The question of determinism in a "theory of everything" is a topic of philosophical and scientific debate. Determinism refers to the idea that every event or outcome is completely determined by preceding causes or conditions, implying that the future could, in principle, be predicted with perfect accuracy if one had complete knowledge of the present state of the universe.
While Albert Einstein expressed a preference for a fully deterministic universe, it is important to note that the nature of determinism in the context of fundamental physics is still uncertain. In the realm of quantum mechanics, which describes the behavior of particles at microscopic scales, there are inherent probabilistic aspects. According to the Copenhagen interpretation of quantum mechanics, the behavior of particles is described by wave functions that give probabilities for different outcomes rather than definite predictions.
However, it is worth mentioning that there are interpretations of quantum mechanics, such as the pilot-wave theory (also known as the de Broglie-Bohm theory), that aim to provide a deterministic description of quantum phenomena. These interpretations introduce hidden variables or additional degrees of freedom to explain the seemingly probabilistic behavior observed in quantum experiments.
In the pursuit of a "theory of everything" that unifies quantum mechanics with general relativity (describing gravity on a large scale), the question of determinism remains an open one. It is not yet known whether a future theory encompassing all fundamental interactions will necessarily be fully deterministic or if it will incorporate some form of inherent randomness or probabilistic elements.
Ultimately, the criteria for a final "theory of everything" are subject to ongoing scientific inquiry and may depend on the philosophical inclinations and interpretational preferences of scientists. While determinism has historically been an important concept in physics, its precise role in a comprehensive theory that unifies all fundamental forces and describes the behavior of the universe at all scales is still an active area of research and speculation.