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> Who made you an infallible authority? I'm not infallible but I do have a PhD in the study of CPV in particle physics so I understand this at a level enough t

• pdonis 4y ago
  > Alternate gravity theories Are not what I'm asking about here. I know Kroupa pushes them, but that's not the part of Kroupa's work that I'm asking about. > Kroupa is still trying to explain the rotational differences between observation and "normal" Newtonian/Einstein gravity. Not in the specific item I'm asking about. In that specific item, he's not talking about any alternative theories of gravity at all. He's pointing out what he claims is a conflict between the predictions of the dark matter hypothesis and actual observations. I've already explained what a counter argument to that would look like. Do you have one?
  • rob_c 4y ago
    Unfortunately you are getting a little crossed from your perspective. You're asking a question that to experts is structured oddly because you can't disentangle things you're trying to separate. I'll try to explain. Again dark matter is an attempt to explain a collection of observations that don't match current accepted theoretical models. There "classical dark matter hypothesises" is just that. That these observations can be explained by a quantizable matter candidate of some form with some yet to be determined properties. The only non particle descriptions of "dark matter phenomena" is a modified gravity framework. These attempt to address the "classical dark matter phenomena" whilst disentangling it from the "CPV phenomena". This is fine but breaks the big bang model at the stage of baryogenesis (matter formation from pure energy). There is the possibility that you can explain "classical dark matter phenomena" without demanding it also be responsible for CPV. However, if you do that the CPV step of the big bang model demands additional particle candidates which then raises the problem of what do they look like and where are they and do they interact with the Higgs field and therefore have mass. There are no counter arguments to "classical dark matter phenomena" because they are just that. Observed natural phenomena which do not fit into our current understanding of the universe. A "complete dark matter theory" tends to explain CPV+DM. These again don't make many testable predictions other than a (potentially TeV scale) weekly interacting particle candidate. So the testable prediction is that a dark matter candidate exists and we can observe it. > I've already explained what a counter argument to that would look like. Do you have one? I'll choose to read that in a relaxed manner, albeit it's a bit direct. There is no counter argument to natural phenomena. The main 2 theories are that dark matter particles exist and we can find them or we can't. MOND et al make few predictions and struggle to observe defined "gravitational phenomena", hence why there is little interest in them. There are differences between DM particle models but almost all agree that the major premise is that we might/should be able to see certain particle types given how they interact.
    • pdonis 4y ago
      > You're asking a question that to experts is structured oddly because you can't disentangle things you're trying to separate. To me this reads as the answer "no" to the question I asked. Nobody actually has a counter argument. "Experts" have simply chosen to dismiss the matter without any argument at all. To expand on this somewhat: you appear to believe that I am asking for some kind of separation of observations, so that we consider only the particular observations Kroupa refers to (orbits of small satellite galaxies around large galaxies) and ignore all the other observations. That is not what I am asking. I am asking for a simple response from "experts" who support the dark matter hypothesis in general to these two questions: (1) Is Kroupa correct in his claims about what dark matter models of "halos" around galaxies predict regarding the orbits of small satellite galaxies around larger galaxies? If not, why not? (2) Is Kroupa correct that actual observations of the orbits of small satellite galaxies around larger galaxies do not match the predictions of dark matter models? If not, why not? These seem to me like straightforward questions of the kind that scientists pose to other scientists all the time, and it does not seem credible to me that "experts" would not have responses to them along any of several obvious lines: (A) Kroupa's computations of the predictions of dark matter "halo" models are wrong. Here are the correct predictions, which match observations. (B) Kroupa's claims about the predictions are correct, but his comparison with the data is wrong. Here is the correct comparison with the data, which shows that the models match observations. (C) Kroupa's claims that the predictions don't match observations in this particular domain are correct taken in isolation. However, when the entirety of all observations are considered, including ones that have nothing to do with individual galaxies (such as the evolution of the early universe), the dark matter models do much better at minimizing the overall error between model and observation than any of the alternative models, including the ones Kroupa favors. You seem to be leaning towards something like (C), but if so, you could just say (C) and be done with it. Instead, you appear to be trying to avoid any possible admission that there is any discrepancy between dark matter models and observations at all, which IMO is not a good strategy. No model ever matches 100% of observations. > dark matter is an attempt to explain a collection of observations that don't match current accepted theoretical models I would not put it that way. I would put it that dark matter is an attempt to explain a collection of observations using currently accepted theoretical models (General Relativity and the relevant solutions to the Einstein Field Equation), by making use of a free parameter in the models, namely the assumed stress-energy tensor (or distribution of matter, if you like). By adding a "dark matter" component to the distribution of matter, which does not interact electromagnetically and therefore is not visible to us by any means other than its gravitational effects, many observations can be matched much better. MOND, by contrast, proposes modifying the theory of gravity in general. That, to me, is a much bigger change than adding a component to the distribution of matter. > There is no counter argument to natural phenomena. So what? I wasn't asking for a counter argument to "natural phenomena". I was asking for a counter argument to a claim that a particular model makes predictions that don't match observations. Claims like this are made all the time in science, and the appropriate response is to give a counter argument along the lines I described. I have not seen one, and as I noted above, all your remarks have given me the strong impression that there isn't one, and that "experts" have no interest in providing one. That answers my question, although no doubt the inferences I draw from that answer will be very different than yours.