Anne’s an experienced adventurer, but almost exploding the Earth when she tried transporting herself into an anti‑Universe was a jolt. It takes her a while to calm down. Fortunately, I’m there to help. <long soothing pause> “Sy, I promise that’s one direction I’ll never ‘push’ to go again.”

“No reason to go there and big reasons not to. <long friendly pause> Hmm. You’ve told me that when you use your superpower to go somewhere, you can feel whether there’d be a wall or something in the way. That’s how you know to get to a safer location before you ‘push.’ Didn’t you get that feeling before you went to meet anti‑Anne?”

“No, it felt just like just any other ‘push.’ Why?”

“I’m curious. Could you feel for just a second in the direction opposite to anti‑Anne? For Heaven sake don’t go there! Just look, OK?”

“All right … <shiver> Now, that’s weird. There’s nothing there, except there’s not even a there there, if you know what I mean.”

“I think I do, and you’ve just given us one more clue to where you almost went. Whoa, no more shivering, you’re back here safe where there’s normal matter and real locations, OK? <another soothing pause> That’s better. So, I was assuming a binary situation, an anti‑Universe obeying a Charge‑Parity‑Time symmetry that’s exactly the reverse of ours. The math allows only the two possibilities. You observed ‘no there there’ when you tried for a third option. That’s support for the assumption.”

“How could we have even two Universes?”

“It goes back to the high‑energy turmoil at the Big Bang’s singularity. Symmetry says the chaos in the singularity should have generated as many anti‑atoms, umm, as many positrons and anti‑protons, as their normal equivalents.”

“Positrons?”

“Anti‑electrons. Long story. The big puzzle is, where did those anti‑guys go? One proposal that’s been floating around is that while normal matter and our normal CPT symmetry expanded from the singularity to make our Universe, the anti‑matter and reversed symmetry expanded in some kind of opposite direction to make the anti‑Universe. You may have found that direction. Here, I’ll do a quick sketch on Old Reliable.”

“Looks like some of the banged‑up painted‑up battle shields I saw a thousand years ago.”

“It does, a little. Over on the top left is our normal‑matter Universe with galaxies and all, expanding out of the singularity at time zero. Time runs vertically upward from that point. I can’t draw three spatial dimensions so just one expanding sideways will have to do, OK?”

“No problem, I do x‑y‑z‑t thinking all the time when I use my superpower.”

“Of course you do. Well, coming down out of the singularity into minus‑time we’ve got the anti‑Universe. I’ve reversed the color scheme because why not, although I expect their colors would look exactly like ours because we know that photons are their own anti‑particles and should behave the same in both Universes.”

“They do. Anti‑Anne looked just like me, white satin and all.”

“Excellent, another clue. Anyway, see how minus‑time increases in the negative direction as the anti‑Universe expands just like plus‑time increases positively for us?”

“Mmm, yeah, but we only call them minus and plus because we’re standing outside of both of them. Looking from the inside, I’d say time in each increases towards expansion.”

“Good insight, you’re way ahead of me. That’s what I’ve drawn on the right side of the sketch. The two are perfectly equivalent except for CPT and anti‑CPT. Time direction, x‑y‑z space directions, even spin orientation, can all be made parallel between the two. However, the charges are reversed. Anti‑Anne’s atoms have positrons where we have electrons, negative anti‑protons where we have positive protons. When anti‑matter meets matter, there’s massive energy release from equivalent charged particles neutralizing each other.”

“Wait. Gravity. Wouldn’t anti‑matter particles repel each other? Your picture has galaxies and they couldn’t grow up with everything backwards.”

“Nope, you’re carrying this model too far. The only thing that’s reversed is charge. Masses work the same in each symmetry. Gravity pays attention to mass, not charge, and it’s always a force of attraction.”

“Anyway, not going back there.”

“Good.”

~~ Rich Olcott