Wizards and Pensives moving through time

[n_longbottom01]

No: HPFGUIDX 142054

I once heard of a version of the legend of King Arthur in which 
Merlin the Magician's life is moving backwards rather than forward in 
time.  So when Arthur meets Merlin for the first time, Merlin already 
knows everything there is to know about Arthur.  And when Arthur 
meets Merlin for the last time in his life, from Merlin's perspective 
he has never met the King before.

The way I picture this working is that Merlin wakes up on Monday, 
moves forward in time like the rest of the world throughout the day, 
and goes to bed.  When Merlin wakes up in the morning, it is Sunday, 
instead of Tuesday.  Everyone else moved forward a day, but Merlin 
moved back a day.  He knows what is going to happen tomorrow, because 
he just lived through it, but he couldn't tell you what happened 
yesterday, because he hasn't gotten there yet.

lucianam73's post # 142002 "How important is the right sluggish 
memory?" got me thinking about this.  She suggested that all of 
Dumbledore's meetings with Harry were carefully scheduled in advance, 
and in the one meeting that wasn't arranged ahead of time, Dumbledore 
seems to react in ways that indicate that he doesn't have all of the 
information that he had in some of their previous meetings.  Lucianam 
suggested this indicates that Dumbledore is moving through time.  My 
idea is that Dumbledore was caught unprepared for this meeting with 
Harry, and slipped up a little bit
 and the previous meetings were 
carefully scheduled so Dumbledore was prepared and there weren't time 
travel related slip-ups.  How does a time traveling wizard prepare 
himself for a meeting with someone who is moving through time in the 
normal fashion?  They use their pensive!

The pensive is moving through time in the normal direction
 
forwards.  The wizard could take those memories that he needs to have 
move through the timeline in the normal way out of his head, and put 
them in his pensive.  If he traveled to a certain day "out of 
sequence" he could use his pensive to know what he was supposed to 
know at the time he was supposed to know it.

Back to the Merlin example: King Arthur stops by Merlin's cave 
unexpectedly on Monday morning to some more about the thing they were 
talking about yesterday.  Merlin doesn't have any idea about what 
Arthur is talking about, because he hasn't gotten to "yesterday" yet 
(moving through time backwards).  Merlin goes over to his pensive, 
pulls a few wispy thoughts out of it, and pops them back into his 
head.  "Ah
 now I know what you are talking about, Arthur."  Since 
the pensive is moving forwards through time, the thoughts in it were 
from the previous day, even though Merlin, moving backward through 
time, hadn't gotten there yet.

--n_longbottom01