“As you know, one of the fears entertained about travel to the past was that the most innocent-seeming acts would cause cataclysmic changes in the present. You are probably familiar with the fantasy in its most currently popular form—if Hitler had been killed in 1930, he would not have forced scientists in Germany and later occupied countries to emigrate, this nation might not have had the atomic bomb, thus no third atomic war, and Venezuela would still be part of the South American continent.
“The traitorous Shayson and his illegal federation extended this hypothesis to include much more detailed and minor acts such as shifting a molecule of hydrogen that in our past really was never shifted.
“At the time of the first experiment at the Coney Island Subproject, when the chronar was sent back for one-ninth of a second, a dozen different laboratories checked through every device imaginable, searched carefully for any conceivable change. There were none! Government officials concluded that the time stream was a rigid affair, past, present, and future, and nothing in it could be altered. But Shayson and his cohorts were not satisfied: they—”
I. Four billion years ago. The chronar floated in a cloudlet of silicon dioxide above the boiling Earth and languidly collected its data with automatically operating instruments. The vapor it had displaced condensed and fell in great, shining drops.
“—insisted that we should do no further experimenting until we had checked the mathematical aspects of the problem yet again. They went so far as to state that it was possible that if changes occurred we would not notice them, that no instruments imaginable could detect them. They claimed we would accept these changes as things that had always existed. Well! This at a time when our country—and theirs, ladies and gentlemen of the press, theirs, too—was in greater danger than ever. Can you—”
Words failed him. He walked up and down the booth, shaking his head. All the reporters on the long, wooden bench shook their heads with him in sympathy.
There was another gong. The two dull spheres appeared briefly, clanged against each other and ricocheted off into opposite chronological directions.
“There you are.” The government official waved his arms at the transparent laboratory floor above them. “The first oscillation has been completed; has anything changed? Isn’t everything the same? But the dissidents would maintain that alterations have occurred and we haven’t noticed them. With such faith-based, unscientific viewpoints, there can be no argument. People like these—”
II. Two billion years ago. The great ball clicked its photographs of the fiery, erupting ground below. Some red-hot crusts rattled off its sides. Five or six thousand complex molecules lost their basic structure as they impinged against it. A hundred didn’t.
“—will labor thirty hours a day out of thirty-three to convince you that black isn’t white, that we have seven moons instead of two. They are especially dangerous—”