What Can We Learn About the Universe from Just One Galaxy?

Imagine if you could look at a snowflake at the South Pole and determine the size and the climate of all of Antarctica. Or study a randomly selected tree in the Amazon rain forest and, from that one tree--be it rare or common, narrow or wide, young or old--deduce characteristics of the forest as a whole. Or, what if, by looking at one galaxy among the hundred billion or so in the observable universe, one could say something substantial about the universe as a whole? A recent paper, whose lead authors include a cosmologist, a galaxy-formation expert, and an undergraduate named Jupiter (who did the initial work), suggests that this may be the case. The result at first seemed "crazy" to the paper's authors.