What do we have in mind when we talk about “behavior”? When we say, “I threw a stone in the air and it slowed and then returned to the ground”, “they made love and she had a baby”, or “I put a piece of wood in the fire and it turned to ash”?

I think we always have in mind some arrangement of atoms in, and distinct from, its environment: what some object does in some setting. If we change either the arrangement or the environment, or how we choose to divide one from the other, the behavior changes. A stone in the fire does not burn. A piece of wood on a glacier’s surface does not burn. I went for a hike in the mountains; the skin on my nose turned red with sunburn.

With this view, we can understand a great deal of what we do as discovering and trying to predict what different objects will do in different environments. Will this steel beam hold 10,000 kg? Or will it break? Will telling this person that I am in love with them make them smile or run? When it rains in those mountains, this canyon fills with raging water. A quartz crystal is hard and stable at room temperature, but in a 10,000 °C furnace, it becomes soft and fluid. If I leave an apple on the ground in this rain forest, it decompose in weeks, but if I leave a stone in the same forest, it remains as is for decades.

Where we divide “object” from “environment” also determines the behavior we observe and report. We might say that after a heavy snow, a skier triggers an avalanche that moves quickly downhill. But, if instead of defining the object as the avalanche snow, and the environment as the skier and the rest of the mountain, we choose to consider a stone caught in the avalanche as the object and the avalanche snow as the environment the behavior is different: the stone just tumbles around in the snow, but doesn’t move dramatically relative to the snow in the way that the snow-with-stone moves relative to the mountain. Are we considering the movement of an aircraft over the Earth’s surface? Or of the movement of the Earth around the Sun, aircraft and all?

We might say that all stones thrown in the air behave the same way: they go up, slow down, and eventually fall back to Earth. But if we consider the details of several stone-throw trajectories, we would see that each is different. One a little higher than another, or perhaps more rotation in some than others. And they would not all land in exactly the same spot. The finer the level of detail we consider, the more we find each toss is unique. If we consider the finest details of surface heating, or the position of individual atoms, we see that no two tosses will ever be exactly the same in every detail.

If I jump off a cliff into a swimming hole, I could describe my behavior as flailing my arms around and feeling an adrenalin rush. Or I could describe the arc and acceleration of my body on the way to the water. There are myriad different behaviors and levels of detail we might describe for any object in its environment, and which behavior we choose influences the accuracy of our prediction and the nature of the behavior we report. If I predict that both of two jumpers will accelerate towards, and land in, the water, my prediction will be accurate. If I make predictions about arm flailing, I may not be as accurate. If I predict the exact arc each will travel, with micrometer and millisecond resolution, I will certainly be inaccurate. Likewise for a coin-toss: If I say the coin will land on the ground, this prediction is good 100% of the time, but if I predict “heads” I will be right only half the time. When we say two behaviors are the “same”, we are also, necessarily, implying a particular choice of behaviors from among many, and a particular level of approximation.

Some choices in what we observe or report reflect our sensory capabilities. We aren’t able to see infrared wavelengths of light, or the motion of atoms, so we don’t include them in our descriptions unless we are using specialized equipment to expand our sensory ability. We detect strong smells, and might consider the smell of a flower or fire, but completely miss the much fainter smells a bear can observe and respond to.

The reason we must make all these choices, either evolutionarily or as individuals, is because Reality is functionally infinite in the scope of possible things we might observe. No system, save Reality itself, has the bandwidth to contain all of Reality in every detail. If asked to describe my surroundings at this moment, I might describe my desk, the room’s size, the window, door, shelves, and photos on the wall. Another person might make a different selection including the texture and color of the carpet, the type of lighting, or objects on the shelves. With enough time and observation, we could give descriptions and locations of each object in the room. No one is likely to measure and describe the predominant orientation of fibers in the carpet, and I am certain no one will describe the length, curvature, and position of each carpet fiber, much less the position of each atom in the carpet. Because we can only observe a minuscule fraction of Reality’s features, we must necessarily select a small, particular portion of items from the incomprehensibly long list of possibilities.

Because we must make choices when we observe Reality and report on it, we are necessarily revealing a great deal about ourselves as well as about the Reality we describe. Our choices of what to observe and describe tell of what we find important and what not, of our evolutionary inheritance, and of our relative size in the Universe between galactic clusters and subatomic particles.

What do we mean when we say we’ve made a “copy”? An automobile factory makes many copies of a car that all go down the road, have seats, audio and climate controls, windshields, etc., but they aren’t all exactly the identical in every respect and detail. It seems we use the word “copy” when two objects behave similarly in ways that are important to us at the moment. In the case of the car, we are interested in its road-worthiness, but we don’t notice, or care, if the tape holding a wire bundle together in one car is in a slightly different position than in another car, or if the bundle in one car was farther left than the other. Neither of these differences would keep us from saying that these cars are copies.

The special case of life is characterized by arrangements that, in certain environments, express the behavior of making copies of themselves. If an arrangement does indeed make a copy of itself (“copy” here defined as the behavior of making another, copy-making copy) then there will be more and more of these arrangements in the environment.

Our definition of evolution reflects the different levels of detail we (must) use to describe behaviors. We say, “reproduction with variation” meaning that a creature (or two) make a copy-making copy (they “reproduce”) but not an exact copy (with “variation”). Since the copies aren’t exact copies, the copy-making behavior of some may be faster or more reliable than others. And the variation in others still may result in no copy-making at all. Differences in copy-making behavior will then yield more copies of some arrangements than of others.

Further, an arrangement that expresses copy-making behavior in one environment will not necessarily also make copies in another environment. In an environment without oxygen, or with very high temperatures, most animal-arrangements no longer exhibit copy-making behavior. Other arrangements may make even more copies in a new environment and become, for a while, a dominant arrangement.

The different levels of detail we choose when talking about a particular behavior are at the foundation of evolution.

A key observation we have made about Reality is that a particular arrangement in a particular environment will behave in a predictable way. This is revealed in our ability to make any predictions at all. Concisely, we observe that Reality is lawful. A stone thrown in the air always returns to Earth (unless we have thrown it faster than escape velocity). The arrangement of steel, rubber, wire, and plastic we call a car always goes down the road. Quartz crystals of the same shape and size in an environment of a particular voltage always oscillate with the same piezoelectric frequency. This is not something we have decided, or even could decide: it is a discovery about the nature of Reality: our opinions, beliefs, and desires about it are irrelevant.

Certainly, we don’t know anything like all possible behaviors. We are discovering them all day every day as we traverse and explore the vast landscape of behaviors particular arrangements express in particular environments. This is the process operating as we design and invent new technologies. But every behavior we have discovered is lawful. Because of this, we have been able to build the Civilization-supporting infrastructure we know, use, and depend on from agriculture and road-building to plumbing and electricity to water heaters and refrigerators to phones and aircraft to drugs and steel beams to government and artificial intelligence. The fact that all of us human copies can observe, that we all express the behavior of observing, is itself a result of the lawfulness of the Universe in which we find ourselves. It is, perhaps, possible that this wasn’t the case. That we found ourselves in a Pottter-ian world of wands and spells, or the world of watchful deities promoted by religions — a world where the same arrangement in the same environment exhibits different behaviors at different times — but this is not what we observe.

Note: Like many others, I find the world we actually live in far more moving, compelling, and magical, infinitely richer, and a vastly greater source of delight and mystery than any fantasy our limited imaginations have ever constructed. All this on top of offering accurate predictions!