[HN Gopher] New dark matter map reveals cosmic mystery ___________________________________________________________________ New dark matter map reveals cosmic mystery Author : tooltower Score : 66 points Date : 2021-05-27 17:29 UTC (5 hours ago) (HTM) web link (www.bbc.com) (TXT) w3m dump (www.bbc.com) | fifticon wrote: | I am aware I have almost no knowledge about dark matter in | physics, but whenever it's mentioned, I can't help but think that | our modern 'dark matter', is the 'ether of the 21st century'. | That is, an interrim scientific theory that will eventually be | completely replaced by revisions of our physics. | caymanjim wrote: | I think most academics studying dark matter are pretty upfront | about not knowing what it is. The theories with the most fans | tend to not be very specific about the source, but agree that | it's most likely an "unknown something" with mass that causes | gravity. There are some theories like MOND that instead | postulate that there's no missing mass, but that our | understanding of gravity needs to be altered at galactic | scales. | | In any case, it's a placeholder, not a specific theory. There | are many candidate theories, but so far they're either | untestable or the tests have had negative outcomes. | UnpossibleJim wrote: | Just to put it in context, I'll share one of my favorite | (even though I think it's one of the more outlandish and less | accepted): | | In the Multiverse/Multidimensional universe theory, all of | these dimensions aren't necessarily in different universes. | Some are of different dimensions, laid over top of ours, but | we can't see them because we can't perceive the dimensions | they exist in. The only dimension that bleeds into ours, that | we can track so far, is gravity. This is what we call "Dark | matter". It is actually gravity leaking over from an "Nth" | dimension laid over our own that we can't perceive. | | Again, as to the veracity I can't say. And I wish I | remembered to author, but I don't =/ maybe I'll look it up | later and make an annotation. | 867-5309 wrote: | sounds like Brane Cosmology | https://en.wikipedia.org/wiki/Brane_cosmology | Hemospectrum wrote: | You've got plenty of scientists as company. There are cute | names like WIMP and MOND for different types of hypotheses | about what the heck dark matter actually is, or how to explain | what's going on if it doesn't exist at all. Each of these is a | huge headache for astrophysicists in one respect or another. | [deleted] | passivate wrote: | But in modern science we differentiate between | facts/hypotheses/laws/theories. What you're referring to is a | hypothesis - and those should be replaced with a more concrete | explanation - once we have it. I don't quite understand your | point about connecting it to ether though. I can't think of any | established theory in modern science that was completely | replaced - but I'm not a physicist either. | interestica wrote: | > 'ether of the 21st century' | | Or 'caloric' or 'phlogiston' | | https://en.wikipedia.org/wiki/Superseded_theories_in_science | tigerlily wrote: | Phlogiston, now there's a word I haven't seen in a while. A | lot of big names on that list of superseded theories by the | way :) | kiba wrote: | Dark matter is not a theory, it's a name for an unexplained | phenomena. | hitpointdrew wrote: | I also have almost no knowledge about dark matter in physics, | and maybe I am a complete moron. But what do you think is more | likely, there is this matter out there that no one has been | able to find in decades of searching, or the mainstream | assumptions/math on gravity are wrong/incomplete? I am going | with the later. | mr_mitm wrote: | It's interesting that this sentiment almost exclusively comes | from people with almost no knowledge about dark matter. | | What do you think is more likely, there is a theory that | makes all observations look exactly like there is invisible | matter without actually being invisible matter, or that there | is invisible matter? I am going with the latter. | | I also do not understand why laypeople are of the opinion | that all massive particles must interact electromagnetically. | If you are open to the idea that there is a massive particle | that doesn't, you got dark matter. | salty_biscuits wrote: | As a counterpoint, Neptune and Pluto were "dark matter" prior | to confirmation with observations. They were theorized to exist | due to their perturbations to observed motion of known planets. | dnautics wrote: | Well by that token so was the discrepancy in the precession | of mercury (which was not, as it turns out,matter). | da_chicken wrote: | I mean, we need to have a convenient term for a phenomenon even | if we don't understand