Tanchedi took his hands off the wheel again and waved them. "-so I envy you, Dr. Padway. Here in Rome we have still some work to do. But pah! It is all filling in little gaps. Nothing big, nothing new. And restoration work. Building contractor's work. Again, pah!"
"Professor Tancredi," said Martin Padway patiently, "as I said, I am not a doctor. I hope to be one soon, if I can get a thesis out of this Lebanon dig." Being himself the most cautious of drivers, his knuckles were white from gripping the side of the little Fiat, and his right foot ached from trying to shove it through the floor boards.
Tancredi snatched the wheel in time to avoid a lordly Isotta by the thickness of a razor blade. The Isotta went its way thinking dark thoughts. "Oh, what is the difference? Here everybody is a doc-tor, whether he is or not, if you understand me. And such a smart young man as you-What was I talking about?"
"That depends." Padway closed his eyes as a pedestrian just escaped destruction. "You were talking about Etruscan inscriptions, and then about the nature of time, and then about Roman archaeol-"
"Ah, yes, the nature of time. This is just a silly idea of mine, you understand. I was saying all these people who just disappear, they have slipped back down the suitcase."
"The what?"
"The trunk, I mean. The trunk of the tree of time. When they stop slipping, they are back in some former time. But as soon as they do anything, they change all subsequent history."
"Sounds like a paradox," said Padway.
"No-o. The trunk continues to exist. But a new branch starts out where they come to rest. It has to, otherwise we would all disappear, because history would have changed and our parents might not have met."
"That's a thought," said Padway. "It's bad enough knowing the sun might become a nova, but if we're also likely to vanish because somebody has gone back to the twelfth century and stirred things up-"
"No. That has never happened. We have never vanished, that is. You see, doc-tor? We continue to exist, but another history has been started. Perhaps there are many such, all existing somewhere. Maybe, they aren't much different from ours. Maybe the man comes to rest in the middle of the ocean. So what? The fish eat him, and things go on as before. Or they think he is mad, and shut him up or kill him. Again, not much difference...