[HN Gopher] Checking in on troubles with dark matter
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Checking in on troubles with dark matter
Author : xqcgrek2
Score : 27 points
Date : 2023-08-05 13:56 UTC (9 hours ago)
(HTM) web link (tritonstation.com)
(TXT) w3m dump (tritonstation.com)
| magicalhippo wrote:
| Was just watching an "intro" lecture[1] on DM over at PIRSA, as
| part of TRISEP 2023[2], a summer school for grad students. There
| he goes over some of the arguments for DM, but with more math and
| details than the usual popsci stuff, but still at a fairly
| accessible level.
|
| I'm just a layman but to me the Bullet Cluster[3] seems very hard
| to reconcile with just modified theories of gravity. On the other
| hand it seems unreasonable to me that General Relativity doesn't
| need corrections due to quantum mechanics, and as this article
| mentions LCDM has a bunch of other issues.
|
| So how about both? Some non-interacting "dark" particle(s) and
| some quantum corrections to General Relativity. Anyone know about
| work trying to combine the two approaches, and see how things
| stack up?
|
| [1]: https://pirsa.org/23060067
|
| [2]: https://pirsa.org/C23020
|
| [3]: https://en.wikipedia.org/wiki/Bullet_Cluster
| naasking wrote:
| Milgrom's view on the bullet cluster:
|
| http://astroweb.case.edu/ssm/mond/moti_bullet.html
|
| LCDM also apparently fails to explain the velocity of the
| bullet cluster, so it's not like it's slam dunk for DM
| (collision velocity better matches MOND).
|
| Some MOND proponents posit "sterile neutrinos" to complete the
| theory in some cases, like the bullet cluster. And then there
| are bullet cluster-like failures for LCDM that get papered
| over:
|
| https://tritonstation.com/2016/12/23/crater-2-the-bullet-clu...
|
| There have also been recent measures that suggest that much
| existing data is actually more consistent with warm regular
| matter that has so far gone undetected rather than cold dark
| matter.
|
| The dark matter "consensus" is a flimsy facade covering a lot
| of gaping holes. Something's gotta give.
| sebzim4500 wrote:
| It's a bit of a false dichotomy. Even the MOND people recognize
| that you need dark matter (even if they don't use the term) to
| explain the bullet cluster, so it isn't really dark matter vs
| MOND.
|
| It's "dark matter" vs "MOND + dark matter"
| magicalhippo wrote:
| I admit I haven't followed the field closely, but when
| reading papers about MOND I've never gotten that impression.
|
| Do you have some examples?
| thriftwy wrote:
| The observation that we seem to live in the emptiest region of
| known space should cast doubt on our understanding of universe.
| Are we watching through fish-eyed lens? Something kills life
| after critical concentration? Funny third option?
| SirIsaac wrote:
| Sooner or later, the physics community will come to their senses
| and realize that every massive particle is surrounded by its own
| dark matter halo. This is the reason that measurements of the
| gravitational constant G suffer from a high uncertainty problem
| not seen with other physics measurements.
|
| Then it will become obvious that the halo is a neutral electric
| field created by real photons, not virtual photons.
|
| Rebel Science
| SubiculumCode wrote:
| hello crankgpt!
| tlogan wrote:
| Can the Modified Newtonian Dynamics (MOND) theory adequately
| explain the Cosmic Microwave Background (CMB) radiation and the
| persistent mass discrepancies observed in galaxy clusters?
|
| Furthermore, as a laiman, I'm puzzled by how certain versions of
| MOND requires introduction of new fields. Doesn't this
| effectively the same as saying there is some new particle we
| neeed to discover?
| aeneasmackenzie wrote:
| There is a relativistic MOND theory that has predicted the CMB
| spectrum[0]. And perhaps. MOND is first of all observational.
| AeST is just the latest (and AFAIK best) attempt to create a
| theory that reproduces the MOND acceleration artifact.
|
| 0: https://tritonstation.com/2023/01/13/what-we-have-here-
| is-a-...
| idlewords wrote:
| MOND is really a rule without a theory; it simply posits that
| there is an acceleration cutoff below which gravity does not
| obey an inverse square law. This conjecture has been shown to
| have impressive predictive power, and it naturally explains a
| bunch of observations that are not obviously related and
| require fine-tuning in a dark matter paradigm. The blog linked
| here goes into a lot of detail on those observations, as well
| as observed phenomena that don't seem to fit well with MOND.
|
| What the theory underlying MOND actually _is_ is anyone 's
| guess, and an area of active conjecture. But that's just as
| true for dark matter.
| SirIsaac wrote:
| Another equally plausible MOND model is one in which the
| gravitational constant G increases with distance. This is
| what is observed in the orbits of stars around the center of
| a galaxy.
|
| Of course, this is a pseudo-increase caused by, you guessed
| it, dark matter.
| ramraj07 wrote:
| Are you still a layman if you're able to ask these questions
| though?
| jraines wrote:
| If you got at least halfway in to Sean Carroll's recent 4
| hour podcast on the subject -- yes ;)
| OldGuyInTheClub wrote:
| I wasn't aware of MOND's successes beyond rotation curves; the
| author lists three more. It does seem like LDCM and MOND are both
| feeling different parts of the same elephant and that someone
| will eventually see the whole critter. This TritonStation fellow
| is worth reading.
|
| So many sophisticated experiments have failed to detect dark
| matter particles. So many theories have predicted still
| unobserved phenomena. On the other hand, many of us side-eyed
| LIGO for decades but when it worked, it worked. Black holes were
| unphysical and abominations until they weren't.
| idlewords wrote:
| That blog is worth a deep dive, it goes into deep and
| fascinating detail about how this stuff is measured, as well as
| the sociology of the field, which has continued to add
| epicycles to dark matter theory to an extent that is starting
| to make even true believers uncomfortable.
| sebzim4500 wrote:
| >which has continued to add epicycles to dark matter theory
| to an extent that is starting to make even true believers
| uncomfortable.
|
| You certainly get this impression from pop-sci, but are there
| prominent people in the field actually saying this? Obviously
| sometimes the scientific consensus can be wrong (see the
| planetary nebula 'debate' for example) but normally
| contrarians turn out to be incorrect.
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