1 Jamie: Here's the plan. You set off every explosive that ever existed or will exist here.
2 Jamie: I'll go back to the beginning of time and set off every explosive that ever existed or will exist there.
3 Jamie: And we'll see if one or the other - or both - create the universe.
4 Jamie: What are you thinking?
4 Adam: Is there any way we can make this more spectacular?

Of course with a time machine, they can both have copies of the same explosives at each time.

Actually, that's a way to make it more spectacular. Have multiple copies of all the explosives ever at each time.