Question

Describe what happens to the expansion rate and age of the universe when you increase the density of the attractive mass in the universe. Why do these changes occur?(mass means gravity)

Answer 1

In order to understand the effect of increasing density of the attractive mass (gravity) in the universe first of all we need to elucidate about the expansion rate of the universe.

In pretext to the observations made by cosmologists and space experts the expansion of the universe can be understood as the velocity at which a distant source(say galaxy,milkyway, stars etc)  is receding away from the observer increasing continuosly with respect to time. Whearas age of the universe is the time elapsed since the Big Bang (Big Bang is a model which describes how the universe expanded from an initial state when universe is of very high density and high temperature)

.As all of us know that gravity is attractive in nature.As the universe expands the volume of space content within it is increases as a result desity of matter decreses.Since we know this fact that density is inversely related to volume. Whether the expansion rate of universe is slowing down or speeding up depends on two factors:- firstly the attractive gravitational force(pull) of matter and secondly the repulsive gravitational force (push) of dark energy. Since density of dark energy is expected to change invariably as the universe expands. Althougha little is known about the dark energy, but is well known evident form the research that the density of the dark energy is much higher than that of matter (all celestial objects viz.stars,planets,galaxies etc.). Hence expansion rate of the universe will depend majorly on the relative trend of variation of density of dark energy and the density of matter as well.

Hence, if dark energy density increases rather than decreases, the universe will eventually undergo a “hyper speedup” that would distort apart galaxies, solar systems, planets and atomic nuclei, in that order. Or the universe might even recollapse if dark energy density falls to a negative value. The only way to forecast our cosmic future is to figure out the nature of dark energy.

If the universe is uniform, then general relativity has a simple solution for the evolution of the geometry of the universe: it either expands (or contracts) uniformly. The density and composition of the universe governs its rate of expansion. The larger the density of the universe, the more effective gravity is at slowing its expansion.