Physics explains how our material Universe works. However, its theories do not currently form a satisfying whole. For example, the theory that describes the fundamental forces and building blocks of our physical world excludes gravity, and we do not comprehend how the Universe was born. As we naturally strive for things to be complete and make sense, we ask that our theoretical conjectures add up too, regardless of the scale we are dealing with.
For this reason, string theory has set the objective of integrating all the current explanations of how our Universe functions, from the very small to the very large, into one coherent Theory of Everything.
Yuval Noah Harari points out in his book ‘Sapiens: A Brief History of Mankind’ that unification is baked into human nature. Historically, he argues, it is the triad of capital, empires and religion that was the unifying driving force behind the global society that we see today. Is it then not only logical that we also pursue the quest of formulating a theory that puts all the physical mechanisms of our Universe under one roof?
But is this even a feasible and realistic goal?
What Is the Problem?
The fate of a Theory of Everything (TOE) lies in the hands of our ability to theoretically pull together all known fundamental forces in our Universe and match this effort with valid experimental evidence.
There are four fundamental forces in nature explaining all interactions between particles — electromagnetism, the weak nuclear force, the strong nuclear force and gravity. The electromagnetic force acts on any particles that carry an electric charge; the weak force comes into play when particles radioactively decay; the strong force holds the protons and neutrons in the atomic nucleus together and equally ensures that the quarks within the protons and neutrons create a tight structure; and gravity is the result of the bending of spacetime due to the presence of a massive object.
Particle physics covers the first three of them, succinctly meshed together in its Standard Model of Elementary Particles. And it is quantum field theory, which builds on quantum mechanics, that describes the behaviour of these subatomic particles.