[tjradcliffe]

There's nothing magical about the required properties, so I'm not sure why anyone would describe them that way. They are no different than the properties imputed to neutrinos or the aether: http://www.tjradcliffe.com/?p=1801

The important thing about extra-galactic dark matter is there is too much of it to be made of ordinary particles: protons and neutrons and electrons. We know how many ordinary nucleons there are because we have a pretty reasonable estimate of the primoridal ratio of hydrogen to helium. As the Big Bang cooled quarks eventually cooled down enough to make protons and neutrons. Free neutrons only live about fifteen minutes so they only had a short time to capture onto protons and make deuterium nuclei which could further colide to make helium. The ratio of He/H in the early universe is therefore a sensitive measure of the denisty of the universe at the time of nucleon condensation, and we know the radius from the temperature, so we can calculate the total number of particles. There aren't enough to make up extra-galactic dark matter. There are enough to make up galactic dark matter, so there may be two totally unrelated dark matter problems.

When physicists talk about "dark matter" we are sliding back and forth between meanings according to context, but this is all lost on outsiders, unfortunately. It's needlessly confusing, but unfortunately it's the way it is.

So amongst the perfectly ordinary, non-magical properties that extra-galactic dark matter has to have is to be something other then ordinary neutrons and protons. There are some other contraints on its various interaction strengths that come from the scale of galaxy formation and larger scale structures in the universe too. Again, these are perfectly ordinary properties, inferred based on the evidence in exactly the same way the properties of aether and neutrinos were.

Dark matter may or may not exist (neutrinos do, aether does not) but there is absolutely nothing out of the ordinary about it. It is just normal science doing what science normally does.

[vorg]

> Dark matter may or may not exist but there is absolutely nothing out of the ordinary about it

18% of matter is "regular" matter that interact with each other via bosons, and the other 82% is "dark" matter that doesn't interact with the known bosons. Could dark matter have its own "bosons"? Even more interesting, could dark matter be partitioned into various categories based on the "boson" they interact with? If so, perhaps the categories would have random but regularly distributed size ratios, for example:

* 25% of matter is zyzotic interacting via yetions

* 18% of matter is hadronic (i.e. quarks, leptons) interacting via bosons (i.e. photons, gluons, W, Z)

* 13% of matter is xenatic interacting via winnions

* 7% is vivacions interacting via ululons

* smaller partitions at 5%, 4%, 2%, 1.9%, 1.8%, 1.8%, 1.7%, 1.7%, 1.7%, 1.7%, etc etc etc

* there'd be millions of partitions overall

* the smallest partitions would consist of only 1 particle each (and perhaps its anti-particle) in the entire Universe

This would put various properties such as mass, etc of the hadronic particles as being randomly determined, perhaps quantumly, a split instance after the Big Bang.

[mixmastamyk]

I'll try to explain what I meant about magic. Your piece was interesting on how building mental models is an important part of science which opened my eyes a bit. However, in terms of this discussion I was thinking there might be lower-hanging fruit that makes dark matter appear farther-fetched.

For example, we have calculated the mass of a galaxy, but it doesn't spin right at that mass. So, instead of:

1. Assuming our calculations are wrong, or

2. There is more interstellar dust/gas/solar-wind mass than we realize, or

3. Heavier Black hole at center, or spinning speed/time dilation occurring?

4. Effects of gravity are weaker at very long distances

a different theory is presented instead.... that 2/3 of the universe is made of a brand-new undetectable substance.

As you mentioned it may or may not be true, and I've learned a lot about why it is convincing in this larger thread. Still, as Sagan said, "extraordinary claims require extraordinary evidence."

It's probably a flaw of the layman that ideas that have yet to be confirmed tend to appear magical.

[Dylan16807]

> 1. Assuming our calculations are wrong

That's what this is. We checked the math 20 times over and we know the model is wrong.

> 2. There is more interstellar dust/gas/solar-wind mass than we realize

We checked.

> 3. Heavier Black hole at center, or spinning speed/time dilation occurring?

Doesn't fit.

> 4. Effects of gravity are weaker at very long distances

Also an extraordinary claim, has not been ruled out.

Plus we already have confirmed 'undetectable' substances, so it's not very strange to suggest a new one.