"Apparently. Nobody knows how they predicted it, but they did. Spotted it coming several years ago, so they've been romping through parallel after parallel trying to find one they can migrate to. They found one, sort of a desperation choice. It's cold and arid and full of impassable mountain chains. With an uphill fight they can make it support a fraction of their population."
Tommy shook his head helplessly. "They picked a very sensible system for getting a good strong Grdznth population on the new parallel as fast as possible. The males were picked for brains, education, ability and adaptability; the females were chosen largely according to how pregnant they were."
Pete grinned. "Grdznth in utero. There's something poetic about it."
"Just one hitch," said Tommy. "The girls can't gestate in that climate, at least not until they've been there long enough to get their glands adjusted. Seems we have just the right climate here for gestating Grdznth, even better than at home. So they came begging for permission to stop here, on the way through, to rest and parturiate."
"So Earth becomes a glorified incubator." Pete got to his feet thoughtfully. "This is all very touching," he said, "but it just doesn't wash. If the Grdznth are so unpopular with the masses, why did we let them in here in the first place?" He looked narrowly at Tommy. "To be very blunt, what's the parking fee?"
"Plenty," said Tommy heavily. "That's the trouble, you see. The fee is so high, Earth just can't afford to lose it. Charlie Karns'll tell you why."
Charlie Karns from Math Section was an intense skeleton of a man with a long jaw and a long white coat drooping over his shoulders like a shroud. In his arms he clutched a small black box.
"It's the parallel universe business, of course," he said to Pete, with Tommy beaming over his shoulder. "The Grdznth can cross through. They've been able to do it for a long time. According to our figuring, this must involve complete control of mass, space and dimension, all three. And time comes into one of the three—we aren't sure which."
The mathematician set the black box on the desk top and released the lid. Like a jack-in-the-box, two small white plastic spheres popped out and began chasing each other about in the air six inches above the box. Presently a third sphere rose up from the box and joined the fun.