question:  How does rejuvenation work?
context: But with the Procyon shuttle arriving yesterday, there was no telling what might turn up. They found it drifting half a light-year out and captured it. For eighty years now, they’d been sending out the little ships that vanished at greater than the speed of light, equipped with every conceivable device to make them return automatically after taking pictures of wherever they arrived. Scientists there had puzzled over it, reset it and sent it back. He had no desire to spend ninety years cooped up with a bunch of callow young emigrants, even in one of the improved Exodus shuttles. And even if Exodus ever got the super-light drive working, there was no reason he should give up his work. The discovery that men could live practically forever had put an end to most family ties; sentiment wore thin in half a century—which wasn’t much time now, though it had once seemed long enough. Faint blur lines indicated it had been moving when the picture was taken. Earth was becoming a backwater world; no real progress had been made in two centuries; the young men were sent out as soon as their first fifty years of education were finished, and the older men were too conservative for really new thinking. It took two accidents to get the thing back to us—and with a half-light-year miss that delayed it about twenty years before the Procyon shuttle heard its signal. Pre-setting a course may take centuries, if we can ever master it. We can’t put human pilots into a ship with our drive until we’ve tested it more thoroughly, Bill, even if they could correct for errors on arrival. Usually it was too easy to realize that, and the sight of the solid, time-enduring buildings outside should have given him a sense of security. Like an automaton, he bent forward, his other hand groping for the mirror that should be in one of the drawers. Dubbins was at his side almost at once, with a hand under his arm to guide him toward his suite.
output:  it re-trains the brain to develop younger cells
options:  it re-trains the brain to develop younger cells  it injects a serum in the body that reverses time  exercises are done to re-energize muscles  drugs convince the body to feel younger