"James, JIMMY BOY, when we hired you on here, we sent you a specific memo, did you get that memo? The one which said not to blow up Earth? I realise it must have seemed somewhat tongue-in-cheek at the time, but there was a firm message there too, which we rather hoped you would take to heart."
"This cannot have happened. Something's gone wrong here," said James, watching the expanding debris of his exploded homeworld. "This planet can't have been Earth. Or it'll come back together again naturally." He poked fretfully at his computer terminal.
"Or you've changed history," said Frank.
"We cannot. Have changed. History," said James, emphasising his point by driving the edge of his right hand into the palm of his left.
"Then what in blazes have we changed?"
"Nothing! Look, we are still here, right? Our worldlines have not been cut and there is no paradox. So somehow, it must all work out. If we go back to the present day everything will be fine."
"If it isn't, my wife is going to... never have existed, and so won't be able to kill me."
"At the exact instant we departed our usual timespace location, we left a gap in the mountain. The mountain will be about to implode on that location, but if we return to the exact place and time we left, we plug the gap the instant after it was created and nobody knows anything went wrong. Clear?"
"Here we go."
An awesome starfield filled with scattered chunks of warm nickel-iron became simply a blank starfield.
"Unless—" began James.
"You're fired," said Frank. "You're fired, for changing history and erasing your job."
James sighed. "All right. All right. Something must have gone wrong with the numbers. Even though these are the smartest mathematicians I've ever had the privilege to work with, the theory they came up with doesn't work. There's at least one other timeline, with no Earth. Which we created. The question now is... well... I was going to say how we get back to the main timeline. But, ah. Perhaps a better one would be, what's that?" He pointed to a small, partially illuminated glowing ball at the far upper right of the immense screen.
"But it's green."
"That green one, then."
"Uranus doesn't look that big. Not from Earth orbit. I guess it could be Uranus, if it was moved in the aftermath from the doomsday explosion. But that seems unlikely."
"Can we get closer? Does this thing have any manoeuvring capabilities?"
"Are you kidding? It's a friggin' cave. I can look around a bit with the sensors though." The starfield swivelled past them, as if spun by a trackball, which it had been. "That red blob there is Mars. And there's Jupiter. So... we're looking at an entirely new planet. Somewhere out in the Mars-to-Jupiter band, maybe nearer and smaller, maybe a bit further and bigger."
"We can't get to it to see? No long-range scanners?"
"Frank, this is a cave, a cave! I made it to go back in time and show you a brief visual demonstration and then come back to where we started. I did not install long-range sensors or thrusters or airlocks or life support, the fact that we even have gravity is due a trivial piece of technobabble that barely withstands scrutiny. The demo was going to take five minutes. All we can do from this range is squint, and ask non-existent technicians to use non-existent image enhancement software on that small, greenish blob."
"No life support? How long until we run out of air?" Frank turned around and regarded the darkened cavern of machinery behind them.
"Air isn't going to be a problem," replied his subordinate, without bothering to look. "And with that weird enveloping anti-ference field I mentioned, we're not going to be radiating heat out at any critical rate either, so we'll stay warm-ish too." He gestured absently to a cluster of vending machines, nestled behind a four-storey pile of machinery half-covered with grey-green tarpaulins and marked with a big J8. "But we only have coffee, coke and out-of-date chocolate to eat and drink. Say a week."
"Great." Frank wandered off into the gloom to find a chair. "Oh, hey, that's better," he added, as the green image on the screen suddenly enlarged itself massively.
"I didn't do anything," said James. "Look, you know how between Mars and Jupiter there's an asteroid belt?"
"No, but go on."
"A lot of people thought - well, some people - well, it kind of makes sense to think that the asteroid belt was just a planet which failed to get its act together, for some reason. Well, we just turned—"
"—I just turned Earth into an asteroid belt. Four and a half billion years ago. Do you think that would be enough of a jostle to the Solar System's status quo to let that extra planet form? The four-and-a-halfth planet?"
Frank, who had now found himself a rolling office chair and slumped into it some feet away from James, gave him a look of utter bewilderment. "Maybe?"
"And for life to evolve on that planet instead of Earth? And maybe evolve slightly faster than Humanity, colonising their solar system with fantastic technology and also radar warning systems? Which could pick up new asteroids instantly, detect life onboard and bring them to local orbit for examination?"
"You think that's what just happened?"
There was a flash of blue-red light and something was there in the middle of the cavern with them. Against all likelihood, it appeared Humanoid, although whatever it was, it was wearing a fat, heavy armoured pressure suit which left the true details of its anatomical structure very much to the imagination. It was built somewhat like a bear. Its long-fingered hands were worrisome. The window of its helmet revealed the suit was full of green gas or liquid. Chlorine?
"Hi!" proclaimed James, striding towards the creature, a hand proferred. "This is a greeting in our culture. I'm James MacPherson, pleasure to meet you. We come in peace. Listen, have you guys discovered time travel yet?"