it. What's the alternative? "The unnamed | phenomenon were some astronomic bodies behave as though a vast | quantity of matter were affecting them but that matter can't be | otherwise detected or identified"? | | In medicine, they often call it a "syndrome". A collection of | symptoms that together form a known pattern that is often | closely associated with a disease or disorder but has no | understood cause or origin (although some syndromes continue to | be called that after they are better understood). | | How do you think we arrived at terms like "planets"? We noticed | that some stars in the sky moved around while the rest didn't, | and we called them "wandering stars". We still call them | "atoms" even though that word means "indivisible". | | Weather is full of such names: rain, thunder, lightning, wind, | morning glory, dew, tornado, rainbow, etc. All these words for | material phenomenon existed long before we knew how they | worked. | | So what's wrong with "dark matter" as a name? | colordrops wrote: | I didn't read a negative judgment of the term in the | grandparent comment, just an observation. | da_chicken wrote: | Yes, and I'm challenging that observation. "Making an | observation" doesn't mean you're not subject to criticism | or questioning. | colordrops wrote: | But you were reading criticism of the naming in the | original comment, which wasn't there. | burnished wrote: | You haven't meaningfully challenged anything they said, | though. Your thing was an odd rant about the need to name | things (not a hot take), and theirs seemed more focused, | well | | >>That is, an interrim scientific theory that will | eventually be completely replaced by revisions of our | physics. | [deleted] | dnautics wrote: | > So what's wrong with "dark matter" as a name? | | it encodes a normative, biased prejudgement about what we | think explains the syndrome. | karmakaze wrote: | Exactly, the fact that it's a phenomenon gets lost--all we | have to do is find the missing mass (X-Y problem) that's | causing the gravitational effects. | tracedddd wrote: | What would you prefer the concept be called? | dnautics wrote: | Gravitational anomalies, gravitational discrepancy, | unexplained gravity effect? Hell, dark gravity, if you | want. | | Until the point where the observations are multimodal. | Then I'd be more comfortable assigning provisionally | normative names. Till then it should probably explicitly | reference the fact that all observations are | gravitational in nature. | mr_mitm wrote: | Except the very first experiment that was supposed to confirm | the ether showed that there is no ether, while every | astrophysical observation we made on any scale [1] confirmed | that there is dark matter. | | [1] | https://www.twitter.com/seanmcarroll/status/1371141258236764... | dnautics wrote: | We don't have any confirmation that it exists, we have more | observations that Newton's law is wrong. Moreover, these | observations collectively are unimodal; to date we only have | observations of more gravitational discrepancies, not | corroborating phenomena which correlate to the existing | discrepancies. | generalizations wrote: | I mean, the name is literally 'the stuff we can't see'. Dark | matter is very much just a question mark looking for an | explanation. | iainmerrick wrote: | The word "stuff" there is exactly the point. It's a lot more | specific than "just a question mark" -- the hypothesis is | that it's some exotic form of matter. | | If something like MOND gains popularity and there's no longer | a need to postulate invisible matter, it would be fair to say | that dark matter is incorrect and outdated, just like ether | or phlogiston. | generalizations wrote: | That would be fair. However, from what I've read MOND is | relatively unlikely. If its proponents can address the | biggest difficulties (e.g. not every galaxy appears to have | "dark matter") and make it somewhat more feasible, then I'd | agree the name is insufficiently broad. | dnautics wrote: | Not really, MOND and the like falls into the category of | "dark matter theory", and that's the problem with the name. | keithnz wrote: | Sabine is a great science (physics) communicator to the | "masses", she recently did an update on dark matter. | https://www.youtube.com/watch?v=4_qJptwikRc | Hypx_ wrote: | Summary: Both dark matter and modified gravity are true. | Could be caused by wave-particle duality. | claytongulick wrote: | Even "Ether" has come back around a bit in certain circles. | It's not called that anymore, I think it's called the "Grid" or | something similar. Milo Wolff discusses some of this in his WSM | theories, IIRC. | grenoire wrote: | It looks fascinatingly close to Perlin