[OAB 29-31,87] It is claimed that many galaxy clusters do not have enough mass to hold themselves together, so that many of them should have drifted apart by now if the Universe is old. Also, it is claimed that "field galaxies" (galaxies that are not part of a galaxy cluster) should exist in an old Universe but do not. The first objection is easily answered by noting that not all stars or galaxies that appear to be in close proximity are actually gravitationally bound. A star or galaxy could simply be passing through a neighboring cluster, and thus it would be no surprise to observe that it is moving too fast to be gravitationally bound to the cluster. Also, the existence of dark matter (for which even further observational evidence was announced as of 30 April 2001) causes clusters to be more massive than they appear, and thus to have enough gravity to hold stars or galaxies at higher velocities. For example, similarly too-fast velocities are observed in spiral galaxies, where the stars show every sign of being in stable orbits. This is almost certainly due to extra mass in the galaxy comprised of dark matter. An excellent discussion of dark matter was written recently by V. Rubin (Scientific American Presents, v.9, no.1 (Spring 1998), or http://www.sciam.com/specialissues/0398cosmos/0398rubin.html). The second part of the objection (the lack of field galaxies) is simply incorrect. Field galaxies are well-known to astronomers, and are an object of ongoing study.