Yeah maybe just have them "not work" rather than vaporize. *nods* It shouldn't be an issue or focus then. 

Well the fantasy world would certainly have magic but probably a low form of it? Like potions or runes or something? I assume the "magic" in the sci-fi world would be more like magic + math/science and as such would be more like energy or laser oriented? And in the modern world, would none exist at all? Maybe that's where the two are destined to converge or something? What if we had some sort of prophecy that originated in the modern world and got passed along from the 1700s to present but having been published somewhere random to hide it, no one's thought much about the idea of three worlds colliding.

But say the prophecy got a little mixed up in the other two worlds?

I'm rambling randomly. Sorry.

Or what if the worlds once got along but back in the day had some war which maybe broke the mirrors so maybe the concept wouldn't be totally "fresh" and weird....?

I'm probably not making much sense. >___>