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.