"Would you even notice," Kayl asked, "if we changed all the locks to your house, but also replaced all your keys as well?"

"Probably not," I thought, but only shrugged in reply. I assumed that was a rhetorical question.

"If that's not something you'd notice, what if we did the same with a person? What if someone out there was constantly replacing the Werner we see here with one from a different pond? At what point would we notice something wrong, if ever?"

"I suppose if he has the same memories in all versions..." I trailed off.

"That's why we can't call him *the* Werner Heisenberg, only *a* Werner Heisenberg." Kayl was looking self-satisfied.

Meeting Werner Heisenberg, or *a* Werner Heisenberg, wasn't my first shock of the morning. The first was when Kayl came up to me and asked if I was thinking about string theory. There was no way she could have known, short of mind-reading, so I was flabbergasted.

Then she introduced Werner Heisenberg to me. Or rather *a* Werner Heisenberg to me. "We're here as tourists for the day," she said.

"Tourists?" I asked.

"Right," said Kayl, "we just want to experience this first hand, instead of from outside your pond."

"My pond?"

"You are a small fish in a small pond, my friend." Kayl smiled. "Your pond is one among countless other ones contained in a larger pond. And that larger one is also one among countless others contained in still bigger ponds."

"I'm not sure I follow." I never knew Kayl to be so weird.

"I'm not the Kayl you know," she said. "I'm *a* Kayl. A Kayl from a different pond. Like I said, me and Werner here are just visiting you for the day."

I wasn't following what she was saying at all. "Where is the Kayl I know then?"

"She's here too," she said. "We've sort of merged temporarily so that I could see your pond for myself. I suppose when I leave, I'll let her have a copy of my own memories as a gift."

She paused. "Well, I'm not sure you can call it a gift. I'm just too lazy to remove them from her."

"So she'll be back to normal then?" I asked.

"Well, as normal as one might expect if one had knowledge of the ponds beyond your own," she said.

"So I'll be able to ask her all about what you know then?"

"Sure, you can also ask me now, it doesn't matter."

Werner was wandering around the room, fascinated, picking up and examining objects as if in a museum.

"So what brings you two here anyway?" I asked.

"We used to have a strict nonintervention policy," Kayl said. "We observed you from the outside but intentionally altering your pond was considered a waste. That was when we didn't have the resources we have now. These days we can spawn a dozen copies of your pond and use them as we wish."

"I'm a copy?" I asked.

"Unfortunately yes," said Kayl. "Your pond is now tainted because of our visit. In another, things are still progressing as if Werner and I never showed up."

"Is that one considered the better one?" I was suddenly anxious.

"We don't have a clear measure of what is or isn't better," replied Kayl. "As you know, Werner here showed that observer and the observed affect one another, even if it is from outside the pond - so in the end, it doesn't really matter."

I wasn't sure if we were still talking about the same Werner but let that go. "So now you guys are tourists going around bending the laws of reality?"

"I wouldn't really say we're bending any laws," she said. "They just appear in different jurisdictions. You know your local laws quite well, but are unfamiliar with the ones beyond your jurisdiction. Even I only know what I've seen. I can only assume there is much more out there that I have not seen yet, nor know how my local knowledge fits into the bigger picture."

"So what is going to happen here after you guys leave?"

"Nothing if you do nothing," she said. "The future of your pond is still up to you and each of you who participate in it, including your original Kayl."

"Will I know if more of you come visiting?" I asked.

"We've given up asking that question ourselves," said Kayl. "Not only might Werner here be replaced from moment to moment, so can everything around you. Imagine the physical world around you as a key, and your mind using that key to access your memories. What if we changed the lock and key at the same time? Would your mind even notice?"

I shrugged again. Sounded like another rhetorical question.

"Even in my own pond," Kayl continued, "we can never be sure if everything was changing around us without our noticing. As a result, we've given up asking that question. There are likely countless ponds that contain ours, and any of them could make arbitrary changes to us at any time."

"I'm not sure how to respond to that," I said.

"Don't," said Kayl, "unless you really want to. I'm probably not going to be back though. No offense, but you're just one among countless others, which means none of you are all that special. None of us are. In some ponds, it wasn't even Werner here who came up with his theories. It was both humans and non-humans going by other names. Nothing is original when you are buried in infinity. All you can do is experience the things you want to experience. For yourself. Someone else is already doing the same thing in a different pond."

"Well, it was a pleasure to meet you in person," Kayl said, shaking my hand as if for the last time, though I knew I'd just see her again the next day.

One instance of her anyway.