4 ms·

It's not "populist" anything. It's the best science that can be done: https://medium.com/starts-with-a-bang/five-reasons-we-think-dark-matter-exists-a122bd606b

by acqq 8y ago

It's not "populist" anything. It's the best science that can be done: https://medium.com/starts-with-a-bang/five-reasons-we-think-dark-matter-exists-a122bd606ba8 https://medium.com/starts-with-a-bang/five-reasons-we-think-... "Five Reasons We Think Dark Matter Exists: No other idea explains even two of these." "1.) Galaxy Clusters" "2.) Galactic Rotation Curves" "3.) The Cosmic Microwave Background" "4.) The Bullet Cluster" "5.) Large-Scale Structure Formation" From these 5, only dark matter matches all. Whereas MOND theories match only one, the "item number 2" and only as an attempt to after-the-fact-explanation of what's anyway observed, not as any prediction of anything new. As I've quoted in my another message here: "the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later. This is not a case of tweaking the model to fit the data; this is a case of the best kind of science you hope for: where you make predictions, make the observations, and what you see validates and confirms the predictions you had made." Moreover, there's nothing "large" of the possible space that is now excluded. The possible space includes everything that "behaves like matter". What's (still just "probably") eliminated is just what were for us, humans, in this particular moment of our history very convenient to happen: that the energies needed are exactly such that WIMPs that were conveniently postulated to be such can be generated by the device which design and maintenance costs less than 2% of the total cost of the F-35 fighter planes (the money invested and planned to be invested in F-35 is 75 times bigger than the international investment in LHC). It would have been luck if it had happened, but the possibilities are much bigger and include such which are going to remain physically unreachable to be produced by our technologies. That we, humans, can't produce some particles doesn't disprove that dark matter exists when we have precise observations that can only be explained by dark matter and effectively by nothing else.

