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> the amount of DM and it's specific distribution is tuned to match each observation This is simply not true. No cosmological theory tries to explain why each

> the amount of DM and it's specific distribution is tuned to match each observation This is simply not true. No cosmological theory tries to explain why each star is in its exact observed location. They try to predict the statistics of galaxies, star formation, etc. If you run a simulation of the universe, beginning with very simple, random initial conditions, and then run physics forward for 13 billion years, you get a universe that statistically looks almost identical to our own. You get the same mix of spiral and elliptical galaxies as observed, clustered together in the same way, with the same star formation history, etc. You don't get exactly our universe, with the Milky Way exactly here and Andromeda exactly there, because you begin with random starting conditions. However, you get a universe that is statistically identical in most ways. Note that this is not the case for Milgromian theories. So far, no one has managed to create a theory without dark matter that can achieve this. Alternative theories generally get one or a few things right, at the cost of getting a whole host of other things wrong. It's not that astrophysicists a priori like dark matter. It's just that dark matter is a very simple paradigm that explains a huge number of phenomena with only a handful of free variables, and none of the alternatives work so far.

naasking 4y ago
> No cosmological theory tries to explain why each star is in its exact observed location. Nice strawman. > Note that this is not the case for Milgromian theories. So far, no one has managed to create a theory without dark matter that can achieve this. LCDM also fails at this (see Dwarf galaxy problem, for one example), so this is not a point in your favour. > It's just that dark matter is a very simple paradigm that explains a huge number of phenomena with only a handful of free variables, and none of the alternatives work so far. LCDM doesn't work that great either. See the review I linked.
- DiogenesKynikos 4y ago
  > see Dwarf galaxy problem, for one example I assume you're referring to the "missing satellites problem." This problem is already essentially solved: 1. Newer, more sensitive surveys have detected more Milky Way satellite galaxies. 2. Reionization and supernova feedback quench star formation in small dark matter halos, meaning that the smallest dark matter halos never form galaxies. > See the review I linked. I think we've talked about this elsewhere on HN before, and I pointed out that the paper you're linking to gets a lot of things wrong and is published in an obscure journal (presumably because it wouldn't survive peer review at any of the major journals).
  - naasking 4y ago
    > This problem is already essentially solved: "Essentially solved" is at best a euphemism for "we speculate that this will solve it". Hardly conclusive. > I think we've talked about this elsewhere on HN before, and I pointed out that the paper you're linking to gets a lot of things wrong and is published in an obscure journal (presumably because it wouldn't survive peer review at any of the major journals). A random HN comment claiming that a paper "gets a lot of things wrong" is not more convincing than the published paper itself. If you have an actual published paper or other review that addresses those points, then please point that out. Speculating as to why they published in an "obscure journal" can be explained by poor quality of the work, but it can also be explained by rampant disinterest in challenging orthodoxy, which also has a documented history of happening. Edit: to be clear, I'm not agreeing with the authors that MOND should be favoured given the evidence, but I disagree with your apparent position that MOND should be disfavoured and that LCDM is largely unproblematic.
    - DiogenesKynikos 4y ago
      > "Essentially solved" is at best a euphemism for "we speculate that this will solve it". Hardly conclusive. No, it means that it's actually been solved. If you compare the theoretically predicted number of satellite galaxies to the observed number, there's no discrepancy any more. There was a discrepancy a decade ago. There isn't any more, both because of better observations (which detect more faint galaxies) and because of better understanding of the consequences of LCDM (in particular, how reionization and supernova feedback affect star formation in low-mass galaxies). > rampant disinterest in challenging orthodoxy That's just not the case. There's huge interest in challenging orthodoxy. If there were a MOND-like theory that worked, there would be tons of astrophysicists who would be very excited to work on it. The problem is simply that none of the proposed MOND theories match the wide range of observations that LCDM does. LCDM is a simple theory that works remarkably well, much to the chagrin of the astrophysics community. It would be really exciting to find a problem in LCDM, and a lot of astrophysicists spend their time searching for such problems. See, for example, the excitement generated by the possible Hubble constant tension.
throwawaymaths 4y ago
> If you run a simulation of the universe, beginning with very simple, random initial conditions, and then run physics forward for 13 billion years, This is actually exactly wrong. If you run LCDM for 13 billion years you don't get galaxies till much later than what we observe via say JWST. However, with MOND you predict early galaxies due to the higher force of gravity at distances causing earlier collapse.
- DiogenesKynikos 4y ago
  > If you run LCDM for 13 billion years you don't get galaxies till much later than what we observe via say JWST. I would not take all the recent claims of extremely high-redshift galaxies, found in initial JWST data, at face value. Several of these claims have already been shown to be false.

