That's an inexact PARALLEL.
The Big Bang Theory Season 3, Episode 2
...that could serve as a portal
to a PARALLEL universe.
The Big Bang Theory Season 6, Episode 8
It's called "PARALLEL play."
The Big Bang Theory Season 8, Episode 3
...who doesn't believe
PARALLEL universes exist.
The Big Bang Theory Season 4, Episode 5
The first 43 PARALLEL universes I've checked
proved to be empty.
The Big Bang Theory Season 6, Episode 8