TFA says that sterile neutrinos have been ruled out.
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.
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...]
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[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 (from 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").
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.
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
(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."
I do not have an ebook reader. However I am working my way through Penrose's "The Road To Reality". I'm halfway though, it's taken me a couple of years so far.
I'm not up for doing graduate maths! Are people saying that you can't think about this kind of stuff, if you don't have graduate maths?
That's patronising.
That sounds like a mere dismissal, but let’s try to formulate an answer to it as an actual question.
For one thing, if a field is full of intentionally confusing/obfuscated nonsense, then hopefully one could legitimately refute it without understanding the nonsense. For example, if some variant of astrology, or some theory of literary criticism, is intentionally so difficult to grasp, that none but it’s advocates have taken the time to understand it, that should not prevent the field from being dismissed as pointless nonsense.
But what is the grounds on which such a dismissal should be based?
Well, in the case of astrology, you can find that whatever predictions it makes are not better than chance. You don’t have to understand how the theory works to evaluate this, you just need the predictions made by the practitioners.
In the case of a nonsensical theory of literary criticism, either it does not make any claims which have a meaning that can be evaluated outside of itself, in which case it can be dismissed as not saying anything that any non-practitioner would care about, or it does, in which case its merit can be judged, in part, based on those claims.
But suppose there is a theory (or related family of theories) which one finds too complicated to understand, but which the community around it(/around them) uses to make accurate predictions.
Can one then potentially offer useful criticism? In some cases, yes! If there is another theory which can be seen to make predictions or judgements which are just as good, or better, and such that one can give a strong argument that it is simpler, then one can put that forth as a good criticism.
But, note, one should have a clear idea of what one means by simpler, or at least, of the basis by which one concludes that the other thing is simpler.
Are there other cases that work? I think so, but suspect they are all, fairly limited in scope.
If a community is able to make predictions well using a theory which has few parameters (in an appropriate way of counting parameters. E.g. no splitting the digits up to turn two parameters into one.) and no community has another theory which makes comparably good predictions, I think that without understanding the theory, or at least without understanding some part of it well, one wouldn’t have many compelling avenues of criticism.
(If one is able to understand some small part of it well, one can potentially demonstrate that that small part of it seems to be e.g. obscurantism around a trivial point, or other issues with that small part. If one does this with a handful of very small parts this could be a quite compelling criticism, especially if no one is able to give a good justification for why it is said like that.)
Of course, one can think all one wants about whatever topic. There is nothing objectionable about anyone thinking about a topic.
But in presenting one’s thoughts, one should express an appropriate level of confidence based on how what one knows compared to what others know, about it.
When people (not like you. I’m not talking about you here. I’m thinking of comments I see on youtube videos) with no math background think that “quantum mechanics is too complicated. It must, therefore, be wrong.”, they are making a mistake.
I'm not trying to make a contribution to a scientific conference; I'm just some dude, trying to have a conversation with smart people, and so become better-informed.
I probably seem rather defensive; I'm no expert, and I know there are experts around here. I'm OK with being slammed down by experts. I can take the punches, I have nothing to prove. But I am sorry that those experts might be hurt by my remarks - I'm just some inquisitive dude on the internet, raising questions.
Amusingly (I think), in my youth I took some astrology training. I read quite a bit on the subject, and attended a few classes. Obviously I had some pretty mad notions.
I'd like to think that the notions I have now are not bonkers; but past form says that I've been wildly wrong before, so the notions I have now are probably wrong too.
I was just giving cases of where something could make sense to really criticize without understanding it,
trying to get closer to a characterization of the situations in which that would make sense.
I certainly didn't mean to suggest that your current notions are "bonkers". I apologize if it came off that way. And, I mean that sincerely, not just in a "sorry if you were offended" way, but like, in a "if that was the way it came across (and it seems it was), then I am at fault, and I am sorry." way.
Even if you didn't take it that way, the way I wrote my comment was probably a bit harsh, and it shouldn't have been.
Certainly I don't have a good enough understanding of cosmology to defend any models of it on at the object level, and it seems to me that there are some that do, who have reasons they prefer non dark-matter (or, ... sorta-non-dark-matter?) explanations?
And I guess, some people from the people-who-understand-cosmology-well community will give simplified accounts for people without the math background for why they suspect their view (either for dark matter or not) will turn out to be the one that is right, and it makes sense that some people in the audience would be convinced one way or the other by some of these explanations.
So, now I realize something I am confused about:
If two experts (who, say, are both generally respected in a field, and who respect one-another) give for-popular-audience simplifications of their reasons for believing their opposing positions regarding a particular question in the field,
and if one of their positions is the more common, almost "standard", view in the field (but where the question isn't considered really settled, and basically everyone in the field agrees that neither is strictly ruled out)
but one finds the for-outsiders explanation of the less common position to be convincing, and the for-outsiders explanation of the more common position to be unconvincing,
what should one believe?
How should one weigh how convincing one finds the simplified versions of the arguments, against the fact that a substantial majority of the field finds the other view more likely?
I am genuinely unsure!
Maybe it depends on, the reason for the differences in how convincing one finds the simplified arguments?
