26. Scientific Determinism, Effective Theories, Free Will

Quantum physics might seem to undermine the idea that nature is governed by laws, but this is not the case. Instead it leads us to accept a new form of determinism: given the state of a system at some time, the laws of nature determine the probabilities of various futures and pasts rather than determining the future and the past with certainty. (Hawking & Mlodinow (2010))

Laplace was perhaps the first to clearly enunciate the basic tenets of scientific determinism (cf. Part 25), according to which, given the state of the universe at one instant of time, a complete set of natural laws fully determines both the future and the past. This was classical scientific determinism. The fantastic success of quantum theory has necessitated a change: We now speak the language of probabilities, rather than certainties, as also of several futures and pasts (cf. Part 4), rather than the future and the past.

Real-life situations are usually so complex that it is not enough to have knowledge of the 'complete set of fundamental natural laws' for explaining all phenomena. It is often found necessary to formulate additional (empirical) laws as 'effective theories'. An example is the gravitational force experienced by a macroscopic object on the surface of the Earth. The gravitational interaction is present between any two atoms, but we cannot formulate and solve the equations governing the gravitational interaction between every atom in the macroscopic object and every atom in the Earth. Instead, an effective theory is formulated in terms of the mass of the object and a few other numbers like the value of the gravity constant (g) at the surface of the Earth.

Similarly, in chemistry we cannot hope to formulate and solve the totality of equations describing the interactions among all the positive and negative charges in a system. Instead, an effective theory involving concepts like valence deals with how chemical reactions occur.

This approach continues as we go up the ladder of increasing complexity. Details at one hierarchical level of complexity are 'summarized' or 'integrated over' to generate some effective parameters which are used for describing the details of the next higher level: From particle physics to macroscopic physics and chemistry; from chemistry to biology; and so on.

An effective theory is essentially a framework we create for modelling certain observed phenomena, without describing in detail all the underlying processes.

The computational limit (cf. Part 25) to understanding the reality of our complex universe manifests itself in a dramatic way when we ponder over the notion, or rather the illusion, of free will. Michael Shermer (2006) described it like this: 

As with the God question, scholars of considerable intellectual power for many millennia have failed to resolve the paradox of feeling free in a determined universe. One provisional solution is to think of the universe as so complex that the number of causes and the complexity of their interactions make the predetermination of human action pragmatically impossible. We can even assign a value to the causal net of the universe to see just how absurd it is to think we can get our minds around it fully. It has been calculated that in order for a computer in the far future of the universe to resurrect in a virtual reality every person who ever lived or could have lived (that is, every possible genetic combination to create a human), with all the causal interactions between them and their environment, it would need . . . .  10²³ bits of memory. Suffice it to say that no computer in the conceivable future will achieve this level of power; likewise, no human brain even comes close.

The enormity of this complexity leads us to feel as though we were acting freely as uncaused causers, even though we are actually causally determined. Since no set of causes we select as the determiners of human action can be complete, the feeling of freedom arises out of this ignorance of causes. To that extent, we may act as though we were free. There is much to gain, little to lose, and personal responsibility follows.

The often-handy notion of free will can be regarded as another effective theory, like the many mentioned above. Even though free will is only an illusion, one can make progress in cataloguing and understanding psychological phenomena by pretending that people have free will (Hawking and Mlodinow 2010).

One goes a step further when modelling economics. The effective theory we use in economics is that people have a free will, and that their behaviour may or may not be rational, and that their decisions may be sometimes based on a defective analysis of the limited data at their disposal.

Although the free-will notion serves as a convenient effective theory for certain situations, we should not lose sight of the fact that biological processes, including those occurring in the brain, are determined entirely by the laws  of physics at the fundamental level (call it 'quantum determinism' or 'probabilistic determinism', if you wish). Our actions are therefore determined entirely by the laws of physics. A large number of experiments done on humans under controlled conditions have demonstrated this. For example, electrical stimulation of appropriate regions of the brain can make a person 'want' to move the hand, arm, or foot. Such findings are in line with the scientific idea of physical causes leading to all effects, and show free will its place: It is only an illusion, or, at best, a useful (though logically unsound) effective theory for certain practical purposes. 

More on free will in a later post.