I wonder how the heck I even wrote this, as I just do not find it to be very interesting. (Plato is way more fun!) I hope it does not bore you!
"There are so very many things we know about the universe. In this brief overview, I will focus on what I deem to be the most important items and how we know them to be true: age of the universe, light, redshift, expansion, dark matter, the Big Bang, geometry, composition, cosmic microwave background, and dark matter. First, I will summarize how we know these things. I can best say it in two words: measurement and light. Measurement is what allows us to understand the empirical evidence for the things we know.
Oversimplified, measurement is what helps us prove that we are a universe that is 13.7 billion years old. The distance we measure is measured by light. Stars play an important role in this measurement of light. Astronomers measure the colors of stars, as they come in red, blue, and yellow, like our Sun. Redshifting, the process by which the frequency of light waves decreases as the universe expands, tells us this.
The universe is expanding. In 1900 it was understood that there was only one galaxy: ours. Today, just one hundred years later, we know there are at least 100 billion galaxies. We also know this from measurement. We must recall that expansion is not an explosion into space, but an explosion of space.
The expansion started with the Big Bang, approximately 13.7 billion years ago. The reason we know this is the 1964 microwave echo of the Big Bang discovered by Penzias & Wilson. Starting with quark soup and the laws of physics, these very hot quarks stuck together. These neutrons and protons made lithium. Lithium, added to the already existing helium and hydrogen created a nuclear reaction, known as the Big Bang.
Einstein shows us three types of geometry: un-curved, curves back on itself, and curves like a saddle. The universe is un-curved, therefore infinite. We know this from the Wilkinson Microwave Anisotropy Probe (WMAP). WMAP is what we have learned since COBE. Mathematical analysis is used to measure the atoms, degrees, and the amount of matter. WMAP also gave us the composition of the universe, showing us it is 4% atoms, 21% dark matter, and 75% dark energy. With an infinite, un-curved area, the universe can keep expanding.
Prior to WMAP, we had COBE, the Cosmic Background Explorer. COBE discovered ripples in the Cosmic Microwave Background which taught us there are lumps in the flat universe. This is important to understand because it led us to higher resolution telescopes and tools such as WMAP.
There are those things that are not light, called dark matter. Dark matter is not the absence of stars but they are particles of matter left over from the Big Bang. We know this from understanding gravity. Gravity is the evidence for dark matter.
In summary, it is difficult to summarize such a vast amount of ideas, theories, experiments, and discoveries. The things we know for sure are measurement and light. We start with measurements of light, distance, and temperature. It allows us to measure speed, distance and time. These two simple ideas allow us to understand many complex ideas and structures of our universe."
