How will this resolve if ´dark matter’ does not exist as a particle(s) and the gravitational anomalies we observe (disk galaxy rotation curves, velocity dispersion profile of elliptical galaxies, galaxy cluster dynamics) are explained by new physics such as MOND?

@mariopasquato would be logical to resolve it to 100%, I think. If there is no new matter, then all the dark matter we thought of is baryonic

@CyfralCoot We have the ability to think up non-existent stuff though. What percentage of phlogiston is made up of oxygen? I get what you are saying but from a different angle your suggestion sounds like setting 0/0=1.

I'm confused. If we discover that no dark matter is baryonic and it's all something else, shouldn't that obviously resolve this to 0%? What am I missing?

@mariopasquato Yes, that's something I didn't consider... Although we can say that oxygen causes nearly 100% of "phlogiston behaviour".... And it seems very unlikely that the dark matter is completely non-existent like phlogiston. There's too much evidence towards the existance of some invisible mass

@CyfralCoot Some other market had “Other” as the explanation for dark matter above 20% though

@IsaacKing You might as well say that all of the (non-existent) dark matter is X, where X is any property, including being baryonic. But if you say you will resolve to 0% then that’s great.

Oh, I see the confusion. I had meant "dark matter" to refer to "whatever causes these observations", but you were interpreting it as actually being matter. I think your interpretation is more in line with normal usage, so that's my bad. I'll update the description to clarify.

@mariopasquato BTW, some of the alternate explanations I heard only fail to count as "matter" by dint of the authors using a definition of "matter" narrow enough that most people in 1850 didn't believe water to be "matter"

@ArmandodiMatteo what is matter? That’s a good question. Two photons with equal energies moving in opposite directions inside a box have rest mass… are they matter? What if I can peek inside the box, do they stop being matter then? Fun stuff

@mariopasquato in the standard definition of words used in cosmology, a gas of non-interacting particles is "matter" if each particle is non-relativistic and "radiation" if each particle is ultrarelativistic, so you have radiation inside the box. A gas of particles each travelling at 0.75c wouldn't clearly fit in either category, but what I was thinking of is stuff not made of particles at all -- which I'd argue should still be called "matter" if its stress-energy tensor, when averaged over macroscopic scales, looks like that of a gas of non-interacting non-relativistic particles.