I will take my stand and keep watch. I will take my place on the tower. And I will keep watch to see what the Lord will say, and how I should answer when He speaks strong words to me.
Then the Lord answered me and said, “Write down the special dream on stone so that one may read it in a hurry."
Habakkuk 2:1-2 New Life Version
A theory of everything (TOE), final theory, ultimate theory, or master theory is a hypothetical single, all-encompassing, coherent theoretical framework of physics that fully explains and links together all physical aspects of the universe. Finding a TOE is one of the major unsolved problems in physics. Over the past few centuries, two theoretical frameworks have been developed that, together, most closely resemble a TOE. These two theories upon which all modern physics rests are general relativity and quantum mechanics. General relativity is a theoretical framework that only focuses on gravity for understanding the universe in regions of both large scale and high mass: stars, galaxies, clusters of galaxies, etc. On the other hand, quantum mechanics is a theoretical framework that only focuses on three non-gravitational forces for understanding the universe in regions of both small scale and low mass: sub-atomic particles, atoms, molecules, etc. Quantum mechanics successfully implemented the Standard Model that describes the three non-gravitational forces – strong nuclear, weak nuclear, and electromagnetic force – as well as all observed elementary particles.
Source: Wikipedia
Nevertheless some questions remain.
Beyond general relativity and quantum mechanics, is there a global theory which explains the values of all fundamental physical constants, i.e., of all coupling constants, all elementary particle masses and all mixing angles of elementary particles?
Is there a theory which explains why the gauge groups of the standard model are as they are, and why observed spacetime has 3 spatial dimensions and 1 temporal dimension?
Are "fundamental physical constants" really fundamental or do they vary over time?
Are any of the fundamental particles in the standard model of particle physics actually composite particles too tightly bound to observe as such at current experimental energies?
Are there elementary particles that have not yet been observed, and, if so, which ones are they and what are their properties?
Are there unobserved fundamental forces?
Why the galaxies do not tore apart despite the high velocity of their stars ?