Abstract

On a mountain top on a clear moonless night the brilliant stars strewn across the sky press down almost oppressively, the Milky Way so full of them it seems about to burst. And yet, we have been learning in the past decade that the visible matter of the universe, the stars that we see, represent only a tiny fraction, perhaps less than one part in 200, of the mass of the universe. The question of what the remainder of the universe is made of is called the Dark Matter Problem. It is one of the most vexing in modern physics.