The difference between quantum mechanics and Newtonian physics with respect to determinism lies in the fundamental nature of how they describe the behavior of particles and systems.
In Newtonian physics, determinism is a core principle. It posits that if the initial conditions of a system are known precisely, the future behavior of the system can be predicted with complete certainty. In other words, given the positions and velocities of all particles in a system at a particular time, their future positions and velocities can be calculated using Newton's laws of motion. Newtonian physics is deterministic in the sense that it suggests a cause-and-effect relationship where every action has a definite and predictable consequence.
However, quantum mechanics introduces a fundamental departure from determinism. It describes the behavior of particles and systems at the microscopic level and is based on the principles of wave-particle duality, superposition, and uncertainty. According to quantum mechanics, particles such as electrons do not possess definite properties, such as position or momentum, prior to measurement. Instead, they exist in a superposition of all possible states until an observation or measurement is made, at which point the wavefunction collapses to a specific outcome.
This inherent probabilistic nature of quantum mechanics challenges determinism. It suggests that even with complete knowledge of the initial conditions, the future behavior of a quantum system cannot be predicted with certainty. Instead, quantum mechanics provides probabilistic predictions, stating the likelihood of different outcomes.
Therefore, the key difference between quantum mechanics and Newtonian physics regarding determinism is that Newtonian physics adheres to determinism, while quantum mechanics introduces inherent uncertainty and probabilistic behavior at the microscopic level.