5 ms·

Why do people in the comments always ignore that dark matter has way more evidence for it than just galaxy rotation curves (something very well explained in th

Why do people in the comments always ignore that dark matter has way more evidence for it than just galaxy rotation curves (something very well explained in the article)? It's quite tiresome to read the same objections as if physicists somehow hadn't thought of them.

scotty79 4y ago
Do you know of any good derivation of existence of dark matter a layman could follow through and be convinced?
- ctchocula 4y ago
  This is a good write-up that justifies dark matter using 7 independent pieces of evidence: https://medium.com/starts-with-a-bang/7-independent-pieces-of-evidence-for-dark-matter-3692126a2283 https://medium.com/starts-with-a-bang/7-independent-pieces-o...
- pja 4y ago
  You could read through the relevant Wikipedia pages for an overview: https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
  - rocqua 4y ago
    Wikipedia is rarely a good introduction for laymen. It tends to be a great reference for people already in the field.
    - ciphol 4y ago
      That's true in mathematics, but I find for any other subject it's a great reference for anyone intelligent enough to understand the subject. (One might remark that I'm just not intelligent enough to understand advanced mathematics, and they might be right...)
- kryptiskt 4y ago
  "The Road to Precision Cosmology" is a good summary of how we ended up with the current theories: https://arxiv.org/abs/2201.04741 https://arxiv.org/abs/2201.04741
mr_mitm 4y ago
Probably because it's the only piece of evidence you can understand with just high school physics. Most laypeople have trouble understanding that the universe is not expanding from a single point, so how would they be able to understand what the cosmic background radiation is, much less why its angular power spectrum has peaks at particular positions? It's a common pattern with crackpots as well, that they focus on "big" but easy to understand things like special relativity, which doesn't involve more math than you learn in high school. No crackpot ever revolutionizes condensed matter physics or statistical mechanics. Although the bullet cluster should be a clear indicator as well, the rest of the evidence of DM appears much more subtle to a layperson. Anyway, cosmology is a weird topic which not only HN reveals tons of arrogance over. Lots of misplaced skepticism. (Probably similar to the Covid topic.)
- MrScruff 4y ago
  Yes exactly. We've all experienced reading an account on our particular domain of expertise by a journalist and realising they have absolutely no clue what they're talking about. I find it amazing how presumably otherwise intelligent people reading Hacker News don't see the issue with offering lay opinions on Cosmology of all topics.
  - deleted 4y ago
    [deleted]
  - pantalaimon 4y ago
    Well there is a connection. Often I read news articles about science where I think "Wait, that doesn’t make sense." or "Hey, this assumption is not explained at all!" and without the original paper to read (or the knowledge to understand it) the only place to take this confusion is the comments section, with the hope that someone might explain it.
  - mumblemumble 4y ago
    I think that's just a factor of the open nature of HN meaning there's always someone ready with a hot take, and plenty of social incentive to provide one. None of us is as dumb as all of us.
Ygg2 4y ago
Because dark matter is too convenient, and it's not like LCDM prediction are 100% on the money. http://backreaction.blogspot.com/2017/01/the-bullet-cluster-as-evidence-against.html?m=1 http://backreaction.blogspot.com/2017/01/the-bullet-cluster-... Another big problem is that all LCDM predictions (MACHO/WIMP) were disproven but it still remains a theory. Now we need energy too high to use in universe. It's eerily similar to Phlogiston theory that at one point was considered to have negative mass.
- pfdietz 4y ago
  MACHO/WIMP was one way to implement LCDM, but not a requirement for LCDM.
rocqua 4y ago
Because it is the only evidence that is presented, and lay-people can easily come up with objections. These people then express their frustration or confusion why some of these objections seem completely unaddressed. These people are effectively asking about these objections. Perhaps many of them are phrasing it differently. But, with exceptions, I think people tend not to be angry or vitriolic. At best they are frustrated. Just treat these remarks as questions. It might be annoying to get the same questions repeatedly, but that is a fault of wider communication about dark-matter.
hsn915 4y ago
Maybe you could have bothered to list some of this "evidence" instead of venting that no one has heard of it?
- furyofantares 4y ago
  It's listed in the article.
lamontcg 4y ago
> It's quite tiresome to read the same objections as if physicists somehow hadn't thought of them. Okay now do climate change and climatologists. And most people just don't bother to read the article at all it seems. No better than reddit. Changing gears, though, and trying to be more useful, if you want more coverage on this topic there's a note in Peter Woit's blog: https://www.math.columbia.edu/~woit/wordpress/?p=13232 https://www.math.columbia.edu/~woit/wordpress/?p=13232 Points to another blog which attacks the "nightmare scenario": https://tritonstation.com/2022/11/29/the-angel-particle/ https://tritonstation.com/2022/11/29/the-angel-particle/ I don't particularly buy that a gravity-only interacting particle "is not physics". If that is what exists, that is what exists. And we've already detected it via dark matter observations. So it is physics. What we can't do is ever really prove it other than by exclusion, but if we racked up a thousand years of failure, we'd have to accept that it was real (hopefully by then not dogmatically and we'd let any kid who wanted to tilt at windmill to go for it). And Woit links to a paper on dark matter being only a right handed majorana neutrino, requiring no real physics beyond the standard model (plus three right handed non-interacting neutrinos): https://arxiv.org/abs/1803.08930 https://arxiv.org/abs/1803.08930 And links to a comment on that in John Baez's blog: https://golem.ph.utexas.edu/category/2022/12/neutrino_dark_matter.html https://golem.ph.utexas.edu/category/2022/12/neutrino_dark_m...
credit_guy 4y ago
Here. I'll come with a different objection. Everything we see in the Universe outside our own galaxy is static. We don't have enough parallax to actually perceive objects (stars) moving outside our galaxy. Ok, there's an exception, people were able to perceive the movement of one star in one of our satellite galaxies in 2012. That's about it. So, when people talk about galaxy rotation curves, that's based on a sample of one, our own galaxy. Actually, we can plot galaxy rotation curves for other galaxies, but based on indirect evidence, such as the redshift. How accurate is that? Come to think of it, we can't estimate directly the distance to any galaxy beyond and including the Andromeda galaxy. But again, we can estimate indirectly. Only that estimation is based on a stack of estimations each with its own uncertainties. Now, if you work in the area, stop me right here and tell me you went through that stack of estimates, and check all the uncertainties, and are confident there's no potential error anywhere. Because, as an outsider, if I do a bit of Bayesian estimation, and I have to choose between the dark matter and the possibility that everything that can be explained with dark matter is actually a result of estimation errors, I'm somewhat on the fence. Every year that the hunt for dark matter brings nothing I'm more inclined to think there's a different explanation out there. Like the frame dragging explanation discussed in [1]. [1] https://physics.stackexchange.com/questions/618981/has-frame-dragging-been-accounted-for-in-galactic-rotation-curves https://physics.stackexchange.com/questions/618981/has-frame...
- doliveira 4y ago
  I'm sorry, but misplaced confidence like yours is the tiresome part. I think you should also apply Bayesian thinking to the whole debate as well. I'm not a cosmologist, but I have a degree in Physics. I won't be able to fill in the details, but all your objections sound pretty basic and unfounded even to my semi-amateur ears. About the cosmic distance ladder (as if parallax were the only way. I guess we don't see Earth's curvature either), about how to propagate errors (literally learnt in the 1st week of Physics. Those bars around the scatter points are literally the error bars, and we propagate them from start to finish). And even about the scientific method itself. No one can claim "there's no potential error anywhere" in anything. And most importantly, which was my original main point, galaxy rotation curves are not our only evidence. BTW, I would encourage you to look at how fossils are dated. To me it sounds kind of similar in spirit to how distances are measured in astronomical scales.

