jp-petit.org/science/colloque2001/Colloque_2001_1.htm
- ok_craig 14y agoThere'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.
- lwat 14y agoWe know this is not the case because intersteller dust absorbs light, while the dark matter does not emit or absorb light at all. The only effect we see is the gravity.
- lloeki 14y agoNot only just light (photons) but no other radiation as well (electromagnetic, like X or gamma rays), except gravity.
- ordinary 14y agoGamma rays and X-rays are photons.[0] _____ [0] http://en.wikipedia.org/wiki/File:EM_Spectrum_Properties_edit.svg http://en.wikipedia.org/wiki/File:EM_Spectrum_Properties_edi...
- derleth 14y agoDust absorbs light, blocking it (creating dark spots) and getting hot (creating light spots in a different frequency range). We know what interstellar dust looks like. Dark matter doesn't look like that; it doesn't look like anything. We only know about it because its gravity affects the things we can see. NASA has a brief page on dark matter and something else we know little about, dark energy: http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/ http://science.nasa.gov/astrophysics/focus-areas/what-is-dar...
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- carterac 14y agoHow 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?
- archgoon 14y agoWell, the particles also have no way to radiate away energy, so the dark matter particles just whisk around each other under the gravitational force. You can check out something like this on your computer http://http.developer.nvidia.com/GPUGems3/gpugems3_ch31.html http://http.developer.nvidia.com/GPUGems3/gpugems3_ch31.html To see what pure 1/r^2 interactions look like. You can download the simulations from here: http://developer.nvidia.com/cuda/cuda-toolkit-40 http://developer.nvidia.com/cuda/cuda-toolkit-40
- InclinedPlane 14y agoThe dark matter halos don't experience friction, and are incapable of emitting heat radiation to cool off and condense. If you take a bunch of marbles and put them in a big bowl they will roll around for a while but eventually end up in the bottom of the bowl because they keep running into each other. But if you put in special marbles that just pass through each other and don't experience friction then you'll end up with marbles rolling around the bowl everywhere for ever, which is the way dark matter works.
- Jarihd 14y agoThis 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.
- InclinedPlane 14y agoSo, 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/1201.1003 http://arxiv.org/abs/1205.1045 http://arxiv.org/abs/1205.1045
- kyberias 14y agoSince this is Hacker News I have to point out that the "weekly interacting massive particle" could be, for example, my over-weight boss whom I have to meet every monday. ;)