"Not at all," said Ed.

"You nonscientists. Well, just trust me on it, then. The point is: multiple universes. The multiverse. What the skip drive does is open a door to another one of those universes."

"How does it do that?" I asked.

"You don't have the math for me to explain it to you," Alan said.

"So it's magic," I said.

"From your point of view, yes," Alan said. "But it's well allowed in physics."

"I don't get it," Ed said. "We've been through multiple universes then, yet every universe we've been in has been exactly like ours. Every 'alternate universe' I ever read about in science fiction has major differences. That's how you know you're in an alternate universe."

"There's actually an interesting answer to that question," Alan said. "Let us take as a given that moving an object from one universe to another is a fundamentally unlikely event."

"I can accept that," I said.

"In terms of physics, this is allowable, since at its most basic level, this is a quantum physics universe and pretty much anything can happen, even if as a practical matter it doesn't. However, all other things being equal, each universe prefers to keep unlikely events to a bare minimum, especially above the subatomic level."

"How does a universe 'prefer' anything?" Ed asked.

"You don't have the math," Alan said.

"Of course not," Ed said, rolling his eyes.

"But the universe does prefer some things over others. It prefers to move toward a state of entropy, for example. It prefers to have the speed of light as a constant. You can modify or mess with these things to some extent, but they take work. Same thing here. In this case, moving an object from one universe to another is so unlikely that typically the universe to which you move the object is otherwise exactly like the one you left—a conservation of unlikeliness, you might say."

"But how do you explain us moving from one place to another?" I asked. "How do we get from one point in space in one universe, to an entirely different point in space in another?"

"Well, think about it," Alan said. "Moving an entire ship into another universe is the incredibly unlikely part. From the universe's point of view, where in that new universe it appears is really very trivial. That's why I said that the word 'drive' is a misnomer. We don't really go anywhere. We simply arrive."

"And what happens in the universe that you just left?" asked Ed.

"Another version of the Modesto from another universe pops right in, with alternate versions of us in it," Alan said. "Probably. There's an infinitesimally small chance against it, but as a general rule, that's what happens."

"So do we ever get to go back?" I asked.

"Back where?" Alan said.

"Back to the universes where we started from," I said.

"No," Alan said. "Well, again, it's theoretically possible you could, but it's extremely unlikely. Universes are continually being created from branching possibilities, and the universes we go to are generally created almost instantly before we skip into them—it's one of the reasons why we can skip to them, because they are so very close to our own in composition. The longer in time you're separated from a particular universe, the more time it has to become divergent, and the less likely you are to go back to it. Even going back to a universe you left a second before is phenomenally unlikely. Going back to the one we left over a year ago, when we first skipped to Phoenix from Earth, is really out of the question."

"I'm depressed," Ed said. "I liked my universe."

"Well, get this, Ed," Alan said. "You don't even come from the same original universe as John and I, since you didn't make that first skip when we did. What's more, even the people who did make that same first skip with us aren't in the same universe as us now, since they've since skipped into different universes because they're on different ships—any versions of our old friends that we meet up with will be alternate versions. Of course, they will look and act the same, because except for the occasional electron placement here and there, they are the same. But our originating universes are completely different."

"So you and I are all that's left of our universe," I said.

"It's a pretty good bet that universe continues to exist," Alan said. "But we are almost certainly the only two people from it in this universe."

"I don't know what to think about that," I said.

"Try not to let it worry you too much," Alan said. "From a day-to-day point of view, all this universe hopping doesn't matter. Functionally speaking, everything is pretty much the same no matter what universe you're in."

"So why do we need starships at all?" Ed asked.

"Quite obviously, to get where you're going once you're in your new universe," Alan said.

"No, no," Ed said. "I mean, if you can just pop from one universe to another, why not just do it planet to planet, instead of using spaceships at all? Just skip people directly to a planet surface. It'd save us from getting shot up in space, that's for sure."

"The universe prefers to have skipping done away from large gravity wells, like planets and stars," Alan said. "Particularly when skipping to another universe. You can skip very close to a gravity well, which is why we enter new universes near our destinations, but skipping out is much easier the farther away you are from one, which is why we always travel a bit before we skip. There's actually an exponential relationship that I could show you, but—"

"Yeah, yeah, I know, I don't have the math," Ed said.

Alan was about to provide a placating response when all of our BrainPals flicked on. The Modesto had just received news of the Coral Massacre. And in whatever universe you were in, it was horrifying stuff.

Coral was the fifth planet humans settled, and the first one that was indisputably better acclimated for humans than even Earth itself. It was geologically stable, with weather systems that spread a temperate growing zone across most of its generous landmasses, and laden with native plant and animal species genetically similar enough to Earth's that they fulfilled human nutritional and esthetic needs. Early on, there was talk of naming the colony Eden, but it was suggested that such a name was karmically tantamount to asking for trouble.

Coral was chosen instead, for the corallike creatures that created gloriously diverse island archipelagos and undersea reefs around the planet's equatorial tropical zone. Human expansion on Coral was uncharacteristically kept to a minimum, and those humans who did live there largely chose to live in a simple, almost pre-industrial way. It was one of the few places in the universe where humans attempted to adapt to the existing ecosystem rather than plow it over and introduce, say, corn and cattle. And it worked; the human presence, small and accommodating, dovetailed into Coral's biosphere and thrived in a modest and controlled way.

It was therefore entirely unprepared for the arrival of the Rraey invasion force, which carried in its numbers a one-to-one ratio of soldiers to colonists. The garrison of CDF troops stationed above and on Coral put up a brief but valiant fight before being overwhelmed; the colonists likewise made the Rraey pay for their attack. In short order, however, the colony was laid waste and the surviving colonists literally butchered, as the Rraey had long ago developed a taste for human meat when they could get it.

One of the snippets broadcast to us via BrainPal was a segment of an intercepted food program, in which one of the Rraey's most famous celebrity chefs discussed the best way to carve up a human for multiple food uses, neck bones being particularly prized for soups and consommés. In addition to sickening us, the video was anecdotal proof that the Coral Massacre was planned in enough detail that they brought along even second-rate Rraey celebrities to take part in the festivities. Clearly, the Rraey were planning to stay.