"You mean time travel?"
"I guess that's what you'd call it."
"Time travel is nonsense," he said. "A logical absurdity. By definition, time is a series of infinitesimally small moments in succession. Once a point in time is established, it can't be changed, any more than energy can be destroyed."
"I didn't say anything about changing anything. I was thinking about—well, talking with somebody in the future."
"Just as paradoxical," he said, shrugging, and taking a huge bite of braised beef tongue. "If you go into the future—or talk to the future—the future affects the change, through you. In other words, if you can't go back into the past, neither can people from the future. And it's inconceivable that such a thing wouldn't make changes. Maybe only small ones, but they'd multiply in time. 'Thou canst not change a flower, without troubling of a star.' That's Francis Thompson. You step on one spider today, and you affect the evolution of spiders, the ecology of all other things in the distant future. By a simple act like that you could destroy or create a whole species to come."
"My head swimmeth," I said. "All I want to know is—"
He wasn't even listening to me. He enjoyed spouting this kind of thing. "Of course, it's theoretically possible for you to witness events out of the past, without being party to them. If, for instance, you could travel away from Earth at more than the speed of light, overtaking the light waves of an event—say, the Monitor and Merrimac fight—"
"Or the Battle of Gettysburg," I said, loyal to the core.
"—you could look back and see it happen. The future? I doubt it. Unless in some way time and space actually curve back upon themselves, as some think."
"Uh huh," I said, and drank my coffee and finally left Clipper Moskowitz.