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Am I wrong to conclude that this result itself is an argument for the existence of dark matter? Because the theories that argue that physical laws behave diffe

Am I wrong to conclude that this result itself is an argument for the existence of dark matter? Because the theories that argue that physical laws behave differently at larger distances would have to work similarly for all galaxies. Physicists please correct me if I am wrong in making this conclusion!

meowface 8y ago
I think that is a reasonable conclusion to make (assuming these findings are correct). The article says the same: >Ironically, the lack of dark matter in these UDGs strengthens the case for dark matter, the researchers say. It proves that dark matter is a substance that is not coupled with normal matter, since they can be found separately.
- acqq 8y ago
  Also: https://medium.com/starts-with-a-bang/mysterious-galaxy-measured-exquisitely-and-contains-no-dark-matter-at-all-753338968df6 https://medium.com/starts-with-a-bang/mysterious-galaxy-meas... “Ironically, the discovery of a galaxy without dark matter — amidst a sea of galaxies that require huge amounts of it — helps prove the validity of the dark matter-rich picture of the Universe. Only if normal matter can be separated out from the dark matter and left to form its own structures would such a galaxy be possible.”
- mikeash 8y ago
  This reminds me of the discovery of oxygen, which was more about discovering the lack of oxygen in a vacuum and in combustion products.
  - everyone 8y ago
    https://en.wikipedia.org/wiki/Phlogiston_theory https://en.wikipedia.org/wiki/Phlogiston_theory
cmroanirgo 8y ago
I've been very reluctant to go 100% with the Dark Matter theories, preferring to think that Kepler's Law was somehow the root problem. Note, I had no real basis for these thoughts! These findings do indicate that the Dark Matter theory is increasingly reliable, in that some galaxies are shown to have different densities (& thereby there's nothing wrong with Kepler's Law, and further proof that my "going with the gut" when compared with empirical science is just silly!) These findings help reinforce that Kepler's Law are working well and seem to indicate that that dark matter is not necessarily tied with matter, but is hanging around in different densities in different galaxies. > Ironically, the lack of dark matter in these UDGs strengthens the case for dark matter, the researchers say. It proves that dark matter is a substance that is not coupled with normal matter, since they can be found separately. To me, it's a bit like how our planet is not uniformly the "same stuff", but we have deposits of Gold and Coal and Granite spread around the place in an uneven manner.
- narag 8y ago
  Why specifically Kepler laws and not the other dozen ways in which our current understanding of physics could be incomplete? Actually Dark Matter is just a way of saying there's something (not necessarily a "substance") we still don't know: the old metaphor of light for knowledge.
  - empath75 8y ago
    I think we can increasingly say that it it almost certainly matter if some kind. I don’t think it’s a state of pure ignorance.
    - narag 8y ago
      Darkness is not an absolute concept either. As an example, your comment is somewhat dark to me ("it it" and "if some kind") but not pitch black :)
    - snapdangle 8y ago
      Why is it that no one in astrophsyics seems to understand that electricity has mass?
dnautics 8y ago
> Am I wrong to conclude that this result itself is an argument for the existence of dark matter? Only if competing arguments that account for the rotational speed discrepancy in galaxies fail to explain "galaxies without dark matter", which... I think they do? (I am not 100% sure on this). Of course occam's razor is only a heuristic, and not a law, but we would prefer a theory that is simpler, and if we have to add an extra level of indirection explaining why some galaxies lack dark matter, then that is less desirable in a theory. Repeating myself, science doesn't necessarily do what we desire.
BenMorganIO 8y ago
It is known that certain types of galaxies can have less dark matter than others. I believe that jury is still out. I'm a little concerned by how many people "believe" there is dark matter. This adds a bias to the proposed solutions and the funding for each. It leads me to be a little skeptical when I hear that dark matter is being found and whatnot through the speed of stars. I'd love for research to be more balanced since the phenomena can be explained through more hypothesise than just increased mass.
- saagarjha 8y ago
  > I'd love for research to be more balanced since the phenomena can be explained through more hypothesise than just increased mass. Such as?
  - legatus 8y ago
    MOND (Modified Newtonian Dynamics) is one, though it has quite a few problems, as you can read here https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics Another interesting one is Superfluid Dark Matter (first proposed, to my knowledge, here: https://arxiv.org/abs/1507.01019 https://arxiv.org/abs/1507.01019). Those are just a few, there are probably more theories that I haven't heard about. Whatever the case, Sabine Hossenfelder recently posted three videos about Dark Matter/MOND/Superfluid Dark Matter that I wholeheartedly recommend: Dark Matter: https://www.youtube.com/watch?v=FN2d2cmi_Gk https://www.youtube.com/watch?v=FN2d2cmi_Gk MOND: https://www.youtube.com/watch?v=2VNcDoLNJk8 https://www.youtube.com/watch?v=2VNcDoLNJk8 Superfluid Dark Matter (note that it's the theory she supports): https://www.youtube.com/watch?v=468cyBZ_cq4 https://www.youtube.com/watch?v=468cyBZ_cq4
    - acqq 8y ago
      > Dark Matter > Superfluid Dark Matter As far as I see, from three theories you listed, two are the dark matter theories. The only "alternative" from your list is MOND and as far as I know it has more problems than it can solve: https://medium.com/starts-with-a-bang/theres-a-debate-raging-over-whether-dark-matter-is-real-but-one-side-is-cheating-d25f28319d70 https://medium.com/starts-with-a-bang/theres-a-debate-raging... "The tests on the largest scales give us the best tests for dark matter. And these are the ones that dark matter not only universally passes, but that MOND has failed spectacularly for, on every account, for the past 35 years. Among cosmologists*, there is no debate, because there is no alternative to dark matter that reproduces the observed successes." https://arxiv.org/abs/1112.1320 https://arxiv.org/abs/1112.1320 "The biggest challenge facing MOND today is the shape of the matter power spectrum. The shape depicted in Fig. 1 is related to the acoustic oscillations observed in the CMB. If the Universe is dominated by dark matter, these matter oscillations, dubbed Baryon Acoustic Oscillations (BAO), are highly suppressed as the baryons fall into the potential wells created by dark matter, leaving only percent level traces of the primordial oscillations. In a no-dark matter model, on the other hand, the oscillations should be just as apparent in matter as they are in the radiation. Indeed, Fig. 1 illustrates that – even if a generalization such as TeVeS fixes the amplitude problem – the shape of the predicted spectrum is in violent disagreement with the observed shape."
wallace_f 8y ago
Both galaxies without dark matter are UDG's. I'm not a physicist, but this strengthens my personal hunch that dark matter doesn't exist. My heretic theory is that it is just a product of some sort of physical law acting as a "ceiling" in local gravitational force which gets conserved by spreading over large distances.
- keypusher 8y ago
  You might be interested in the work of Erik Verlinde and so called "emergent gravity". While there are still significant problems that the theory needs to explain, it is certainly an interesting perspective to consider. https://www.forbes.com/sites/startswithabang/2017/02/28/is-dark-matter-about-to-be-killed-by-emergent-gravity/#4b69e9b05359 https://www.forbes.com/sites/startswithabang/2017/02/28/is-d... http://www.astronomy.com/news/2018/05/the-case-against-dark-matter http://www.astronomy.com/news/2018/05/the-case-against-dark-...

