Big Bang Cosmology Fundamentals

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Big Bang Cosmology Fundamentals

We start out with the basic Cosmological Principle for an
isotropic and homogeneous Universe. We then review Hubble’s Law that came from the discovery that the Universe was expanding. We go into some depth to illustrate what expanding space is and how it impacts the basic idea of ‘distance’. This includes a definition of Cosmic Distance and how it leads to the Visible Horizon.

We then develop a concept of how the Universe’s expansion would work using Newton’s gravitational theory including his Shell Theorem. We use this to define a cosmic scale factor and use it to see what happens in a matter dominated Universe. We then expand that to include a radiation dominated Universe. With the Newtonian mechanics view in hand, we update to Friedmann’s equation based on Einstein’s General Theory of Relativity along with the Equation of State. We examine the impact of flat, spherical and hyperbolic space on the cosmic sale factor, and identify the Critical Energy Density needed in order to have flat space. We end with a look at cosmological redshift, and an observation on galaxy counts that lead to the conclusion that we exist in flat space-time{

How was our Universe created? How did it come to be the seemingly infinite place we know of today? And what will become of it, ages from now? These are the questions that have been puzzling philosophers and scholars since the beginning the time, and led to some pretty wild and interesting theories. Today, the consensus among scientists, astronomers and cosmologists is that the Universe as we know it was created in a massive explosion that not only created the majority of matter, but the physical laws that govern our ever-expanding cosmos. This is known as The Big Bang Theory.

For almost a century, the term has been bandied about by scholars and non-scholars alike. This should come as no surprise, seeing as how it is the most accepted theory of our origins. But what exactly does it mean? How was our Universe conceived in a massive explosion, what proof is there of this, and what does the theory say about the long-term projections for our Universe?

The basics of the Big Bang theory are fairly simple. In short, the Big Bang hypothesis states that all of the current and past matter in the Universe came into existence at the same time, roughly 13.8 billion years ago. At this time, all matter was compacted into a very small ball with infinite density and intense heat called a Singularity. Suddenly, the Singularity began expanding, and the universe as we know it began.

Timeline of the Big Bang Theory
Working backwards from the current state of the Universe, scientists have theorized that it must have originated at a single point of infinite density and finite time that began to expand. After the initial expansion, the theory maintains that Universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms. Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies.

This all began roughly 13.8 billion years ago, and is thus considered to be the age of the universe. Through the testing of theoretical principles, experiments involving particle accelerators and high-energy states, and astronomical studies that have observed the deep universe, scientists have constructed a timeline of events that began with the Big Bang and has led to the current state of cosmic evolution.

However, the earliest times of the Universe – lasting from approximately 10-43 to 10-11 seconds after the Big Bang – are the subject of extensive speculation. Given that the laws of physics as we know them could not have existed at this time, it is difficult to fathom how the Universe could have been governed. What’s more, experiments that can create the kinds of energies involved have not yet been conducted. Still, many theories prevail as to what took place in this initial instant in time, many of which are compatible.

Questions?