Supergirl, Season 1

[Barry Allen is explaining to the others about the multiverse and how he arrived.]

Barry Allen:
[drawing circles on a whiteboard] All right. So imagine there are multiple versions of Earth. One where, uh... the Nazis won World War II , one where Kennedy was never assassinated...

Winn:
[raising a hand like he's in a classroom] Okay, one where all of us are evil.

Barry:
Been there. It sucks. So all of these Earths occupy the same place in space, but they vibrate at a different frequency, so they can't see one another.

Winn:
Yeah, yeah, but it's like, if you can go fast enough, then it's possible to open, like, a breach and then travel between worlds.

Barry:
Yeah.

James:
But how could you travel that fast?

Barry:
[amused] Uh, well, um...

[Barry races out of the room at super-speed, then returns seconds later, giving each of them an ice cream cone.]

Kara:
[overjoyed] Yeess!!

Barry:
Yeah. So, um... I was struck by lightning the same night a particle accelerator exploded, and I became a... superhero.

[Kara giggles, impressed and a little smitten.]

James:
So, so, so... y-you're a superhero, too.

Barry:
Mmm-hmm.

James:
[subdued] Tha-that's cool, I guess.