And as I noted, if I now think my earlier notions were bonkers, it would be sensible to consider that my present notions might be no less bonkers.
I would like to be able to understand what experts think is how the Universe works. I think it's a duty on people to try to understand the world they live in; same as I think a citizen has a duty to try to understand government policy, even if they are not experts in political economy or whatever.
So I live in a town with a couple of good universities. I have an batchelor's degree in Philosophy. I did maths and advanced maths at 16, but bailed out after that. Surprisingly I got top grade in advanved maths, and bottom (pass) grade in regular maths. I doubt I'd get a place on a postgrad course in anything but Philosophy, and I got a poor grade in that (I think partly because of my option choices).
Which degree course should I sign-up for? I'm interested in number theory, logic, and cosmology. I'd particularly like to be able to talk to people about cosmology.
I don't need a first or anything; I'd only be doing it to educate myself.
Whether there is a community is neither here nor there. What matters is the predictions. Quantum theory is incomprehensible, but makes super-precise predictions, that have been tested and confirmed. These three theories aren't like that, are they?
I don't know why a professional cosmologist should feel patronised by some twat like me. Some people up-thread have had a go at explaining things; I've learned, and I have some study leads. I don't learn from patronising insults.
I don't think you are supposed to mock the rest of us, because we don't know as much as you know. I've never pretended to be anything other than an interested layman. I'm pretty surprised at the downvotes and hostility I've met.
I mean, I knew my opinions were unpopular; I expected downvotes, but not hostility.
I’m not a cosmologist. I don’t have a degree in physics. But when I read your comment, I was as upset as any of them would’ve been.
When I were a lad, the Big Bang theory was treated with scepticism; the orthodoxy was Hoyle's steady state. Big Bang is now orthodoxy, steady state is dead, and Penrose is out in the weeds. Similarly the idea of a black hole was considered pretty left-field. It's now more-or-less proved. These changes have happened in my lifetime.
My point is that what is considered orthodox can change in just a couple of decades; it's not insane to question whether an orthodoxy that's been in place for just a couple of decades (and is itself pretty speculative) should have the status of scientific fact.
I'd be a fool to think that modern cosmological theory is in any way a final answer. Sure, I wouldn't recognise a Lagrange equation if it slapped me in the face. Similarly, I'm not an economist; I can't prove that Friedman had the wrong end of the stick. But I can still make reasonable judgements about a government's economic policies, and my judgements are sometimes more right than those of experts.
There will clearly be more revolutions in physics over time. We know the Standard Model is are wrong. Dark Matter and Dark Energy may be right or wrong. We need more experimental evidence to help us decide. This is not a new insight that you've had. Literally every physicist knows this.
> it's not insane to question whether an orthodoxy that's been in place for just a couple of decades (and is itself pretty speculative) should have the status of scientific fact.
What makes you think that physicists think that anything that's been discussed is scientific "fact"?
More importantly, there is no value in you, me, or any layman without an even undergraduate-level understanding of math and physics questioning anything that you don't know a single thing about. You don't even know what you don't know, and despite your claims of humility, your earlier writings clearly demonstrated either incredible arrogance, naivety, or both.
> Similarly, I'm not an economist; I can't prove that Friedman had the wrong end of the stick. But I can still make reasonable judgements about a government's economic policies, and my judgements are sometimes more right than those of experts.
This analogy is wrong. I could go into why you probably didn't even understand why the experts believed what they believed, but I don't have time for that. Even a broken clock is right twice a day. And even if someone is wrong, their thought process could have been better and more informed than yours.
Your analogy breaks down because none of that has any bearing to cosmology. You don't understand any foundational knowledge required to even begin to have an elementary conversation. Saying "I don't buy these existing theories" is actually making a very strong statement, because it implies that you understand what the current theories are, why they are what they are, and all of the other theories that have been ruled out for various reasons. And if you don't know any of this, then your opinion is literally worthless in the epistemological sense.
When I was an undergraduate studying computer science, I met a graduate mathematics student at a programming competition. I asked him if he could explain his research to me. He said "no". I wasn't upset, nor did I tell him that his theories were wrong. Rather, I was enlightened. I realized that there was no way he could possibly explain the abstract concepts that he was studying to a person who barely understood linear algebra. It would have taken me years of hard studying to begin to be able to grasp the kinds of problems that he was tackling, the approaches that he was taking, and why. This is no different.
It's not something "I don't know a single thing about". I know some things about it. Perhaps I could observe (since we're on the topic of what people don't know) that you don't actually know what I do and don't know.
> You don't even know what you don't know,
I cheerfully concede that the number of things I don't know is infinite.
> and despite your claims of humility, your earlier writings clearly demonstrated either incredible arrogance, naivety, or both.
If it's "incredible", then you would appear to have a problem; it seems that you are convinced by my demonstration of arrogance and naivety, even though it's not believable to you. Make up your mind.
I've not insulted anyone; all I've done is to question certain ideas. You, on the other hand, have written a long comment that consists of nothing but personal insults, and contains no information.
Back in the Usenet days, one would have said <plonk>.
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.