 Why can't Joe go back to 1960?
A gun is an interesting weapon; it can be hired, of course, and naturally doesn't care who hires it. The evening was dark, it was unlikely that the other even saw the circle of steel that was the mouth of the shotgun barrel, now resting on the car's window ledge. And at that moment, the universe caved inward upon Joseph Marie Prantera. Joe had been born in Naples and his mother had died in childbirth. His father hadn't brought him to the States until the age of five and by that time he had a stepmother. Joe gingerly tried swinging his feet to the floor and sitting up, while the other stood watching him, strangely. Joe Prantera stared at him, said finally, flatly, "What's it all about?" He wondered, all over again, if this was some kind of pressure cooker. Whatever the something else was, a slot opened in the middle of the table and a glass, so clear of texture as to be all but invisible, was elevated. "What is the date, Old Calendar?" "2133," Reston-Farrell said. Joe Prantera had never been exposed to the concept of time travel. Reston-Farrell said, "Suffice to say, you are now one hundred and seventy-three years after the last memory you have." Joe Prantera's mind suddenly reverted to those last memories and his eyes narrowed dangerously. For the second time, Reston-Farrell said, "Where would you go, Mr. Prantera?" The two men of the future said nothing more for long minutes while Joe Prantera's mind whirled its confusion. Joe Prantera's irritation over this whole complicated mess was growing. Joe snapped: "Everything you guys say sounds crazy. Our pedagogues are hard put to convince their students that such ever existed. More than a century and a half ago our society eliminated the reasons for international conflict. For that matter," he added musingly, "we eliminated most international boundaries. Depressions? Overnight, for all practical purposes, the whole world was industrialized, automated. The second industrial revolution was accompanied by revolutionary changes in almost every field, certainly in every science. Your ancestors found, Mr. Prantera, that it is difficult for a man to be free so long as others are still enslaved. Today the democratic ethic has reached a pinnacle never dreamed of in your own era." "So everybody's got it made. What I wanta know is what's all this about me giving it ta somebody?
 Time only moves one way.
 Temple-Tracy destroyed the vortex manipulator.  The time circuits were damaged when they brought Joe into the future.  Temple -Tracy destroyed the time transmitter.  Time only moves one way.