[HN Gopher] Why dark matter feels like cheating (and why it isn't) ___________________________________________________________________ Why dark matter feels like cheating (and why it isn't) Author : spekcular Score : 29 points Date : 2023-02-11 16:49 UTC (6 hours ago) (HTM) web link (4gravitons.com) (TXT) w3m dump (4gravitons.com) | thriftwy wrote: | The photons of CMB has lost near the same order of magnitude of | energy as the postulated dark energy, if I'm not mistaken. This | happened via red shift. | | I wonder where that energy went and they acquired that much | energy in the first place. | d--b wrote: | What about dark energy? Dark matter seems quite solid. | | But then dark energy does feel like a hack, right? Throwing the | whole "dark thing" concept under the bus. | lisper wrote: | > Dark matter seems quite solid. | | So to speak :-) | | >But then dark energy does feel like a hack, right? Throwing | the whole "dark thing" concept under the bus. | | Yes, dark energy really is nothing more than a mathematical | hack (at least for now). There's a reason that a certain | personality type chooses to go into physics and not marketing, | with the result being that the market for physics often leaves | something to be desired. | kloch wrote: | > For dark matter, we keep those standards. The evidence for some | kind of dark matter, that there is something that can't be | explained by just the Standard Model and Einstein's gravity, is | at this point very strong. | | Option 1: Do more research on Gravity to see what we might be | missing there. The difficulty in measuring G, and the flyby | anomaly would be good places to start. | | Option 2: Make up fully unconstrained variable 'X' that can take | any value you want at any location or time in the universe[1]. | This is amazing because it can perfectly solve so many difficult | problems! | | Obviously many people will and should be skeptical of throwing | full confidence at option 2 in it's current state. | | [1] Unlike neutrinos or black holes, there is no theory for what | dark matter is made of, and how it is created or destroyed. Thus | there are no constraints on how much you can have at any given | location or time. | ajross wrote: | The point of the article is that dark matter is the result of | doing 1, not 2. What's this "fully unconstrained" nonsense? We | have outrageous amounts of data that need to be fit. Why is | "the flyby anomaly" a useful place to start and not a century's | worth of galactic rotation and mass estimates? | | Dark Matter persists _precisely because_ it 's the best theory | that fits the available observations. Arguments against it are | the bits predicated on squishy stuff like "aesthetics". | | No one thinks we have all the answers, but demanding we throw | out the best model we have is going backwards. | kloch wrote: | being "skeptical of throwing full confidence at option 2 " is | not the same as "demanding it be thrown out". It just means | show us something more than "magic variable 'X' fits all | curves." | ajross wrote: | You want... _more_ from a theory than that it fit the data? | That 's not how theories work. | | I think what you're asking for is a lab-testable prediction | from a dark matter theory. And no, we don't have that. It | would be nice if we did, but we don't. We don't have it | from MOND either, though, so I still don't get your | denialism. If you don't want us to do science to figure | this out, what are you asking for? | teddyh wrote: | God of the gap matter. | awinter-py wrote: | > we can map dark matter's location | | this has always felt circular to me -- someone drops an astronomy | paper like 'we found a galaxy with no dark matter' and I wish | someone would rewrite it as 'dear non physicist, here are ten | critical takes you just thought of and why we discarded each' | | this is mostly a knock on my own knowledge, and slightly a knock | on pop science press, but I don't know the steps between 'mass as | inferred from light doesn't explain galactic rotation curves' and | '80% of mass is ghosts' | remote_phone wrote: | The fact that dark matter has never been seen "but it must be | there!" is basically the same argument that religious people | make. It's 100% a religious, faith-based argument and non- | scientific. There I said it. | | There's an explanation for all of this behavior that we are | measuring but saying that it's something we can't see but it's | there!! is objectively absurd. | lll-o-lll wrote: | Dark Matter is unintuitive for the layman (which I am), and | extremely intuitive for the physicist, which I suspect is where | the origins of this problem lie. This article is another in long | line of _you