Such an interesting point about what it is that brings an elementary quantum phenomenon to a close so you can say the definite result. It's a little like a trial or a title deed after it's all written out and printed: that's it. If the observation that you're making is registered in an indelible form, then that is really the completion of a quantum phenomenon. But if it's only in a temporary form, there's always the question whether it will disappear and whether what you thought was a result will not be undone. So, Bohr was very careful to talk about a phenomenon brought to a close by an irreversible act of registration. My wonderful colleague, Eugene Wigner, used to ask, in his Hungarian version; "What means irreversible?" And that's a matter of degree rather than [of] kind, as we see it today.