The question of whether the universe can use quantum theory to describe itself is an interesting and philosophical one. Quantum theory is a mathematical framework that has been remarkably successful in describing the behavior of particles and systems at the microscopic scale. It provides a probabilistic description of physical phenomena, allowing for the superposition of states and the entanglement of particles.
When it comes to the universe as a whole, however, things become more complicated. The universe is a vast and complex system, encompassing a wide range of scales and interactions. Quantum theory, as currently understood, provides a description of phenomena at the microscopic level, but it may not be directly applicable to the universe as a whole.
One of the challenges is that quantum theory and general relativity, which describes gravity on a large scale, are not fully compatible with each other. While there have been attempts to develop theories that unify these two frameworks, such as quantum gravity or string theory, a complete and experimentally validated theory of quantum gravity is still elusive.
Moreover, the question of whether the universe can "use" a theory to describe itself presupposes a certain level of consciousness or agency on the part of the universe. Consciousness is a complex phenomenon that is not yet fully understood, and it is unclear whether it can be attributed to the universe as a whole.
In summary, while quantum theory has been highly successful in describing phenomena at the microscopic level, its direct applicability to the universe as a whole is uncertain. The nature of the universe and its relationship to fundamental physical theories like quantum theory and general relativity is an active area of research and a subject of ongoing scientific inquiry.