tag:blogger.com,1999:blog-22973357.comments2015-07-29T02:32:32.434-04:00BackreactionSabine Hossenfelderhttps://plus.google.com/111136225362929878171noreply@blogger.comBlogger39093125tag:blogger.com,1999:blog-22973357.post-29577377262542240682015-07-28T09:14:39.999-04:002015-07-28T09:14:39.999-04:00VINOD,
It's not a direct process, but normall...VINOD,<br /><br />It's not a direct process, but normally mediated by other particles. That better be so, because otherwise the annihilation would occur very quickly, but then there wouldn't be enough dark matter left around. The exact annihilation process depends on the model, but the dark matter might for example interact through fermion loops which then create a photon pair. Best,<br /><br />B.Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-14426187197131269402015-07-28T08:37:15.369-04:002015-07-28T08:37:15.369-04:00Dark matter is supposed to manifest its presence t...Dark matter is supposed to manifest its presence thru gravitational inflence only. It is insulated from e.m field and does not interact with photons in any manner. Due to its characteristic of non-interaction with e.m forces, it is not detectable like normal luminous baryonic matter. When dark matter is non-interacting with e.m forces, where is the question of dark matter particles annihilating and emitting gamma rays?VINOD KUMAR SEHGALhttp://www.blogger.com/profile/17333205971995047294noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-52892593408692053092015-07-27T18:18:18.154-04:002015-07-27T18:18:18.154-04:00In this context, one should also consider the well...In this context, one should also consider the well-known core/cusp problem regarding DM in galactic centers. <br /><br />Any satisfactory ad hoc fixes for LCDM yet? <br /><br />Or are we left with a failed prediction?Robert L. Oldershawhttp://www.blogger.com/profile/15396555790655312393noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-64320782932773639052015-07-27T14:43:53.539-04:002015-07-27T14:43:53.539-04:00@Phillip Helbig, gently.
http://hyperphysics.phy-...@Phillip Helbig, gently.<br /><br />http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/barfor.html<br /><br />Dark matter only gravitationally interacts. DM is spherically inflated against gravity by its primordial temperature, above link. 5.47 times galactic baryonic matter DM "atmosphere" is dense at galactic central black holes, and consumed. Spiral galaxies cannot display constant Tully-Fisher relation over visible time.<br /><br />Observe a racemic mixture cryogenic molecular beam (frozen vibrations) rotational temperature. If two spectra, not one degenerate spectrum, are observed, spacetime is quantitatively chiral toward hadronic matter. Milgrom acceleration is Noetherian leakage of <i>exact</i> angular momentum conservation given trace vacuum anisotropy; no DM. Baryogenesis is sourced. One day. Rigid cage extreme chiral molecules with published good yield syntheses:<br /><br /><i>D</i>_3-4,7,11-trioxatrishomocubane (oblate symmetric top, Raman)<br /><i>D</i>_3-4-oxatrishomocubane (oblate symmetric top, microwave)<br /><i>D</i>_3-trishomocubane-4-one (asymmetric top, microwave)<br />Uncle Alhttp://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54428117065364289852015-07-27T02:42:17.939-04:002015-07-27T02:42:17.939-04:00You have to tell us the astrophysicist's name....You have to tell us the astrophysicist's name. :-)<br /><br />AGN are powered by accretion onto a central black hole with a mass millions of times that of the Sun. There is no obvious connection to dark matter at all. Sure, it could be there, and interact at some level, but if he wants to use AGN observations to rule out dark matter, a) that's the first I've heard of it and b) I'd like to examine his arguments.<br /><br />Is he really an astrophysicist who works on AGN or does he just play one on the internet?<br /> Phillip Helbighttp://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-39840148388634594692015-07-26T14:19:45.714-04:002015-07-26T14:19:45.714-04:00Bee, I was hoping you'd know more than me, whi...Bee, I was hoping you'd know more than me, which is not much. I think he said the present AGM models that work would not do so if five times the visible mass was hanging around. What was clear was that he, at least, was very hostile to the DM community.DaveChttp://www.blogger.com/profile/06275342568564790792noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23817918065011941902015-07-26T12:00:01.046-04:002015-07-26T12:00:01.046-04:00Thanks, Bee! It is nice to see some progress on th...Thanks, Bee! It is nice to see some progress on this scientific puzzle!Arunhttp://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-19849675064670144742015-07-26T02:17:08.828-04:002015-07-26T02:17:08.828-04:00DaveC,
Well, that's interesting. No, I have n...DaveC,<br /><br />Well, that's interesting. No, I have no opinion because I don't know what you (or he) means with "there is no room for dark matter"? Best,<br /><br />B.Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-9879601068821615202015-07-25T16:41:39.689-04:002015-07-25T16:41:39.689-04:00I recently met an astrophysicist working on active...I recently met an astrophysicist working on active galactic nuclei who said there is no room for dark matter in the current models of AGN, even though the DM advocates tell him insistently that it must be there in the middle of any galaxy (he is quite hostile to them). Do you have an opinion on this?DaveChttp://www.blogger.com/profile/06275342568564790792noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18442177485787914082015-07-24T21:36:45.759-04:002015-07-24T21:36:45.759-04:00RIP hooperons?
