The big bang theory

Big Bang Theory is a theory that attempts to explain the origins of the universe. "Discoveries in astronomy and physics have shown beyond a reasonable doubt that our universe did in fact have a beginning. Prior to that moment there was nothing; during and after that moment there was something: our universe" (All About Science). However, scientists have not been able to establish, beyond that same reasonable doubt, how the universe came into being. One theory is the Big Bang Theory. Currently the Big Bang Theory is the preferred theory about the origins of the universe, but it remains only a theory.

History of the Theory

The Big Bang Theory has been around for just under a century, though it was not fully developed when it originated. George Lemaitre first proposed the idea that the universe began much smaller than it currently is. This idea was reinforced by Edwin Hubble's observations that the universe is currently expanding. Finally, Arno Penzias and Robert Wilson's discovery of cosmic radiation seems to support the notion of a Big Bang (National Geographic).

George Lemaitre

George Lemaitre was a Belgian scientist and Catholic Priest. In 1927, he published a paper that suggested that the universe was expanding. While prior scholars had discussed the theory that systems might be expanding, Lemaitre was the first one to really suggest that the universe in which we live is expanding (Soter and Tyson). The idea of an expanding universe is a central component of the Big Bang Theory.

Edwin Hubble

While Lemaitre was able to suggest that the universe was expanding, he could not prove his suggestion. However, Edwin Hubble, an astronomer who had already made a groundbreaking discovery when he proved the existence of galaxies other than the Milky Way, was able to provide that proof. In 1929, Hubble "determined that the farther a galaxy is from Earth, the faster it appears to move away. This notion of an "expanding" universe formed the basis of the Big Bang theory, which states that the universe began with an intense burst of energy at a single moment in time -- and has been expanding ever since" (Space Telescope Science Institute).

Arno Penzias and Robert Wilson

Arno Penzias and Robert Wilson discovered further support for the Big Bang Theory in a different area. While prior researchers had suggested that the universe's continuing expansion helped provide support for a Big Bang, Penzias and Wilson provided a different type of evidence. "The glow of cosmic microwave background radiation, which is found throughout the universe, is thought to be a tangible remnant of leftover light from the big bang. The radiation is akin to that used to transmit TV signals via antennas. But it is the oldest radiation known and may hold many secrets about the universe's earliest moments" (National Geographic).

The Beginning

One of the most difficult concepts of the Big Bang Theory is the idea that the universe was once nothing. According to the Big Bang Theory, somewhere between 10 billion and 20 billion years ago, the universe was created from a singularity. This singularity somehow exploded, which resulted in the creation of the universe, released a tremendous amount of energy, and continues to propel the outward expansion of the universe.

Singularities

It is difficult to define a singularity because "Singularities are zones which defy our current understanding of physics" (All About Science). Scientists believe that singularities exist inside of black holes. They are thought to be areas of infinite density. The singularity at the beginning of the Big Bang did not begin in space; it was the origin of space.

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 slow.