21. A basic example is mass density . 22. This appeared to confirm earlier intimations of a universe with a mass density too low to fit many theories. 23. Growing or shrinking " R " with time means expanding or collapsing universe, depending on the mass density inside. 24. Therefore the rate of diffusion of different gases is inversely proportional to the square root of their mass densities . 25. When combined with estimates of the stellar masses, this yields a mass density estimate of g / cm 3. 26. A typical mass density for a globular cluster is, which is 500 times the mass density near the Sun. 27. Knowing the mass density of the universe, in both ordinary and dark matter, is a critical issue in cosmology. 28. The first quantitative estimates of the mass density in supermassive black holes were 5-10 times higher than SoBtan's estimate. 29. So the Oort constants can tell us something about the mass density at a given radius in the disk. 30. A typical mass density for a globular cluster is, which is 500 times the mass density near the Sun.