On Jul 8, 3:40 am, Immortalist <reanimater_2...@yahoo.com> wrote: > What sort of things are they if they are things? > > One natural answer is that they comprise continua, three-dimensional > in the case of space, one-dimensional in the case of time; that is to > say that they consist of continuous manifolds, positions in which can > be occupied by substances and events respectively, and which have an > existence in their own right. > > It is in virtue of the occupancy of such positions that events and > processes are to be seen as taking place after each other and > substances are to be seen in certain spatial relations. > > Or do space and time have properties of their own independent of the > objects and events that they contain? > > Did Einstein show, through his theory of relativity, that since space > and time can change in shape and duration that space and time are more > complex than just sustained perceptual constants? > > Metaphysics - by D. W. Hamlynhttp://www.amazon.com/exec/obidos/tg/detail/-/0521286905/
When discussing the nature of time, in particular the arrow of time, people often raise the "grandfather paradox", namely that if travel back in time were possible you could go back and kill your own grandfather.
Well it struck me the other day (and forgive me if this is old hat to physicists, although I haven't seen it mentioned in the many popular books and blogs I read) that maybe grandfathers _are_ killed all the time, almost all of them. But they must be extremely small, and they and their grandchildren are conventionally called virtual particles.
If one works on that assumption (and I fully concede it may be kooky) then broadly speaking studying particle physics amounts to eludating the conditions and symmetries under which particles don't or somehow can't, or are least likely to, or are slowest to, go back and murder their ancestors.