Big Bang Theory

Informative Essay

4-22-00

Freshman English 1

Big bang theory

It is always a mystery about how the universe began, whether if and when it will end. Astronomers construct hypotheses called cosmological models that try to find the answer. There are two such models: the Big Bang theory and the Steady State model. Because of many observational evidences, the Big Bang theory best explains the creation of the universe.

The Big Bang model postulates that about 15 to 20 billion years ago, the universe violently exploded into being, in an event called the Big Bang. Before the Big Bang, all of the matter and radiation of our present universe was packed together in an extremely hot, dense state. During the Big Bang, the matter and radiation of that early stage rapidly expanded and cooled. Several million years later, it condensed into galaxies. The universe has continued to expand, and the galaxies have continued moving away from each other ever since. Today, it has been observed that the universe is still expanding.

The Steady State model says that the universe does not evolve or change with time. There was no beginning in the past, nor should there be any changes in the future. This model assumes the perfect cosmological principle; that the universe is the same everywhere on the large scale, at all times. It maintains the same average density of matter and energy forever.

There is much observational evidence that proves the Big Bang model is more reasonable than the Steady State model. For example, the observed red shifts of distant galaxies. Red shift is a Doppler effect that occurs when an object, such as a galaxy, is moving away from the observer. The spectral line of the galaxy will have a shift to the red end of the light spectrum. The faster the galaxy moves, the farther the shift. If the galaxy is moving closer, the spectral line will be shifted toward the blue end. If the galaxy is not moving, there is no shift at all. However, as astronomers have observed, the more distant a galaxy is from Earth, the more red shifted it is on the spectrum. This means the further a galaxy is, the faster it is moving. This all implies that the universe is expanding, and the Big Bang model is more reasonable than the Steady State model.

Another supporting piece of evidence is the radiation produced by the Big Bang. The Big Bang model predicts that the universe should still be filled with a small remnant of radiation left over from the original violent explosion. The almost instantaneous expansion would have sent strong short-wave radiation in all directions into space. In time, that radiation would spread out, cooled, and filled the expanding universe uniformly. By now it would strike Earth as microwave radiation. In 1965 physicists Arno Penzias and Robert Wilson detected microwave radiation coming equally from all directions in the sky, day and night, year round. This radiation is assumed to be the radiation that was produced by the Big Bang. This casts serious doubt on the Steady State model. The Steady State cannot explain the existence of this radiation, so the model is thought to be wrong in explaining the beginning of the universe.

Now that the Big Bang model has been shown to better fit observational evidence, it can be explained in greater detail. Around 15 to 20 billion years ago, time began. The points that were to become the universe exploded in the primeval fireball called the Big Bang. The exact nature of this explosion may never be known. However, recent theoretical breakthroughs, based on the principles of quantum theory, have suggested that space, and the matter within it, masks an infinitesimal realm of utter chaos, where events happen randomly, in a state called quantum weirdness. Before the universe began, this chaos was all there was. At some time, a portion of this randomness happened to form a bubble, with a temperature in excess of 10 to the power of 34 degrees Kelvin. Being that hot, naturally it expanded. For a brief and short period, billionths of billionths of a second, it inflated. At the end of the period of inflation, the universe may have had a diameter of a few centimeters. The temperature had cooled enough for particles of matter and antimatter to form, but they instantly destroyed each other, producing fire and a thin haze of matter; probably because slightly more matter than antimatter was formed. This fireball was the universe at an age of trillionth of a second. The temperature of the expanding fireball dropped rapidly, cooling to a few billion degrees in few minutes. Matter continued to condense out of energy, first protons and neutrons, then electrons, and finally neutrinos. After about an hour, the temperature had dropped below a billion degrees, and protons and neutrons combined and formed hydrogen, deuterium, and helium. In a billion years, this cloud of energy, atoms, and neutrinos had cooled enough for galaxies to form. The expanding cloud cooled still further until today, where the temperature is a couple of degrees above absolute zero. In the future, the universe may end up in two possible situations.

From the initial Big Bang, the universe attained a speed of expansion. If that speed is greater than the universe’s escape velocity, then it will not stop expanding. Such a universe is said to be open. If the velocity of expansion is slower than the escape velocity, the universe will eventually reach the limit of its outward thrust, just like a ball thrown in the air comes to the top of its arc, slows, stops, and starts to fall. The crash of the long fall may be the Big Bang to the beginning of another universe, as the fireball formed at the end of the contraction leaps outward in another great expansion. Such a universe is said to be closed, and pulsating. If the universe has achieved escape velocity, it will continue to expand forever. The stars will redden and die, the universe will be like a limitless empty haze, expanding infinitely into the darkness. This space will become even emptier, as the fundamental particles of matter age, and decay through time. As the years stretch on into infinity, nothing will remain. A few primitive atoms such as positrons and electrons will be orbiting each other at distances of hundreds of astronomical units. These particles will spiral slowly toward each other until touching, and they will vanish in the last flash of light. After all, the Big Bang model is only an assumption. No one knows for sure exactly how the universe began and how it will end. However, the Big Bang model is the most logical and reasonable theory to explain the universe in modern science.

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