It's not comparable. Dark matter involves hypothesizing something that is being hypothesized solely to explain certain cosmological problems. If we didn't have those cosmological problems that need explaining, no one would be suggesting dark matter.
The possibility of gravity being repulsive between matter and antimatter was hypothesizes long before we ran into those cosmological problems, and has been subject of sporadic ongoing debate at least as far back as the early to mid 20th century.
> If we didn't have those cosmological problems that need explaining, no one would be suggesting dark matter.
The thing is, the dark matter hypothesis explains more than just certain cosmological problems. It also explains the rotation curves of galaxies, gravitational lensing by galaxy clusters, and the velocity dispersions of galaxies, galaxy groups, and galaxy clusters.
Dark matter is not an ad hoc hypothesis to solve a single problem; rather, it's an ad hoc hypothesis (though still more plausible than any alternative) that explains a large number of observed phenomena over many different length scales.
Dark matter involves hypothesizing something that is being hypothesized solely to explain certain cosmological problems
Much as in the 1840s, Urbain Le Verrier predicted the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus?
> Dark matter involves hypothesizing something that is being hypothesized solely to explain certain cosmological problems.
Waiiiiit.... isn't this the way with ALL unknowns? We see some thing we can't explain (a "problem"), and we come up with a hypothesis solely to explain it? Sometimes we're wrong, and we start over with a new hypothesis?
We hypothesized the existence of some hitherto unknown and "dark" agent we called a "germ" to explain infection. We hypothesized the existence of an unknown and invisibile "X-ray" to explain how film got ghostly images on it. Etc.
I'm sure I'm missing your meaning here; can you clarify?
The distinction I'm making is being hypotheses that involve new objects and hypotheses that involve new properties for old objects.
For instance, consider planetary motion before Newton. You could have hypothesized a "dark" force that moved the planets. Or you could hypothesize that a force you already know exists (gravity near the Earth's surface) also exists for each body of the solar system, has unlimited range, and follows an inverse square law.
Ok, I get your distinction, but (and I'm a complete neophyte non-professional here, so bear with me), the layman's explanation for dark matter has been, "We don't know what's causing it, but it acts like gravity, and the only thing we know of now that has gravity is matter, and it appears (hah) to be invisible to all of our known electro-magnetic radiation, so we call it "dark"".
So I apologize if I've misunderstood, but based on that I don't think hypothosizing this unknown phenomenon as some sort of "dark matter" is entirely out of line.
The possibility of gravity being repulsive between matter and antimatter was hypothesizes long before we ran into those cosmological problems, and has been subject of sporadic ongoing debate at least as far back as the early to mid 20th century.