5 ms·

TFA says that sterile neutrinos have been ruled out.

by vecter 5y ago

denton-scratch 5y ago
"TFA"? OK, too bad. I still think there are seriously-hard problems in cosmology that are not explained: DM, DE, and inflation. I'm not convinced by the explanations that are on the table. Nobody has to convince me of anything, of course; I'm just some old dude with a laptop, and a long interest in cosmology. I just think there's something wrong: those three proposed mechanisms are very hairy, in Occam's Razor terms. It would be deliciously sweet, if the observations they purport to explain could in fact be explained by a single, simple theory.
- SquibblesRedux 5y ago
  My experience is that there is always something wrong with current theories, no matter what field or what time. We linger on the theories we find useful, but we never know how deep the rabbit hole goes, really, and there is always another surprise waiting to be revealed.
- raattgift 5y ago
  > long interest in cosmology Good, let's start with that expression of interest and run with it. Here's my high level challenge to let you reflect for yourself (privately) on how interested you really are. > those three proposed mechanisms are very hairy, in Occam's Razor terms Write down a standard gravitation-containing effective Lagrangian or the action on the one hand, and an alternative (see e.g. Famaey & McGaugh 2012 in Living Reviews in Relativity, 15, 10, §§6-7) and run it through your favourite character-counting tool. Then try an analytical or numerical solution for a simple toy model in either of them. Then tell us which one you think is hairy and why, and whether your idea about how to assess hairiness has differed during this little study programme. There is local help available for you in doing this at a local community college or small state-funded university (or local equivalents) in the physics department. It won't take long to walk you through it at a STEM undergraduate level (I would start with the Einstein-Hilbert action with the cosmological constant and proceed to perturb that in small steps [1]), go deeper if you can follow the mathematics, and aim you at further resources if you are honestly interested in them). I think this will be more satisfying for your intellectual curiosity than making self-admittedly uninformed negative comments on Internet forums (even this one). I'm pretty sure that if you asked in the comments here you'd have several people offering to help put you in touch with someone local to wherever it is you are. Satisfying honest intellectual curiosity is catnip to academics. > seriously-hard problems in cosmology that are not explained Yes, you're right. Cosmologists collectively are working towards a consistent and complete and explanatory model, but are not done, despite the "corpses" of many many ruled-out possibilities. (It is easy to dream up a possibility, hard to write it down consistently, and almost always really easy to kill it on first contact with real astronomical data; Einstein went through this many times including on papers he sought to have published). However, I think you can get closer to understanding what those problems are, and why they're hard, and what we know can't solve them, assuming you retain your interest. > [DE] ... could in fact be explained by a single simple, theory. The Cosmological Constant is literally just a scalar multiplier on the curvature. Practically the only way to make it simpler is to zero it out, which is exactly what had been done before the discovery of the apparent acceleration of the expansion of the universe. Dark energy research (on the theoretical side) is principally, "in order to improve the accuracy of our modelling compared to data from various observatories, do we need to change the Cosm.Const., which is the \Lambda in the \Lambda-CDM model, into a more complicated function? If we do so, what observables are generated (especially if they would appear in already-gathered