The question of whether the quantum level is the smallest scale of physics or if there could be an underlying level of physics is an open question in theoretical physics. Currently, our best understanding of the fundamental structure of matter and the laws governing it comes from quantum mechanics and the Standard Model of particle physics.
Quantum mechanics provides a framework for describing the behavior of particles and their interactions at very small scales. It introduces concepts such as wave-particle duality, superposition, and quantum entanglement. The Standard Model, which is a highly successful theory, describes the fundamental particles and three of the fundamental forces: electromagnetism, the weak nuclear force, and the strong nuclear force.
However, there are several reasons why scientists speculate that there might be physics beyond the quantum level:
Incompleteness of the Standard Model: The Standard Model does not include a description of gravity, which is described by general relativity. Efforts to combine quantum mechanics and general relativity into a single unified theory, such as string theory or loop quantum gravity, suggest that there could be additional structures or levels of physics at play.
Unresolved questions: The Standard Model does not provide answers to certain fundamental questions, such as the nature of dark matter and dark energy, the hierarchy problem (why the Higgs boson mass is so much lighter than the Planck scale), or the origin of the universe itself. These open questions suggest that there may be deeper layers of physics yet to be discovered.
Experimental hints: Some experimental results, such as neutrino oscillations and the behavior of dark matter, hint at phenomena that cannot be explained within the framework of the Standard Model alone. These observations could be pointing towards new physics at smaller scales.
Conceptual limitations: Quantum mechanics itself introduces certain conceptual challenges and paradoxes, such as the measurement problem or the nature of time in quantum theory. Exploring physics beyond the quantum level may provide insights into these foundational questions.
It is important to note that while these reasons suggest the possibility of physics beyond the quantum level, there is currently no experimental evidence or consensus on what form this physics might take. Exploring and understanding physics at smaller scales is an active area of research, and future discoveries may shed light on whether there are deeper levels of reality beneath the quantum realm.