What are the problems with the argument for hard determinism?

There are a bunch of criticisms that can be levelled against it, ranging from the vague to the fairly concrete.

Here are two that seem to me particularly interesting.

• Quantum mechanics seems to show us that we could never, even with unlimited resources, actually measure the state of everything in the universe (or even in a human brain) and then apply rules that would predict exactly what it’s going to do next. Not even in principle. It’s not only that the outcome of quantum measurement are mathematically truly random, but also that we have to make a choice about what to measure, which influences the thing we’re trying to measure.
  
  So this ends up resembling the metaphorical philosophical question “If a tree falls in a forest and no-one sees it fall, does it really fall?”. If we assert that there is a deterministic mechanism but we can never hope to watch it in action in enough detail to predict what it will do, and that appears to be fundamentally impossible even for a god (operating within the laws of physics), how do we know the universe is really deterministic? We can assert that it is, but we cannot prove it.
  
  These “random” effects make their way very easily into the macroscopic world, even in the case of many quite simple systems. They are more the norm than the exception. The fact that we have to make choices that determine what random outcome we observe is a problem for any attempt to prove that the universe is deterministic. It throws into question the whole notion of everything having an existing state, upon which determinism is predicated.
• If human brains are deterministic, why do we experience emotion? A car engine would not be expected to feel anything; if it did, its emotions could not influence how its engine works without violating physical laws. Its emotions would therefore be a useless and surprising phenomenon. Even though the human brain is much more complex, the same idea would apply to it. The key difference is, car engine are built to be as deterministic and quantifiable as possible, whereas the human brain cannot be fully measured and quantified to the point of predicting behaviour to any significant extent.
  
  There are experiments that claim to be able to predict a person’s future choices, but few philosophers or scientists consider them to actually show that any freely-willed action can be predicted in advance with any reliability. They show only that we mentally “gear ourselves up” to do things, which we already know. Often we then suddenly change our minds.

A related point is that Gödel’s theorems show us that we cannot always expect to predict what a system will do, even if it is deterministic, except by actually running that system or an equivalent system. Often a system will run indefinitely, and we cannot know (without running it) whether it will ever stop. However the no-cloning theorem in quantum mechanics tells us that we cannot create exact copies of any system unless we first carefully prepare it in a particular state that we determine. This means that we cannot create an exact copy of a brain in order to figure out what it will do, for example.

If a brain was a system that had been arranged so as to be as deterministic as possible, like a car engine or a digital computer (which are deterministic except when they aren’t — which is when we consider them to have “gone wrong”), that wouldn’t be a problem — but the brain is not such a system, and neither are most of the system that we are surrounded by.

So while we can contrive system that behave deterministically most of the time, providing we don’t look too closely and we discount events that aren’t supposed to happen, we don’t have a solid basis for arguing that all systems are deterministic, nor that they are random.

A counter argument is the argument from incredulity that a system “must” either be random or deterministic — because, what else could it be? Only something that we cannot imagine, or not using logic. However, such systems clearly do exist, and must exist, due to inherent mathematical limitations of mathematical logic. No matter how we set about analysing a system logically, ultimately we come to a point where we are stuck with axioms that cannot be proven using logic itself and cannot be said to derive from other axioms, unless you commit to an infinite series of axioms which you say must exist and which do not follow any discernible pattern, even though time and space prevents you from listing them.

Although I do tend to believe in Determinism, I a troubled by the paradigm’s failure to provide a logically coherent explanation of how the universe began, which results in the paradigm being paradoxical.

As I understand it, Determinism (which I take to be Causal Determinism) posits that all activity in the universe is both (i) the effect of [all] prior activity, and (ii) the only activity that can occur given the prior activity. That is what is meant by saying that everything is “determined” — it is the inexorable consequence of activity that preceded it. In a deterministic universe, everything that has ever occurred, is occurring, and will occur since the universe came into existence (however that might have occurred) can only occur exactly as it has occurred, is occurring, or will occur, and cannot possibly occur in any different manner.

The logical flaw in Determinism is that is does not, and cannot, account for the commencement of activity. It seems to me that Determinism must accept either (i) that something without a prior cause commenced the inexorable chain of causation that followed, or (ii) that activity of the universe has always existed without a beginning. Either option, however, sets up a paradox, because both options defy the fundamental premise of Determinism that all activity is the effect of prior activity.

The paradox can be avoided by saying that Determinism accounts only or the way the universe operates after its creation, and that the mechanism of creation, which is not governed by Determinism, is unknown (and possibly unknowable). Accepting that solution, however, sets up the possibility that whatever caused the activity of the universe to commence could, one day, act to interfere with the chain of causation that previously was set in motion — thereby allowing for the potential of two different futures at any given time.

Notwithstanding the paradoxical nature of Determinism, I still accept it as a workable paradigm. Moreover, I have found that every paradigm that purports to describe the operation of the universe tends to have an inherent contradiction and/or an unsolvable gap that requires a leap of faith. I choose to put my faith in Determinism, but I can understand if others put their faith elsewhere. After all, Determinism tells me that nobody has any choice in what they believe anyway.

The simplest and most valid argument for Hard Determinism is that the whole Universe is based on the conservation of Momentum but that is not actually true at relativistic speed. And that matters because everything is determined at subatomic level where all speeds are relativistic. The problem is that contributions made to the flux relate to an absolute reference frame whereas what is given back is in a relative reference frame,and this means that Conservation of Momentum is not a firm Law at all and neither is fhe Universe reversible in Time. You cannot rewind the handle back to the start. There is no Time symmetry in that sense.

Gravitational Charges and Flux by David Wrixon EurIng on Quantum Gravity Explained

Defining Concepts of Momentum by David Wrixon EurIng on Quantum Gravity Explained

It leads to logical absurdity. It’s easy to set up an experiment showing that we can and do take actions that don’t seem to have any cause other than our own free intent. For example, hold two balls in your left and right hands. At someone else’s direction drop one of them, whichever you want. It just seems ridiculous that there is any more cause and effect than me making a decision about left or right each time. If there is some cascade of causally determined actions simply depending on physics that mandates each outcome and can’t be overcome by our decision: left or right, then that needs to be demonstrated.

One reason I think some people accept hard determinism is that we often do not have this free will over events in our lives…our choices frequently are forced in many ways by outside factors, even if we are technically making a choice. But believing in free will doesn’t mean you always have it or even that it’s common…only that it’s possible sometimes.