Advanced Background Information
Geometry of Space
There are three possible geometries of space. Space is closed, flat or open. In a closed Universe the geometry of space is equivalent to living on a globe. If you travel in a straight line, eventually you will return to the same place. In a flat Universe, the geometry is like living on a flat sheet of paper. An open Universe, like a closed Universe is curved, but light traveling in a straight line diverges. The geometry of this space looks like a saddle. It has been determined that our Universe has a flat geometry.
Inflation
Inflation was an episode of extremely rapid and accelerating expansion in the early Universe. At 10 - 3 7 second from the beginning the Universe underwent inflation and increased in size by an inconceivable factor of 10 5 0! It is possible that this may have happened just before the end of grand unification, as the result of the development of a "false vacuum" with a high density of vacuum energy. There is no accepted explanation for why this would have happened but inflation solves several perplexing problems.
Inflation resolves the horizon problem. The horizon problem is the issue that without inflation the universe would not have been able to be in thermal equilibrium at the time of the last-scattering surface. Consequently, the CMB radiation at a constant temperature of 2.725 K within 1 in 10,000 is unexplainable without inflation, which enables the early universe to have the time and the proximity to be in thermal equilibrium before the tremendous expansion.
Another problem that inflation resolves is the flatness problem. The Universe has an energy density that is almost exactly equal to the critical density that determines whether the Universe will eventually contract or expand forever. It has been determined that the energy density is almost exactly equal to the critical density with an unimaginable accuracy. If the energy density was even slightly different than the critical density in the early universe, the value would have diverged very rapidly. This is equated to trying to stand a pencil on its point. The pencil will stand on its point initially, but the pencil will lean in the direction that it started because it is not perfectly centered at its center of gravity. This effect is magnified by gravity the more that the pencil leans so the pencil accelerates in its fall. So how could the Universe have existed in this state of balance for 13.7 billion years? It is statistically impossible and we know of no reason why the Universe would have started with a value so nearly equal to the critical value.
Inflation also presents an explanation for the origin of cosmic structure. In Inflation, a very small part of the Universe expanded to become our entire known universe. The expansion of this small region would actually have magnified the quantum fluctuations known in quantum mechanics. This gives an explanation for how the fluctuations of matter could have resulted in the known variations in matter density that resulted in the formation of galaxies and clusters.
Although Inflation is a very challenging concept, it is a very attractive theory because it is able to explain a wide variety of problems that otherwise elude explanation. There are variations on the inflationary theory, but it appears that there is sufficient circumstantial evidence to validate the theory. (Guth)
Alternative Theories to the Big Bang
There are alternative theories to the Big Bang. The Steady State Model was popular. The Steady State Model suggested that the Universe was static. Later variations included the possibility that the Universe was expanding but that matter was created to maintain a constant density. Albert Einstein was so convinced that the Universe was static that when his formula indicating a non-static universe he inserted the cosmological constant, L, to force his formula to be static. He later acknowledged the error of this approach, but ironically, his cosmological constant is one of the leading explanations for the repulsive force that is the predominant constituent of our Universe.
The Unification of the Four Forces
The explorations into the events of the early Universe are defining the very nature of the Universe and suggest that the four fundamental interactions were unified in the tremendous temperatures within the first second of the Universe. In these extreme early conditions matter and energy were interchangeable and even the four fundamental forces of physics (gravity, electromagnetic, the strong and the weak interactions) were unified. The equivalence of "phase transitions" were removed and symmetry was restored (Weinberg,149; Freedman and Kaufmann,664).
Black Body Spectrum
In a perfect black body spectrum photons do not involve radiation, but rather photons permeate space. There is an implication that time is involved and photons are energy that has been spread out, but they do not arrive. They have always existed where they are but space has expanded, causing them to be a lower frequency.
The CMB can be calculated using Wein's law 
. So if we
know the current wavelength, we can project backwards to calculate the temperature at various times in the early
universe.
Gravitationally Bound Objects
High matter density region, like within galaxies, do not expand because the Coulomb force and gravity prevent their expansion.
Nature of Light
What is the nature of light? What does the limit of the speed of light tell us about the nature of reality? What does it tell us about the relationship of space and time? For an object traveling at the speed of light, time does not elapse. This is equivalent to the time dimension disappearing. For an object accelerating toward the speed of light, the mass and therefore the energy, relativistically goes to infinity. What does this tell us about the nature of light and the nature of reality itself? How can the limit of the speed of light have a unit of time when time is dilating (Heinz Ahlers, personal conversation)? Should it cause astronomers and physicists consternation that there is a limit to the speed of light? Is this limit telling us something fundamental about nature?
Determining Astronomical Distance
It is very difficult to determine astronomical distances. The process involves determining the distance to stars or galaxies using geometry by the method of parallax. Astronomers use the distance known as a parsec. A parsec is the distance that results in an angle of 1 arc second that encompasses 1 AU. One parsec is equal to 3.2 light years. In addition, astronomers use the intrinsic brightness of an object because the luminosity is related to the brightness and the distance from the object. The apparent brightness of an object as observed from Earth (technically referred to as energy flux) is L/4∏d 2.
Comments: