In making the Map of Physics, Walliman more or less followed the historical development of physics, starting with Newton’s contributions to classical physics. In his Laws of Motion, Newton described the connections between force and motion of objects, action and reaction, etc. This not only forms the foundation of classical mechanics, but also helps to understand how stars and planets move around each other by introducing gravitational force between them. Newton has also made great contributions to optics, which studies light and how it interacts with various materials. Optics is closely related to waves and electromagnetism (electromagnetic wave). Together with fluid mechanics describe the behaviour of fluidic materials, and chaos theory and thermodynamics for the properties of systems containing large amount of particles, we have all the sub-disciplines that collectively form classical physics.
Classical physics describes the behaviour of ordinary objects around us very accurately, so much so that until about 1900, it was believed that one can predict the future of the universe and everything in it if accurate measurements could be made. However, this belief was challenged by couple of observations that couldn’t be explained by classical physics, as described in the video, which eventually led to the development of theory of relativity and quantum physics.
Theory of special relativity predicts that the speed of light is constant for all observers and when an object moves at speed close to it, strange things starts to occur such as time slows down. It also suggests that energy and matter are different aspects of the same thing, and linked by the famous equation E=Mc². Theory of general relativity uniforms space and time together into spacetime and gravity is due to the bending of spacetime by objects. In general, theory of relativity works well with big objects and objects moving at high speed. On the other hand, quantum physics deals with things that are very small, electrons, protons, etc. It proves to be the best tool to work out how these sub-atomic “particles” behave in different environments. Applying quantum mechanics to electrons in atoms (atomic theory) helps us to understand atomic structure, unique properties of various elements, chemical bonding, etc. Applying quantum mechanics to electrons in solid (solid state physics) explains the various properties of solids and enables the modern electronic industry. Particle physics deals with the most fundamental “particles” that make up everything in this universe.
For decades, physicists have been trying to unify all the different theories of physics into one grand theory. Towards that end, quantum field theory brings quantum physics and special theory of relativity together, yet gravitation is not included. At the “chasm of Ignorance” as Walliman called it, open questions are described.