Dark matter cannot be any sort of matter that is known to science. - Mordehai Milgrom

The nice thing is that MOND has not had to change or adjust itself to the many observations that came after it was proposed. … In the end, the process that might sway people's minds could be a slow one, in which they become disillusioned and dissatisfied with DM, while MOND explains more and more of the observations. And, if MOND does turn out to have some truth to it, the fact that it encountered so much opposition will just show how nontrivial a thought it was.

I did encounter much opposition and sheer disregard, and this was against my expectation. I was surprised that people thought that this was not a legitimate avenue to explore. Many times I heard people say that it is too early to start considering such heretical ideas. Why? I wondered. I thought it was legitimate to consider anything.

To explain the appearance in MOND of a cosmological acceleration constant, a₀, I suggest that MOND inertia — as embodied in the actions of free particles and fields — is due to effects of the vacuum. The same vacuum effects enter both MOND (through a₀) and cosmology e.g. through a cosmological constant Λ).