wn as omega and estimated at roughly six hydrogen atoms per cubic meter, necessary to pull the universe back in on itself. In this model, referred to as the "open" model, the universe will continue to expand and cool indefinitely. If however, the density of he universe is greater than omega then the universe will eventually, after billions of years, collapse in what physicists call the "big crunch. "A third and highly unlikely possibility is that omega equals precisely one; in this model, the universe gradually slows and cools to a static state.
While it would seem at first glance that the fate of the universe-that is, whether matter exceeded omega or not - could be determined by the admittedly complex but not impossible task of calculating the amount of matter and dividing it by the dimensions of the universe, in fact, there is a complicating factor. The galaxies and nebulae, or primordial dust clouds out of which stars and galaxies, do not pull on themselves or on each another as they should. That is to say, they behave as if there was more mass and, hence, gravitational pull than can be observed. For example, the Andromeda galaxy, the nearest neighbor to our own Milky Way galaxy, is rushing toward us at 200,000 miles per hour, a speed that cannot be explained by the gravitational force of the matter in the two galaxies. In fact, the two galaxies are coming together at a pace requiring some 10 times that amount of matter. Physicists offer the possibility that there is dark matter in the universe, that is, an unknown type of matter that does not emit or reflect enough electromagnetic energy to be observable by current means. Such dark matter, according to this hypothesis, exists in haloes around galaxies and may be what composes black holes and massive clouds of neutrinos, particles formed from radioactive decay with little mass and no electric charge. Such dark matter would imply a universe that eventually collapses in on itself, except for an additional complicating factor.
Scientists hypothesize that there is also a dark energy in the universe counteracting both matter and dark matter, a kind of anti-gravitational force that is also undetectable with existing technology. While dark matter is believed to constitute 22 percent of the universe, dark energy is believe to compose 74 percent. These numbers, along with the difficulties of detecting dark matter and energy make it impossible for physicists as of the early twenty-first century to come to a definitive conclusion about the ultimate fate of the universe.
Pre-Twentieth Century Ideas of Universe's Origins
The origins of creation have, of course, preoccupied humanity since at least the beginning of civilization itself. Virtually every culture around the world has created myths to explain how the universe came into being, even if they did not necessarily comprehend the universe's magnitude and complexit...
