> The point they're making is that the particular distribution of dark matter and the initial conditions at the big bang have to be tuned to match observations

> The point they're making is that the particular distribution of dark matter and the initial conditions at the big bang have to be tuned to match observations because the natural predictions of CDM don't match observations. This isn't true. The distribution of dark matter in LCDM matches the observed distribution remarkably well. There are still some uncertainties at the cores of galaxies, where baryonic physics is more complex (for example, star formation and black hole feedback are difficult to simulate accurately), but on larger scales, LCDM does very well without any tuning. > By contrast, in MOND many observations follow only from the amount of visible matter. MOND isn't an actual theory. It's an idea of how one might modify Newtonian mechanics, but any fully fleshed-out theory is relativistic. Which theory of modified general relativity are you referring to, specifically? > LCDM itself requires a number of assumptions to match observations It requires 6 parameters, as I said earlier, to explain everything in cosmology. > LCDM requires visible matter + postulating invisible matter in a specific distribution. You keep saying this, but it's simply wrong. LCDM only requires a Gaussian random field as an initial condition. It has one free parameter to specify that field's density distribution: a scalar spectral index. We actually know for certain that the universe was in such a state early on (from the Cosmic Microwave Background), so this is a very solid assumption. LCDM takes that initial state, applies the known laws of physics, and ends up with the matter density distribution we see today, without any tuning. > By contrast, most astrophysicists that are gung-ho on LCDM sweep under the rug the inconvenient tuning that's needed to actually match observations. Astrophysicists are not "gung-ho" about LCDM. They're constantly looking for ways in which it might break. It's actually quite depressing that LCDM does so incredibly well, because it would be exciting to find something new. Astrophysicists are actually very open-minded about modified gravity. The problem is that, contrary to what the paper you've found is claiming, there's no theory of modified gravity that explains away dark matter, while reproducing all the cosmological phenomena that are observed. Every theory of modified gravity messes up something big, like the halo mass function, the elemental abundances or the speed of gravitational waves. The only theories that don't mess things up are tiny modifications of general relativity, but those theories require dark matter.