nonbel 8y ago
>"only dark matter matches all." Dark matter can be placed arbitrarily so it can match pretty much anything. I remember recently there was a galaxy with negligible deviation of the GR-predicted rotation curve and that was taken as evidence for dark matter too (even though MOND was still the better fit for that case). "Dark Matter" started out ok but has become a "god of the gaps" argument, I expect eventually MOND or similar solutions will be developed for all those issues. Also, I gather that while MOND does seem not predict these observations exactly, it is not fully developed yet and often the presence of some "normal" cold gas (undetectable via light) could make it fit. Also, to get dark matter to fit the observations requires post-hoc assumptions and parameter adjustments. Eg: "The amplitude of the third peak observed by WMAP merely falsifies the simple ansatz I used to make the prediction, not MOND itself. Indeed, I pointed out in the original papers that the ansatz must fail at some level, so I am hardly surprised that it does. All this means is that there are degrees of freedom (like a scalar field) that can oscillate separately from baryons in whatever the relavistic parent theory of MOND might turn out to be. The real test was for ΛCDM: the third peak had to be higher than predicted by pure baryonic damping. ΛCDM survives this test. It "wins ugly" in that, in order to obtain a fit, we have had to nearly double the baryon density over what it was so confidently known to be before it wasn't. That, and the no-CDM prediction for the second peak is still bang on. Amazing coincidence, that." http://astroweb.case.edu/ssm/mond/ http://astroweb.case.edu/ssm/mond/ >"the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later." I'm afraid I have never seen this although I have looked into this topic (as a layperson). Can you give an example of this? It would make the dark matter idea much more convincing.
- acqq 8y ago
  > Dark matter can be placed arbitrarily so it can match pretty much anything. Quite the opposite, and that statement is obviously uninformed. The science behind dark matter is very precise and exact. That's why the alternative theories can't come even near: once the same rigor which was applied to test dark matter is applied to the alternatives, the alternative theories simply break. > I'm afraid I have never seen this ... Can you give an example of this? I've given you the link to the complete articles and also highlighted the major points. Try to read and understand them fully, then search for more. For example, even on the MOND page that you linked you can read: "2013: ΛCDM provides an excellent fit to the improved CMB data just as MOND provides an excellent fit to improved rotation curve data. As before, one's interpretation depends entriely upon which you find more impressive." Note: "rotation curve" from that quote is the "item 2" from my posts before. So, no, still the match of the single "item 2" is definitely not "more impressive." The "CMB" mentioned on your page is the "item 3" from all 5 which are explainable by ΛCDM (and specifically, ΛCDM is the model part of which the "dark matter" is: https://lambda.gsfc.nasa.gov/education/graphic_history/univ_evol.cfm https://lambda.gsfc.nasa.gov/education/graphic_history/univ_... see there 4 and 5). Edit: response to your later response below: > The claimed predictions from the 1970s and 1980s are not mentioned on that page. They are mentioned even on the very page that you linked to: that page, among other points, followed the history of the tests and effectively concludes that, yes, finally, in 2013 ΛCDM wins the "item 3". Read carefully. Learn what ΛCDM is. MOND can still only claim "item 2." Which actual "authority" can show anything else? Also, behind "darkmattercrisis" blog are just a few guys with very fringe positions.
  - nonbel 8y ago
    >"Quite the opposite, and that statement is obviously uninformed. The science behind dark matter is very precise and exact." From what I have seen they can get precise post-dictions but not precise pre-dictions because there are so many free parameters (basically you can put dark matter wherever you need it). >"I've given you the link to the complete articles and also highlighted the major points. Try to read and understand them fully, then search for more." The claimed predictions from the 1970s and 1980s are not mentioned on that page. Also, that "startswithabang" guy is more like a catholic inquisitor than a scientist. I wouldn't consider him a reliable source because this behavior indicates he lacks the required capacity for curiosity, he can only repeat what authority figures say: "The blogger (@StartsWithABang) contacted @scilogscom on January 24 by replying to a 15-day old tweet that announced our blog’s move to the new domain. He tweeted “Bummed that @scilogscom is in the business of promoting contrarian scientist viewpoints.”, and asks the SciLogs.com community manager (@notscientific) “[Why] are you allowing @scilogscom to promote contrarian voices that undermine public understanding of [science]?”, adding “You have taken on “Dark Matter Crisis” blog, whose mission is to undermine all of physical cosmology & promote MOND.” The two agreed to discuss the issue via email, with the blogger adding that he was “personally worried that you are promoting clicks & false controversy over quality science content”, and states that he is “very, VERY disappointed about this move that @scilogscom has made”. By now the SciLogs.com community manager has explained to us what happened after these tweets. He and the publishing director responsible for SciLogs.com unfortunately assumed that the blogger’s criticism was justified. They decided to close our blog without conferring with others or asking us for a statement. After we complained about the discontinuation, they performed an internal investigation, which involved reaching out to astrophysicists and other people, and have realized that discontinuing our blog was a big mistake. We attribute SciLogs.com’s poor judgement to two factors: neither the community manager nor the publishing director has an (astro)physical background, it was the first time that SciLogs.com had experienced an attack against one of its blogs." https://darkmattercrisis.wordpress.com/2013/03/08/the-dark-matter-crisis-continues-on-the-difficulties-of-communicating-controversial-science/ https://darkmattercrisis.wordpress.com/2013/03/08/the-dark-m... Anyway, I can tell you know even less about this topic than me so let's leave it at that.
dnautics 8y ago
http://backreaction.blogspot.com/2017/01/the-bullet-cluster-as-evidence-against.html http://backreaction.blogspot.com/2017/01/the-bullet-cluster-...

by acqq 8y ago

nonbel 8y ago

>"only dark matter matches all." Dark matter can be placed arbitrarily so it can match pretty much anything. I remember recently there was a galaxy with negligible deviation of the GR-predicted rotation curve and that was taken as evidence for dark matter too (even though MOND was still the better fit for that case). "Dark Matter" started out ok but has become a "god of the gaps" argument, I expect eventually MOND or similar solutions will be developed for all those issues. Also, I gather that while MOND does seem not predict these observations exactly, it is not fully developed yet and often the presence of some "normal" cold gas (undetectable via light) could make it fit. Also, to get dark matter to fit the observations requires post-hoc assumptions and parameter adjustments. Eg: "The amplitude of the third peak observed by WMAP merely falsifies the simple ansatz I used to make the prediction, not MOND itself. Indeed, I pointed out in the original papers that the ansatz must fail at some level, so I am hardly surprised that it does. All this means is that there are degrees of freedom (like a scalar field) that can oscillate separately from baryons in whatever the relavistic parent theory of MOND might turn out to be. The real test was for ΛCDM: the third peak had to be higher than predicted by pure baryonic damping. ΛCDM survives this test. It "wins ugly" in that, in order to obtain a fit, we have had to nearly double the baryon density over what it was so confidently known to be before it wasn't. That, and the no-CDM prediction for the second peak is still bang on. Amazing coincidence, that." http://astroweb.case.edu/ssm/mond/ http://astroweb.case.edu/ssm/mond/ >"the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later." I'm afraid I have never seen this although I have looked into this topic (as a layperson). Can you give an example of this? It would make the dark matter idea much more convincing.

