Dr. Arnold Mayer: [Addressing a lecture hall audience, possibly at the United Nations] We’ve talked about quarks and anti-neutrinos. But, what about people? It’s quite a step from demonstrating that sub-atomic particles can travel backward through time to saying that people can. What would be the result of people traveling in time? For one thing, paradoxes become possible. Say you build a time machine, go back and murder your father when he was ten years old. That means you were never born. And if you weren’t, how did you build the time machine? It’s the possibility of paradoxes that make most people rule out time-travel by human beings. Still, why not? If you were careful, you could do it. You would not go back to kill Adolf Hitler, much as you might like to, ’cause it would change history. A time-traveler would have to be careful, but he could do a surprising number of things. He could observe, for one. He could find out once and for all who was on the grassy knoll that day in Dallas. And he will know what we can only guess at… that we are destroying the planet we live on by complacency. He will have to live with our legacy of pollution & acid rain. Our negligence today is producing a world in which our children’s children will be barren, and the human race heading towards extinction. He could also take things, providing they wouldn’t be missed: a cup of water from the Pacific Ocean, a stone from the Grand Canyon. This may sound pointless, but sometimes very small differences can be crucial. The difference between a dead man and a man who’s alive can be very small. What about a man who’s about to die… a man no one will ever see alive again? This is the hard part about looking for time travelers: they don’t want to be found. You must look for them in places where no one is. Or where there are people no one will ever see alive again.