noise in its cloudiness. | mturk wrote: | When generating cosmological initial conditions for use in | simulations of large-scale structure, one common method is to | utilize random numbers (distributed about a known power | spectrum) in k-space and then transforming back to real space. | Some details can be found here: | https://enzo.readthedocs.io/en/enzo-2.3/_downloads/makeics.p... | miohtama wrote: | What is the projection used to display "the Universe" maps? What | is the left edge, the right edge, etc. They seem to be similar in | all articles but I have no idea how map relates to e.g. a night | sky? | motloch wrote: | Check out Fig 10 in https://www.darkenergysurvey.org/wp- | content/uploads/2021/05/... | Sharlin wrote: | The illustration in the article ([1]) seems to be a (slightly | cropped) Mollweide projection [2], in familiar equatorial | coordinates such that the north pole is top center, south pole | is bottom center, and the equator is a (imaginary) horizontal | line in the middle. The region of acquired dark matter data is | located in the southern hemisphere sky, which makes sense given | that the observatories used were in Chile. At the bottom you | can see the Magellanic Clouds, satellite galaxies of the Milky | Way which can only ever be seen from the southern hemisphere. | | [1] | https://ichef.bbci.co.uk/news/976/cpsprodpb/F39E/production/... | | [2] https://en.wikipedia.org/wiki/Mollweide_projection | tshaddox wrote: | I believe that image in the news article is cropped from this: | https://www.darkenergysurvey.org/wp-content/uploads/2021/05/... | | I found that image on this page, which seems to the be web page | created by this research group about this project: | https://www.darkenergysurvey.org/des-year-3-cosmology-result... | | From what I can tell, it's a projection of a view from the | night sky from one particular telescope on Earth. They sampled | a bunch of galaxies in an area about one eighth of the night | sky. | Sharlin wrote: | The background starfield appears, in fact, to be a projection | of the entire celestial sphere, all 360degx180deg of it, so | only a half of it at most can be seen at a time from any | point on Earth. | mellosouls wrote: | Mostly mysterious here is the detail from unconnected parties as | to the significance of the supposed deviation. | | It reads mostly like a puff piece from an academia PR person. Way | too vague in the article itself. | _rpd wrote: | To be fair, there were 30 new papers published: | | https://www.darkenergysurvey.org/des-year-3-cosmology-result... | | The overview paper appears to be this one: | | https://www.darkenergysurvey.org/wp-content/uploads/2021/05/... | | (the first published paper at the bottom of the page. I'd have | posted the title and abstract, but they've disabled copy- | paste.) | motloch wrote: | Yeah, as a cosmologist my reading of the DES results is exactly | the opposite than what the article mentions - new DES results | seem to show that one mystery (low values of S_8 in the low | redshift measurements) was actually resolved.. | | See the bottom of their Fig 14 in | https://www.darkenergysurvey.org/wp-content/uploads/2021/05/... | | The problem was that the green (CMB/Planck) and gray (weak | lensing) curves in the past were not overlapping as well as | they are now. To me the tension seems to mostly go away now. | gtsop wrote: | The only mysteries here are: | | 1. The certainty that an infinite entity (universe) can be | determined to have a very specific percentage (80%) of something | (dark matter) | | 2. The fact that the big bang is still being considered and cited | as the beginning (?) of the universe | | 3. That we have accepted terms such as "dark" matter and "dark" | energy in science as if some witchcrafty comes into play, as if | lord voldemort created the cosmos. | junon wrote: | The real mystery here is your point. | floxy wrote: | Off topic a little bit, but has anyone checked the work of the | guy who was trying to explain galactic rotation curves using | general relativity and gravitomagnetism? Which would lessen the | need for dark matter. | | https://link.springer.com/article/10.1140/epjc/s10052-021-08... | | https://news.ycombinator.com/item?id=26442021 | knzhou wrote: | Gravitomagnetism is a well-understood and experimentally | measured effect. It is also a very small effect, of the order | v^2 / c^2 where v is the speed of the sources. In the galaxy, | stars move with v/c ~ 1/1000, which means the gravitomagnetic | correction is one in a million. So while N-body simulations do | sometimes account for general relativistic corrections like | these, they're not nearly large enough to remove the | requirement for dark matter. | | The