That is, all contingent chaos butterflies are responsible in some sense for all important events like hurricanes and typhoons - and newspaper titles. When a typhoon, or a newspaper tycoon, topples an empire, that event is caused by everything, all those butterflies, that preceded it. Because change in any one - or perhaps just in one of a very large number - can derail the important event.
So everything must be caused by everything before it, not just by a thin string of causality.
We think about causality as a thin string, a linear chain of events, link following link following link ... probably because that's the only way we can hold any kind of causal sequence in our minds. As we'll see, that's how we deal with our own memories and intentions, but none of this means that the universe can isolate such a causal string antecedent to any event at all, important or not. And surely 'important' or `trivial' is usually human judgement, unless the universe really does `smear out' most small changes (whatever that means), and major events are those whose singular influence can be distinguished at later times.
Because they are stories, committed to the way our minds work and not to the way the universe works its own causality, most timetravel stories assume that a big (localised) change is needed to have a big effect - kill Napoleon, invade China ... or save Lincoln. And time travel stories have another convention, another `conceit', because they are stories, nearer fee-fi-fo-fum than physics. This is the remembered timeline of the traveller. Usually the plot depends on it being unique to him. When he comes back to his present he remembers stepping on the butterfly, or killing his grandfather, or telling Leonardo about submarines. .. but no one else is conscious of anything other than their `altered' present.
Let's move from large events, large or small causes, to how we influence the apparent causality in our own lives. We have invented a very strange oxymoron to describe this: `free will'. These words appear prominently on the label of the can of worms called `determinism'. In Figments of Reality we titled the free will chapter: `We wanted to have a chapter on free will, but we decided not to, so here it is' in order to expose the paradoxical nature of the whole idea. Dennett's recent book Freedom Evolves is a very powerful treatment of the same topic. He shows that in regard to `free will' it doesn't matter whether the universe, including humans, is deterministic. Even if we can do only what we must, there are ways to make the inevitable evitable. Even if it is all butterflies, if tiny differences chaotically determine large historical trends, nevertheless creatures as evolved as us can have `the only free will worth having', according to Dennett. He writes of dodging a baseball coming for his face, and this being perhaps a culmination of a causal chain going right back to the Big Bang - yet if it will help his team, he might let it hit his face.
But then, what decides it is: will it help his team? That's not a free choice.
Inevitable, evitable.
Dennett's best example is more ancient: Odysseus's ship approaching the Sirens. Inevitably, if his men hear the Sirens' song, they will steer the ship on to the rocks. But the steersman must be able to hear the surf, so there seems no way to avoid their lure. Odysseus has himself lashed to the mast, while all his sailors plug their ears with wax so they cannot hear the Sirens. The vital issue for Dennett is that humans, and on this planet probably only humans, have evolved several stages beyond the observing-and-reacting that even quite advanced animals do. We observed ourselves and others observing, so got more context to embed our behaviour in - including our prospective behaviour. Then we developed a tactic of labelling good and bad imaginary outcomes, just as we labelled our memories with emotional tags. We, and some other apes - perhaps also dolphins, perhaps even some parrots - developed a `theory of mind', a way to imagine ourselves or others in invented scenarios and to anticipate the associated feelings and responses. Then we learned to run more than one scenario: `But on the other hand, if we did so-and-so, the lion couldn't get us anyway...', and that trick soon became a major part of our survival strategy. So with Odysseus ... and fiction ... and particularly that dissection of hypothetical alternatives that we call a time-travel story.
In our minds, we can hold many possible histories, just as Mead showed that every discovery about today implies a different past leading up to it. But whether there is any sense in which the universe has several possible pasts (or futures) is a much more difficult question. We've argued that popularisations of quantum indeterminacy, particularly the many-worlds model, have got confused about this. They tell us that the universe branches at every decision point, whereas we think that people have to invent a different mental causal path, a different explanatory history, for each possible present or future.
Antonio Damasio has written three books: Looking for Spinoza, Descartes' Error, and The Feeling of What Happens. These are popular accounts of what we know about the important attributes of our minds. He has documented our discoveries, now that we can use various experimental techniques to `watch the brain thinking' and see how the different parts of the brain are involved in what we feel about the things we think. We tend to forget that our brains are continually interacting with our bodies, which supply the brain with stance-determining hormones for longer-term behaviour, and moodchanging emotion-provoking chemicals for short-term modulation of our intentions and feelings, directing our thoughts.
According to these books, the result of having lived with a brain which we think we direct using a kind of tiller, but which actually is continually affected by cross-winds, occasional storms, rain and warm sun that provokes us into lazy days, is that we have evolved a series of memories with different flavours. Or, the result of having lived with a brain that we think we direct using a kind of automobile steering wheel and foot controls, but whose route is actually continually affected by long-term goals that change (`Let's go to a hotel, not to Auntie Janie's again'), short-term road signs and other traffic, is that we have evolved a series of memories with different flavours. Or, each of us has a personal history which we explain internally by feelings attached to emotional memories, so we have evolved a series of memories with different flavours.
Damasio has imported emotional biasing into how we think about our own intentions, choices, other people, memories, and prospective plans. He claims that this is what emotion is `for', and most psychologists now agree that emotionally labelled memories are the effect of having a brain whose interaction with its body paints emotions on to memories and intentions.
We habitually assume that real physical history, and particularly social history, works the same way as our own personal histories, with events labelled `good' or `bad' ... but it doesn't. It's misleading to think of the Big Bang, for example, as an explosion like a bomb or a firework, seen from outside. The whole point of the Big Bang metaphor is that at the moment the universe was bom, there was no outside. More subtly, perhaps, we tend to think of the birth of the universe in the same way that we think of our own birth, or even our conception.
Real history, post whatever the Big Bang `really' was, relies on the accumulation of countless tiny sequences of cause-and-effect. As soon as we begin to think about what any of these sequences looks like, taking it out of the context that drives it, we lose its causality. This seething sea of processes and appearances and disappearances, where no causality can be isolated, is sometimes called `Ant Country'. The name reflects three features: the seething, apparently purposeless activity of ants, which, in aggregate, makes ant colonies work; the metaphorical Aunt Hillary in Douglas Hofstadter's Godel, Fscber, Bach, who was a sentient anthill and recognised the approach of her friend the anteater because some of her constituent ants panicked; and Langton's Ant, a simple cellular automaton, which shows that even if we know all the rules that govern a system, its behaviour cannot be predicted except by running the rules and seeing what happens. Which in most people's book is not `prediction' at all.