3 ms·

>> I'm surprised to read an article with so much assumed knowledge about dark matter - about how it heats, etc. Exactly! I'm astounded at the amount of - quite

>> I'm surprised to read an article with so much assumed knowledge about dark matter - about how it heats, etc. Exactly! I'm astounded at the amount of - quite literally - made up unsubstantiated assumptions about DM. My favorite is to "explain" a galaxy rotation curve by assuming a spherical distribution of DM around the galaxy, but never explaining why or how it would take on such a distribution. Just don't ask questions...

roywiggins 3y ago
The paper is trying to explain some unexpected observations by the JWST. It starts with the idea that maybe these observations are dark stars, works backwards to show that there are a couple of models of dark matter where this would work, and then predicts that, if these really are dark stars, they'll have a measurably different spectrum than regular stars. Measuring the spectrum would then substantiate (or not) a model of dark matter. This sort of thing is how they might nail down a more likely model of dark matter. This is not unlike trying to explain those observations with ordinary matter, working backwards to try and work out what distribution of ordinary matter could produce the observations and what sort of physics would create such a distribution.
mr_mitm 3y ago
> Just don't ask questions... The insinuation packed in this statement is beyond ridiculous. As if there was a giant conspiracy by Big Cosmology. What makes you think asking questions isn't welcome? Go visit your local college, they probably have a weekly seminar open for everybody. Observe how they interact. Scientists and students ask each other questions (and I mean hard questions) all the time. Pointing out failures in each other theories is the scientists' favorite past time. It's literally how science works. The structure formation of dark matter is extensively studied and simulations are in good agreement with observations (not perfect though, look up the dwarf galaxy problem). > I'm astounded at the amount of - quite literally - made up unsubstantiated assumptions about DM. This is done all the time in cosmology: let's assume X is true just for the heck of it, what does that mean for Y? Could we observe it? Would it perhaps explain several observations at once? Even toy worlds or toy models are explored all the time, by which I mean worlds or models that we know do not describe our world. Valuable insights can still be gained. And why wouldn't they make some assumptions? Would you prefer it if certain ideas are forbidden to be explored?
- phkahler 3y ago
  >> As if there was a giant conspiracy by Big Cosmology. What makes you think asking questions isn't welcome? Because they're not? Proposing a specific distribution of fairy dust immediately begs two questions. "What is it?" - ok I'll let that slide, but "why that distribution?" is critical. It is claimed to influence regular mater via gravity, so why should it take on a different distribution? It "solves" one problem but creates many more. Hey if there's a math model to explain one phenomenon, why does it differ from the existing stuff under the same influence? If peer review doesn't force them to address such questions, there is no hope for me to do so.
  - sebzim4500 3y ago
    There is no shortage of explantions aimed at a smart highschool or undergraduate student which will answer most of those questions. Obviously not "what is it?", that is one of the biggest open questions in cosmology.
  - jeremyjh 3y ago
    The answer is you have to understand the math to understand the theory. Popular accounts are always an approximation, but if the theory were easily refuted by lay people, scientists would not be basing entire research programs on it.
  - cvoss 3y ago
    The inevitable process of science involves raising questions that, at first, do not have answers. Publications are not exam papers where peer reviewers have the answer key. The process of science is also a communal activity, where one scientist raises a question in one forum, and the answer comes from a different scientist years later. Peer review should not and does not (per your own admission) suppress the raising of unanswered questions. And this contradicts your earlier claim that asking questions isn't welcome.
cvoss 3y ago
You're are implicitly assuming something that cosmologists do not assume: that DM even exists. It is not assumed to exist. It is proposed to exist as an explanation for observations we have made. As such, the proposing scientists are free to set the terms of their own proposal. The whole reason DM was proposed is because, if true, it explains gravitational phenomena of galaxies that we can observe but can't otherwise explain under the current best theory of gravity. (Some alternative proposals include very different theories of gravity, rather than DM. [0]) The weakly-interacting property of the proposed DM (again, this property is not an assumption; it's part of the proposal) is what leads to the spherical distribution. It is a (very well explained) mathematical consequence of the lack of interaction that the DM retains a spherical distribution while the ordinary matter collapses to a plane. [0] https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
AnimalMuppet 3y ago
But if the dark matter gravitationally affects the visible matter in the galaxy, then the visible matter in the galaxy should gravitationally affect the dark matter. So even if there was reason for the dark matter to initially assume that shape, what's keeping it in that shape against the pull of the visible matter?
- consilient 3y ago
  > what's keeping it in that shape against the pull of the visible matter? Dark matter halos do flatten out, just much more slowly than baryonic matter, since gravitational interactions radiate off energy much more slowly than electromagnetic ones.

