A Tale of Two Paradigms: the Mutual Incommensurability of LCDM and MOND

Understand

The concordance model of cosmology, LCDM, provides a satisfactory description of the evolution of the universe and the growth of large scale structure.

• Despite considerable effort, this model does not at present provide a satisfactory description of small scale structure and the dynamics of bound objects like individual galaxies.
• In contrast, MOND provides a unique and predictively successful description of galaxy dynamics, but is mute on the subject of cosmology.
• Here I briefly review these contradictory world views, emphasizing the wealth of distinct, interlocking lines of evidence that went into the development of LCDM while highlighting the practical impossibility that it can provide a satisfactory explanation of the observed MOND phenomenology in galaxy dynamics.