[uoaei]

The flaw in this reasoning is ironically a philosophical (epistemological) one: by what authority is it said we "know" the laws of physics? We "believe" theories, even go so far as to sometimes call them "laws", but as we've seen with Newtonian interpretations (the "law" of gravity) they can obviously be superceded by more elegant, positive (not merely deductive) theories, i.e., general relativity. Who is to say our current understanding is the correct or best one? Granted, it's a good place to start for the experimentalists, but for some reason theoreticians have also drank the Kool-aid rather than honestly examining the other proposed theories.

> The known laws of physics have been formed on math that checks out and is consistent with all our other observations

You will of course note that "all the other observations" conveniently reside in the limit of high-mass-density regions of spacetime, where other theories also expect the current best theories of physics to hold. Where the confusion still lies is in the low-mass-density regions. At least other theories posit some explanation besides "there's still mass it just exists in other dimensions". Sounds like sci-fi crackpottery when put so plainly, but I'm sorry to say this characterization is accurate enough for our needs here.

> where does the scepticism end?

Strange application of slippery slope fallacy. It obviously ends where the theories still hold, i.e., high-mass-density regions. This is IMO enough of a response to most of your "philosophical" arguments.

No one's denying that particles exist. I'm only arguing for a theory that actually posits something besides "oops there's a gap". You've articulated a reason why dark matter is offered but it is nothing more than a deduction about where matter would be should it exist. I swear I'm going to have to spin up some cycles on the cluster to fit dark matter models on a geocentric universe to get you people to understand the non-reality of any dark matter paper.

Gosh I love being mansplained on this site by people who obviously have no personal experience with this stuff. Really gets me going.

Edit to reply to your edit:

> when gravity is more of an emergent property of the geometry of spacetime?

Emergent gravity and dark matter are incompatible theories in their usual forms, though there's probably ways to mash them together into a chimera. I suggest reading more into emergent gravity -- entropic gravity is interesting but still in its early stages. I'm not advocating for any particular theory, just humility from those who repeatedly insist that dark matter is already correct and we just need to find the matter.

> since alternative theories (a) also include dark matter, to a lesser extent

No they don't.

[freedomben]

> Gosh I love being mansplained on this site by people who obviously have no personal experience with this stuff. Really gets me going.

I say this in the hope that it's constructive. You should try not to sink to this level of rudeness and assumption of other people's motives/situation/perspectives. Not only is it a rude assumption about something that (to me) looks to be a good faith attempt at conversation that also clearly took some time to compose, but it's an emotional response that shows that you take it personally and emotionally when you're challenged. I'm not implying that GP is an idiot (I'm too ignorant on this subject to know), but I've been challenged in subjects where I'm well versed by idiots many times and I tend to react the same way that you did. It can be enraging (especially when surrounded by down votes and social/group reinforcement from other idiots), but you immediately lose any power of persusasion with other people when you stoop to that level rather than keeping on the high road and keeping it factual/scientific. IMHO you're rarely if ever going to convince the person you replied to, but the third party observers are often much more persuadable. They're the people I mainly try to write comments/replies for.

[uoaei]

I'm not responding to the challenge to my points. I'm responding primarily to the infantilizing tone explaining how science works, and especially triggering is how inaccurate it is yet delivered with such confidence. It often feels like commenters want to cosplay intelligence and see how far they can get -- in other words, there's a lot of bullshitters on this website.

If others cannot judge an argument on its merits, that is not really something I can control. I understand your point about rhetoric re: persuasion I'm just resistant to playing civility games in what should be a facts-based discussion.

I acknowledge I am impatient with those who refuse to offer good faith responses. In my opinion such good faith would mean engaging with the facts of the matter not running through a phil.sci. 101 lecture, however sincerely.

Thanks for your engagement. Your point about third parties is a good one, one I keep forgetting and re-learning.

[wanda]

It was not my intention to trigger anyone. I only wanted to say why dark matter is given the time of day. If I came across as condescending or as a know-it-all, I apologise, it was not what I wanted at all.

I also must apologise for my use of the term "emergent property" regarding gravity — judging by your response, I seem to have alluded (unintentionally) to a whole other theory of gravity; I only wanted to say that gravity itself is the curvature of the geometry of spacetime rather than a force in the conventional way it is described.

