 Why can't Joe go back to 1960?
Joe had been born in Naples and his mother had died in childbirth. Reston-Farrell said, "Suffice to say, you are now one hundred and seventy-three years after the last memory you have." 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. More than a century and a half ago our society eliminated the reasons for international conflict. 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.
 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.