All of Rip's Comments + Replies

If you look through a telescope and expect to see a planet, but instead you see a planet and two moons, do you assume your telescope is broken? That seems to be what you are advocating. I also think you are blind to the fact that there are particles that we know to exist (not by calculation but by direct observation) that are impossible to detect with an optical or radio telescope, for the simple fact that they barely interact with ordinary matter at all. That makes counting them and adding them up through a telescope impossible (that's how they discovered the discrepancy, btw). In light of that evidence, the most plausible explanation is that there is a big mass of this stuff floating around that we simply cannot see. We need to be sure it isn't there before we decide the theory is wrong. Now, if there is strong evidence that Neutrinos and their ilk are not the cause of all the extra gravity, then we have to take a very hard look at General Relativity, which is what predicted the movement of the galaxy in the first place.

I think you are confused about what dark matter is believed to be. Dark Matter is believed to be non-baryonic matter. Simple as that. We have direct observations of non-baryonic matter. The largest telescopes in the world are actually designed to detect non-baryonic matter (and they succeed). They have to be buried deep in the earth because it is too easy to get noise from various types of radiation, but this is no problem, because non-baryonic matter doesn't interact with ordinary matter except in the rarest of situations. Neutrinos are probably the most well known type of Dark Matter, and those have certainly been directly observed. Scientists are even reasonably certain of the tonnage of neutrinos produced each year by our Sun. There are believed to be other types of Dark Matter, but the nature of the particles make them extremely difficult to study. But not impossible. The point is that expectations don't match up with reality, and the only sensible explanation is that the difference is caused by non-baryonic matter (since if it were baryonic, we'd almost certainly be able to see it). You can make predictions about what you should find based this theory, which can then be falsified. Dark Matter is falsifiable. That's probably the most important thing to know about it.

Photo of black hole https://www.jpl.nasa.gov/edu/news/2019/4/19/how-scientists-captured-the-first-image-of-a-black-hole/

That's a bad analogy. Mindbound already addressed black holes. Dark matter is however something where we know there's something weird going on, and the simplest explanation that doesn't involve completely throwing out general relativity is to posit that there's mass out there we can't see. Specific variants of that hypothesis each make different testable predictions (indeed we can even just test the general dark matter hypothesis by looking for other signs of dark matter, such as through gravitational lensing which confirms the presence of dark matter). The comparison doesn't hold.

It seems somewhat hard to understand why are black holes being included in this list - for objects that by their definition cannot be observed directly, there certainly seems to be a whole lot of a solid observational evidence for their existence, both in the case of stellar and supermassive ones.