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I think I need to ask this question now, because it's in my mind for several years and I just can't find an answer to it. After observations of those galaxtic rotation curves, it's pretty clear, that there must be some additional thing, responsible for the additional gravity that is needed to hold those galaxies together.

enter image description here

Dark matter is what would be a easy explaination -> just more matter, not visible to us, and it will be there for sure.

But wouldn't the most simple explaination just be, that the spacetime around the galaxy is warped? Doesn't it make sense for such big things to have a "torsional force" to spacetime itself? Or Maybe our frame of reference is warped as well, so if a star in a far away galaxy goes around in a circle, it's just our observation from our point of view. Here is a quick sketch of what I mean: It's not perfect, but with the explaination I think it makes a lot of sense. If our frame of reference or the spacetime is torn like this, we could actually observe stars moving in a circle while in reality they are not moving in a circle around the galaxy but in a more straight line away from it, if that makes sense. So it depends on the frame of reference ;)

enter image description here

I am not sure if it's the same thing described here, because I am not a physicist :(

https://en.wikipedia.org/wiki/Frame-dragging https://de.wikipedia.org/wiki/Lense-Thirring-Effekt

enter image description here

But to me this makes the most sense and is in my opinion the most easy explaination for this observation. You should never trust your eyes only if relativity is involved so I want to know if a real scientist had the same idea once and did some calculations ^^ This question has been in my head for years and finally it's out now, please don't roast me >_<

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    $\begingroup$ From the article on frame-dragging you linked: The Lense–Thirring effect is very small – about one part in a few trillion. To detect it, it is necessary to examine a very massive object, or build an instrument that is very sensitive. That is undoubtedly too small to explain the rotation curves, if there is even an effect. $\endgroup$
    – Allure
    Jun 18, 2021 at 10:35
  • $\begingroup$ Bear in mind as well that the evidence for dark matter comes from multiple angles. Galaxy rotation curves is the easiest one to explain without dark matter, but the other observations (especially the CMB data) are much, much harder. $\endgroup$
    – Allure
    Jun 18, 2021 at 10:36
  • $\begingroup$ Ah, thank you very much. But isn't it weird that spacetime behaves this way? like.. something that can be bended but not rotated or only ever so slightly... <_< It's very hard to imagine. $\endgroup$
    – Tankbuster
    Jun 18, 2021 at 10:43

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Welcome to Stackexchange. You will find many questions here regarding rotation curves of galaxies. No, warped spacetime isn't the right tree to bark up because the galaxy is non-relativistic, so Newtonian gravity is perfectly adequate. Yes, alternative theories of gravity (such as MOND) can explain this one evidence for dark matter as well but fail given the large number of other observations. Evidence for dark matter spans from cosmology to astrophysics, and from the Cosmic Microwave Background to galaxy clusters and galaxies.

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  • $\begingroup$ Thank you :) part of the question is why scientists talk about "dark matter" when to my understanding all they have found is a weird "gravitational interaction" Isn't that naming convention a trap? Even if this theory is good at predicting the movement of celestial objects, proving it that way doesn't proof that there is any matter involved, unless a giant telescope can picture a large ring of rocks or non Baryonic Dark Matter or whatever around a galaxy..... $\endgroup$
    – Tankbuster
    Jun 18, 2021 at 14:22
  • $\begingroup$ We have evidence for "weird gravitational interaction" from CMB, structure formation, BAO, gravitational lensing, galaxies, virialization, merging clusters, etc... all that can be explained at once if you assume it's due to dark matter. There is not a single alternative hypothesis that explains all these observations. $\endgroup$
    – rfl
    Jun 18, 2021 at 15:27
  • $\begingroup$ ignorance is a bliss $\endgroup$
    – rfl
    Jun 21, 2021 at 19:15

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