acqq 8y ago
> Dark matter can be placed arbitrarily so it can match pretty much anything. Quite the opposite, and that statement is obviously uninformed. The science behind dark matter is very precise and exact. That's why the alternative theories can't come even near: once the same rigor which was applied to test dark matter is applied to the alternatives, the alternative theories simply break. > I'm afraid I have never seen this ... Can you give an example of this? I've given you the link to the complete articles and also highlighted the major points. Try to read and understand them fully, then search for more. For example, even on the MOND page that you linked you can read: "2013: ΛCDM provides an excellent fit to the improved CMB data just as MOND provides an excellent fit to improved rotation curve data. As before, one's interpretation depends entriely upon which you find more impressive." Note: "rotation curve" from that quote is the "item 2" from my posts before. So, no, still the match of the single "item 2" is definitely not "more impressive." The "CMB" mentioned on your page is the "item 3" from all 5 which are explainable by ΛCDM (and specifically, ΛCDM is the model part of which the "dark matter" is: https://lambda.gsfc.nasa.gov/education/graphic_history/univ_evol.cfm https://lambda.gsfc.nasa.gov/education/graphic_history/univ_... see there 4 and 5). Edit: response to your later response below: > The claimed predictions from the 1970s and 1980s are not mentioned on that page. They are mentioned even on the very page that you linked to: that page, among other points, followed the history of the tests and effectively concludes that, yes, finally, in 2013 ΛCDM wins the "item 3". Read carefully. Learn what ΛCDM is. MOND can still only claim "item 2." Which actual "authority" can show anything else? Also, behind "darkmattercrisis" blog are just a few guys with very fringe positions.
- nonbel 8y ago
  >"Quite the opposite, and that statement is obviously uninformed. The science behind dark matter is very precise and exact." From what I have seen they can get precise post-dictions but not precise pre-dictions because there are so many free parameters (basically you can put dark matter wherever you need it). >"I've given you the link to the complete articles and also highlighted the major points. Try to read and understand them fully, then search for more." The claimed predictions from the 1970s and 1980s are not mentioned on that page. Also, that "startswithabang" guy is more like a catholic inquisitor than a scientist. I wouldn't consider him a reliable source because this behavior indicates he lacks the required capacity for curiosity, he can only repeat what authority figures say: "The blogger (@StartsWithABang) contacted @scilogscom on January 24 by replying to a 15-day old tweet that announced our blog’s move to the new domain. He tweeted “Bummed that @scilogscom is in the business of promoting contrarian scientist viewpoints.”, and asks the SciLogs.com community manager (@notscientific) “[Why] are you allowing @scilogscom to promote contrarian voices that undermine public understanding of [science]?”, adding “You have taken on “Dark Matter Crisis” blog, whose mission is to undermine all of physical cosmology & promote MOND.” The two agreed to discuss the issue via email, with the blogger adding that he was “personally worried that you are promoting clicks & false controversy over quality science content”, and states that he is “very, VERY disappointed about this move that @scilogscom has made”. By now the SciLogs.com community manager has explained to us what happened after these tweets. He and the publishing director responsible for SciLogs.com unfortunately assumed that the blogger’s criticism was justified. They decided to close our blog without conferring with others or asking us for a statement. After we complained about the discontinuation, they performed an internal investigation, which involved reaching out to astrophysicists and other people, and have realized that discontinuing our blog was a big mistake. We attribute SciLogs.com’s poor judgement to two factors: neither the community manager nor the publishing director has an (astro)physical background, it was the first time that SciLogs.com had experienced an attack against one of its blogs." https://darkmattercrisis.wordpress.com/2013/03/08/the-dark-matter-crisis-continues-on-the-difficulties-of-communicating-controversial-science/ https://darkmattercrisis.wordpress.com/2013/03/08/the-dark-m... Anyway, I can tell you know even less about this topic than me so let's leave it at that.

dnautics 8y ago

http://backreaction.blogspot.com/2017/01/the-bullet-cluster-as-evidence-against.html http://backreaction.blogspot.com/2017/01/the-bullet-cluster-...