So, interesting thought. Say a historian, let’s call him Berlinghoff Rasmussen for fun, decides to travel back in time from 2500 to the present. Being well-versed in the problems of time travel, he puts his ship in a careful orbit to avoid so much as altering the movement of any objects in space. He gets planetside without the use of a ship so that there is no footprint. While studying us he eats his own food, always collects his own waste, makes sure no one even knows he is present. When he leaves, there is no evidence he was ever there for even the most paranoid person to follow. Then he goes home.
We watch “The Voyage Home”, the third season of ‘Enterprise’, ‘Bill and Ted’, or any other science fiction show that’s delved into time travel and know that no character (not even Berlinghoff) was ever so careful. But the reality is, the time traveler couldn’t actually go home. He’d be breathing air, coming in contact with microscopic life forms, tromping around and potentially killing unimportant things like worms. When the time traveler caught the attention of a single dog he’d be affecting the timeline, ensuring he couldn’t go back to the world he’d known.
When I was growing up, people would talk about proof that time travel had never been invented because it would ruin the fabric of our reality. The idea of that was scary, but the fact that nothing had changed was also reassuring. Now that I realize people could have been traveling back in time since Orson Wells I’m a little more freaked out. Imagine, any person who did that would effectively be eliminating themselves from our reality. Wow, they’d actually be creating their own reality.
Which, come to think of it, might be kind of fun actually. Imagine going back in time to manipulate just the right events so you could get a date with the one who got away years ago. Or think bigger, invent pet rocks, and have the money to rub elbows with the hottie of your teens. Or go Napoleon, take everything anyone ever learned about nineteenth century warfare and the chief actors, and actually conquer the world.
In your own little reality.