Minecraft – the stuff keeps being deleted from the nether

According to this thread in the Minecraft Forums that seems to have peeked into the code, length dilation does not affect the y-axis.

http://www.minecraftforum.net/topic/345806-nether-portal-science/

Summary version

• Calculate coordinate of destination based on entry coordinate. (X, Y, Z) <---> (X*8, Y, Z*8)

• At destination, look for the closest active nether portal within a 128 block radius of the player (257x257x128 area centered on destination) (the Euclidean distance (the 3D distance)). Teleport player there if one exists.

• If no portal exists in the 128 block radius, the game creates one by looking for the closest possible nearby position within a 16 radius column (33x33x128 area) that has enough space to spawn a portal. And teleports the player there.

• And if there's no possible spawn position with solid ground, it just creates a portal at the destination anyway, converting any blocks in the way into a portal.

It seems you are playing in creative mode, so you can easily make a new portal to go back to the overworld. If you don't want to, remember you can always double tap space to fly; that should make your hunt easier.

Even if you aren't, if you created your portal at spawn, the nether end of it should be in the general neighbourhood of X: 0 and Z: 0 (mostly within a 100 meters range of that). Press F3 to show your coordinates and try to head in a direction that brings both X and Z close to zero (Y is your altitude, confusingly). Keep in mind your portal might be high up enough that you can't see it.