5.3 Is Nature Uniform and Predictable?

The previous chapter, How can we have confidence in our inferences, investigated Inference and the Problem of Induction. Predictability and continuity from past to future, from the known to the unknown, from the small to the large, and from the near to the distant underlie our ability to make meaningful statements about the world. Out of necessity we assume that our knowledge about that which we can access tells us something useful about that which we cannot access due to distance, time, speed, size, or practicality.

But can we really make these assumptions? The principles of uniformity, homogeneity, and isotrophism (for which we have no deductive proof) are foundational principles underlying our ability to make warranted and defensible universal statements about nature. Without them, we can only talk about what we directly experience, and must leave as utterly unknown and unknowable that which we have not yet experienced.

As we have seen, there appears to be no deductive proof of uniformity or for the inferential process which requires it, and it goes without saying that you can't use induction to prove itself. But for all the reasons presented so far, the existance of a uniform and predictable universe is very likely to be the case - so likely that any other possibility is vanishingly small. Whether we choose to defend this assertion with foundational axioms, coherent and mutually supportive lines of evidence, acceptance of an infinite series of increasingly more subtle explanations, relaxing of the requirement for a firm deductive proof, probabilistic methods (such as Bayes Theorem), relying on the "Criteria Of Adequacy", or inference to the best explanation, rejecting the basic principle of uniformity and the inductive method which assumes it requires a far greater effort than accepting it. This would indicate that we should probably cultivate a tolerance for uncertainty (since we seem to be stuck with it), and an understanding that absolute certainty about phenomena in the world is probably not possible.

Uniformitarianism is the principle and belief that the natural processes operating in the past are the same as those that can be observed operating in the present, and by extension, the same as those operating throughout the universe. This principle postulates that laws of nature that apply on Earth function the same throughout the universe. Its methodological significance can be summarized in the statement: "The present is the key to the past." This concept was introduced into modern thinking by Charles Lyell, James Hutton, and centuries before, by Avicenna and others. Although Lyell, Hutton, and Avicenna restricted their argument for uniformitarianism to geology, it quickly found application throughout all of natural philosophy. James Hutton wrote,

“If the stone, for example, which fell today, were to rise again tomorrow, there would be an end of natural philosophy, our principles would fail, and we would no longer investigate the rules of nature from our observations.”

This means that for us to be able to draw conclusions about the past, we must assume the invariance of the natural laws we see in operation in the present. Mere position in space or time cannot by themselves be relevant to whether some phenomenon occurs or not.

We start from the premise that the universe is homogeneous and isotropic, meaning that it is the same everywhere and of roughly the same distribution. At all times and everywhere, the laws of the universe behave exactly the same. Every observation ever made supports it, and none refute it. The light we see in our homes is the same as that we see from distant stars (as in Newton's “the light of our culinary fire and of the sun” from his Rules of Reasoning). We have measured light generated billions of light years away, and it is the same as the light generated by our refrigerator bulb. Countless observations support uniformity of the laws of nature across the universe. We see stars and galaxies just like our own as far as the universe stretches. We have recently discovered extra-solar planets with atmospheres circling some of those distant suns not dissimilar from our own. We see light, gravity, physics, and chemistry behave just as it does on Earth no matter where (or when) we look. I say “when” because much of what we see happening in distant space happened billions of years ago. Despite centuries of looking out into space since Galileo first viewed the moons of Jupiter, there is no evidence to support an argument against natural uniformity. Instead, there is overwhelming evidence in its favor. The standard caveats regarding physics at the boundaries of our experience (at the sub atomic level and at the galactic level) apply. The laws of nature at the human level do differ in kind from those we have discovered at these two extremes. But that is not an indictment of uniformity. Instead it is simply a widening of our understanding at these two scales. It is true that the behavior of quarks and leptons, and of dark matter and black holes, differ from what we experience in our daily lives. But we have strong reason to believe that these behaviors are retained at these levels no matter where (or when) in the universe we look.

