> It doesn't make any sense to have something which is in 1970 yesterday
> and in 1980 today.  Something's in 1980 when it's in 1980; there's no
> difference between being in 1980 now, and being in 1980, period.  (What
> happens if I travel back to yesterday, does the wave move back from 1980
> to 1970 again?) 

No. Let's take Back to the Future as example. He travelled back to 1955
and screwed up his Mom meeting his Dad. When he looked at a picture of him
and his brother and sister, the brother began vanishing first, then the
sister as that is the order in who was born first. The brother was born,
then the sister, then Marty. The disruption Marty caused in time was
slowly changing time in the future by affecting what happened closer to
1955 first, thus his brother was the first to disappear. Just the same way
Kain affected the past, thus causing a slow disappearance of Tenchi as he
was born, then the rest of the gang came to Earth. If Washu hadn't stopped
Tenchi from vanishing, then after Tenchi was gone (following the TV Series
timeline), Ryoko and Mihoshi would start to disappear and reappear
wherever they would be if Tenchi hadn't been born. Then Ayeka, then
Sasami, then Washu, then Kiyone. You see, sort of like throwing a rock in
water. The ripples it causes don't start at the shore and go towards the
rock, but the ripples go from the rock towards the shore, or, go from the
disruption in the past towards the present.

Sorry for the long oration.