There are many different bubbles within the Material Plane. Here is a list of all known alternate timelines in Threshold.

Threshold 001 "IRL" - This is our world, the one we are living in right now. "Real" life.

Threshold 002 "Early Vel" - Similar to the "Prime" timeline, but with Vel appearing much earlier.

Threshold 003 "Ranch" - An offshoot of "Early Vel" in which Christine does not meet Clarion and Rasper.

Threshold 004 "Prime" - The current Threshold timeline as seen in the Threshold YouTube series.

Threshold 005 "Rasper 125" - Rasper is pulled into the 125th century in this far-future Threshold.

Threshold 28.7 "28.7" - A timeline in which everything happens 28.7 years later.