Why did Einstein object to the indeterminacy of quantum mechanics?

Albert Einstein objected to the indeterminacy of quantum mechanics because he held a deterministic view of the physical world. He famously expressed this stance by stating that "God does not play dice," rejecting the idea that nature is fundamentally governed by intrinsic randomness.12

Einstein believed that the probabilistic nature of quantum mechanics suggested the theory was "incomplete". He argued that if a physical system’s properties could be predicted with certainty without disturbing it, those properties must correspond to an "element of reality," implying that underlying, objective facts exist regardless of whether they are currently measurable.34

Consequently, Einstein and other critics proposed that there must be "hidden variables"—presently unknown properties—that, if known, would allow for precise predictions of physical outcomes, thereby restoring causal determinism to physics. He engaged in historic debates with Niels Bohr and utilized thought experiments, such as the EPR paradox, to challenge the Copenhagen interpretation and its renunciation of deterministic causality.5642