Fitting an elephant with four non-zero parameters

Post by Retric » Tue, Jul 16, 2024, 5:37 AM UTC

andrewflnr wrote: post #140

Retric wrote: post #117

Earlier quoted context omitted.

All observations of individual galaxies occur at a specific point in time. We can’t use light speed delay to see the evolution of individual galaxies only completely different galaxies at some other point in time. As such each galaxy gets its own value for the amount of dark matter. At minimum this is a ~200 billion parameter model, and more if you’re looking at smaller structures.

That's equally true of the distribution of baryonic matter. We have to assess each galaxy individually to figure out what it's made of? What a crime against science. Never mind that they're still all made of a small handful of types of parts, which can nevertheless combine to form lots of possible histories and shapes for individual objects. Just like literally everything else in the observable universe . Seriously,…

Post by olalonde » Tue, Jul 16, 2024, 9:32 AM UTC

gowld wrote: post #131

olalonde wrote: post #101

Earlier quoted context omitted.

Kolmogorov complexity[0] solves this loophole :) [0] https://en.wikipedia.org/wiki/Kolmogorov_complexity

Kolmogorov complexity is an effort to wrangle it. It's impossible to fully solve. You can change measured complexity by altering the baseline assumptions.

Post by Retric » Tue, Jul 16, 2024, 4:42 PM UTC

andrewflnr wrote: post #142

Retric wrote: post #141

Earlier quoted context omitted.

The availability to detect visible light from stars or detect that light being blocked by baryonic matter. With dark matter it’s two steps removed where we’re inferring the behavior of baryonic matter and then inferring the amount of baryonic matter we aren’t observing and then calculating the existence of dark matter to get that behavior after accounting for undetected baryonic matter.

Yeah, that's a pain, but calculating mass from photons is still pretty indirect. More importantly, and independently of "directness", no one pretends that galaxies having different masses introduces two billion parameters into our models of cosmology. Because that's not what a model of cosmology is.

Post by Retric » Tue, Jul 16, 2024, 6:23 PM UTC

andrewflnr wrote: post #146

Retric wrote: post #145

Earlier quoted context omitted.

Calculating the percentage of the universe’s observable mass is dark matter adds 200+ billion parameters because the mass fraction of each galaxy varies. So there’s no simple way to calculate it from say looking at the Milky Way alone and extrapolating from the baryonic mass of the rest of the universe. Trying to approximate things from a representative sample is its own problem.

You're still confusing a physics model with a map of the universe. That said, it's sure a heck of a coincidence that the number they get from adding up estimated dark matter in galaxies lines up with the number they get from other cosmological measurements, isn't it? Almost like galaxy rotation curves aren't the only evidence for dark matter and haven't been for a long time. https://en.wikipedia.org/wiki/Dark_matter#…

Post by munchler » Wed, Jul 17, 2024, 12:15 AM UTC

maitola wrote: post #16

I love the ironic side of the article. Perhaps they should add the reason for it, from Fermi's and Neumann's. When you are building a model of reality in Physics, If something doesn’t fit the experiments, you can’t just add a parameter (or more) variate it and fit the data. The model should have zero parameters, ideally, or the least possible, or, even at a more deeper level, the parameters should emerge naturally fr…