Also, regarding alternatives still requiring dark matter, it is my understanding that MOND and its derivatives explain galaxy rotation curves but not other phenomena that dark matter is purported to resolve (galaxy cluster formation/structure, gravitational lensing, CMB). If I am wrong about this, I would welcome correction. On the other hand, if your comment simply meant that there are alternatives to DM and MOND that require no DM, fair enough, I should have been clearer and said that some of the foremost competitor theories still require DM.

But I stress again, I am not fighting DM's corner or saying that alternatives are wrong. My stance on it is irrelevant, and I have no more belief in it than any other explanation, belief is irrelevant and doesn't enter into the matter. I was just saying that I understand why a theory that inflates mass arbitrarily, and understandably ruffles some feathers as a result, is given any credence at all.

Personally, I understand your frustration with DM, it does not seem like very good science to let unexpected or inexplicable observations make us simply add parameters without making further predictions to test if that's the right thing to do. Does seem like we're manipulating facts to fit the theory where we should be altering the theory to fit the facts.

Since DM is a substance that, for all intents and purposes, defies detection by any means at our disposal, it makes no further predictions, it just lets us push the square block into the round hole — what we should be doing is finding the square hole.

[nyssos]

> Since DM is a substance that, for all intents and purposes, defies detection by any means at our disposal, it makes no further predictions

This is completely untrue. All serious dark matter candidates are observable. For example:

- MACHOs should show up in gravitational lensing surveys. We did the surveys, they didn't, MACHOs were rejected. Exactly the way it's supposed to work.

- Axions convert to photons in sufficiently intense magnetic fields. ADMX has ruled out part of the parameter space for axions and is undergoing upgrades to test the rest of it.

- Other WIMPs still interact via the weak force, and therefore with nucleons. There are many experiments looking for WIMP scattering. A few of them have gotten signals but not enough to be convincing.

Dark matter candidates are not just "mass with no further properties" sitting out there to make the model fit. They're proposed extensions to the standard model (which is nothing but proposed extensions to quantum electrodynamics which ended up working out), and therefore very tightly constrained by the standards of any other scientific field.

[uoaei]

Unfortunately those are all candidates which are conjured ex post facto to explain the "mass with no known properties" that is inferred. As you say, none of them are convincing. It's also just bad science to reach for factors that are just-so explanations of the observed phenomena.

[nyssos]

They are not. MACHOs definitely exist, it just turns out there aren't nearly enough of them. Axions were proposed as a solution to the strong CP problem years before anyone went looking for dark matter candidates. Sterile (i.e. right-handed) neutrinos are motivated by the need to explain why left-handed neutrinos, contrary to the predictions of the standard model, have mass. Supersymmetry was originally an attempt at strong-electroweak unification.

[wanda]

At no point did I say the laws of physics are beyond question or doubt, and neither did I say dark matter is correct.

I just said it makes more sense to give DM priority because what is the point of having a model if you don't start from it.

Also why are you being so hostile towards me exactly? I didn't express any love for dark matter or the standard model, and I am not a fan of perpetuating a status quo or any form of academic dogma.

All I said, quite unsuccessfully it would seem, is why people think its likely for dark matter to be there — because if you add in "invisible" mass with existing laws of physics, you get something that looks like what we see through our telescopes. I think many would prefer to suppose that there is non-EM-interacting mass (a lot of it apparently), than there being as yet unknown behaviours of gravity/spacetime geometry, which we like to think we understand pretty well.

Though I agree that we don't understand the universe as well as we like to think; and that the universe is not intuitive at all most of the time; and a preference based on how intuitively likely something seems is irrelevant to what the truth will turn out to be.

Edit: just FYI, I am not downvoting your responses by the way. I am not bothered if you dislike me or disagree with things I have said, though these two things should be distinct from each other.

I'm nobody and I didn't seek to "mansplain" anything whatever this term is supposed to mean. I was just talking, always happy to debate, something I thought people came here to do. I won't make the mistake again.

