Black Holes

While singularities are difficult to define and to prove, black holes are not. Black holes are areas with such extreme gravitational pull that the velocity an object would need to escape them is greater than the speed of light, and, thus, unattainable. Bl.ack holes are observable and have been proven to exist. They may be created when a star collapses, though this is also a theory.

Infinite Density

Because the gravitational pull of a black hole is immense, objects cannot escape from it. Moreover, as the objects approach the event horizon of the black hole, the gravity becomes more and more intense, so that, eventually objects are unable to escape. This means that the black hole continues to engulf matter. Furthermore, the intense gravity that exists in a black hole means that this matter is all compressed into a tiny spot.

Expansion

At some point in time, for reasons unknown, the singularity released a tremendous amount of power.

Initial Expansion

The initial speed of expansion was well beyond the speed of light. "The theory maintains that, in the instant -- a trillion-trillionth of a second -- after the big bang, the universe expanded with incomprehensible speed from its pebble-size origin to astronomical scope" (National Geographic). The expansion has slowed from its initial speeds.

Current Expansion

While expansion has slowed, the universe continues to expand. In fact, observations of this expansion are what led to the formation of the Big Bang Theory. Of particular interest is Hubble's Law, which is that galaxies are moving away from us at speeds that are proportionate to their distance; in other words, the farther away they are, the slower they are moving away. This suggests that expansion is continuing to...

What will occur at that time period is speculative. There is a relationship between time and relativity, so that some people have suggested time will stop; while others suggest that the gravitational pull that is presumably causing the expansion of the universe to slow will then begin to cause the universe to contract. The reality is that the Big Bang Theory does not adequately posit what will occur when expansion stops.
Conclusion

The Big Bang Theory is the most popular theory to explain the beginning of the universe, but it is not the only model. Moreover, its complexity means that it has many flaws, because some of the cornerstones of the model, such as the existence of a singularity, and the impetus for the initial "bang" are not explained, even within the model. There are also philosophical underpinnings to the theory that might impact its scientific validity. However, while these flaws might all be true, it is equally true that the Big Bang Theory provides one explanation for why the universe is expanding.

Works Cited

All About Science. "Big Bang Theory- an Overview." All About Science. N.p. 2012. Web.

11 Dec. 2012.

Space Telescope Science Institute. "Hubble Essentials: About Edwin Hubble." Hubblesite.

N.p. 2012. Web. 11 Dec. 2012.

National Geographic. "Origins of the Universe: An Expanding World. National Geographic.

N.p. 2012. Web. 11 Dec. 2012.

Soter, Stephen and Neil deGrasse Tyson. "Profile: Georges Lemaitre, Father of the Big Bang."

American Museum of Natural History. N.p. 2000. Web. 11 Dec. 2012.