I had written, "That's what science does. It observes phenomena and develops narratives that account for them to predict future phenomena. The stability of galaxies could not be explained by the existing physics, so new physics was called for." Disagree. As I said, that is a description of what science is and does. If you disagree, you should be able to provide a reason that explains why my comment is incorrect. Explain which part of the comment cannot be correct. Is it the science observes phenomena part that you think doesn't happen? Is it the idea that science develops narratives to account for observed phenomena that you consider nonsense?
It's an attempt to account for an observed phenomenon not explainable with the physics. Once again, that's what science does. Its gravitational effect has already been found. Other effects may be difficult to discern if it doesn't generate any electromagnetic waves. Perhaps gravitational waves from dark matter can be detected by LIGO and/or LISA. Or perhaps some theoretical or observational data will suggest a new particle. Or perhaps it will remain a mystery indefinitely. That's sceicne, too.
The laws of motion work fine elsewhere, and so don't need revision. What was needed was a new substance capable of generating gravity but not electromagnetic radiation. Only matter is known to generate or respond to gravity, hence it behaves like visible matter, but is dark.
Galaxies don't repulse. They are dominated by gravity, which attracts only.
Our star has orbited galactic center since its birth. It's orbit undulates perpendicular to the plane of the galaxy, but our star orbits our galaxy's central supermassive black hole the way its planets orbit it. Planets do occasionally wander closer and further from the sun, but not regularly. They say Jupiter visited the inner solar system for a while, put repulsive forces were not involved, just collisions and gravity. From
Jupiter, Destroyer of Worlds, May Have Paved the Way for Earth - Scientific American :
"One example is the “grand tack” scenario, which posits that in the first few million years of our solar system’s existence Jupiter migrated into and then back out of the inner solar system, following a course similar to a sailboat’s when it tacks around a buoy. Back then Jupiter would have still been embedded in a gas-rich disk. Much of that gas was spiraling down toward the sun—so much that the action would have sapped some of Jupiter’s angular momentum, too, causing the giant planet itself to spiral in to the vicinity of where Mars is today. Jupiter would have kept falling in toward the sun if not for being caught by the subsequent formation of Saturn, which began drifting in as well. As the two giant planets came closer together, they were caught in an orbital resonance."
Supernovae do explode, and discharge matter as well as radiation. The explosions cause concussion waves in distant nebulae, seeding them with heavy elements and causing them to collapse into solar systems.
We're not really making any more progress here on your claim of modern cosmology being a mess. You haven't demonstrated a mess, just a frustration of your own. I don't see a mess, and cosmologists apparently consider their science to be making progress, seem excited about tackling its current problems, and don't report a mess, either.