One more in an endless series?RIP hooperons?<br /><br />One more in an endless series?Robert L. Oldershawhttp://www.blogger.com/profile/15396555790655312393noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-71007280456394995322015-07-24T12:01:08.670-04:002015-07-24T12:01:08.670-04:00If dark matter annihilates at galactic centers,
1)...If dark matter annihilates at galactic centers,<br />1) What mechanism exists for particles exhibiting only gravitation and infinitesimal cross-section inelastic scattering?<br />2) The Tully-Fisher relation, spiral galaxy mass distribution remaining ordered over all visible time, does not vary. Dark matter annihilation implies a monotonic age-dependent variation.<br />3) Spiral galaxies contain central supermassive black holes scavenging dark matter whose persistent radial distribution is thermally inflated. Greater dark matter density at the galactic center of mass echoes depth-dependent atmospheric pressure.<br /><br />If spacetime is not <i>exactly</i> mirror-symmetric toward hadronic mass (e.g., baryogenesis), that chiral anisotropy relaxes Noetherian coupling of <i>exact</i> vacuum isotropy with angular momentum conservation, hence MoND's Milgrom acceleration. Dark matter curve-fits the Tully-Fisher relation. Spacetime mirror-asymmetry toward matter is testable at least six different ways - all chemistry-based.Uncle Alhttp://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-65174437214169566132015-07-23T07:12:40.175-04:002015-07-23T07:12:40.175-04:00I think this article may be of some relevance to t...I think this article may be of some relevance to the above discussion. arXiv:1502.04320<br /><br />Best,<br />DDaniel Coumbehttp://www.blogger.com/profile/04245217592187021011noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-15223403528175862402015-07-22T14:31:05.616-04:002015-07-22T14:31:05.616-04:00Here's another weird coincidence! I wrote this...Here's another weird coincidence! I wrote this comment before reading Zephir's:<br /><br />You know it was this whole train of thought which led me to the idea of bi-simulation on non-well-founded sets - which I have unsuccessfully tried to convey to you and, through you, to Renate Loll. So, I'll express it here and then drop it forever!<br /><br />As so eloquently expressed in Smolin's Three Roads to Quantum Gravity, the high degree of fine-tuning we witness defies probabilities; this, to me, strongly suggests retro-causation or, in other words, a distinct final condition. So why couldn't you use the adinkras of James Gates to develop a bi-simular model? I don't see why you couldn't because essentially adinkras are analogs to graphs and the folding process establishes relations between nodes:<br /><br />http://www.cs.indiana.edu/cmcs/bisimulation.pdf<br /><br />So, you develop one adinkra which evolves from a distinct initial condition "forward" in time and another bi-simular adinkra which evolves from a distinct final condition "backward" in time. These adinkras are not symmetrical, rather, they simulate one another, hence, bi-simulation. At forward time step t = a the adinkra folding "forward" in time may have gone through y folds while the adinkra folding "backward" in time may have gone through xy folds but both processes result in the same system state at forward time step t = a. They simulate one another. Would this not put an interesting constraint on the initial and final conditions? And what if what we think of as initial and final conditions are in actuality phase transitions? Could such a model perchance be illuminating?<br /><br />Some scientists say non-well-founded sets are incompatible with quantum theory but Ben Goertzel, an expert on non-well-founded sets, dispenses with that myth in chapter seven of his book Chaotic Logic.<br /><br />In case you missed the subtleties in my last comment, I'm not suggesting that the error-correction takes place in the world we perceive, what you call Minkowski space and Will Tiller calls D-space, rather, the error-correction occurs in Will Tiller's R-space. It occurs in the "electron-clock" described by the Zitter Model of David Hestenes and it's super-luminal. This is why the world we perceive appears coherent and consistent.Wes Hansenhttp://www.blogger.com/profile/00913503952284529871noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-49467653418853052002015-07-21T20:00:58.479-04:002015-07-21T20:00:58.479-04:00This is the evolution, which is not difficult to p...This is the evolution, which is not difficult to predict (for example here https://www.reddit.com/r/Physics_AWT/comments/2htmk5/science_graduates_are_not_that_hot_at_maths_but) It's the increasing complexity of formal models and decreasing cost of computer time, which will force the physicists to orient itself to numeric calculations and even simulations, despite some of them are still proud of their analytical skills by now.Zephirhttp://www.blogger.com/profile/06010623752049244967noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-89300527908641531172015-07-21T15:08:26.920-04:002015-07-21T15:08:26.920-04:00Believe it or not I wrote this comment before I re...Believe it or not I wrote this comment before I read Arun's comment, it's purely coincidental . . . <br /><br />I thought this issue was settled long ago!?! Numerical methods have really been indispensable to science since the 70's with the parallel advent of more efficient computation and dynamical chaos. How did Feigenbaum discover Universality in phase transitions? And in my opinion it was Feigenbaum's discovery which put the renormalization group on a solid foundation, at least philosophically. And even when Lanford, a pure mathematician, developed a proof, which the community deemed rigorous, the proof depended to a large degree on numerical methods.