If you physically traveled back in time..

[Sirian_A]

And met a deceased friend.. whose soul would be using that body?

Assuming he/she/it died, then you traveled back to when they were alive, who is in that body, since their soul is immediately in the astral following death? Hmmm?

[Sariel]

Because everything is happening simultaneously one soul-personality can be and it is at many places at the same time in different realities and dimensions of existences. On the astral and on the physical plane.