data (e.g. DES)?". [See the parenthetical three paragraphs up...] - -- [1] An actual lecture for grad students (and some undergraduates) at McGill University in Montréal has this section: https://www.youtube.com/watch?v=pjn_wZ-1ne0 https://www.youtube.com/watch?v=pjn_wZ-1ne0 (from https://www.mcgill.ca/study/2021-2022/courses/phys-514 https://www.mcgill.ca/study/2021-2022/courses/phys-514 ETA: n.b. at the 41min58sec mark re my approach above) Please feel free to reply in the comments about whether this is interesting but too difficult to follow, and I will try to aim you at something more suitable for you. (You also will probably find lots of HN commenters directing you at e.g. PBS Spacetime and similar, but I think that's not really a path to understanding what hairy even is). Really I'm guessing you'd be better off with an informal tutorial session, which might cost you a coffee and a decent sandwich brought to some physics teacher's office, and some diplomacy beforehand (don't start with "I want you to show me how to argue on the Internet about physical cosmology's failings", for instance, much less "give me a devastating 240-character slogan I can repeat until all the relevant physicists get different jobs or mute me").
  - denton-scratch 5y ago
    > someone local to wherever it is you are. Satisfying honest intellectual curiosity is catnip to academics. I live about a mile or two from Roger Penrose; I have wanted for years to ask him out for a beer. I believe he has views that are very interesting to me, that he hasn't published on (not his field). I know someone who knows him. But I'm terrified. > what hairy even is Several people have picked up on me using that word, and run with it. I was only using the word casually, to refer to something that looks like it could be cut with a Razor. I'm beginning to get the impression that it's sort of a technical term with an established meaning. [Edit] I'm not sure if any such established meaning might be related to the observation that "black holes have no hair". I'm not using it that way, TTBOMK.
  - denton-scratch 5y ago
    Goodness, that was pretty patronising. I didn't do maths past 18, so I'm not doing your math exercises (and you're rather obviously bandying jargon around for purposes of belittling). Doesn't matter. Your opening remark hooked me; I thought you were going to tell me something interesting. Disappointment ensued.
    - raattgift 5y ago
      Ok. I thought your comments were even more patronising, since you repeatedly discounted the work of many thousands of cosmologists around the world who did not stop maths at 18, and was provoked by them. A low math book I wholeheartedly recommend is A Journey into Gravity and Spacetime by Wheeler, which you can borrow from https://archive.org/details/journeyintogravi0000whee https://archive.org/details/journeyintogravi0000whee (Apart from writing this neat book, Wheeler is also the coauthor of one of the standard graduate-level textbooks on General Relativity.) Unfortunately the book is fairly rare, but there are usually purchase options and a public library might have a copy, or could get one via inter-library lending. I cannot gauge your level of interest other than that you expressed some; I also did not know until now, in spite of your disclaimer about not being a physicist (and being "an armchair cosmologist"), how little maths you have. I'll end with a Feynman quote that seems relevant when gauging one's own interest in and ability to talk about a topic that one does not know well: "The first principle is that you must not fool yourself and you are the easiest person to fool."
not2b 5y ago
My understanding from following reports on these experiments (including this article) is that the simplest version of sterile neutrinos, where instead of three kinds of neutrinos there are four, and one interacts only gravitationally, has been ruled out, but maybe some more complex version is still possible.

