User:GangofOne/sandbox

beware of kitty litter

It is difficult to write clearly about quantum mechanics. Even Dirac wrote 4 editions of his text Fd. of QM, his terminology, changing in each edition, until the last which has the eponymous notation that all since have known and loved. So I have no idea way you refer to the earlier editions when you are making a point about what Dirac said, when he Himself rejected that earlier terminology and expostition.

Steve I agree with

 is the scaler product of two kets, |a> and |b>, regardless of where or when the kets exist or not. It's just a notation, and implies nothing else about an experimental setup. In some experiment you could assign one of the two to be the before and after states, but that is only in that context so defined.

"Most writers do not mention a physical distinction between bras and kets, but a few interpret them as distinguishing initial and final conditions of a phenomenon. Auletta, G., Fortunato, M., Parisi, G. (2009), p. 121: "In this context, we see that kets may be thought of as input states, whereas bras as output states of a certain physical evolution or process."

Notice words "In this context". He is discussing a particular case, in which he assigns these meanings. The article is not about any particalar case, but the general math formalism.

Clear?