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The Big Bang

The Big Bang
Early Universe
Life and Death of Stars
Galaxy Formation
The Solar System
Exotic objects
End of the Universe
Who created the universe?
What is Time?
Life beyond Earth
NASA Missions
Particle Map

By the middle of the 20th century, two different theories to explain the creation of the universe had been proposed. Some cosmologists supported the steady-state theory, which states that the universe has always existed and will continue to exist in its current form. Others believe in the Big Bang theory, which proposes that the universe was created in a massive explosion-like event (actually an instantaneous expansion) from a single point of infinite heat and density and infinitessimal size, about 13.7 billion years ago. The Big Bang theory enjoys widespread acceptance while the Steady State theory has largely fallen into obscurity. In this chapter, I will present the history of the Big Bang theory and an overview of the evidence that supports it.

Smallest, densest, hottest, oldest: these are the words that describe that distant, singular event in history we call the Big Bang. It is by far the oldest, most important and most puzzling event in history. It goes something like this. There was nothing. There was no space, no time, no matter. Then, in an instant, all the matter there is and ever will be, as well as time itself, sprang into existence. To summarize: there was nothing and then there was everything. From each miniscule particle of dust to the largest galaxy clusters, all of it emanated from that one explosive moment. From a super hot, infinitely dense singular point, smaller than an atom, everything that ever was or ever will be was created in an instant. Think of it as the genesis atom, the seed of creation from which space and time sprang forth. And the Bang continues unabated to this day at an ever-accelerating rate. It is popularly believed that the Big Bang was a huge explosion. This needs some clarification. The "explosion" we call the Big Bang was actually a sudden (and continuing) inflation of nothing into everything. It is like a balloon being inflated, where the surface of the balloon is the universe. As the balloon fills with air, its surface gets bigger and bigger, and any objects on the surface of it, representing stars and planets, get farther and farther apart from each other. So the explosion is really the beginning and continuation of an accelerating expansion of nothing into everything. One more point of interest: the accelerating expansion of the universe is the one case where the speed of light is exceeded.

In the first second after the Big Bang, matter as we know it did not yet exist. The temperature was hot beyond comprehension, approaching 1000 trillion (1,000,000,000,000,000, 1 quadrillion) degrees Celsius at just a tiny fraction of a second after the expansion began. In the first fractions of the first second there was only pure energy and what was to become the universe began to expand outward, symmetrically, in all directions at once at light speed or beyond. How is it possible for the expansion of the universe to exceed light speed? It is a matter of relativity or, rather, a lack of it. As will be explained below, objects in space are not actually moving away from us faster than light but the space between them is inflating faster than light, making the objects appear to move. As all of space is expanding at once there is no movement of an object relative to an observer. The temperature began to cool and, still within the first minute or so, the first primordial particles began to appear, the first matter. At this point, there was only a plasma soup made up of of pure energy and the elementary particles that make up atomic nucleons, such as quarks.

Hubble's Law
Some proponents of the Big Bang theory would say that it was not an explosion as commonly understood, as much as the sudden expansion of the genesis atom outward in all directions evolving into the expanding universe as it exists today. The evidence for Hubble's Law was observed as a reddish tint of distant galaxies when observed through an advanced telescope, known as the Doppler Shift. When an observer watches objects receding into the distance, the wave length (frequency) of the light emitted from the object increases (the waves get smaller) and the objects will reveal a slight reddish tint. When objects approach, the opposite occurs as the wave length of the light from the object decreases (the waves get larger) and they display a blueish tint. The Doppler Shift works both with light and with sound because sound travels in waves also. An obvious example of a Doppler Shift in sound waves is the familiar lowering of the pitch (amplitude) of the sound of a train as it recedes into the distance or an increase in the pitch of the sound as the train approaches. Edwin Hubble's observation of receding galaxies tinted red and the universe continuously expanding outward was the beginning of Hubble's Law, which states that the other galaxies in the universe beyond the Milky Way are constantly moving away from each other at a speed directly proportional to their distance from each other. Actually, the objects in space are not really moving away from each other, rather the spacetime between all objects is expanding in all directions and really fast at that. Imagine a red carpet with a throne placed at the end of the carpet. It is as if the carpet leading up to the throne is continually gaining new material and getting longer, while the throne at the end is not moving at all. In such a case, it is possible for the universe to expand faster than the speed of light. It could be inferred that the galaxies have always been moving away from each other and that if time is played back in reverse, the galaxies come closer together, with the universe initially existing at a single point of infinite density and energy. In a very real sense, the farther out into the universe you look, the farther back in time you are seeing. The initial, explosive expansion of that point into the early universe became known as the Big Bang.

Asymmetry between matter and anti-matter particles
Immediately after the Big Bang, the universe was tremendously hot as a result of particles of both matter and antimatter rushing apart in all directions. When matter and anti-matter collide they destroy one another creating pure energy. Fortunately for us, there was an asymmetry in favor of matter in the amount of about one part per billion. As the universe expanded, this discrepancy grew larger and the matter particles dominated those of anti-matter. Consequently, this almost insignificant majority grew and the universe evolved allowing this small surplus of matter to persist. The surplus matter was to become all of the matter that exists today. Consider this. Imagine a room with a perfectly flat floor, filled with little balls. The natural state would be that the balls are equally spaced from each other across the entire floor. It is the force of gravity that would cause the balls to be spaced equally apart in all directions, by pulling on all of the balls equally. In this scenario, nothing would happen and the balls would remain fixed in their equidistant locations from each other, because gravity is pulling on all the balls equally in all directions. Fortunately for us, it is a fundamental fact that there is always imperfection in nature. This means that there would be a very small number of missing balls in the grid - the grid would not be perfect. Consequently, gravity has an opportunity as the pull on the balls is no longer evenly spaced and some of the balls would move away from the spaces (missing balls) in the grid because gravity would be pulling on them just a little harder than the rest. This imperfection in the spacing of the balls would result in the remaining balls to start clumping together. This is the beginning of the process of accretion, by which small bits of matter would begin clumping into larger and larger bits and would eventually evolve into stars, planets and other astronomical objects. Gravity is the dominant force driving the process of accretion, the forming of objects in space.

Cosmic Microwave Background
Working at Bell Labs in Holmdel, New Jersey, in 1964, Arno Penzias and Robert Wilson observed uniform radio noise emanating from their antenna. At first they thought that they were receiving some random radio interference, and did everything they could think of to elimninate the noise locally. They systematically eliminated all sources of recognizable interference from their receiver. They removed the effects of radar and radio broadcasting, and suppressed interference from the heat in the receiver itself by cooling it with liquid helium to -269 C, only 4 C above absolute zero. This included cleaning pigeon droppings from the antenna. When they had eliminated all possible causes for the noise from their equipment, the noise persisted and they realized that the noise was coming from all directions in space equally.

Later, a group of astrophysicists at Princeton University was able to identify this noise as the afterglow of the radiation produced by the Big Bang, called the Cosmic Microwave Background, or CMB for short. This afterglow of the radiation generated by the Big Bang provides us with a persisting view of the universe in the moment after creation. It is like a recording of the radiation of the big bang in a state of constant playback. The group at Princeton, jointly with Penzias and Wilson published their results to avoid personal conflict and, in 1978, Penzias and Wilson were awarded the Nobel Prize for Physics for their joint discovery.