Universe, Origin of

Hubble Expansion and Inflation

The expansion of the universe was discovered by Edwin Hubble in 1929 and until recently has appeared to be linear; that is, the average recessional speed of galaxies from Earth was proportional to their distance. In 1998, two independent research groups made the surprising discovery, since confirmed by further independent observations, that the expansion is actually accelerating. The universe is falling up!

The latest data also strongly support a model proposed in the early 1980s called inflation, in which the Hubble expansion was preceded by an exponential expansion lasting only about 10−35seconds during which the universe increased in size by hundreds of orders of magnitude. This implies that by far the greatest portion of the universe that exploded from the same source lies beyond our visible horizon, the farthest distance we can see given the finite propagation speed of light. This rapid expansion flattened out the geometry of the universe analogous to the surface of a large balloon and further implied that the energy density of the universe is very close to what it should be if the universe began with zero total energy. That is, no energy from outside was required to produce the universe. The birth of the universe did not violate the law of conservation of energy or any other basic principle of physics.

Various models of inflation predict the existence of other universes besides our own, each appearing by the same process. Although we have no way of empirically verifying these universes, neither do we have a way of ruling them out. While some people have contended that science should not consider objects that cannot be directly observed, this argument is refuted by the fact that science has done so many times with great success, such as with the theory of atoms in the 19th century.

Dark Matter, Dark Energy, and Quintessence

Today visible matter, which constitutes all stars and galaxies seen with the most powerful optical telescopes, comprises only 0.5% of the mass of the universe. In fact, normal atomic matter, including that which is nonluminous, such as the matter in planets or dead stars, totals only 4%. The remainder of the universe is composed of some yet-unidentified substance called dark matter, comprising 26% of the mass of the universe, and an even more mysterious dark energy that is the largest component, fully 70% of the universe's mass. The dark energy is responsible for the repulsive gravity that drives the accelerated expansion. Furthermore, it is expected that this acceleration will continue to increase with time so that the universe is destined to become more and more dilute.

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