Students will make observations of two containers in order to identify differences in content, justify their claims, and make comparisons to dark matter observations. Materials 2 clear jars or bottles with lids Loose change, washers, or nuts and bolts Water Management Prepare the jars as described in Step 1 of Procedures prior to student arrival or class starting. Background Cosmologists, or people who study the origin and evolution of the universe, have discovered that what we think of as ordi