I was inspired to write this blog post when I saw an advert online for "Dark Matter Day", which mainstream physics is trying to set for 31st October. I think it should actually be celebrated on the 32nd October, since dark matter doesn't exist. How do I know it doesn't exist? This blog entry is intended to present some of the evidence against it.
1. Renzo's rule. When we look at galaxy rotation curves (how the orbital speed of the stars varies as you go out from the centre) the variations in the orbital speed are always coincident with variations in the light intensity (ie: the visible mass). The rotation curve follows the light curve. This means that the speed is determined totally by the visible mass, and not by anything invisible. Renzo's rule has been generalised and broadened by Lelli et al. (2016) (see the references below).
2. Milgrom's acceleration cutoff. As pointed out by Milgrom a long time ago, galaxies only start to misbehave when the acceleration of the stars as you go out from the centre drops below about 2x10^-10 m/s^2. This dynamical relation is very difficult to explain with any sort of matter distribution. This cutoff is also suspiciously close to the cosmic acceleration, a clue that should not be ignored.
3. Globular clusters. In order to fudge general relativity to predict galaxy rotations right, astrophysicists have to add dark matter in a particular smooth halo in and around the galaxies, and so they have to invent physics for it to stay smoothly spread out. This is why the result of Scarpa et al. (2006) is so crucial. They showed that tiny globular clusters (little conglomerations of stars within galaxies) also showed a galaxy rotation problem writ small and this cannot be explained by dark matter, which must be smooth and not congregate, without messing up the full scale galaxies.
4. Even more revealing than globular clusters, binary star systems definitely should not contain lumps of diffuse dark matter, and yet when two binaries are orbiting very far apart (so-called wide binaries) they too show a galaxy rotation problem writ even smaller (Hernandez et al., 2012).
5. The cusp-core problem. The lambda-CDM (cold dark matter) model dominates astrophysics since it predicts the CMB spectrum (if you set its arbitrary numbers right), but when it is used to predict the distribution of dark matter in galactic centres, it produces a distribution that causes GR to predict the wrong rotation speeds, and so this disribution is 'adjusted' (de Blok, 2009). A fudge of a fudge!
6. Lack of evidence. Dark matter has not been found after 40 years or so of expensive looking, something not mentioned by most cosmology books, just as the aether was not found..
7. Philosophical objections. dark matter was invented because general relativity did not predict the rotation of any real galaxies. It had failed, but instead of changing the theory astrophysicists worked out with computers what complex distribution of invisible matter was needed to make GR work and went to look for it. This has worked in the past, look at Neptune which was needed to explain the odd orbit of Uranus, but Neptune was a small amount of mass in the plausible shape of a planet, whereas dark matter is the invention of 10 times as much mass as is seen (sometimes up to 1000 times), in a completely arbitrary distribution, and requiring new dark-physics to go with it. You can explain almost anything with a hypothesis like that, and yet predict nothing..
8. Quantised inertia predicts the rotation of disc galaxies of all scales very simply, non-arbitrarily and without dark matter (see my latest paper).
As said above, I shall celebrate Dark Matter day on the 32nd October and I invite you to join me :)
Lelli, McGaugh, Schombert & Pawlovski, 2016. One Law To Rule Them All: The Radial Acceleration Relation of Galaxies https://arxiv.org/abs/1610.08981
Scarpa et al., 2006. Globular Clusters as a Test for Gravity in the Weak Acceleration Regime https://arxiv.org/abs/astro-ph/0601581
Hernandez et al., 2012. Wide binaries as a critical test for Gravity theories https://arxiv.org/abs/1205.5767
de Blok, W.J.G., 2009. The core-cusp problem. https://arxiv.org/abs/0910.3538