User blog comment:VonGlusenburg/Alternate universes, probability and alternative outcomes/@comment-1777104-20120816175000

I'm with TheB on this one. ASB is a term used in this genre for changes that cannot otherwise be expected to happen. The quantum mechanics theory of multiple universes is what allows for our genre to flourish. However, the small decisions we make -- like my taking time to respond to this blog -- probably do not change the world. The very act of my typing certainly does not "change air currents" since these are so localized (even if I were outside) that a butterfly effect does not have a way to begin. Besides that, the "butterfly effect" is one that takes a very long time to change a timeline (the further back, the bigger the change). We apply the term in AH to changes to others that pivotal events eventually have on the rest of us.

Let's say I did not write this response, but rather did the chores I have to get back to and then left the house on other chores. Suppose, then, that I witnessed a crime in progress and either prevented it or, more likely, was the key witness to bring the criminal to justice. It is possible, in such a case, that my witness to this put an end to a criminal carreer that would include the assassination of a public official that otherwise would have happened. Such things are the way alternate history writers develop their storylines. If we wanted to change the past for a story, the same principle would come into play. Booth or Oswald, for instance, may have been stopped by just such a witness not there in our time line.

ASB, on the other hand, has something occur that did not occur and is probably not likely to have occurred. Some people even consider things like geophysical events that did not happen, but could have happened, as ASB. Their point is that the only alternate history that stands the test of plausibility is that which depends on the unpredictability of human actions.