Quantum mechanics is a fundamental theory that describes the behavior of matter and energy at the atomic and subatomic levels. It has been extensively tested and verified through numerous experiments and observations. However, if quantum mechanics were to not apply in the universe, several conditions or circumstances would need to be true:
Deterministic Nature: Quantum mechanics is inherently probabilistic, meaning it deals with uncertainties and describes the behavior of particles in terms of probabilities rather than definite outcomes. If the universe were deterministic, where every event and outcome could be precisely predicted, quantum mechanics would not be necessary.
No Wave-Particle Duality: Quantum mechanics introduces the concept of wave-particle duality, which suggests that particles such as electrons and photons can exhibit both wave-like and particle-like properties depending on how they are observed. If the universe did not exhibit this duality and particles could only behave as classical particles or classical waves, quantum mechanics would not apply.
No Superposition: Quantum mechanics allows for the existence of superposition, where particles can exist in multiple states simultaneously until measured or observed. If the universe did not permit superposition and particles were always in definite states, quantum mechanics would not be applicable.
No Quantum Entanglement: Quantum entanglement is a phenomenon in which two or more particles become correlated in such a way that their states are dependent on each other, regardless of the distance between them. If the universe did not allow for quantum entanglement, one of the key features of quantum mechanics would not exist.
No Uncertainty Principle: The Heisenberg Uncertainty Principle is a fundamental principle of quantum mechanics that states there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be known simultaneously. If the universe did not exhibit this uncertainty and it was possible to measure both properties with arbitrary precision, quantum mechanics would not be applicable.
It is important to note that our current understanding of the universe is based on the application of quantum mechanics to explain and predict a wide range of phenomena. The theory has been extremely successful in describing the microscopic world, and there is a vast amount of experimental evidence supporting its validity.