meowface 8y ago

I think that is a reasonable conclusion to make (assuming these findings are correct). The article says the same: >Ironically, the lack of dark matter in these UDGs strengthens the case for dark matter, the researchers say. It proves that dark matter is a substance that is not coupled with normal matter, since they can be found separately.

acqq 8y ago
Also: https://medium.com/starts-with-a-bang/mysterious-galaxy-measured-exquisitely-and-contains-no-dark-matter-at-all-753338968df6 https://medium.com/starts-with-a-bang/mysterious-galaxy-meas... “Ironically, the discovery of a galaxy without dark matter — amidst a sea of galaxies that require huge amounts of it — helps prove the validity of the dark matter-rich picture of the Universe. Only if normal matter can be separated out from the dark matter and left to form its own structures would such a galaxy be possible.”
mikeash 8y ago
This reminds me of the discovery of oxygen, which was more about discovering the lack of oxygen in a vacuum and in combustion products.
- everyone 8y ago
  https://en.wikipedia.org/wiki/Phlogiston_theory https://en.wikipedia.org/wiki/Phlogiston_theory

cmroanirgo 8y ago

I've been very reluctant to go 100% with the Dark Matter theories, preferring to think that Kepler's Law was somehow the root problem. Note, I had no real basis for these thoughts! These findings do indicate that the Dark Matter theory is increasingly reliable, in that some galaxies are shown to have different densities (& thereby there's nothing wrong with Kepler's Law, and further proof that my "going with the gut" when compared with empirical science is just silly!) These findings help reinforce that Kepler's Law are working well and seem to indicate that that dark matter is not necessarily tied with matter, but is hanging around in different densities in different galaxies. > Ironically, the lack of dark matter in these UDGs strengthens the case for dark matter, the researchers say. It proves that dark matter is a substance that is not coupled with normal matter, since they can be found separately. To me, it's a bit like how our planet is not uniformly the "same stuff", but we have deposits of Gold and Coal and Granite spread around the place in an uneven manner.