<br /><br /> <br /><br />I think people who express disdain for numerical methods are just inherently dishonest, with themselves and others. All knowledge is provisional in that it rests on a foundation of induction and numerical methods bring this to the forefront. And that, to me, is a good thing; it dispels dogma! As the early chaos pioneers liked to say, numerical methods develop intuition. Dogmatists quite often see causation where only correlation exists anyway!<br /><br /> <br /><br />This is really what made me wonder if perhaps James Gates hadn't discovered the reason why Universality appears with his adinkras. If you're not familiar with Gates, he works with SUSY and his adinkras are Feynman diagram analogs which represent oftentimes complicated systems of super-differential equations. To evolve the system you fold the adinkra but this folding process can be quite complex and if you're not careful you can lose SUSY. So what Gates did was assign each node in the adinkra a binary word and he discovered, quite by "accident," that the folding process which maintains SUSY conforms to one of Hamming's error-correction codes! So perhaps one sees Universality in phase transitions due to some error-correction process?<br /><br /><br /><br />http://arxiv.org/pdf/hep-th/0408004v1.pdf<br /><br /><br /><br />http://www.bottomlayer.com/PWJun10gates.pdf<br /><br /><br /><br />The last link is to an article which appeared in Physics World, 2014.Wes Hansenhttp://www.blogger.com/profile/00913503952284529871noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-35540513073241222262015-07-21T14:19:35.410-04:002015-07-21T14:19:35.410-04:00I read a story years ago (unfortunately I cannot r...I read a story years ago (unfortunately I cannot remember the title) that imagined a future where numerical solving programs grew in power to the point where they answered fundamental questions. However, just like Chris Anderson's quote above <i>"... and science can advance even without coherent models, unified theories, or really any mechanistic explanation at all."</i>, the numerical results based upon numerical results based upon... led to answers without any understanding or explanation for where it came from. And worse, there were further results appearing to be answers to questions that no one even knew to ask. It was an interesting cautionary tale about tools outpacing understanding and the interplay between answering a question and understanding a question and understanding an answer.Michael Mussonhttp://www.blogger.com/profile/17360143418083381579noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-69075352949590240152015-07-21T13:32:24.253-04:002015-07-21T13:32:24.253-04:00"Correlation supersedes causation"
someo..."Correlation supersedes causation"<br />someone needs to tell all those machine learning researchers working on causal graphical models they are wasting their time - or, perhaps, now that Causation has become a going concern within wheel houses proximate to Chris Andersen's own, it isn't such a useless thing to study after all. I'm not trying to put him down for it- deciding subjects which don't put food on your own plate are uninteresting is the mark of a professional. A working scientist. A survivor. <br /><br />We should take that into account when human creatures tell us what is and isn't interesting. They might just be saying, there's no low hanging fruit on that tree for me to eat. Doesn't mean the view from the top of that tree isn't important. <br /><br />The most obvious subject for Machine Learning to eat would be experiment.regretacleshttp://www.blogger.com/profile/00849406662712673245noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23930436898906117692015-07-21T05:52:51.906-04:002015-07-21T05:52:51.906-04:00Quite an interesting story about your grandmother....Quite an interesting story about your grandmother. She would have been about the same generation as my parents. I well remember our dad meticulously balancing his checkbook by hand, back in the 1950s. Even attending High School between 62-65 we did all calculations by hand. When my older brother bought a pocket calculator in the early 70s, for 200 dollars, it was an absolute marvel.