Timeline for Is there a Dark Matter Paradox?
Current License: CC BY-SA 4.0
9 events
| when toggle format | what | by | license | comment | |
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| Jun 17 at 14:44 | comment | added | timm | Alfred, thanks for your explanations. | |
| Jun 17 at 14:37 | comment | added | Alfred | This hard calculation is certainly the topic of the paper for which you give the link. But, once more, it anly works for a galawy with its axis in the right direction. So since galaxies have axes in all possible directions, this paper is mathematically interesting in its own, but of no value in a cosmological sense. | |
| Jun 17 at 14:36 | comment | added | Alfred | @timm Here we are considering a galaxy with normal matter in it. So the equations for the distribution of mass in the spacetime (still axisymmetric because it is assumed that the axis of rotation of this particular galaxy is parallel to the preferred direction) determined by the combination of the outer axisymmetric spacetime far away and the deformation due to the normal matter of the galaxy is rather complicated. This is a long and hard calculation, because the repartition depends on the precise deformation of spacetime which is affected by this very distribution. | |
| Jun 17 at 12:33 | comment | added | timm | Alfred, If I understand you correctly it is well known that an axisymmetric spacetime with cylindrical symmetry must have flat rotation curves due to the chosen symmetry. Is that right? But why then perform the calculation if the result is fixed from the start? | |
| Jun 16 at 22:10 | comment | added | Alfred | @timm The paper you refer does not use the FLRW-spacetime ! It is homogeneous but not isotropic. It has a preferred direction and is axisymmetric around that preferred direction. Therefore those spiral galaxies with their axis in that direction can be explained without Dark Matter. But observation shows us that galaxies exist with axes oriented and thus this paper is irrelevant for our Universe. It is just a nice amusing model, but without any connection with our Universe. | |
| Jun 16 at 20:56 | comment | added | timm | Thanks for clarifying 2. - "However, I have very serious doubts about the solution proposed in the preprint you link to in the top of your question. It supposes an axisymmetric universe." Not sure if I understand this point. The Schwarzschild Black Hole universe can be understood as being embedded in the FLRW-spacetime (as far as I know). Doesn't that apply to the spiral galaxy universe too? | |
| Jun 16 at 17:18 | comment | added | Alfred | @timm The paper does not indicate at all that Dark Matter does not exist. Axial symmetry can only explain the rotation curves of galaxies the axes of which are exactly (or within a few degrees) of the axis of symmetry of the Universe, and makes the rotation curves of galaxies much more difficult to interpret for the much more numerous galaxies with axes at large angles. So 2. is not relevant. | |
| Jun 16 at 16:23 | comment | added | timm | Thanks. "I have no doubt that the calculations done in that paper for a single galaxy are correct." The paper doesn't claim anything else. Given that's correct there seem to be two possibilities. 1. Dark matter exists, then we stay with the paradox I mentioned. Any idea how to resolve it? 2. The paper indicates that Dark matter does not exist meaning that the L-CDM model is wrong. 3. ? What do we prefer, 1. or 2. ? How to argue differently? | |
| Jun 16 at 14:00 | history | answered | Alfred | CC BY-SA 4.0 |