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This is the picture and article that made Dark Matter "click" for me, as a total layman: https://www.nasa.gov/mission_pages/chandra/news/08-111.html https://www
by MrPatan 4y ago
This is the picture and article that made Dark Matter "click" for me, as a total layman: https://www.nasa.gov/mission_pages/chandra/news/08-111.html https://www.nasa.gov/mission_pages/chandra/news/08-111.html
With lensing we can "see" that dark matter (or whatever) passed through each other on a collision, while some "normal" matter actually collided and stopped in the middle (or slowed down).
Now, maybe "modified gravity" still makes sense somehow, but how come this modified gravity is following the previous path of a cluster in space like that?
This is as opposed to "The galaxies rotate too fast" argument, where the obvious problem is "Maybe it's rotating exactly as it should and you just don't know how fast it should rotate?"
This is a comment entirely about what's inside my head, not about the actual astronomical merit of any theory.
- HardlyCurious 4y agoInterestingly, YouTuber and physicist Sabine Hossenfelder claims that same cluster is actually evidence against dark matter.
- MrPatan 4y agoWell, that's swell. Can you point to the specific video? I see a few about dark matter and want to have a look. Now that I thought I finally got the point....
- NotYourLawyer 4y agohttp://backreaction.blogspot.com/2021/05/dark-matter-situation-has-changed.html http://backreaction.blogspot.com/2021/05/dark-matter-situati... > Then there are collisions of galaxy clusters at high velocity, like the bullet cluster or the el gordo cluster. These are difficult to explain with particle dark matter, because dark matter creates friction and that makes such high relative velocities incredibly unlikely. Yes, you heard that correctly, the Bullet cluster is a PROBLEM for dark matter, not evidence for it.
- halter73 4y agoThat's funny. The parent's NASA link uses the high relative velocities as "direct evidence for dark matter and supports the view that dark matter particles interact with each other only very weakly or not at all, apart from the pull of gravity." The lack of friction seems obvious with this view of limited interaction between dark matter particles.
- MrPatan 4y agoThat's also how I understood it. No photons, no electrical interaction, no friction.
- floxy 4y agoChandrasekhar dynamical friction is just a function of gravity: https://en.wikipedia.org/wiki/Dynamical_friction https://en.wikipedia.org/wiki/Dynamical_friction
- MrPatan 4y agoWell, ok, but that means there's still _less_ friction with those particles because they don't interact electrically, right? So I still would expect the same result of the 4 blobs in different positions in space. What's wrong with that view?
- HardlyCurious 4y agoI'll take a look and see if I can remember which one. Would be great if there was a way to search videos CC to skip to timestamps...
- burnerburnito 4y agoIf a video has manmade captions and not auto-generated, you actually can check the transcription which has timestamps.
- HardlyCurious 4y agoAh found it. https://youtu.be/4_qJptwikRc https://youtu.be/4_qJptwikRc 6:50 or so for relevant piece.