A tennis ball is real. A tennis court and tennis players are real. But is a tennis match real? Common sense and philosophers like Aristotle assert that the basic things in the universe are ordinary objects like human beings, tennis balls and trees.
Modern science disagrees, and says instead that atoms or quarks are basic; human beings and tennis balls are built up from these smaller particles. Both of these views, however, are examples of ontologies in which the basic objects persist through time. That is, a tennis ball or an atom exists at one moment, and the next, and the next. Loosely put, one and the same object moves through time.
Some physicists and philosophers think that relativity has definitively shown that our world does not consist of persistent objects: there are no such things. Tennis balls and tennis courts are not real. Instead, the basic objects are events like tennis matches, elections or weddings. These are fixed at a particular time and place and never occur at another time and place. These are the basic objects of an event ontology. According to this view, the ordinary objects that appear to persist through time are really just collections of events. We see a tennis racquet striking a ball, a ball in flight, a ball nipping a net, a ball skidding on a court and a ball hitting the opponent’s racquet.
This sequence of events is usually believed to involve one and the same ball. But in an event ontology, these events are each real and distinct. Events are not made up of persisting objects. There is no single ball moving through the events. Rather, there is a similar- looking, yellow fuzzy patch in each of a series of events.
Philosophers usefully distinguish between persistence and endurance. An object that moves through time from one moment to the next persists. A sequence of similar but distinct events that creates the illusion of persistence is called an “enduring object”. Events are sometimes thought of as parts of the enduring object, which is itself just a long-lasting event. In debates over relativity, an enduring object is sometimes called a spacetime worm because it is a consecutive series of events snaking through space and time. Thus, in an event ontology, both people and quarks are reinterpreted as spacetime worms.
Compare this to a reel of film shown in the cinema. Each still photograph on the reel is the picture of an event at a particular time and place. The photographs do not change, but the sequence creates the illusion of motion. An event ontology is similar: in reality there are only unchanging events in fixed sequences and, therefore, the illusion of motion, change and persistence through time.
But surely we experience motion and change? We see it all around us! Defenders of event ontologies agree that we have an illusion of movement and change, but deny their actual existence. The sensation of movement that we might experience in a moving car is just that – a sensation. It occurs at an instant in our minds, and is not itself direct evidence for motion outside our minds. Even common sense agrees that there can be sensations of motion without real motion, as when someone is sick with vertigo.
Likewise, defenders of event ontologies argue that, strictly speaking, we do not in fact see motion. We see an object at one place and have a memory of a similar object in another place; the visual image and the memory together, they argue, produce an impression of motion. The existence of the memory is a fact about the present, and not itself direct evidence for true motion. Moreover, since motion occurs across time, we could not experience it directly. That would imply experiencing a past moment in the present. In short, defenders of an event ontology say that all experience occurs at a moment in time, and such experience cannot be direct evidence for motions and changes that stretch out through many moments. Thus an event ontology is compatible with all our direct experience, and therefore strictly in accordance with all observation and experiment.
Some philosophers criticize event ontologies, saying that they make the similarity of events in a sequence an incredible accident.
Why should the event of the racquet striking the ball be followed by another event that includes the ball? This makes sense if the ball moves through time to the next event. But if there is no true movement and change, why should consecutive events be similar at all? Could a ball at one moment be followed in the next by a swallow in mid-flight? Why do we not see series of events that look like “cuts” in a film, in which the scene changes instantly and there is no relation between consecutive stills?
The answer to this objection is interesting. Defenders of event ontologies admit that the similarity of events that follow one another has no physical explanation: it is just a “brute fact” about which nothing more can be said. Perhaps God just decreed that events have a pleasing order. But, the defenders continue, in the common-sense universe, where objects are supposed to be real and persist through time, there is a corresponding mystery. Physical laws account for movement through time, and these are also just brute facts. Thus both views have to accept unexplainable brute facts.
In an event ontology, there is no explanation for similarities among sequences of events; in a common-sense universe, the movements of persistent objects are explained by laws, but these laws themselves – at some level – have no explanation.
Thus in both there remains a mystery about the nature of movement and change. (Moreover, some philosophers say that such laws are just regular patterns of events, which would make the mystery of laws identical to the brute mystery of ordered events.) In short, event ontologies seem peculiar but are surprisingly coherent and compatible with all our experience. Does relativity theory decide the question of whether persistent objects or events are real?