It remains unknown whether the universe will expand forever or will contract again. One approach to solving this problem is to learn the average density of matter in the universe. The mass of each galaxy multiplied by the number of galaxies is only 5 to 10 percent of Friedmann’s critical value. Multiplying galactic cluster mass by the number of clusters results in an average density near the critical value. The difference between these results suggests the presence of invisible matter, the so-called dark matter, outside the galaxies but within the clusters. Until the missing-mass phenomenon is understood, this method of determining the fate of the universe will be inconclusive.