[forgotpwd16]

>"there's still mass it just exists in other dimensions"

What? Dark matter is there. Leading models consider it to be particles that don't interact with e/m field and interact weakly with gravity so is undetected in low-density regions. That doesn't make it other-dimensional.

>Sounds like sci-fi crackpottery

Like the prediction of particles in standard model? Is Higgs boson that went undected for 50 years sci-fi crackpottery?

There're issues with dark matter but it also (sadly some may say) happens to be the best explanation of the observed phenomena since all alternative models fall (plus although simpler at first sight quickly get more complex) in more ways than dark matter.

>I suggest reading more into emergent gravity

Emergent (either entropic or induced) gravity has nothing to do with the comment. It's obvious what GP meant. The correct should've been intrinsic property but this is nitpicking.

[uoaei]

Being able to fit models is very far from being able to say "it's there", especially the kinds of models that are being fit. See my responses to sibling comments. "Leading theories", especially given the human impulse toward consensus, got the charge of the electron wrong for a long time before the culture readjusted and decided to look fresh at the problem with new experiments.

> happens to be the best explanation

The people who repeat this in popular science are just repeating what they hear from academics who, surprise!, have invested their entire career and reputation in the scientific community on that being true. Science demands more skepticism and interest in the truth than parroting status quo. It's also technically true only if you assume that explanations built on fitting extremely flexible nonparametric models are theories, but that doesn't seem like a mindset that's very interested in those theories representing truth per se.

> Like the prediction of particles in standard model? Is Higgs boson that went undected for 50 years sci-fi crackpottery?

Transparent straw man. Barely worth acknowledging.

[raattgift]

> interact weakly with gravity

It would be better to rearrange this to "interact gravitationally, and maybe non-gravitationally at the scale of the weak nuclear force".

In the standard cosmology \Lambda-CDM, cold dark matter ("CDM") is allowed to interact at the scale of the weak nuclear force (wnf), which may allow participation in nuclear interactions. This motivates the search for direct detection in various track and scintillator experiments, where a WIMP (weakly interacting massive particle) could take recoil energy from an atomic nucleus, the latter leaving behind a trail of charged particles and/or emitted photons. There are of course other hypothesized interactions between WIMPs and normal matter which do not literally engage the wnf, but instead have some new interaction at no more than the same energy scale ("weak scale"). And for completeness, there are CDM models which have stronger but rarer individual interactions which average out to the weak scale (or effective collisionlessness) across volumes comparable to the size of galaxies or galaxy clusters.

(In the standard cosmology what matters is that the equation of state for dark matter is 0 or close to it so that expansion dilutes it away like cold baryons; in structure formation and galactic dynamics it's more important that most dark matter is in a halo outside the luminous structure. Both are incompatible with decays or collisions which emit relativstic particles (w > ~ 1/6 leads to early evaporation of overdensities; galactic dynamics is less tolerant of (non-radiative) clumping and other mechanisms which concentrate/gravitationally-collapse halos).

> interact ... with gravity

In a system of coordinates that absorbs linear and angular momentum, all matter -- dark or otherwise -- interacts gravitationally in proportion to its mass (or energy-density).

In General Relativity, this is the universality of free fall, which descends from Newton's Law of Universal Gravitation.

Unless we modify or abandon General Relativity, a dark matter particle and an alpha particle occupying the same starting point and having the same initial velocity will follow the same trajectory together forever barring some interaction (examples: intrinsic: one of the particles decays emitting radiation, or there is some weak scale interaction between them that imparts a recoil on one or both of the initial alpha or DM; extrinsic: scattering of a photon off the alpha, or the alpha captures electron(s) imparting a recoil -- a force that shoves the alpha onto a different trajectory, a non-gravitational acceleration). This is the weak equivalence principle (WEP), <https://en.wikipedia.org/wiki/Equivalence_principle#The_weak...> from a somewhat Fermi-Walker perspective; the "weak" in WEP is unrelated to the weak nuclear force.

Finally, dark matter and baryonic matter (and all other matter and radiation) interact the same way with the curvature of spacetime. If dark matter and baryons interact non-gravitationally at all, the (averaged) interaction is at no more than the weak scale. \Lambda-CDM does not require any non-gravitational interaction between CDM and baryons.

> so is undetected in low-density regions

Density of what?