27. Actions, Reactions, Interactions, and Causality

The question of free will, which I mentioned briefly in Part 26, is linked to that of causality. The causality principle says that every phenomenon or event is an 'effect' for which there must be a 'cause' that precedes it. I shall argue here that this principle is, at best, only an effective theory, often useful in day-to-day situations, particularly when it comes to understanding simple (or simplifiable) macroscopic systems. But an effective theory may not always have a sound logical basis, and is often just a label or nomenclature for something we do not understand very well.

Habitually we tend to subscribe to the idea that any action is followed by a reaction. In fact, we have Newton's 3^rd law of motion, which says that to every action there is an equal and opposite reaction. But can we really talk in terms of actions and reactions, or causes and effects, always? No.

Consider two protons, moving towards each other. The force of repulsion between them is not much when they are far apart, but increases as they approach each other, resulting in a bending of their trajectories. They cannot get too close to each other because of the repulsion, and go their separate ways after coming as close as they can.

Both proton trajectories have been affected. Can you tell which is the cause and which the effect? No. Instead of cause and effect, or action and reaction, it makes better sense here to talk only of an interaction. Bring in a third proton and it would become even easier for you to agree with me.

Cut to our solar system. Does the Sun go around the Earth, or does the Earth go around the Sun?

There are complications because of the Moon and other planets etc. (and other celestial bodies), so imagine a simpler situation in which we have only the Sun and the Earth. Most people will still say that it is the Earth that goes around the Sun. The psychology of such an attitude is that the Sun is much heavier than the Earth. But the reality is that the two go around each other. There is a 'centre of mass' for the Sun-plus-Earth system taken as whole, and they both go around that point.

The human tendency is that the larger object is taken as causing the effect on the smaller object(s). The real thing is that there are only interactions, rather than actions and reactions. Philosophers have been tying themselves into knots by carrying the action-reaction or causality idea too far. The absurdity of it all becomes palpable when they even talk of 'downward causality'. Why not just talk of interactions, rather than actions (causes) and reactions (effects)?

As I said, the cause-and-effect approach is at best an effective theory, albeit convenient to use in a large number of practical situations, with the proviso that the effect never precedes the cause. And the last part of this statement is subject to what the special theory of relativity theory demands (cf. Part 10), namely that a signal from the cause cannot travel faster than the speed of light. What this implies is that the meaning of the word 'simultaneous' is observer-dependent. The cause precedes the effect for all inertial observers. The cause and the effect are separated by a 'timelike' interval, and the effect is in the future of the cause.

And according to the general theory of relativity, the effect must belong to the future 'light cone' of its cause, even when the spacetime is curved.

When we come to quantum field theory, the causality idea gets linked to the much-debated 'principle of locality'. But let us not get into those things here.

Consider a beehive. It is a complex system. It has 'swarm intelligence'. No one is in command, not even the queen bee. Each bee follows some very simple 'local rules', and interacts with other bees in the hive. The effect here is the 'emergent' property of swarm intelligence. What is the 'ultimate' cause of this intelligence? Not the action of any one bee. The beehive is the archetypal example of a system in which it is meaningless to talk about causes and effects, or actions and reactions. It is interactions, through and through. This is not an isolated example. Complex systems are generally like that.

The causality idea is well-entrenched in the human psyche, in spite of the above-mentioned limitations. There is no need to abandon it, of course. In fact, much of our conventional science is based on it (conventional or 'traditional' science follows reductionism and constructionism). Logical reasoning in conventional science is one big chain of cause-effect-cause-effect-cause- .... interpretations: An effect becomes the cause for the next event or process, and so on. But conventional science is often quite inadequate for tackling complexity-related, highly highly nonlinear, problems. Radically new thinking is needed when any simplifying assumption can destroy the very essence of the complex system being investigated, or when it is impossible to model a system in terms of an adequate number of differential equations, or difference equations. But some of the unconventional approaches formulated have met with strong resistance from many practitioners of conventional analytical science. Mindsets do not change easily.

Be prepared to think in terms of interactions and correlations when necessary, rather than actions and reactions all the time. Such an approach will help you better understand the properties of complex systems, and keep you away from absurdities like 'downward causality'.

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.

Spirituality Deconstructed