Stable patterns in Conway’s Game of Life are hard not to notice, especially the ones that move. It is natural to think of them as persistent entities, but remember that a cellular automata is made of cells; there is no such thing as a toad or a loaf. Gliders and other spaceships are even less real because they are not even made up of the same cells over time. So these patterns are like constellations of stars. We perceive them because we are good at seeing patterns, or because we have active imaginations, but they are not real.
Well, not so fast. Many entities that we consider “real” are also persistent patterns of entities at a smaller scale. Hurricanes are just patterns of air flow, but we give them personal names. And people, like gliders, are not made up of the same cells over time. But even if you replace every cell in your body, we consider you the same person.
This is not a new observation — about 2500 years ago Heraclitus pointed out that you can’t step in the same river twice — but the entities that appear in the Game of Life are a useful test case for thinking about philosophical realism.
In the context of philosophy, realism is the view that entities in the world exist independent of human perception and conception. By “perception” I mean the information that we get from our senses, and by “conception” I mean the mental model we form of the world. For example, our vision systems perceive something like a 2-D projection of a scene, and our brains use that image to construct a 3-D model of the objects in the scene.
Scientific realism pertains to scientific theories and the entities they postulate. A theory postulates an entity if it is expressed in terms of the properties and behavior of the entity. For example, Mendelian genetics postulates a “gene” as a unit that controls a heritable characteristic. Eventually we discovered that genes are encoded in DNA, but for about 50 years, a gene was just a postulated entity.
— Allen B. Downey, Think Complexity