scotty79 4y ago

Do you know of any good derivation of existence of dark matter a layman could follow through and be convinced?

ctchocula 4y ago
This is a good write-up that justifies dark matter using 7 independent pieces of evidence: https://medium.com/starts-with-a-bang/7-independent-pieces-of-evidence-for-dark-matter-3692126a2283 https://medium.com/starts-with-a-bang/7-independent-pieces-o...
pja 4y ago
You could read through the relevant Wikipedia pages for an overview: https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
- rocqua 4y ago
  Wikipedia is rarely a good introduction for laymen. It tends to be a great reference for people already in the field.
  - ciphol 4y ago
    That's true in mathematics, but I find for any other subject it's a great reference for anyone intelligent enough to understand the subject. (One might remark that I'm just not intelligent enough to understand advanced mathematics, and they might be right...)
kryptiskt 4y ago
"The Road to Precision Cosmology" is a good summary of how we ended up with the current theories: https://arxiv.org/abs/2201.04741 https://arxiv.org/abs/2201.04741

mr_mitm 4y ago

Probably because it's the only piece of evidence you can understand with just high school physics. Most laypeople have trouble understanding that the universe is not expanding from a single point, so how would they be able to understand what the cosmic background radiation is, much less why its angular power spectrum has peaks at particular positions? It's a common pattern with crackpots as well, that they focus on "big" but easy to understand things like special relativity, which doesn't involve more math than you learn in high school. No crackpot ever revolutionizes condensed matter physics or statistical mechanics. Although the bullet cluster should be a clear indicator as well, the rest of the evidence of DM appears much more subtle to a layperson. Anyway, cosmology is a weird topic which not only HN reveals tons of arrogance over. Lots of misplaced skepticism. (Probably similar to the Covid topic.)

MrScruff 4y ago
Yes exactly. We've all experienced reading an account on our particular domain of expertise by a journalist and realising they have absolutely no clue what they're talking about. I find it amazing how presumably otherwise intelligent people reading Hacker News don't see the issue with offering lay opinions on Cosmology of all topics.
- deleted 4y ago
  [deleted]
- pantalaimon 4y ago
  Well there is a connection. Often I read news articles about science where I think "Wait, that doesn’t make sense." or "Hey, this assumption is not explained at all!" and without the original paper to read (or the knowledge to understand it) the only place to take this confusion is the comments section, with the hope that someone might explain it.
- mumblemumble 4y ago
  I think that's just a factor of the open nature of HN meaning there's always someone ready with a hot take, and plenty of social incentive to provide one. None of us is as dumb as all of us.