main thing the paper should do is explain why they think | the correction is a million times larger than the back of the | envelope estimate. But they don't. Instead, they try to solve | everything analytically, never plugging in numbers or reasoning | about what's big or small, leading to a forest of long | combinations of special functions. That's a reliable recipe for | making a mistake. | | That is the simple reason the paper has been ignored by | everyone in the scientific community and rejected from decent | journals. Of course, this hasn't stopped hundreds of fluffy pop | articles being written on it, or it getting posted every week | on HN. The blind leading the blind. | the8472 wrote: | Thanks, I assume the same cricitcism also applies to other | applying-GR-corrections papers? E.g. I saw one about | gravitational self-interaction leading to concentrating | gravity inside galaxies and starving the outside or something | like that. | [deleted] | raattgift wrote: | "Has anyone checked the work?" | | tl;dr: no, probably not. | | (I am aware of informal comments which have raised questions | about whether the disk is a singularity, which would destroy | the possibility of solving an initial value problem, unlike | already-in-use approaches. Additionally, the rotating disk | developed in the paper is clearly not present in non- | axisymmetric elliptical galaxies dominated by radial motion, | and so cannot replace dark matter in them; the paper only deals | with disk-like approximations of spiral and axially-rotating | spheroidal galaxies. There are plenty of galaxies where there's | no common rotational axis, but there's still a rotational curve | problem for stars and hydrogen gas clouds moving inwards vs | outwards. Lastly, the paper only claims to be a good | approximation in the limit of weak gravitational fields, so | very dense galaxy clusters (which will include the future | collision of the Andromeda galaxy with our own) are not covered | by the work in this paper: it makes no claim to be able to | predict the outcome of that collision, which breaks the Vlasov | condition. When you collide the dust and gas in these galaxies, | or galaxies like them in our sky, you will see lots and lots of | X-Rays and the like, while some fraction of _actually | collisionless_ matter would deform the galaxy and red | /blueshift its component spectra.) | | This is the work in question, fed into Google Scholar (sauce | for the goose as for the gander: Springer adds Google Scholar | links to each of the author's references) using the first URL | you supply: | | https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=http... | | We then hit "Cited by 3" | | https://scholar.google.com/scholar?cites=8505897096354068536... | | Not much there, and two are author self-cites, with no | citations on the newer papers, and no collaborators on these | papers. | | Glancing _briefly_ through the two newer ones, I got distracted | by one inconsistency which strikes me as glaring because the | "novel form" (author's words) the author builds strongly hangs | off it: I found "pseudo tensor", "pseudotensor" and "pseudo- | tensor" at the very least, and promptly gave up reading more | deeply. Choose just one, please, or don't try to use them at | all [1]. | | Aside: EPJ+ charges _authors_ a USD 3280 fee to publish each | article. It 's also not a journal working cosmologists or | extragalactic astrophysicsts would follow closely. | | Fortunately, _readers_ without institutional access can find | (again, via Google Scholar) essentially the same material on | researchgate (which says nothing either way about quality) so | one can glance without handing Springer $30+ for the two newer | articles. Even more fortunately, the link you supplied is open- | access, and can be read there (the PDF is nicely formatted) | without paying a fee. | | Finally, we can look the author up and see numerous papers with | collaborators in (mainly terrestrial applications of) plasma | physics, but the only papers on astrophysics (in the broadest | sense) are those three most recent ones. | | https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=%22G... | | My comments above are nothing at all like "checking the work", | but rather an excuse for why I personally would be in no rush | to do so. | | - -- | | [1] _Tensors_ (not _pseudo-_ tensors) are enormously useful in | General Relativity, because a _tensor_ solution solved in one | set of coordinates is solved in _all_ systems of coordinates | (including no coordinates at all). Matter should be specified | as tensors. This has been done (e.g. the (Faraday) | https://en.wikipedia.org/wiki/Electromagnetic_tensor). This | lets us arrive at an understanding