A while ago, I asked folks on Facebook what they would like me to blog about. I got this response from an old friend Alix from college:
Is it important that we know about things that we do not see? I suppose this is a human version of the tree falling in the forest. The girls were interested to talk last night about what would have happened had we simply walked by the restaurant and not gone in: would all of these people said the same things? Would the music have been different? Does it matter?This is an interesting question... so interesting, one might write a dissertation on it, or an article. (See The Truth about Possibility and Necessity" and "What if? Modality and History,” History and Theory 38 (1999)). The initial question is quite broad, and would include more than the counterfactual claim the girls were asking. I argued in both the dissertation and the article that we need to use the facts we know and the rules about how systems transform to answer these questions, always recognizing that many systems are so complex that either no answer can really be given, or the answers are so speculative so as to not be worth the effort. Chaos theory makes such answers all the more tricky, as tiny but imperceptible changes in a system may alter it drastically, so that our predicting what would have happened had something different take place may be even more complex.
First, a techincal detail" A claim like "If x had happened, y would have happened" is called a counterfactual conditional. All sentences of the form "If ____, then ___" are conditionals, and in counterfactuals, the initial claim, called the antecedent, is false, and hence against the facts. To claim that something would have happened is quite strong, and usually unwarranted, but not always. The example I use in my article concerns the last play of a football game, as time runs out. Suppose a field goal wins the game, and suppose the kicker misses. It seems quite true that "If the kicker had made the field goal, they would have won." But suppose the missed field goal takes place very early in the game. It is easy to see that the choices the coaches made would be very different, and then that the whole game would have unfolded differently, and hence the claim no longer seems obviously true.
That example also shows an important part of the truth of the statement. The counterfactual needs to be "connected" in some way to the consequent of the conditional. It would make little sense to say "If I had blown my nose at 2:00 am, they would have won the game" because there is no connection between my blowing my nose, and the game being won. Now, perhaps that is wrong, and my blowing my nose has some sort of magical connection to the team winning the game. But in that case, we re-establish the connection, and hence still demand, if the counterfactual is true, some type of connection must exist between the antecedent and the consequent. This connection need not be causal, but it must exist.
It seems also true for a counterfactual to be relevant, the antecedent must be in fact possible, and also tied to choices, possibilities. Suppose we consider the following: "If Lee had a machine gun, he would have won the battle of Gettysburg." This may be true, but no one cares until, and this is the key point, someone shows that he might have had a machine gun at the battle. Suppose, for example, he had a weapons research project going, and were close to creating the first machine gun. then suddenly the counterfactual has new life. Now it becomes interesting.
So let's take a look at the original counterfactual:
The girls were interested to talk last night about what would have happened had we simply walked by the restaurant and not gone in: would all of these people said the same things? Would the music have been different?It is easy to see that things may well have been different, or roughly the same. If their entrance were remarkable in any way, then someone may well not have said something had they not entered. If someone, for example, had said "Look at those shoes!" then it is extremely likely that had they not entered, that comment would not have been made, and people would not have have said the same things. It is aslo possible, but less likely, that the rest of the conversation may have veered on tangents totally different from the original conversation. That is, the shoes led to a general discussion of shoes, fashion, and on to God knows what (Does He? Does God know what you would have talked about had your daughter not gone into the restaurant?) So it seems possible that had they not entered, some conversations would have been quite different. If, on the other hand, little note was made of their entrance, then it is unlikely that things would have gone differently.
Does this matter? In my article on history, I show that counterfactuals and other modal claims (claims about what might have been, and what would have been) are extremely important to the way we understand the world. Despite their high BS potential, we judge people, characters, events in history and cause and effect using counterfactual claims, claims like "If McClellan had attacked at Antietam, he would have won the battle and the war" is widely held to be true, and a key reason historians hold his generalship in low regards: he could have attacked, he did not, and if he had, it would have been successful. Let us not debate whether all these are true, but note: if they were all true, it gives us ground to judge McClellan. This is no mere matter of academia, it lead to McCLellan's dismissal, because Lincoln thought so, too.
I doubt anything so serious hangs on whether or not your girls entered the restaurant. But the general question, can things we do not see matter, the answer is 'yes.' We take them quite seriously. We even use them in law courts to determine the guilt, innocence and depth of just punishment.
Btw, I just saw that my article is now part of a graduate course in political science at McGill: http://www.mcgill.ca/files/politicalscience/course06_poli432.pdf