[college_physics]

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

[lisper]

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]

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.

[mr_mitm]

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

[naasking]

> 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.

This is so oversimplified that I'd call it incorrect. The galaxy rotation curves cannot be predicted a priori using dark matter models, the distribution has to be tuned a posteriori to fit the curve. This is in contrast to MOND which can make successful a priori predictions. There's clearly something missing in the dark matter picture.

[college_physics]

This simply says that the gravitational footprint of dark matter is consistent. The opposite would be quite remarkable though.

[zinclozenge]

I've posted this before, but never in my entire academic physics career did I ever get the impression, either in coursework or research, except in the courses covering classical theories (ie mechanics, electrodynamics, etc). As soon as you start learning things beyond non-relativistic quantum mechanics, it's consistently drilled into us that all we have are _effective_ theories. For god's sake, we don't even have a Grand Unification Theory, let alone a Theory of Everything.

[college_physics]

Unifying gravity requires insights into energy scales so remote from our own that you cant hold against eg string theorists for not nailing what happens at such extremes where fundamental notions may break down

Dark matter, being (likely?) a low energy kind of thing feels like a genuine gap within the realm we claim as understood. In this sense its more fascinating.

[at_a_remove]

This was originally true of the neutrino. It was just a placeholder. Took quite a while before we found out that it wasn't just a convenient mathematical fudge factor.