just don't get it man_ , which is true. Sabine | Hossenfelder has some great videos that actually explain the | concepts in a way that the layman can grasp, while also pointing | out a number of problems with the standard orthodoxy. | | The problems don't indicate that Dark Matter (the theory) is | wrong necessarily. MOND is much better at explaining a number of | observations of large scale (better meaning simpler in this | case), but Dark Matter is better for other observations at | smaller scale. Unfortunately it seems that the physicist | community (outside of a small subset) is unwilling to research in | the MOND space; it has the _taint_. So physicists just pile on a | bunch of extra variables to make Dark Matter fit certain | observations, when MOND describes those observations very simply. | | Sabine argues long and hard that modern particle physicists have | made no fundamental progress for 50 years due to poor scientific | method, and she's acerbic and popular with the plebs (such as | me). I'm glad she's a voice out there, but I'm sure she has put | herself offside with a number (maybe most) working particle | physicists. | | It's unfortunate. The phenomenon that MOND and Dark Matter seek | to explain are really interesting, and the depths have clearly | not been plumbed. The continual search and failure to find the | Dark Matter particle is not doing physics any favours. | throwawaymaths wrote: | Why exactly is dark matter unintuitive to the layperson? (Any | more so than say, germ theory, or praying to an interventionist | god)? | nitwit005 wrote: | Let us imagine the view of a "normal person". Pop open a science | textbook, and it will likely suggest the scientific method | requires you to state your hypothesis, and test it as best you | can. | | So this normal person looks to see if this has happened, finds | there are several rival theories, and no experiment done on Earth | had produced results. Naturally, they start to doubt. | imiric wrote: | But doubt what, exactly? All science tells us is that there | should be something there, but we don't know what it is. | Nobody's asserting the contrary. | mdorazio wrote: | Doubt that magic pixie dust is the correct answer to "what's | there?". | throwawaymaths wrote: | Moreover they find that alternatives have made many _specific | predictions_ that have panned out (linear Tully-fisher with a | specific slope, EFE, early galaxies), whereas mainline dm | theories make fewer a priori predictions, but lots of a | posteriori explanations. Notably, efe was shown by a group that | set out to measure that it wasn 't there to try to support | LCDM. So, what is a layperson to do? | college_physics wrote: | Maybe it is not "cheating" but it certainly casts a dark shadow | over the otherwise fairly cooky stance of fundamental physics | that "we have figured things out" | | As an explanatory concept is has very low utility: there is not | much else you can do with it except plug what you find missing. | You can't say, for example, that because of this and this aspect | of dark matter I predict this cool effect and then go search for | it and either falsify or strengthen the confidence of your | thought framework | mr_mitm wrote: | Sure you can. | | Example: you observe wonky rotation curves of galaxies. You | reckon there might be some extra invisible matter. From that | you predict that you should also see this extra matter in | lensing observations. You make the lensing observations and lo | and behold, you see the same amount of extra matter that is | needed to explain the rotation curves. | | I wrote a longer comment on this before: | https://news.ycombinator.com/item?id=34365591 | lisper wrote: | That's not true. There have been many hypotheses advanced | regarding the nature of dark matter (WIMPs, MACHOs) and the all | have made experimental predictions. The problem is that none of | those predictions have actually been confirmed by experiment, | and we're running out of ideas. But this is not much different | than the situation on the eve of the discovery of relativity | and quantum mechanics at the beginning of the 20th century. So | all of this is just business as usual for cutting-edge physics. | college_physics wrote: | Every plausible but failed hypothesis (its been half a | century now?) bakes-in an intractability that may become | permanent for any relavant timescale. There is still some | hope as cosmological observations feel less exhausted than | particle physics. But its a very awkward admission of defeat | after some fairly triumphant decades last century. ___________________________________________________________________ (page generated 2023-02-11 23:00 UTC)