THE BIG BANG THEORY

Four Key Points to the Big Bang Model

1. Expansion of the universe.

2. Origin of the cosmic background radiation.

3. Nucleosynthesis of the light elements.

4. The formation of galaxies.

EXPANSION OF THE UNIVERSE

The big bang model asserts that the universe was created in a titanic explosion some 10 to 20 billion years ago from a primordial atom.  Every particle in the universe went flying off into every direction creating space and time as the expansion continued.  The current observation of galaxies receding away from us is evidence that this expansion is still taking place today; and if you were to, in essence, run this "movie" backwards, the galaxies would all come flying back to one central point.  This point is where the big bang began. This is picture is hard to imagine, but the best analogy I've heard is where you take a balloon, color some dots on it and blow it up.  Although this is only two dimensional, you can see the dots appear to move away from each other. The earth does not lie at the center of the universe even though it seems to be rushing away from us in all directions.  That the universe appears the same, no matter where we look is known as the cosmological principle.  It states that the universe appears the same in every direction from every point in the cosmos.  Our place is of no preference.  And there is evidence for this; from the distribution of galaxies throughout the universe to perhaps the best evidence of all; the cosmic microwave background radioation, which is a leftover relic of the big bang itself.

THE COSMIC BACKGROUND RADIATION

From the time of the Big Bang the universe had been nothing but a sea of free particles in a very, very hot universe.  When the universe had cooled enough (about 100 seconds after the bang), protons and neutrons were able to bind together to form helium nuceli.  Element formation has started, but it is still too hot for atoms to form. For the next several thousand years the universe is nothing more than a hot plasma consisting of photons, neutrinos, unbound protons and electrons and helium nuclei.  The universe is dominated by massless photons moving at the speed of light(electromagnetic radiation) and heavier atoms are still unable to form because of collisions with these high energy photons that strip the nucleus of any atom that might try to form.  About 100,000 years later temperatures have cooled to about 3000 Kelvin to 4000 K and electrons and nuclei can begin to form matter.  As matter continues to grow, the background radiation continues to cool until today where it is about 3 Kelvin.  The discovery of this background radiation in 1964 by Penzias and Wilson showed evidence that the big bang had indeed occurred as the radiation observed was the same in every direction, lending evidence to an expansion of the universe that began long ago.

SYNTHESIS OF LIGHT ELEMENTS

As the universe continued to cool and deuterium atoms formed, other elements also formed. Hhelium-3 and helium-4 and lithium were also developing.  A hydrogen atom has one proton and one neutron.  All other isotopes of hydrogen also have only one proton, but their neutron number varies.  Deuterium has two neutrons to go with its one proton.  In helium there are two protons and two neutrons.  Helium isotopes could have 3 or 4 neutrons.  Theory states that certain amounts of these elements would have been produced and that is in agreement with observations today.  Heavier elements would not be formed until much later in the insides of the stars.

THE FORMATION OF GALAXIES

As time continued to pass and temperatures continued to cool to the point where heavy particles began to dominate instead of radiation.  With this the gravitational force began to play a major role and any chang in matter density meant that this force could take affect.  It did and what we see today is the result. Billions of galaxies and other large structures that permeate the universe.  While we can understand the formation of galaxies, we still do not understand the fluctuations in matter that occurred at 10,000 years to yield this result.  More research in this field could help to provide some answers.

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