However, who is to say time travelers would want to come to our time anyways? Would it make sense for highly evolved beings to travel to a time as polluted and dangerous as ours when there are endless amounts of time more suitable for leisurely travel.
I mean, if I wanted to swim in the untainted waters near Cyprus, the same place where Aphrodite rose out of the sea, would I want to do it in a time when that land was surrounded by commercial development and societal upheaval, or would I travel to a time in the more distant past?
Or, to take the idea further, if I wanted to retire, would I want to do it in modern or ancient times? In the present, a time traveler could only impress the authorities so much before he/she was put on lock down and milked for all their technological know-how. On the other hand, ancient societies might see their technological advances and revere them as gods.
this aside, there is the question of a universe-destroying paradox to think about. Theoretically, a paradox occurs when changes to the past make those changes impossible to begin with. Such as, going back in time and killing your grandfather before he met your grandmother. Or, in the case of Back to the Future, having your mom get the hots for you instead of your dad. In any case, the new future would spawn a world where the time traveler wouldn't exist, thus negating their effects on the past.
Confusing? Yes, but it makes for interesting fiction at times.
Who knows, someday we might discover that our first civilizations ranging from Minoan to Egyptian were merely the retirement homes for more advanced time travelers. Far fetched? Perhaps, but I wonder if it is any more likely that nomadic apes evolved into empires led only by survival instincts.
As for me, I'm no Billy Pilgrim and I have no choice but to ride the one-way time train into the future. By the time you read this, I'll already be there.