Comment by throwawaymaths
Comment by throwawaymaths 5 days ago
this should be able to be used to test dark matter theories.
Comment by throwawaymaths 5 days ago
this should be able to be used to test dark matter theories.
it's a theory. when you present multiple observations just the fact that you group them together is not a value-free action and implies a common cause. calling it an observation is a crude and philosophically improper attempt to elevate it to a less refutable status.
This feels like you'd say that just because apples fall from trees and a bowling ball falls in much the same way when tossed off a building, that grouping those things together implies a common cause and that we should call that cause a theory because we aren't 100% certain that they are caused by the same effect.
They could be two different reasons.
I do prefer Occom's razor for these things. We've seen a bunch extremely large celestial objects move in ways that our models cannot account for with the things that we can see. Sure, there could be more than one thing out there causing all of those extremely similar effects. But that's far less likely than there just being one reason.
It's pretty reasonable to invoke occam's razor for claiming that in general unexpected galaxy rotation curves have a common explanation. It's another thing to claim without blinking an eye that these are phenomenologically connected to baryon acuoustic oscillations in the CMB (which is what Angela does)
Since it's been a _long_ time since my physics undergrad I honestly can not speak to how baryon acoustic oscillations tie into dark matter. Hell the paper describing it came out after my first trip through college!
I'll confess the paper is a bit over my head. Astrophysics was never my passion and I became a software engineer right out of college anyways, so I'm a little rusty. However, in the 2005 paper they state that the BAO, specifically the way that the BAO has propagated, can't be explained by baryonic matter alone, which in their words would show a much larger effect than observed. This seems to be yet another observation that is consistent with dark matter.
However, since you must be a working astrophysicist, could you enlighten me with what you think is wrong with the interpretation of those observations? Do you think the >3 sigma confidence isn't enough for astrophysics?
I am genuinely curious.
This is, in fact, part of the support for Dark Matter, both with galaxies (the amount of lensing requires the galaxy to include a lot of Dark Matter) and between galaxies, where other lensing effects occur that can only be explained by filaments of Dark Matter between galaxies and galaxy clusters.
This is a great podcast, with episode 6 concentrating specifically on Dark Matter and the evidence for it: https://podcasts.apple.com/us/podcast/crash-course-pods-the-...
no. you can't say it's evidence for dark matter versus any given other theory until after you have computed the expected metrics created by any alternative theory.
in any case, you can't say it's support for dark matter in this specific case without actually running the numbers (what are the rotational speeds and what is the bending curvature)
dark matter halos must have a somewhat specific distribution that goes beyond the perimeter of the visible galaxy itself.
however the more that i think about it this example is likely to be unhelpful. the closer galaxy looks elliptical and most dense elliptical galaxies "have no dark matter" (in basic MOND this is a phenomenon that falls out if the gravity law). We'd really need lensing from a more "normal" looking galaxy.
I wasn't saying, as a layman, that this is evidence for Dark Matter. I'm saying that the current thinking in astrophysics is that this is evidence for Dark Matter. Katie Mack, the astrophysicist in the podcast I linked, is a reknowned expert, and discusses how running the numbers on exactly these things provides evidence for Dark Matter, and how alternatives fail.
then she is being misleading, at best. To date no observed galaxies (versus galaxy clusters) have had the arrangement (as is in this image) wherein the galaxy is so perfectly in line with a background galaxy and close enough to estimate the rotation curves (and the background galaxy is of the right disposition to know if dark matter halos extend beyond the galaxy and estimate by how much space). Without both those factors it's really difficult to do a proper correlation of dark matter distribution around galaxies and the observed light bending.
They're not collecting all of this data to make pretty pictures, it's going to be used to test all sorts of theories. Ones that explain Dark Matter as well.
(I do agree with Angela Collier, youtuber nee physicst, Dark Matter is not a theory, it's an observation. We've looked out into the universe and have seen something that we call Dark Matter that our current theories don't match up with.)