1 Jamie: It's not necessarily a parallel universe, Adam. It could just be that we're changing our own history by meeting ourselves for the first time.
2 Adam: Hmmm. We need some experiment to distinguish the possibilities. We could kill our younger selves and see if we still exist.
3 Jamie: That sounds a little drastic.
3 Adam: But it's for science!
4 Young Adam: (to Young Jamie} I have a really bad feeling about this.

You can justify anything... For science!

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2020-07-26 Rerun commentary: I think if you find yourself in your own past and meeting your younger self, you pretty much have to try killing your younger self to see what happens. I mean, if you don't, then you'll probably end up doing it accidentally anyway, given how these things inevitably work.

Either that or your younger self will kill you. May as well get in first.