"Naturally," Ho Dyak flashed back, "but your helicopter, that you planned to use for exploration on that other planet—"
"Mars," supplied Nelson. "Gosden financed the trip and purchased the ship for me. I'd had experience with submarines and aircraft during the Second War, and Gosden knew me then. His sister stowed away aboard. We were several thousand miles out into space when we discovered her. We turned back to Earth then; our supplies were insufficient."
Ho Dyak smiled. "When was it," he wanted to know, "that you realized something was so terribly wrong—that this was not your home planet?"
"Almost as soon as we had sighted your world of Thrane," said Nelson. "Then we saw the three suns and the two extra planets of your system." He lighted one of his last cigarettes. "Just how did we get here?"
"Probably hit a space-time-material eddy. Our scientists created an artificial eddy, a sort of gateway you might say, between parallel worlds. That's how we lost our dense protective atmospheric envelope. The vibrational gateways, in the course of many years' usage, became permanent. Our ancestors no longer could seal them shut by cutting off the power.
"And so our precious atmosphere drained off into a dozen parallel dimensional worlds. Fortunately the gateways were on the upper plateaus and so a thin envelope of denser air remains. But one of those doors leads through to Earth! Maybe several of them."
Nelson gripped Ho Dyak's bulky shoulder.
"You mean," he gasped, "this is really Earth? Only changed?"
Ho Dyak agreed. "Something like water and sand," he explained, "when they're mixed together. They're distinct but occupy the same space." He turned toward the sea of fog and stepped down into it.