Board Thread:Questions and Answers/@comment-27447115-20151222024029/@comment-27281875-20151222100053

To okabe it looked like the past has changed, this is just my opinion though, but,

say, there are a lot of worldline existed with different world aspects (such as ruka's gender as example), and since okabe has the reading steiner ability that makes him "The observer" of the "active worldline". The worldline Reading Steiner took him into become the active worldline, while the past are rewritten according to this new worldline, okabe's memory right before reading steiner kicks in got transferred to the okabe in the new worldline and replace his new worldline past memory. and yes just like you say, the ruka that wants to be a girl still continue living in the worldline okabe left off.

take a note also the message contained in DMAIL WILL change the world divergence, no matter how small the number is, it changed, but if the change is not massive enough to the past, present, and the future (also look on the butterfly effect it creates), Reading Steiner won't active, let's say RS kicks in when at least a divergence number raised by 0.000001%, any DMAIL that may create huge differencies makes a big effect in the past, present, and future will rise the number many times bigger, but unimportant things sent in the DMAIL like kurisu sent "Okabe was an| Airhead" to okabe's phone MAY create 2 different worldline, in which one is the worldline where The dmail was sent, and another one where it was received, but the effect on the past, present, and future is not so relevant that the message sent and received ended in the same worldline.

So basically the "Changed past" is just how Okabe describes his Reading Steiner ability, while to me it was more like, the DMAIL interfered the past created 2 possible worldline in which one is the worldline where the dmail was sent and "The past is not changed" and the other one is the worldline where the DMAIL arrived and "the past is rearranged/changed"

hope this makes it more clearer