roywiggins 3y ago

The paper is trying to explain some unexpected observations by the JWST. It starts with the idea that maybe these observations are dark stars, works backwards to show that there are a couple of models of dark matter where this would work, and then predicts that, if these really are dark stars, they'll have a measurably different spectrum than regular stars. Measuring the spectrum would then substantiate (or not) a model of dark matter. This sort of thing is how they might nail down a more likely model of dark matter. This is not unlike trying to explain those observations with ordinary matter, working backwards to try and work out what distribution of ordinary matter could produce the observations and what sort of physics would create such a distribution.

mr_mitm 3y ago

> Just don't ask questions... The insinuation packed in this statement is beyond ridiculous. As if there was a giant conspiracy by Big Cosmology. What makes you think asking questions isn't welcome? Go visit your local college, they probably have a weekly seminar open for everybody. Observe how they interact. Scientists and students ask each other questions (and I mean hard questions) all the time. Pointing out failures in each other theories is the scientists' favorite past time. It's literally how science works. The structure formation of dark matter is extensively studied and simulations are in good agreement with observations (not perfect though, look up the dwarf galaxy problem). > I'm astounded at the amount of - quite literally - made up unsubstantiated assumptions about DM. This is done all the time in cosmology: let's assume X is true just for the heck of it, what does that mean for Y? Could we observe it? Would it perhaps explain several observations at once? Even toy worlds or toy models are explored all the time, by which I mean worlds or models that we know do not describe our world. Valuable insights can still be gained. And why wouldn't they make some assumptions? Would you prefer it if certain ideas are forbidden to be explored?

phkahler 3y ago
>> As if there was a giant conspiracy by Big Cosmology. What makes you think asking questions isn't welcome? Because they're not? Proposing a specific distribution of fairy dust immediately begs two questions. "What is it?" - ok I'll let that slide, but "why that distribution?" is critical. It is claimed to influence regular mater via gravity, so why should it take on a different distribution? It "solves" one problem but creates many more. Hey if there's a math model to explain one phenomenon, why does it differ from the existing stuff under the same influence? If peer review doesn't force them to address such questions, there is no hope for me to do so.
- sebzim4500 3y ago
  There is no shortage of explantions aimed at a smart highschool or undergraduate student which will answer most of those questions. Obviously not "what is it?", that is one of the biggest open questions in cosmology.
- jeremyjh 3y ago
  The answer is you have to understand the math to understand the theory. Popular accounts are always an approximation, but if the theory were easily refuted by lay people, scientists would not be basing entire research programs on it.
- cvoss 3y ago
  The inevitable process of science involves raising questions that, at first, do not have answers. Publications are not exam papers where peer reviewers have the answer key. The process of science is also a communal activity, where one scientist raises a question in one forum, and the answer comes from a different scientist years later. Peer review should not and does not (per your own admission) suppress the raising of unanswered questions. And this contradicts your earlier claim that asking questions isn't welcome.

cvoss 3y ago

You're are implicitly assuming something that cosmologists do not assume: that DM even exists. It is not assumed to exist. It is proposed to exist as an explanation for observations we have made. As such, the proposing scientists are free to set the terms of their own proposal. The whole reason DM was proposed is because, if true, it explains gravitational phenomena of galaxies that we can observe but can't otherwise explain under the current best theory of gravity. (Some alternative proposals include very different theories of gravity, rather than DM. [0]) The weakly-interacting property of the proposed DM (again, this property is not an assumption; it's part of the proposal) is what leads to the spherical distribution. It is a (very well explained) mathematical consequence of the lack of interaction that the DM retains a spherical distribution while the ordinary matter collapses to a plane. [0] https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

AnimalMuppet 3y ago

But if the dark matter gravitationally affects the visible matter in the galaxy, then the visible matter in the galaxy should gravitationally affect the dark matter. So even if there was reason for the dark matter to initially assume that shape, what's keeping it in that shape against the pull of the visible matter?

consilient 3y ago
> what's keeping it in that shape against the pull of the visible matter? Dark matter halos do flatten out, just much more slowly than baryonic matter, since gravitational interactions radiate off energy much more slowly than electromagnetic ones.