Another adventure, full of information that may not be the direct purpose of your blog, and yet delightful.

First of all let me congratulate you on your light touch:

Dark matter is a key topic in high energy physics and cosmology today. This situation does not originate from randomness or the madness of some physicists.

😆 Nothing like a chuckle to keep the reader interested.

Then the gems of information that are new to me.

stars lying farther from the galactic centre are slower

And, in our own solar system, planets further from the sun move more slowly around it.

Also, the event you call recombination--380,000 years after the Big Bang--and the fact that photons from that time are still around.(!)

Just some information I picked up along the way to your dark matter discussion.

Now to Dark Matter: I understand that you need a mediator particle to interact (connect) the dark matter particle with the standard model. The result of this coupling will not be directly observable (the dark matter particle), but the consequence will be.

Physics 101: thank you @lemouth.

By the way, I think you are correct to offer a long blog with a great deal of information. There are those, (like me) who are new to this and cannot possibly challenge your observations or statements. But you want the blog to hold up under scrutiny of people who do know a great deal about the material. You manage to straddle two worlds with the blog: a professional reader, and a lay person who is wandering around wide-eyed.

PS: That title is perfect. I have watched the movie, *The Hitchhicker's Guide to the Galaxy, at least 3 times.