 Possibilism seems to capture much of the way we think about time and being. While the sparse symmetry of presentism is attractive, there are many deep asymmetries concerning past and future that it fails to reflect. I can easily ascertain, for instance, yesterday’s closing number for the Dow Jones Industrial Average, but by no efforts, however great, can I now ascertain tomorrow’s close. And it seems as if my future actions (or certain sorts of quantum measurements) can actualize some future possibilities as opposed to others, whereas past actions (or the results of past quantum measurements) seem no longer to admit of past alternatives. Even if one allows for the possibility of retrocausation, that is, for the possibility of an effect preceding its cause in time, it is generally held that a present cause can not change or alter the past. It would merely make the past what it was. (See the entry on  backwards causation  for further consideration of this topic.)