TFA says that sterile neutrinos have been ruled out.

by vecter 5y ago

TFA says that sterile neutrinos have been ruled out.

"TFA"? OK, too bad. I still think there are seriously-hard problems in cosmology that are not explained: DM, DE, and inflation. I'm not convinced by the explanations that are on the table. Nobody has to convince me of anything, of course; I'm just some old dude with a laptop, and a long interest in cosmology. I just think there's something wrong: those three proposed mechanisms are very hairy, in Occam's Razor terms. It would be deliciously sweet, if the observations they purport to explain could in fact be explained by a single, simple theory.

SquibblesRedux 5y ago
My experience is that there is always something wrong with current theories, no matter what field or what time. We linger on the theories we find useful, but we never know how deep the rabbit hole goes, really, and there is always another surprise waiting to be revealed.
raattgift 5y ago
> long interest in cosmology Good, let's start with that expression of interest and run with it. Here's my high level challenge to let you reflect for yourself (privately) on how interested you really are. > those three proposed mechanisms are very hairy, in Occam's Razor terms Write down a standard gravitation-containing effective Lagrangian or the action on the one hand, and an alternative (see e.g. Famaey & McGaugh 2012 in Living Reviews in Relativity, 15, 10, §§6-7) and run it through your favourite character-counting tool. Then try an analytical or numerical solution for a simple toy model in either of them. Then tell us which one you think is hairy and why, and whether your idea about how to assess hairiness has differed during this little study programme. There is local help available for you in doing this at a local community college or small state-funded university (or local equivalents) in the physics department. It won't take long to walk you through it at a STEM undergraduate level (I would start with the Einstein-Hilbert action with the cosmological constant and proceed to perturb that in small steps [1]), go deeper if you can follow the mathematics, and aim you at further resources if you are honestly interested in them). I think this will be more satisfying for your intellectual curiosity than making self-admittedly uninformed negative comments on Internet forums (even this one). I'm pretty sure that if you asked in the comments here you'd have several people offering to help put you in touch with someone local to wherever it is you are. Satisfying honest intellectual curiosity is catnip to academics. > seriously-hard problems in cosmology that are not explained Yes, you're right. Cosmologists collectively are working towards a consistent and complete and explanatory model, but are not done, despite the "corpses" of many many ruled-out possibilities. (It is easy to dream up a possibility, hard to write it down consistently, and almost always really easy to kill it on first contact with real astronomical data; Einstein went through this many times including on papers he sought to have published). However, I think you can get closer to understanding what those problems are, and why they're hard, and what we know can't solve them, assuming you retain your interest. > [DE] ... could in fact be explained by a single simple, theory. The Cosmological Constant is literally just a scalar multiplier on the curvature. Practically the only way to make it simpler is to zero it out, which is exactly what had been done before the discovery of the apparent acceleration of the expansion of the universe. Dark energy research (on the theoretical side) is principally, "in order to improve the accuracy of our modelling compared to data from various observatories, do we need to change the Cosm.Const., which is the \Lambda in the \Lambda-CDM model, into a more complicated function? If we do so, what observables are generated (especially if they would appear in already-gathered data (e.g. DES)?". [See the parenthetical three paragraphs up...] - -- [1] An actual lecture for grad students (and some undergraduates) at McGill University in Montréal has this section: https://www.youtube.com/watch?v=pjn_wZ-1ne0 https://www.youtube.com/watch?v=pjn_wZ-1ne0 (from https://www.mcgill.ca/study/2021-2022/courses/phys-514 https://www.mcgill.ca/study/2021-2022/courses/phys-514 ETA: n.b. at the 41min58sec mark re my approach above) Please feel free to reply in the comments about whether this is interesting but too difficult to follow, and I will try to aim you at something more suitable for you. (You also will probably find lots of HN commenters directing you at e.g. PBS Spacetime and similar, but I think that's not really a path to understanding what hairy even is). Really I'm guessing you'd be better off with an informal tutorial session, which might cost you a coffee and a decent sandwich brought to some physics teacher's office, and some diplomacy beforehand (don't start with "I want you to show me how to argue on the Internet about physical cosmology's failings", for instance, much less "give me a devastating 240-character slogan I can repeat until all the relevant physicists get different jobs or mute me").
- denton-scratch 5y ago
  > someone local to wherever it is you are. Satisfying honest intellectual curiosity is catnip to academics. I live about a mile or two from Roger Penrose; I have wanted for years to ask him out for a beer. I believe he has views that are very interesting to me, that he hasn't published on (not his field). I know someone who knows him. But I'm terrified. > what hairy even is Several people have picked up on me using that word, and run with it. I was only using the word casually, to refer to something that looks like it could be cut with a Razor. I'm beginning to get the impression that it's sort of a technical term with an established meaning. [Edit] I'm not sure if any such established meaning might be related to the observation that "black holes have no hair". I'm not using it that way, TTBOMK.
- denton-scratch 5y ago
  Goodness, that was pretty patronising. I didn't do maths past 18, so I'm not doing your math exercises (and you're rather obviously bandying jargon around for purposes of belittling). Doesn't matter. Your opening remark hooked me; I thought you were going to tell me something interesting. Disappointment ensued.
  - raattgift 5y ago
    Ok. I thought your comments were even more patronising, since you repeatedly discounted the work of many thousands of cosmologists around the world who did not stop maths at 18, and was provoked by them. A low math book I wholeheartedly recommend is A Journey into Gravity and Spacetime by Wheeler, which you can borrow from https://archive.org/details/journeyintogravi0000whee https://archive.org/details/journeyintogravi0000whee (Apart from writing this neat book, Wheeler is also the coauthor of one of the standard graduate-level textbooks on General Relativity.) Unfortunately the book is fairly rare, but there are usually purchase options and a public library might have a copy, or could get one via inter-library lending. I cannot gauge your level of interest other than that you expressed some; I also did not know until now, in spite of your disclaimer about not being a physicist (and being "an armchair cosmologist"), how little maths you have. I'll end with a Feynman quote that seems relevant when gauging one's own interest in and ability to talk about a topic that one does not know well: "The first principle is that you must not fool yourself and you are the easiest person to fool."

not2b 5y ago

My understanding from following reports on these experiments (including this article) is that the simplest version of sterile neutrinos, where instead of three kinds of neutrinos there are four, and one interacts only gravitationally, has been ruled out, but maybe some more complex version is still possible.