Ygg2 4y ago

Because dark matter is too convenient, and it's not like LCDM prediction are 100% on the money. http://backreaction.blogspot.com/2017/01/the-bullet-cluster-as-evidence-against.html?m=1 http://backreaction.blogspot.com/2017/01/the-bullet-cluster-... Another big problem is that all LCDM predictions (MACHO/WIMP) were disproven but it still remains a theory. Now we need energy too high to use in universe. It's eerily similar to Phlogiston theory that at one point was considered to have negative mass.

pfdietz 4y ago
MACHO/WIMP was one way to implement LCDM, but not a requirement for LCDM.

rocqua 4y ago

Because it is the only evidence that is presented, and lay-people can easily come up with objections. These people then express their frustration or confusion why some of these objections seem completely unaddressed. These people are effectively asking about these objections. Perhaps many of them are phrasing it differently. But, with exceptions, I think people tend not to be angry or vitriolic. At best they are frustrated. Just treat these remarks as questions. It might be annoying to get the same questions repeatedly, but that is a fault of wider communication about dark-matter.

hsn915 4y ago

Maybe you could have bothered to list some of this "evidence" instead of venting that no one has heard of it?

furyofantares 4y ago
It's listed in the article.

lamontcg 4y ago

> It's quite tiresome to read the same objections as if physicists somehow hadn't thought of them. Okay now do climate change and climatologists. And most people just don't bother to read the article at all it seems. No better than reddit. Changing gears, though, and trying to be more useful, if you want more coverage on this topic there's a note in Peter Woit's blog: https://www.math.columbia.edu/~woit/wordpress/?p=13232 https://www.math.columbia.edu/~woit/wordpress/?p=13232 Points to another blog which attacks the "nightmare scenario": https://tritonstation.com/2022/11/29/the-angel-particle/ https://tritonstation.com/2022/11/29/the-angel-particle/ I don't particularly buy that a gravity-only interacting particle "is not physics". If that is what exists, that is what exists. And we've already detected it via dark matter observations. So it is physics. What we can't do is ever really prove it other than by exclusion, but if we racked up a thousand years of failure, we'd have to accept that it was real (hopefully by then not dogmatically and we'd let any kid who wanted to tilt at windmill to go for it). And Woit links to a paper on dark matter being only a right handed majorana neutrino, requiring no real physics beyond the standard model (plus three right handed non-interacting neutrinos): https://arxiv.org/abs/1803.08930 https://arxiv.org/abs/1803.08930 And links to a comment on that in John Baez's blog: https://golem.ph.utexas.edu/category/2022/12/neutrino_dark_matter.html https://golem.ph.utexas.edu/category/2022/12/neutrino_dark_m...

credit_guy 4y ago

Here. I'll come with a different objection. Everything we see in the Universe outside our own galaxy is static. We don't have enough parallax to actually perceive objects (stars) moving outside our galaxy. Ok, there's an exception, people were able to perceive the movement of one star in one of our satellite galaxies in 2012. That's about it. So, when people talk about galaxy rotation curves, that's based on a sample of one, our own galaxy. Actually, we can plot galaxy rotation curves for other galaxies, but based on indirect evidence, such as the redshift. How accurate is that? Come to think of it, we can't estimate directly the distance to any galaxy beyond and including the Andromeda galaxy. But again, we can estimate indirectly. Only that estimation is based on a stack of estimations each with its own uncertainties. Now, if you work in the area, stop me right here and tell me you went through that stack of estimates, and check all the uncertainties, and are confident there's no potential error anywhere. Because, as an outsider, if I do a bit of Bayesian estimation, and I have to choose between the dark matter and the possibility that everything that can be explained with dark matter is actually a result of estimation errors, I'm somewhat on the fence. Every year that the hunt for dark matter brings nothing I'm more inclined to think there's a different explanation out there. Like the frame dragging explanation discussed in [1]. [1] https://physics.stackexchange.com/questions/618981/has-frame-dragging-been-accounted-for-in-galactic-rotation-curves https://physics.stackexchange.com/questions/618981/has-frame...

doliveira 4y ago
I'm sorry, but misplaced confidence like yours is the tiresome part. I think you should also apply Bayesian thinking to the whole debate as well. I'm not a cosmologist, but I have a degree in Physics. I won't be able to fill in the details, but all your objections sound pretty basic and unfounded even to my semi-amateur ears. About the cosmic distance ladder (as if parallax were the only way. I guess we don't see Earth's curvature either), about how to propagate errors (literally learnt in the 1st week of Physics. Those bars around the scatter points are literally the error bars, and we propagate them from start to finish). And even about the scientific method itself. No one can claim "there's no potential error anywhere" in anything. And most importantly, which was my original main point, galaxy rotation curves are not our only evidence. BTW, I would encourage you to look at how fossils are dated. To me it sounds kind of similar in spirit to how distances are measured in astronomical scales.