It's called "PARALLEL play."
The Big Bang Theory Season 8, Episode 3
...that could serve as a portal
to a PARALLEL universe.
The Big Bang Theory Season 6, Episode 8
If there are an infinite number
of PARALLEL universes...
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
...who doesn't believe
PARALLEL universes exist.
The Big Bang Theory Season 4, Episode 5