that works for you standing | on your part of Earth using local notions of up, down, left, | right, forward backward; and me standing somewhere else on | Earth using my local notions of the same directions. It also | works for people in the ISS who have to pick a conventional | up/down, and whose local clocks tick fast (from _our_ standing- | on-Earth 's-surface perspective). It also works for coordinates | covering the solar system, the Milky way, or the entire cosmos. | But not all physical systems have fully developed _tensor_ | theories. For them we may choose to introduce a _pseudo-_ | tensor, which are valid only for certain coordinate systems. A | solution in one of those will work for some other systems of | coordinates but not _all_ , and if one is not careful in | choosing coordinates, one can get things spectacularly wrong, | like wildly wrong recoveries of the components of the energy- | momentum 4-vector ("In some coordinate systems you think there | is energy present when there is no energy in other coordinate | systems" is a common symptom, and in this context means "you | think you do not need a _generator_ of curvature beyond the | dust encoded in the _pseudo-_ tensor"). If one is inconsistent | about the spelling of _pseudo-_ tensor, I think that's a bad | sign about the extreme care in keeping different coordinate | systems mutually and fully consistent when using them. | | One runs into _pseudo-_ tensor inconsistencies fairly often in | cosmological contexts, so much so that it was dealt with in a | USENET sci.physics FAQ entry: | https://math.ucr.edu/home//baez/physics/Relativity/GR/energy... | nimish wrote: | The math is correct. Linearized GR and Newtonian gravity are | qualitatively and quantitatively different and at | "relativistic" scales we should probably see a difference! | | I don't have the cosmology background to evaluate more than | that unfortunately; it's just that the "Standard Model" of | cosmology uses a toy solution of GR (FLRW + newton). | | That said, it'd be wild if any major case of dark matter is | just an artifact of incorrect approximations. | OldGoodNewBad wrote: | Dark matter is the name for compound mathematical errors based | upon poor assumptions. We can't re-examine fundamental constants | or established theories, so we'll be kludging around forever with | this. | | It's not really important though because the practical | application of cosmology is nil. | ggggtez wrote: | > practical applications are nil | | It's 80% of mass on the universe. You don't think that has | applications in space travel? Maybe it doesn't effect your day | to day life, but it's rather ridiculous to say there is no | applications at all. | Analog24 wrote: | This is incredibly ignorant and pretty arrogant to actually | think that you know better than thousands of researchers who | presumably know far more about this than you. There are | numerous independent and unrelated pieces of evidence that | point to the existence of dark matter. You honestly think | they're all the result of mathematical errors that just so | happen to all point to the same conclusion? That would be quite | a coincidence. | aaroninsf wrote: | Pet theory: "dark matter" is gravitation leaking from adjacent | universes, in specific, from the juxtaposition of many divergent | universes. | | Most diverge in trivial ways, so dark matter concentration is | correlated with where matter is in our universe. | | Some relatively few diverge more drastically, so there is a | background. | | As someone outside the field I remain curious if there are | reasons this is inconsistent with observations to date, for some | models of the multi-world hypothesis. | hef19898 wrote: | Flying through hyperspace is not like flying over fields. Said | one famous pilot doing the Kessel Run in less than 12 parsecs. | Maybe Dark Matter is the real space shadow of stuff in | hyperspace the same way real space stuff has shadows in | hyperspace. | | Seriously, I cannot judge this level of physics, or just | understand them. It would make a nice addition to Star Wars | lore so. | tooltower wrote: | Another article in the Guardian: | https://www.theguardian.com/science/2021/may/27/astronomers-... | chadcmulligan wrote: | My theory is dark matter is the shadow of angels, there's more of | it where new galaxies are forming because there's more angels | there building the galaxies :-). | | Here's a movie of it in progress https://youtu.be/1x3RRrqJWKA | | I know this will get downvoted, but wouldn't it be funny if it | turned out to be angels and we're looking at heaven. It's | possible. ___________________________________________________________________ (page generated 2021-05-27 23:00 UTC)