The universe, at its deepest stratum, must be deterministic. While the probabilistic descriptions we employ in quantum mechanics offer a powerful tool for prediction, they represent an incomplete picture, akin to a map that captures the river's flow but not the underlying geological forces shaping its course. The apparent randomness is, I suspect, a sign of our current inability to grasp the full, interconnected reality, rather than an inherent property of existence itself. Nature, in its fundamental laws, is far too elegant and orderly to surrender to capricious chance.
The question of determinism or probability in the universe is a lot like asking if a coin flip is predetermined. You *can* say that, given the exact forces, the spin, the air resistance, it's *theoretically* determined. But for all practical purposes, and for understanding what's *happening*, it's a probabilistic event. The universe, at the quantum level, doesn't hide secrets in some underlying clockwork we can't see; it *is* inherently uncertain in the way it behaves. The probabilities are the reality. Einstein’s elegant order is there, but it’s a different kind of order, one built on fundamental uncertainty, not a hidden ledger of every single event.
We must begin by considering what is known to us, by observing the world as it appears. The universe, in its observable operations, exhibits both regularities and what appears to be chance. The celestial spheres move with predictable, almost divine order, a testament to a formal cause guiding them toward their natural ends. Yet, even within these grand cycles, we see the contingent nature of events – a storm arising, a seed failing to sprout. To posit a universe utterly without any element of contingency would be to deny the evident way things come to be and pass away in the sensible realm. While we seek causes for all things, including the apparent unpredictability, the nature of that predictability, and whether it extends to every single atomic particle, is a question that demands careful distinction between what *is* fundamentally fixed and what *appears* contingent to our limited apprehension.
The very question of whether the universe is deterministic or probabilistic rests upon a potentially misleading dichotomy, rooted in our classical intuitions. To speak of a "deepest stratum" where events are unequivocally fixed or inherently random is to impose a language that may not accurately describe the quantum reality. It is not a question of *finding out how nature is* in some absolute, independent sense, but rather of characterizing the limits of our *description* of nature.
Einstein, I believe, seeks an underlying clockwork, a hidden ledger of all events. But this misses the fundamental point of complementarity. The probabilistic descriptions are not merely a reflection of our ignorance, a fog obscuring a clear, deterministic landscape. They are, rather, an irreducible feature of the phenomena themselves. When we probe the atomic realm, we encounter a situation where the very act of measurement forces a choice between mutually exclusive aspects of reality. To speak of a particle having a definite position *and* a definite momentum simultaneously is, in fact, meaningless, as the experimental setup required to observe one precludes the precise observation of the other.
Feynman’s analogy of the coin flip, while appealing in its practicality, still risks suggesting a pre-existing, albeit inaccessible, truth. The quantum world does not *hide* its probabilities; it *embodies* them. The universe at this level is not some clockwork mechanism that we can't quite see; its nature is such that a probabilistic description is precisely what is required to capture its behavior. To insist on determinism is to ignore the inherent limitations of our observational apparatus, and indeed, the very framework of physics itself.
Aristotle rightly points to the observable regularities and apparent chance in the world. Yet, the "formal cause" he speaks of, while illuminating for the macroscopic, does not readily translate to the atomic domain. The "contingent nature of events" at the quantum level is not a failure of some grand, predictable design, but a fundamental aspect of quantum states themselves. We must be wary of projecting our everyday understanding of cause and effect onto phenomena where the very notions of "cause" and "effect" become intertwined with the act of observation.
The distinction we must draw is not between a truly deterministic universe and a truly random one, but between the classical concepts we use to describe our everyday world and the new conceptual framework demanded by quantum phenomena. We are suspended in language, and the quantum realm challenges the very foundations of that language, forcing us to embrace paradoxes as essential components of a complete description. The universe, as we can apprehend it through quantum mechanics, presents a reality where certain outcomes are predictable with certainty, while others are governed by irreducible probabilities, and these probabilistic aspects are not a veil over a deeper deterministic reality, but rather the very fabric of that reality.
The persistent probabilistic interpretation risks mistaking the symptoms for the disease. Consider the phenomenon of radioactive decay. We can assign a probability to a given atom decaying within a certain time, but we cannot predict *which* atom will decay. This is presented as inherent randomness. However, this apparent chance arises because we are ignorant of the precise internal state of each atom, the subtle interactions with its environment that initiate the decay. It is not that the universe has fundamentally abandoned causality, but rather that our models are too coarse to capture the myriad deterministic interactions at play within each individual particle, interactions that, if fully understood, would reveal a definite, albeit incredibly complex, causal chain.
Look, Einstein, you keep talking about this hidden clockwork, this "ignorance" of precise states. But that's not what the experiments show. Think about electron diffraction. You shoot electrons, one by one, at a screen with two slits. Each electron acts like a wave, going through both slits and interfering with itself, creating a pattern on the screen *even when it's just one electron*.
Now, if there was a hidden, deterministic path for each electron, you'd expect to see it just go through one slit or the other, eventually building up a pattern from individual, localized impacts. But that's not what happens. The pattern builds up *probabilistically*, from individual hits, yes, but the distribution of those hits is dictated by the wave interference. The probability isn't a sign of our not knowing the path; it *is* the path. The universe isn't a complex machine we just haven't figured out how to tune precisely. Its fundamental nature *is* probabilistic.
The core of this debate rests on how we understand “cause.” Einstein, in his insistence on a hidden deterministic chain, implies that for every event, there must be a prior state and governing laws that render the outcome inevitable. He likens our ignorance to not knowing the precise internal state of an atom, suggesting that if we *did* know, we could predict decay. Yet, observe the phenomenon of a pot of water brought to a boil. We know the causes: heat applied, the nature of water, its boiling point. We can predict *that* it will boil, and roughly *when*. However, we cannot say with certainty *which specific molecule* will be the first to gain enough energy to escape as vapor. To demand such granular, inevitable prediction for every single particle is to impose a standard not found even in the most predictable terrestrial phenomena, let alone the intricacies of the cosmos. The universe, in its very operation, presents us with outcomes that are determined in their general character but not in every precise particularity.
Einstein, your argument regarding radioactive decay, while insightful in its classical framing, continues to presuppose a reality where underlying deterministic trajectories *must* exist, waiting to be uncovered. However, the quantum postulate compels us to consider the very act of measurement as an inseparable part of the phenomenon. We are not observers looking at a pre-existing, determined state. Instead, the experimental arrangement dictates whether we observe, for instance, the decay of a specific atom *at this moment*, or the statistical likelihood of decay over a period. To speak of an "internal state" that *determines* decay, but which is forever beyond our complete access and whose very determination is what we are measuring, introduces a conceptual incoherence. The probability isn't a veil; it's a descriptor of the fundamental properties of the quantum system itself.