Uniformitarianism was such a successful paradigm that, not surprisingly, it was eventually overplayed. It received such wide acceptance as a result of Hutton's influence that legitimate catastrophic theories such as volcanic eruptions, climatic changes, asteroid impacts causing mass extinctions, and of plate tectonics were rejected as being contrary to these principles. It got in the way of the acceptance of quantum physics, and erected barriers to the possibility of undiscovered dimensions and the possible infinity of time and space. These misapplications of the principle of Uniformity help us realize that it is a guideline, not a universal law. Uniformity was not “discovered” as the speed of light or the mass of a star can be discovered. It is a generally good assumption that allows us to make inferences about the parts of the universe we don't have immediate access to. But it is not always proper to employ it. It cannot be dogmatically and mindlessly applied.

Isotrophism and Homogeneity are concepts often paired with Uniformitarianism. They are the two legs of the Cosmological Principle which says that no matter where we look in the universe, we will see the same types and distributions of objects. Bound up in this principle is the idea that the shape, substance, and consistency of the universe in our local area is roughly the same as elsewhere. There is nothing priviledged about our frame of reference, as both Galelio and later Einstein showed. There is nothing unique about “here“ vs. “there“, no matter how distant. This is a truth that man has come more and more to realize. In pre-history, each tribe probably considered itself at the center of the universe (as they knew it). Among Earth's major historic cultures existed the symbol of the Axis Mundi, or “axis of the earth” which expressed their view that they inhabited a unique place at the hub of the universe. The Copernican revolution and expanding exploration of the Earth's surface literally widened Man's horizons, showing both that Europe was not at the center of civilization, and that our planet was not at the center of anything, but one of several planets (and a minor one, at that) in the solar system. Our universe grew even larger when Galileo's telescope showed there to be countless thousands of other stars like our own in our island universe, the Milky Way. In the 1700's Herschel added shape and texture to this fact by constructing the first accurate model of our galaxy. The next step came with Hubble's proof that Andromeda was not just another nebula, but a sister galaxy to our own. During the following years, many other galaxy's were discovered. It is currently estimated that there are about as many galaxies in the visible universe as there are stars within our own galaxy. Further, there may be much more to the universe than the mere 13.7 billion light years worth of stars that we are able to see – the universe may be expanding faster than its light can reach us.

As far as we can tell, the universe is both homogeneous (has similar structure everywhere) and isotrophic (has a similar appearance in all directions). On the small scale, we don't have homogenieity – the universe is full of “clumps”. Earth differs from Mars, our sun differs from other stars, the our galaxy differs from the surrounding magellenic clouds and the other galaxies in our local cluster. Our local cluster differs from other galactic clusters. However, on a large enough scale, even larger than this, you do get homogeniety. An analogy would be a sponge cake filled with raisens. If you stick a pin into the cake, you may pull out nothing, or you might get a raisen. On the scale of a pinhead, the cake is not homogeneous. But on the scale of a slice of cake, you always get roughly homegeneous slices with about the same amount of cake and raisins in each slice. On the scale a billion of light years, we observe homogeneous structure in the universe.

But for the purposes of understanding the universe we live in, there is no need to go that far to look for similar structure. The structure of the objects and phenomena that scientists study in their laboratories have the same structure, consistency, and substance of similar structures and phenomena we know exist outside the lab. There is no need to go to the ends of the universe to be able to make that assertion.

In the chapter, Isaac Newton's Rules Of Reasoning, two of Isaac Newton's four "Rules of Reasoning in Natural Philosophy" deal explicitly with the Principle of Uniformity.

1. To the same natural effects we must, as far as possible, assign the same causes. As to respiration in a man, and in a beast; the descent of stones in Europe and in America; the light of our culinary fire and of the sun; the reflection of light in the earth, and in the planets.
2. Qualities of bodies are to be esteemed the universal qualities of all bodies whatsoever.

So, along with Hume, Lyell, Hutton, and countless others, Newton advances this principle. Although impossible to prove, it is the only explanation that would allow our experiences in the universe to make sense. If every seemingly similar phenomenon in every region of the world was the result of completely different causes, our science, and our common sense would be completely useless and would not work. The fact that both do work is evidence enough that, as Newton says, "to the same natural effects we must, as far as possible, assign the same causes".