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> Specifically, the amount of DM and it's specific distribution is tuned to match each observation ...and? If we look at the way a star wobbles, then tune the

> Specifically, the amount of DM and it's specific distribution is tuned to match each observation ...and? If we look at the way a star wobbles, then tune the amount and distribution of planets around it to fit, isn't that just science?

naasking 4y ago
> ...and? If we look at the way a star wobbles, then tune the amount and distribution of planets around it to fit, isn't that just science? That is science because gravity has been extensively tested and confirmed in that regime. Gravity on the scales where dark matter is relevant has not been tested to this extent, so we're just assuming our theory is correct in this new regime and thus inferring the DM distribution based on that assumption and then saying, "this must be the case because we understand gravity". Except as I said, our understanding in that regime has yet to be confirmed, so that's ultimately a circular argument. By contrast, modified gravity theories can match many of the predictions of DM theories using only direct observations of visible matter. It actually made some successful predictions before observations were made, where those observations required adjusting DM models to fit. Successful prediction with fewer parameters is exactly what you want from a scientific theory, and that's what MOND has done. See the review I linked for more information. At this time, neither theory is fully satisfactory as discussed in that review. Superfluid dark matter models were compelling for awhile because they combined MOND and dark matter in a compelling way, but the early models were also inconsistent with some other observations. This is far from a solved problem and the LCDM model gets too much credit and attention given its problems.
- AnIdiotOnTheNet 4y ago
  > Gravity on the scales where dark matter is relevant has not been tested to this extent, so we're just assuming our theory is correct in this new regime Couldn't we just as easily say the same about EM or any of the other forces? The reason we think it is some kind of matter is because we know that matter interacts with gravity in ways that would explain our observations, as long as we assume that matter isn't visible for some reason. And it isn't like there aren't candidates even within the current standard model that might have the right properties. > By contrast, modified gravity theories can match many of the predictions of DM theories using only direct observations of visible matter. ...and curve fitting. They keep having to add parameters to MOND to make it fit what we see and currently attribute to dark matter, like the bullet cluster. That's the physics equivalent of code-smell.
  - naasking 4y ago
    > Couldn't we just as easily say the same about EM or any of the other forces? We've tested other forces in more regimes than gravity because gravity is so weak, but in principle, if predictions of those theories mismatched observations to the same extent as gravity, then we absolutely should be questioning those theories too. > They keep having to add parameters to MOND to make it fit what we see and currently attribute to dark matter, like the bullet cluster. I don't know why people keep saying this like cold dark matter model doesn't do this. LCDM has been refuted many times if this is your criterion. The review paper I cited shows numerous examples of parameterization and curve fitting for LCDM.
marcosdumay 4y ago
Well, yes. That's because we have a pretty strong prior about the existence of planets orbiting stars. It was there before we started adding planets to explain the stars wobbles. With DM the rationale goes the other way around. What means it's not a solid explanation. That is perfectly fine, as long as proponents don't go saying it's settled knowledge and start fighting the people looking for alternatives. When they start doing that, they stop being scientists, and start being believers.
- AnIdiotOnTheNet 4y ago
  > With DM the rationale goes the other way around. No it doesn't. We have strong priors that the movement of bodies is affected by gravity, and gravity comes from matter. When we see movement we cant' explain given the matter we can see, the most obvious explanation is matter we cannot see for some reason.

naasking 4y ago

> ...and? If we look at the way a star wobbles, then tune the amount and distribution of planets around it to fit, isn't that just science? That is science because gravity has been extensively tested and confirmed in that regime. Gravity on the scales where dark matter is relevant has not been tested to this extent, so we're just assuming our theory is correct in this new regime and thus inferring the DM distribution based on that assumption and then saying, "this must be the case because we understand gravity". Except as I said, our understanding in that regime has yet to be confirmed, so that's ultimately a circular argument. By contrast, modified gravity theories can match many of the predictions of DM theories using only direct observations of visible matter. It actually made some successful predictions before observations were made, where those observations required adjusting DM models to fit. Successful prediction with fewer parameters is exactly what you want from a scientific theory, and that's what MOND has done. See the review I linked for more information. At this time, neither theory is fully satisfactory as discussed in that review. Superfluid dark matter models were compelling for awhile because they combined MOND and dark matter in a compelling way, but the early models were also inconsistent with some other observations. This is far from a solved problem and the LCDM model gets too much credit and attention given its problems.

AnIdiotOnTheNet 4y ago
> Gravity on the scales where dark matter is relevant has not been tested to this extent, so we're just assuming our theory is correct in this new regime Couldn't we just as easily say the same about EM or any of the other forces? The reason we think it is some kind of matter is because we know that matter interacts with gravity in ways that would explain our observations, as long as we assume that matter isn't visible for some reason. And it isn't like there aren't candidates even within the current standard model that might have the right properties. > By contrast, modified gravity theories can match many of the predictions of DM theories using only direct observations of visible matter. ...and curve fitting. They keep having to add parameters to MOND to make it fit what we see and currently attribute to dark matter, like the bullet cluster. That's the physics equivalent of code-smell.
- naasking 4y ago
  > Couldn't we just as easily say the same about EM or any of the other forces? We've tested other forces in more regimes than gravity because gravity is so weak, but in principle, if predictions of those theories mismatched observations to the same extent as gravity, then we absolutely should be questioning those theories too. > They keep having to add parameters to MOND to make it fit what we see and currently attribute to dark matter, like the bullet cluster. I don't know why people keep saying this like cold dark matter model doesn't do this. LCDM has been refuted many times if this is your criterion. The review paper I cited shows numerous examples of parameterization and curve fitting for LCDM.

marcosdumay 4y ago

Well, yes. That's because we have a pretty strong prior about the existence of planets orbiting stars. It was there before we started adding planets to explain the stars wobbles. With DM the rationale goes the other way around. What means it's not a solid explanation. That is perfectly fine, as long as proponents don't go saying it's settled knowledge and start fighting the people looking for alternatives. When they start doing that, they stop being scientists, and start being believers.

AnIdiotOnTheNet 4y ago
> With DM the rationale goes the other way around. No it doesn't. We have strong priors that the movement of bodies is affected by gravity, and gravity comes from matter. When we see movement we cant' explain given the matter we can see, the most obvious explanation is matter we cannot see for some reason.