<br /><br />I just finished reading (online) the very nicely written article in Scientific American "A Geometric Theory of Everything" by A. Garrett Lisi and James Owen Weatherall, that covers the evolution of the Standard Model to its present plateau - SU(3), SU(2), U(1). This is followed by an elucidation of how the E(8) Lie group is utilized to embrace both the Standard Model and gravity into a single, unified geometric structure. <br /><br />The article just skims the surface of how Lie groups apply to the physics of particles and fields. But the full mathematical complexity of this field of endeavor is quite mind boggling, and I could well imagine the need for A1 supercomputers to assist, or even completely take over, the model building process. David Schroederhttp://www.blogger.com/profile/18048116250413347228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-12964224667868426482015-07-20T20:25:21.561-04:002015-07-20T20:25:21.561-04:00Slightly off-topic, but not entirely, the movie Ex...Slightly off-topic, but not entirely, the movie Ex Machina is highly recommended for artistic elegance and thought-provoking subject matter.Robert L. Oldershawhttp://www.blogger.com/profile/15396555790655312393noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11168847054574132542015-07-20T14:48:32.400-04:002015-07-20T14:48:32.400-04:00A very interesting story about your grandmother. A...A very interesting story about your grandmother. A few years ago I read the fascinating book <a href="http://amzn.com/0691091579" rel="nofollow">When Computers Were Human</a> by David Alan Grier. It came out of him looking into an aspect of own his grandmother's past: her casually mentioning studying mathematics as a college student. A highly recommended read!Igor Khavkinehttp://www.blogger.com/profile/03255652837539396267noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-12166573026704608512015-07-20T14:37:55.876-04:002015-07-20T14:37:55.876-04:00Facial recognition is something your eyes & br...Facial recognition is something your eyes & brain do automagically. But trying to replicate that with computer and camera requires both computation and analytic understanding. E.g., <a href="https://en.wikipedia.org/wiki/Eigenface" rel="nofollow">Eigenfaces</a>Arunhttp://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-68824318076348991052015-07-20T14:35:12.588-04:002015-07-20T14:35:12.588-04:00You need to be able to prove error bounds on your ...You need to be able to prove error bounds on your numerical computation, which is presumably well-understood in the case of standard functions.<br /><br />I'm assuming that the existence proof (that the computation is meaningful) already exists.<br /><br />Numerical computations slso need to give insight into limiting cases, asymptotic forms, and how input parameters or boundary conditions change the output.<br /><br />Also, how would you arrive at the notion of the renormalization group from purely numerical calculations? Arunhttp://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33886164669615424792015-07-20T13:35:17.685-04:002015-07-20T13:35:17.685-04:00Chris, you not have to go very far in algebra. Mat...Chris, you not have to go very far in algebra. Matiyasevich theorem (1970) negatively solves the Hilbert's tenth problem.nicolas pouparthttp://www.blogger.com/profile/17722878242014554884noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-62462627908378405782015-07-20T12:28:10.889-04:002015-07-20T12:28:10.889-04:00Isn't there a more fundamental difference, in ...Isn't there a more fundamental difference, in term of "complexity class" or "hardness", between problems (e.g. differential equations) having analytical solutions vs. those having none? For example, if the solution can be expressed as y = f(x) with f a polynomial function, we can evaluate it at any point with finite accuracy in polynomial time. Would this be true if we had to perform a numerical integration of the equation instead (requiring the same accuracy in the solution)?<br /><br />The concept of algorithmic complexity does seem to differentiate the two cases, since in both cases the unknown number is expressed as a very compact string of character (the equation itself or its analytical solution). Is there any other relevant measure of complexity applicable here ?Chrishttp://www.blogger.com/profile/05513930613221402247noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73065847099568975522015-07-20T11:44:26.604-04:002015-07-20T11:44:26.604-04:00Even more strange is when mathematics itself requi...Even more strange is when mathematics itself requires the use of the computer to validate a theorem like the four-color theorem, first of its kind. Such a solution has widely divided the community of mathematicians, is that still the mathematics when the mathematical demonstration itself is not verifiable by a human? The validation moves from the verification of theorem to the validation of the verification software.<br /><br />As for thinking machines, in 2011 when IBM Watson became Jeopardy world champion I realized it was the end of the domination of man for thought. Though I know the theory, I never thought to see it in my lifetime. As soon as the machine can read and do math, good luck humanity ; how 1 KHz can compete with GHz?nicolas pouparthttp://www.blogger.com/profile/17722878242014554884noreply@blogger.com