[HN Gopher] Why dark matter feels like cheating (and why it isn't)
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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.
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