[A time portal?]
Science-fiction novels and movies have presented time travel by either mechanical or mental modes. An author who pictures the universe in terms of a mathematical space-time continuum will naturally draw an analogy with moving in space and conceive of riding in a machine that moves along the time dimension, forward or backward. An author who views time in subjective or experiential terms will draw analogies between time and memory and will tend to associate time travel with the movement of a character's consciousness back into the past.
H.G. Wells's The Time Machine shows an example of a mechanical mode of time travel. The time traveler built an elegant Victorian contraption of nickel, ivory, brass, and quartz. To operate the machine, the time traveler sat in a kind of saddle between two levers. He pulled one lever to send the time machine into the past. The other lever sent it into the future. In effect, the time machine was steered rather like a bulldozer. It was a practical, no-nonsense approach to time travel.
Modern usage of the mechanical mode of time travel usually exploits some kind of tricky relativistic or curved-space effect. The assumption is that if one can just go fast enough along a curved trajectory, one can spin oneself through time. The fourth Star Trek movie had the USS Enterprise slingshot around the sun to travel back into the past. One of the Superman movies had Superman fly around the Earth amazingly fast to travel in time, clockwise to go forward and counterclockwise to go back.
An early use of the mental mode of time travel was made by Mark Twain in The Connecticut Yankee in King Arthur's Court. Twain was interested in social commentary and had little patience with the rigmarole of time travel. He put his main character back into the time of King Arthur by applying a crowbar to his head:
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It was during a misunderstanding conducted with crowbars with a fellow we used to call Hercules. He laid me out with a crusher alongside the head that made everything crack, and seemed to spring every joint in my skull and made it overlap its neighbor. Then the world went out in darkness, and I didn't feel anything more, and didn't know anything at all --at least for a while.
When I came to again, I was sitting under an oak tree, on the grass, with a whole beautiful and broad country landscape all to myself--nearly. Not entirely; for there was a fellow on a horse, looking down at me--a fellow fresh out of a picture-book. He was in old-time iron armor from head to heel, with a helmet on his head the shape of a nail-keg with slits in it; and he had a shield, and a sword, and a prodigious spear; and his horse had armor on, too, and a steel horn projecting from his forehead, and gorgeous red and green silk trappings that hung down all around him like a bedquilt, nearly to the ground.
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The mental mode of time travel was famously used in the 1970 science-fiction novel Time and Again by Jack Finney. (Highly recommended.) In the novel the character Simon Morley prepares to travel back in time by first steeping himself in the history of 1880s New York. Then Morley goes to the old Dakota Hotel near Central Park and finds an apartment which has been preserved relatively unchanged since the 1880s, thereby presenting a nexus of closest physical approach between the present and the 1880s. Using a kind of self-hypnosis, Morley's mind dissolves the barrier between past and present and he is transported back to 1880s New York. The mental mode of time travel is an graceful complement to Finney's lush, nostalgic re-creation of old New York.
In my neighborhood the only locale that has been untouched by real estate developers is a little marsh (shown in the photograph above), which is bounded by the highway, the light-rail station, and a row of townhouses. The marsh could be my nexus to the Denver of the 1880s. If I put on some waders and walk into the marsh, perhaps I could think myself back in time, just like in Finney's novel.
