Introduction to Cosmology - 2.2.3
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#Cosmology
In this video we will discuss a bit about one of the most complex areas of physics. This topic is of course cosmology. While this topic traditionally had nothing to do with relativity, I've chosen to add it here because modern cosmology has a lot to do with relativity. When we look into space, we see many objects, and in order to see objects we must receive photons or light from these objects. Light was first understood with the help of special relativity and modern electrodynamics. As discussed previously, in modern cosmology we also use general relativity as one of the main tools to understand and model the universe that we observe. But of course, cosmology is about much more than relativity. This field of study uses all aspects of physics including Newtonian mechanics, thermodynamics, quantum mechanics and quantum field theory. Thus, to tackle cosmology we more or less use the whole toolbox of physics to at least attempt to understand the universe we live. In this video we will discuss some general aspects of cosmology and then we can discuss details in separate videos.
Cosmology is one of the oldest topics in physics. It became a rigorous science after the Copernican principle was introduced in the 17th century. This principle states that all celestial objects are governed by the same physics. This might seem obvious today, but back then it wasn't clear if physical laws would be different on Mars as an example. With Newtonian mechanics we got the first laws that allowed us to understand things like planetary orbits, and this we have already discussed in another video. But back then we couldn't understand much outside our own solar system. The field of cosmology only began to really get moving with Einstein and his theory of general relativity in 1915. We finally got a theory that corrected the mistakes of Newtonian mechanics, which we could trust for describing the universe beyond our solar system. The theory of general relativity gave us many new things such as black holes, gravitational lensing, where light bend around objects. After 1915 many interesting discoveries and observations were made in the following years and with the Friedmann equations we got a model of the universe as a whole. Not long after did Erwin Hubble discover galaxies outside our galaxy, the milky way. All these developments of the 20th century form the core of modern cosmology, but we are still discovering new things and learning more about our universe.