naasking 4y ago

> No cosmological theory tries to explain why each star is in its exact observed location. Nice strawman. > Note that this is not the case for Milgromian theories. So far, no one has managed to create a theory without dark matter that can achieve this. LCDM also fails at this (see Dwarf galaxy problem, for one example), so this is not a point in your favour. > It's just that dark matter is a very simple paradigm that explains a huge number of phenomena with only a handful of free variables, and none of the alternatives work so far. LCDM doesn't work that great either. See the review I linked.

DiogenesKynikos 4y ago
> see Dwarf galaxy problem, for one example I assume you're referring to the "missing satellites problem." This problem is already essentially solved: 1. Newer, more sensitive surveys have detected more Milky Way satellite galaxies. 2. Reionization and supernova feedback quench star formation in small dark matter halos, meaning that the smallest dark matter halos never form galaxies. > See the review I linked. I think we've talked about this elsewhere on HN before, and I pointed out that the paper you're linking to gets a lot of things wrong and is published in an obscure journal (presumably because it wouldn't survive peer review at any of the major journals).
- naasking 4y ago
  > This problem is already essentially solved: "Essentially solved" is at best a euphemism for "we speculate that this will solve it". Hardly conclusive. > I think we've talked about this elsewhere on HN before, and I pointed out that the paper you're linking to gets a lot of things wrong and is published in an obscure journal (presumably because it wouldn't survive peer review at any of the major journals). A random HN comment claiming that a paper "gets a lot of things wrong" is not more convincing than the published paper itself. If you have an actual published paper or other review that addresses those points, then please point that out. Speculating as to why they published in an "obscure journal" can be explained by poor quality of the work, but it can also be explained by rampant disinterest in challenging orthodoxy, which also has a documented history of happening. Edit: to be clear, I'm not agreeing with the authors that MOND should be favoured given the evidence, but I disagree with your apparent position that MOND should be disfavoured and that LCDM is largely unproblematic.
  - DiogenesKynikos 4y ago
    > "Essentially solved" is at best a euphemism for "we speculate that this will solve it". Hardly conclusive. No, it means that it's actually been solved. If you compare the theoretically predicted number of satellite galaxies to the observed number, there's no discrepancy any more. There was a discrepancy a decade ago. There isn't any more, both because of better observations (which detect more faint galaxies) and because of better understanding of the consequences of LCDM (in particular, how reionization and supernova feedback affect star formation in low-mass galaxies). > rampant disinterest in challenging orthodoxy That's just not the case. There's huge interest in challenging orthodoxy. If there were a MOND-like theory that worked, there would be tons of astrophysicists who would be very excited to work on it. The problem is simply that none of the proposed MOND theories match the wide range of observations that LCDM does. LCDM is a simple theory that works remarkably well, much to the chagrin of the astrophysics community. It would be really exciting to find a problem in LCDM, and a lot of astrophysicists spend their time searching for such problems. See, for example, the excitement generated by the possible Hubble constant tension.

throwawaymaths 4y ago

> If you run a simulation of the universe, beginning with very simple, random initial conditions, and then run physics forward for 13 billion years, This is actually exactly wrong. If you run LCDM for 13 billion years you don't get galaxies till much later than what we observe via say JWST. However, with MOND you predict early galaxies due to the higher force of gravity at distances causing earlier collapse.

DiogenesKynikos 4y ago
> If you run LCDM for 13 billion years you don't get galaxies till much later than what we observe via say JWST. I would not take all the recent claims of extremely high-redshift galaxies, found in initial JWST data, at face value. Several of these claims have already been shown to be false.