The Universe, reality, has a nature. Part of its nature, we have discovered, is that its nature is lawful. It is predictably this way, predictably not that way. This lawfulness, along with observation and reason, have ummasked deep mysteries and made us unimaginably wealthy.
But what do we mean when we use the word “nature”? To my mind, it is useful to think in terms of arrangement and behavior. How are the elements of reality arranged, and what are their behaviors? A stone and the Earth, separated only by 100 meters of air, will move towards each other. Sufficient excesses of positive and negative electric charges equilibrate with a spark. A rabbit will seek out vegetation and avoid coyotes.
When we talk about the nature of reality, we are always talking about some arrangement set in some circumstance. How much can that nylon rope hold? The rope is a particular arrangement of atoms, and implied in the question is a particular gravitational field (Earth’s), and a temperature and chemical environment that does not significantly change the rope’s arrangement. How will this drug affect a person with such-and-such disease? The person with the disease is a particular arrangement of atoms, and we are wondering how that arrangement will change in an environment that includes the drug. Research and experimentation can be understood as putting various arrangements into various circumstances, and observing the arrangements’ ensuing behavior. It is how we come to know the nature of reality.
Different arrangements have different behaviors in the same environment, and the same arrangements have different behaviors in different environments. An opened watermelon will dry up and shrink in the desert sun, while a bar of iron will retain its shape for decades. At “normal” temperatures, say 20 °C, an amethyst is hard, durable, and maintains its shape, while in an environment of 10,000 °C, it softens and becomes liquid.
A defining behavior of living organisms is that they make copies. We are an arrangement of atoms that, under certain circumstances, make copies of our arrangement. Under other circumstances, extremes of temperature, or in the jaws of a predator, they do not.
Of course, being me, I also want to consider what we mean by arrangement. We can say that this tree is arranged closer to us than that tree, or the lake is to our east and the hill to our west. Or we could be more detailed in our description, saying how far or close or what bearing east or west. Or we couldn describe the specific arrangement of each atom, including bond lengths and angles, in our amethyst. We could even contemplate describing the fine scale position of its atoms as their thermal energy moves them around. Or even the positions of the subatomic particles in each atom. Reality is exquisitely detailed, far more detailed than we ever attempt to describe, or are even capable of describing. Our descriptions of arrangements are always limited and approximate models of actual reality. In any practical instance, “arrangement” means an approximate description of the actual arrangement of items in reality. Consequently, what we in fact describe tells as much, perhaps more, about us as it does about reality. What, from the functionally infinite array of possible observations and descriptions, did we choose to observe and describe?
Further, the division between an arrangement and its environment is arbitrary; chosen by us to suit our purpose or question. So, we can ask how a leaf moves, caught in the environment of a stream, or we can ask how the leaf and water move in the environment of the stream bed. How does a piece of wood behave in the environment of a fire, or how does a fire behave in the environment of a oncoming rain storm? We draw a cognitive circle around an arbitrary group of atoms of interest, arranged in a particular fashion, call everything else around it its environment, and ask about the arrangement’s behavior. Again, our choice for dividing an arrangement and its environment tells as much about what is important and interesting to us as it does about the arrangement.
Likewise with behavior. As a stone and the Earth move towards each other, we could say simply that they move towards each other, or we could describe the stone’s speed and acceleration relative to the Earth. Or, we could describe details of its orientation, its rotation, and even the thermal motion of atoms on the leading edge as they heat up from collisions with air molecules. We might observe that human speech makes small changes in air pressure nearby, or we might observe that this environment of air atoms makes another person do something different than what they were doing before. We might choose any of these behaviors to describe but, like arrangements, we choose some arbitrary aspect of an arrangement’s behavior to describe; one that tells about our purpose and focus.
So, when we talk about the nature of reality, we are generally talking about the behavior of a particular group of atoms, an arrangement, in its environment, with the division between “arrangement” and “environment” chosen by us for its relevance to our goals. There are an uncountable number of different arrangements, environments, and ensuing behaviors, all potentially described with different focuses and levels of detail.
Tinkering with different arrangements and environments and observing their behaviors, in both controlled settings and our day-to-day lives, is how we come to know the Universe to the extent that we know it. Reasoning around these observations yields our internal models of these behaviors from which we make predictions about everything from where to put our foot so we don’t fall over, to how much to turn the steering wheel so we don’t go off the road, to how big a beam to put in our roof to prevent collapse, to how to arrange atoms so they compute for us, to how natural selection works, to the distance to the stars, to what words will bring a spark to our lover’s eyes and joy to his or her heart.
And lastly, since no two arrangements are exactly the same in every detail, just what do we have in mind when we use the word “copy”? To my mind, we mean that one arrangement is similar enough to another that, in a similar-enough environment, its behavior is also similar. A photocopy of a page of text is a copy in that the behavior of interest, that it can be read, is the same. Two Model A Fords are copies in that they can both go down the road, even though one may be more rusted than the other, or have tires with different wear and, of course, though their detailed arrangement of atoms are radically different. The two daughter copies of an amoeba that has undergone division are copies in that they can both feed and in turn make further copies, but the two are not exactly the same in every detail.
The detailed differences between “copies” that we, at first glance, may ignore, may become evident under changing circumstances. Our two Model A Fords may both behave similarly on flat terrain, but if the fuel filter is clogged more in one than the other, it may not be able to climb a steep hill, while the other can.
So when we use the word “copy” or “duplicate” we are inescapably implying a particular, approximate description of the arrangement, environment, and behavior of interest. And revealing a great deal about ourselves in the process.