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This is related to this question which provided evidence about dark matter, and this question which asked what would happen if dark energy started disappearing.

This question assumes that dark matter is an actual real 'thing' of 'something', just like any other known particle.

The question I wanted to ask is, what would happen if all dark matter was removed from the universe?

Would the galaxies rotation speeds just slow down or are there any other known (or realistically assumable) effects (locally, or on the universe scale)?

Update: what I am looking for is are the 'beneficial functions' that does dark matter provide, sort of like its 'raison d'être'.

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  • HBO, "The Leftovers" . That's only partly a joke. – Carl Witthoft Oct 29 '15 at 18:07
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    rotations will not slow down, rather the galaxies and galactic cumulus would spread apart (but nothing will happen with smaller objects such as stars) –  Oct 29 '15 at 18:26
  • All else being equal, if you remove dark matter from the universe, then there wouldn't be a universe as you know it. The remaining matter would not have enough gravity to form galaxies and stars and the universe would be accelerating much faster. To be honest, though, you can't do this. Dark matter exists for some very deep reason which we just don't know, yet, and you can't simply cut it out and do a "what if" analysis in science. That's by definition of science as a rational explanation system for the observed world. – CuriousOne Oct 29 '15 at 20:24
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    @CuriousOne, you seem to don't like experiences of thought, how useful they can be to figure the role of things for many people :-) . A way to understand the role of dark matter in the balance is to evaluate the unbalance that would result in the proposed case. So that's not a bad question. ;-) – Fabrice NEYRET Oct 29 '15 at 23:04
  • @FabriceNEYRET: Quite to the contrary, but removing something already observed is not a thought experience (or do you mean though experiments?) but a plain violation of scientific reasoning. We have known about dark matter for longer than you live (unless you were born before 1932?), it just wasn't in the scientific news much, so all the people who are just discovering "now" how strange the universe is have simply been subject to a primary education that is still closer to the 19th than the 21st century (me included!). Let's get that corrected, shall we? – CuriousOne Oct 30 '15 at 02:01
  • thought/though: well, I'm not native English speaker, I copy-pasted from https://en.wikipedia.org/wiki/Thought_experiment . What would be the difference in meaning ? – Fabrice NEYRET Oct 30 '15 at 09:18
  • I guess you missunderstood the question (or, at least one of us is :-D ). The guy don't pretend "let remove the asumption that dark matter exists". He asked "if black matter was suddenly put away, what would happen". He could have asked as well "if I suddenly suppress this physical force", or "if I suddenly unbanlanced the charges in the universe (or in a star) by transforming + into -" or "if I doubled / halfed G, or H, or ...". – Fabrice NEYRET Oct 30 '15 at 09:22
  • @CuriousOne, as to "you can't simply cut it out and do a "what if" analysis in science." In fact "what if" analysis is the part of reductio ad absurdum, a common technique for proving theories in math and sciences by contradiction. Creating these proofs requires a consideration of the "what if" scenarios. – x457812 May 15 '16 at 17:50
  • @FabriceNEYRET: Science has a clear definition which centers around the description of reality. It is not in the business or redefining reality and can not be. We don't know what would happen if we could do X. We are not God and world building is not part of our job description, if that is what you mean. There are some speculative papers on these topics, but besides being fun, they are still not physics proper. – CuriousOne May 15 '16 at 20:18
  • @x457812: We are not mathematicians, either, we don't do proofs. I don't know which schools teach these things wrong, but some teachers have failed their mandates every time somebody shows up here with the idea that somehow physics has to "prove" things. Physics does nothing of that kind. We observe and then we describe. We don't postulate, we don't axiomatize, we don't derive. We observe and then we guess our way to the correct description. That may not sound like the high flying intellectual version of physics that you have in mind, but that is how it works and it is seriously hard. – CuriousOne May 15 '16 at 20:22
  • You just don't understand the pedagogical vertue of playing with the idea a world with this added or remove (e.g. flatlands), to help understanding the direct and indirect effect of various elements. Not so far, it is useful to play with the idea a the various observable consequence a different c value in the past would have, to debunk some crank theories, but also to illustrate the various place where c appears. – Fabrice NEYRET May 16 '16 at 07:33
  • @CuriousOne: Beside, very often you act nastily in your comments and marking, on a way that is not at all the spirit of science and science popularisation (you would agress Feynman the same way, I guess. Why "Curious" in your pseudo, then ?). BTW you pretend to explain me "what is science", while I am a senior full-time researcher, occasionally writting popularization about what science is (and is not). You do know your physics very well, congrats. But you don't seem to be able to explain to (and respect) non university-level physics students. – Fabrice NEYRET May 16 '16 at 07:39
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    @FabriceNEYRET: You have to forgive me. I have been a working experimental physicist who was focused on producing data about the real universe. That is what working physicists do. Of course there is a place for philosophers who think about all the other things that don't exist. That's all fun and games, but it is not physics. – CuriousOne May 16 '16 at 09:36
  • Here, you are not in an evaluation committee judging OPs. "why ? how ? what if ?" is the way people interrested in science but not professionnal scientistist enough (at least in the domain) to ask Perfect Master-level Question do to improve their understanding (and later, the quality of their notions and questions). Don't piss them off. Help them improving while answering. On the professionnal side: Experimental physics is great. Does it means that theoretical reasonning and though experiments should be discouraged ? Please be tolerant, especially here. Encourage people being curious. – Fabrice NEYRET May 18 '16 at 06:17

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If anything I believe that without dark matter everything in the universe would be accelerated as someone pointed out. But reason being is that particles that form anything with a gravitational force possibly feed off of that dark energy and is what makes it has it own gravity. That being said maybe dark matter is attracted to different substances and masses therefore effecting gravity and messing up orbits or creating new ones.

Dark Magician
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