“Wait, Sy, you said something about my matryoshka*‑*cascade multiverse, that the speed of light might not match between mama and baby Universes. How can that be?”

“Deep question, Susan. The answer is that we don’t know. Maybe gravitational stress at a supermassive black hole’s singularity is intense enough to birth a new Universe inside the Event Horizon, or maybe not. Suppose it does. We don’t have theories strong enough to determine whether the speed of light inside there would or would not match the one we have out here.”

“Talk about pregnant questions.” <*sips latte*> “Ah! Here’s another thing. Both my matryoshki and your bubbly multiverse are about spreading Universes across space. Neither one addresses the timeline splits we started talking about. Maybe I decide on noodles for lunch and another me in a different Universe opts for a sandwich, but how about one me that splits to follow parallel paths right here? Could a multiverse work that way?”

“Another deep question. Timeline splits require a five*‑*dimensional spacetime. Want to talk about that?”

“Just a moment. Oh, Al, can I have another mocha latte, please, and add a dash of peppermint to it.”

“That’s a change from your usual recipe, Susan.”

“Yes,” <*side glance my way*> “I’m splitting my timeline. Thanks, Al. Ok, Sy, let’s go for it.”

“It’s about degrees of freedom.”

“I like freedom, but I didn’t know it comes in degrees.”

“In certain contexts that’s a matter of geography, law and opinion. I’m talking Physics here. For physicists each degree of freedom in a system is a relevant variable that’s independent of other specifications. Location parameters are a prime example. On a *Star Trek* vessel, how does the Captain specify a heading?”

“When they know where they’re going she’ll say ‘*Set coordinates for*‘ wherever, but for a course change she’ll say ‘*some‑number MARK some‑number*‘. Ah, got it — that’s like latitude and longitude, two arcs along perpendicular circles. Two angles and a distance to the target make three degrees of freedom, right?”

“A‑k‑a three dimensions of space. How about time?”

“All you can do is go forward, no freedom.”

“Not quite. Conceptually at least, you can go forward *and* back. Timewise we’re moving along a line. That’s a one‑dimensional thing. Combine time and space as Minkowski recommended and you’ve got a four‑dimensional spacetime. Relativity may serve us time at different rates but we’re still trapped on that line.”

“Ah, now I see why you said five dimensions. High school geometry — you’d need a second time dimension to angle away from the one we’re on. Ooo, if it’s an angle we could do time‑trigonometry, like the sine would measure how different two timelines get divided by how long it took to get there.”

“Cute idea, Susan, but defining time fractures in terms of time would be a challenge. I think a better metric would be probability, like what are the odds that things would be *this* different?”

A rustle of satin behind me and a familiar voice like molten silver. “Hello, Sy, I read your posts about multiverses so I thought I’d drop by. You’re Susan? Hi, my name’s Anne.”

“Um … hello.” Anne is kind of breath‑taking.

“Hi, Anne. It’s been a while. Funny you should show up just as we’re getting to the idea of a probability dimension.”

“Mm-hm, how ’bout that? Sorry, Susan, but time‑trig won’t work. I’ve got a better idea for you. Sy’s physicists are so used to thinking thermodynamically. Entropy’s based on probability, isn’t it, Sy? The split‑off dimension should be marked off in units of information entropy.” <*giggle*> “You haven’t told Susan your twenty‑dimension idea yet, have you?”

“Anne, you’ve always been too fast for me. Susan, the Physics we have so far still has about twenty fundamental constants — numbers like the speed of light — whose values we can’t explain in our best models of how things work. Think of each as a coordinate in a twenty‑plus‑four-dimensional hyper‑Universe. The Anthropic Principle says we and my entire bubble Universe happen to be at the twenty‑way intersection where those coordinates are just right for life to exist. Each of your matryoshki Universes may or may not be there. “

“Lucky, aren’t we?”

~~ Rich Olcott