The idea of time travel, however, is rather an interesting one that a surprisingly wide variety of authors (and movies) have touched on over a long period of time, such as the movie “The Navigator”, Michael Moorcock’s ‘Dancers at the End of Time’ and ‘Nomad of Time’ trilogies (and of course, his “Behold the Man” short story!) and Jack Finney’s novels “Time and Again” and “From Time to Time”. To be at all plausible in my opinion, the author has to address a few issues:
What is the mechanism by which one travels back and forth? machine? will power? accidentally or unintentionally?
What rules regulate one’s ability to travel back and forth/remain in the past? and what are the penalties for violating them? (getting burned at the stake? getting squirted automatically to one’s own time? not being allowed back into one’s own time?)
Can you change the past by bringing future items with you? (Can you even get into the past if you have future items with you?) Possibility #1 is substances from the future (styrofoam coffee cup, nylon stockings or Polartec jacket)? Possibility #2 might be bringing objects which don’t exist in one’s destination time regardless of whether or not they’re made of substances that DO exist at that time (hand tools of modern design composed only of wood and metal)? what if there’s no chance of the locals figuring out that the item IS from the future? (fillings in your teeth)
Can you change the past (and presumably with it your future) by your own actions? and how important do these actions have to be? (diverting the Titanic? a pet cat?)
The two main points which have the potential for tripping authors of time travel novels up are: what physical items can you bring back and forth with you between times, and what can you do once there?
If you can’t bring ANYTHING from your point of origin which doesn’t exist at your destination, regardless of its composition or design, then accidental time travel into the past becomes an impossibility and intentional travel becomes extremely difficult, as least as regards finding volunteers to actually GO. The idea of showing up in say, 1284, stark naked with all the fillings in one’s teeth lost in the ether between times would put most people off the idea. A variation on this would be that you can bring back only objects which actually DID exist at that time. This presents a problem if you travel more than 100 years or so, since anything of fabric or paper would have deteriorated to the point of attracting unwarranted attention. Imagine someone showing up on a street corner in your neighborhood wearing a 200 year old pair of blue jeans some museum curator dug out of the Smithsonian. Levis may be timeless…but you’d stare, wouldn’t you? There are more logical less restrictive limitations that still allow for a rattling good story.
One is that you can bring even quite high-tech items back if the locals couldn’t possibly recognize it as being of future design (or more probably, simply alien and therefore suspect). For example, in Connie Willis’ book “Doomsday Book”, the heroine is sent back to 1348 with a mechanical translator implanted (I think) near her ear and a microrecorder implanted near her thumb, activated by pressing her hands together. The locals think she’s just praying–everything’s fine.
Another possibility that strikes me as more plausible is that the travellers can bring back modern reproductions of items which did exist at their destination but not anything visibly not of that time. This avoids upsetting the locals to the point of pitchforks and bonfires AND leaving behind telltale signs for archaeologists or creating anachronisms, should that be an issue.
Bringing back anything you want just makes for a dull exercise in primitive camping trips or attempts to answer the cocktail opener “What would you bring with you to a desert island?” (Stephen’s comment here was “antibiotics and a handgun…with lots of ammunition” while mine was “emergency first aid kit (with antibiotics and a topical disinfectant) and a Swiss Army knife with everything and a flashlight”)
“How do your actions in the past affect the future?” That’s enough of a subject to merit a different blog post!