> isn't dark matter simply a plug because mass of galaxies and large scale astronomical structures calculated from light and other electromagnetic radiation, do

> isn't dark matter simply a plug because mass of galaxies and large scale astronomical structures calculated from light and other electromagnetic radiation, doesn't agree with mass calculated by observing they're gravitational interaction? One might more generously say that dark matter is a proposed explanation for many measurements deviating from predictions based on visible matter in a way very consistent with the existence of large amounts of non-electromagnetically-interacting matter. I don't think there's anything fundamentally ridiculous about this. For instance, while you characterise it as 'radically' different to any matter that we observe directly, the neutrino has most of the relevant properties, and e.g. supersymmetry has been noted to include dark matter candidate particles. While one may doubt that supersymmetry is actually correct, I think it demonstrates that the combination of properties (massive + electromagnetically inert + maybe weak force interacting) isn't necessarily a problem.