Activity

That’s the paradox.  Assume someone invents a time machine a hundred years from now.  As time goes on and more machines are built, there would be more and more time travelers visiting the past (our present).  There would be no way that we wouldn’t encounter one every now and then.  Oh wait, you say — there’s a government agency that strictly monitors time travel and polices it so that such meetings never take place.  Then we’d be meeting up with those agents every now and then.  And you’re saying they never make mistakes?  Seriously?  Remember we’re talking about a theoretically infinite future full of time travelers.  (See Isaac Asimov’s novel “The End of Eternity”)

Of course there are websites which claim that we ARE encountering time travelers from time to time (ha-ha).  They dig up old, old pictures with people wearing odd shirts or holding a hand up against the sides of their faces and claim these people are using cell phones, or things like that.  They can be pretty amusing.