Even a GUTS is incomplete because it would not include spacetime and therefore gravity. It is hypothesized that a “Theory of Everything” (TOE) will bring together all the fundamental forces, matter and curved spacetime under one unifying picture. For cosmology, this will be the single force that controlled the Universe at the time of formation. The current approach to the search for a TOE is to attempt to uncover some fundamental symmetry, perhaps a symmetry of symmetries. There should be predictions from a TOE, such as the existence of the Higgs particle, the origin of mass in the Universe.
One example of a attempt to formula a TOE is supergravity, a quantum theory that unities particle types through the use of ten dimensional spacetime (see diagram below). Spacetime (4D construct) was successful at explaining gravity. What if the subatomic world is also a geometric phenomenon.
The idea that gravity is different from the other forces. While it is extremely long ranged, gravity is extremely weak (notice that a small magnet on the refrigerator can overcome the entire gravitational force of the Earth). Perhaps gravity is weak because it is ‘spread’ out over many dimensions. This type of theory is called brane or membrane theory and hypothesizes that the 3D world is just one splice of a multi-dimensional space where gravity propagates between the branes (slices).
In fact, the brane theory doesn’t necessary have to use stacks of other, ‘nearby’ dimensions, the other dimensions could be small and ‘curled’ into the microscopic world. Many more dimensions of time and space could lie buried at the quantum level, outside our normal experience, only having an impact on the microscopic world of elementary particles.
It is entirely possible that beneath the quantum domain is a world of pure chaos, without any fixed laws or symmetries. One thing is obvious, that the more our efforts reach into the realm of fundamental laws, the more removed from experience are the results.