narag 8y ago
Why specifically Kepler laws and not the other dozen ways in which our current understanding of physics could be incomplete? Actually Dark Matter is just a way of saying there's something (not necessarily a "substance") we still don't know: the old metaphor of light for knowledge.
- empath75 8y ago
  I think we can increasingly say that it it almost certainly matter if some kind. I don’t think it’s a state of pure ignorance.
  - narag 8y ago
    Darkness is not an absolute concept either. As an example, your comment is somewhat dark to me ("it it" and "if some kind") but not pitch black :)
  - snapdangle 8y ago
    Why is it that no one in astrophsyics seems to understand that electricity has mass?

dnautics 8y ago

> Am I wrong to conclude that this result itself is an argument for the existence of dark matter? Only if competing arguments that account for the rotational speed discrepancy in galaxies fail to explain "galaxies without dark matter", which... I think they do? (I am not 100% sure on this). Of course occam's razor is only a heuristic, and not a law, but we would prefer a theory that is simpler, and if we have to add an extra level of indirection explaining why some galaxies lack dark matter, then that is less desirable in a theory. Repeating myself, science doesn't necessarily do what we desire.

BenMorganIO 8y ago

It is known that certain types of galaxies can have less dark matter than others. I believe that jury is still out. I'm a little concerned by how many people "believe" there is dark matter. This adds a bias to the proposed solutions and the funding for each. It leads me to be a little skeptical when I hear that dark matter is being found and whatnot through the speed of stars. I'd love for research to be more balanced since the phenomena can be explained through more hypothesise than just increased mass.

saagarjha 8y ago
> I'd love for research to be more balanced since the phenomena can be explained through more hypothesise than just increased mass. Such as?
- legatus 8y ago
  MOND (Modified Newtonian Dynamics) is one, though it has quite a few problems, as you can read here https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics Another interesting one is Superfluid Dark Matter (first proposed, to my knowledge, here: https://arxiv.org/abs/1507.01019 https://arxiv.org/abs/1507.01019). Those are just a few, there are probably more theories that I haven't heard about. Whatever the case, Sabine Hossenfelder recently posted three videos about Dark Matter/MOND/Superfluid Dark Matter that I wholeheartedly recommend: Dark Matter: https://www.youtube.com/watch?v=FN2d2cmi_Gk https://www.youtube.com/watch?v=FN2d2cmi_Gk MOND: https://www.youtube.com/watch?v=2VNcDoLNJk8 https://www.youtube.com/watch?v=2VNcDoLNJk8 Superfluid Dark Matter (note that it's the theory she supports): https://www.youtube.com/watch?v=468cyBZ_cq4 https://www.youtube.com/watch?v=468cyBZ_cq4
  - acqq 8y ago
    > Dark Matter > Superfluid Dark Matter As far as I see, from three theories you listed, two are the dark matter theories. The only "alternative" from your list is MOND and as far as I know it has more problems than it can solve: https://medium.com/starts-with-a-bang/theres-a-debate-raging-over-whether-dark-matter-is-real-but-one-side-is-cheating-d25f28319d70 https://medium.com/starts-with-a-bang/theres-a-debate-raging... "The tests on the largest scales give us the best tests for dark matter. And these are the ones that dark matter not only universally passes, but that MOND has failed spectacularly for, on every account, for the past 35 years. Among cosmologists*, there is no debate, because there is no alternative to dark matter that reproduces the observed successes." https://arxiv.org/abs/1112.1320 https://arxiv.org/abs/1112.1320 "The biggest challenge facing MOND today is the shape of the matter power spectrum. The shape depicted in Fig. 1 is related to the acoustic oscillations observed in the CMB. If the Universe is dominated by dark matter, these matter oscillations, dubbed Baryon Acoustic Oscillations (BAO), are highly suppressed as the baryons fall into the potential wells created by dark matter, leaving only percent level traces of the primordial oscillations. In a no-dark matter model, on the other hand, the oscillations should be just as apparent in matter as they are in the radiation. Indeed, Fig. 1 illustrates that – even if a generalization such as TeVeS fixes the amplitude problem – the shape of the predicted spectrum is in violent disagreement with the observed shape."

wallace_f 8y ago

Both galaxies without dark matter are UDG's. I'm not a physicist, but this strengthens my personal hunch that dark matter doesn't exist. My heretic theory is that it is just a product of some sort of physical law acting as a "ceiling" in local gravitational force which gets conserved by spreading over large distances.

keypusher 8y ago
You might be interested in the work of Erik Verlinde and so called "emergent gravity". While there are still significant problems that the theory needs to explain, it is certainly an interesting perspective to consider. https://www.forbes.com/sites/startswithabang/2017/02/28/is-dark-matter-about-to-be-killed-by-emergent-gravity/#4b69e9b05359 https://www.forbes.com/sites/startswithabang/2017/02/28/is-d... http://www.astronomy.com/news/2018/05/the-case-against-dark-matter http://www.astronomy.com/news/2018/05/the-case-against-dark-...