Naive realism

"Reality is exactly like it seems to us" could summarise what a naive realist believes.

So, if it seems to me that there are colors, scents, sounds, etc. out there, then they are all realities out there..

Our senses are a reliable way of knowing what is real and what is not: if I can sense something, that is real. If I can not sense something, it does not exist. Our senses are the ultimate judges of what is real and what it is not.

Naive realism is called "naive" because it is a very simple, unreflective view of reality. It does not take into account any of the considerations we have made in the above section and several others we could add, such as:

• Do electrons exist? I have never seen an electron, and I never will.

• Sometimes (such as when I get the flu) food does not taste the same. So, are flavors real? 

We can be realists, but not of the naive kind.

Scientific realism

"Reality is what science tells us there is" could summarise what a scientific realist believes. But this it is not very useful untill we get a clear understanding of what science is:

• There is not a single science but many sciences, in plural. Each science investigates one aspect of reality. So for instance Biology deals with cells and genes, Chemistry reduces every substance to atoms and Physics tells us that atoms are made of quarks and electrons. Each science deals with different realities. Some think that all sciences will eventually converge to a single and simple reality, so reducing the currently different realities to just one. But this reductionistic approach is just one possibility and scientific realism does not require it.

• We can talk of science in singular if we focus on the method that all sciences use. A key feature of this method is that knowledge is revisable through critical thinking, novel ideas and discoveries. Science is a work in progress, so our ideas about what is real are also revisable and improving. The answer to the question "what is real?" must therefore start with "according to our most recent scientific theories..."

Experimental sciences get some of their information directly from our senses, but sciences do not rely uncritically on them. Sensations must be validated by many observers and interpreted according to our best theories. Intelligence (reason) plays a central role and is the ultimate judge of what is real and what it is not.

Deterministic systems

Using the concepts of system and state and also the concepts of past and future, we can define determinism as follows:

A system is determinate if and only if its present state is followed by one and only one future state.

If we consider a car as a closed system, the state of its headligths one minute from now is determined by the state of its battery and the relevant switches and lamps.

If we isolate our solar system from the effects of the rest of the galaxy, Earth's position and velocity are completely determined by its position and the positions of the rest of the solar bodies. 

On the contrary:

A system is indeterminate  if and only if its present state is followed by one among several future states.

Determinism as a global, most general thesis about reality says that every closed system is determined, and the universe as a whole, complete system, is also determined. 

Chaotic systems

Are all systems deterministic? At first sight is seems easy to find non-deterministic ones. Take for example a dice. When you throw it, its future state seems open to several possible states.

Or consider the time take by an driver to complete its daily commute. Let's take the whole city, its vehicules, pedestrians, traffic lights and so on as a closed system and ask ourselves: is its position in, say, half an hour, determined by the current state of the traffic?

An imperceptible change in the angle of your hand may cause a completely different result. Just a different reaction of just one driver in front of an amber light may provoke a cascade of consecuences that results in a two minutes or maybe a two hours delay in the journey of another driver. 

A system whose future state is greatly affected by minuscule changes in its current state is called a chaotic system. That explains why it is very difficult to predict the result of a dice roll and why people get sometimes late to their jobs.

But now we are not interested in our knowledge of reality but in how reality behaves. Is the dice future state not determined by its current state? Is the state of the traffic one minute from now not determined by its current state? If they are not determined by the states of their parts, then what could possibly determine their future states?

No, chaotic systems, although very difficult or even impossible to predict, are deterministic systems. A very, very detailed description of their current states plus a sufficiently precise knowledge of the causal links among its elements could in principle let us predict their future.

The advance of sciences has discovered that apparently indeterminate systems are in fact determinate. Maybe in the future we will be able to accurately predict the roll of a dice, the traffic in a city or the Earth's weather. Or maybe not, and we will have to accept that all we will ever have are approximate predictions. But whatever our knowledge, that does not change the fact that these are deterministic systems: their current state determines (is followed by) a single future state.

Non-deterministic systems

Are there truly indeterminate systems? Systems that, whatever the accuracy of their descriptions evolve non-deterministically: their current state is followed by one among several future states.

For a long time, the general consensus was that there were not truly indeterminate systems and therefore that determinism was true. Now we know better: the behaviour of atoms and subatomic particles is indeterminate according to our current understanding of them. For example, some atoms are inestable and they disintegrate. Atomic disintegration is called radioactivity.

Atoms are fairly simple systems, some of them are composed of just a handful of protons, neutrons and electrons. Let's consider two inestable atoms of the most simpler kind: trittium. Two trittium atoms are identical in all its parts and they can be in the same state. But because they are inestable, they will disintegrate after a certain amount of time. But when?  And do they disintegrate at the same time? Physicists have observed this phenomenon and have corroborated time and again that:

• Disintegration is not affected by any external factor. It is an internal atomic process, but it is unpredictable not because of our ignorance but because it is intrinsically indeterminat. After lots of experiments, we are still unable to predict when an inestable atom disintegrates.

• Each individual atom disintegrates at a different time: one trittium atom may disintegrate in the next minute, another may be remain intact for a year, even when nothing differentiates one from the other. Same initial state, two very different future states.

In 1935 the physicist Erwin Schrödinger devised a thought experiment for illustrating the macroscopic effects of the indeterminacy of radioactivity. The key of his experiment is that atomic disintegration is indeterminate: because of that, we can not predict if the cat is dead or alive. Only when we open the box we know.

All realities seen up to this point can be characterized as natural. Naturalism is the philosophical thesis that affirms that all realities are natural realities. But, what do we mean by "natural"? There are several non-overlapping characteristics of natural entities:

• Just ordinary, devoid of any "spiritual" meaning.

• Repeatable, possibly controllable realities.

• Can be known (completely or at least partially) by human reason. Usually that knowledge is scientific: shared and subjected to criticism and improvement.

Naturalism can be seen as a work in progress: as our scientific knowledge expands, so the realities now understood will enter the realm of nature.

There was a time when illness was considered the product of witchcraft, sin or just bad luck. But medicine has replaced those supernatural notions with scientific knowledge that makes illness something ordinary and in many cases under control.

Naturalism can be wrong: there may exist entities that belong to a supernatural realm. Entities that defy our attempts to know them rationally but that we somehow know of their existence. They may even influence us and be an important part of our lives, but they are not natural.

Mysticism or supernaturalism is the opposite of naturalism: it affirms that there are non-natural realities; not everything that exists belongs to nature.

The characteristics of supernatural entities are just the opposite of natural ones:

• Having an spiritual quality or meaning.

• Extraordinary, non-repeatable, unique and uncontrollable by us.

• Can't be known by human reason. Religious experiences, emotions or art may be the ways to connect with supernatual entities.

Inmortal souls and deities are among the most discussed supernatural entities. Do they exist? The arguments in favour of the existence of God and the inmortality of the soul are far from convincing, but maybe this is to be expected because they are by definition beyond rational comprehension. That is the starting point of mysticism: there are realities beyond human comprehension. Nevertheless, the burden of the proof corresponds to those who defend the existence of supernatural entities. 

Mysticism can be wrong: by rational or irrational means we may arrive at the conclusion that there are no supernatural entities. Or maybe we will explain them naturalistically (rationally) so no mistery remains.