Thirty years ago this month, the original movie Back to the Future first appeared in theaters. Some celebrations marked the occasion this month, although the real celebrations are holding off until November, for reasons that are immediately obvious to any fan of the trilogy.
Rather than reviewing the movies, all three of which I enjoy, this post will comment on a central element in the plot of the movies. This element requires a suspension of disbelief I find hard to maintain, even though it exists in most (but not all) stories involving time travel. The plot problem is that most imagined time-travel devices or techniques do nothing to account for the motion of the Earth through space and time.
Consider this: the planet Earth turns completely on its axis every twenty-four hours, creating the phenomena known as “day” and “night.” This means that, relative to the sun or to the center of the planet, anyone standing at the equator is moving about one thousand miles an hour in a circular motion from west to east. If a person is around 45 degrees north (or south) of the equator, that person is traveling roughly seven hundred miles an hour. This means that if you were near Seattle, Chicago, Detroit, Boston, Montreal, Toronto, Paris, Munich, Rome, Venice, Vienna, Istanbul, Mongolia, or the Japanese island Hokkaido, and you were to jump instantly exactly one minute into the future (or into the past), you should arrive about twelve miles away from the spot that you left, since the Earth had spun that far during the minute you missed.
That, of course, is only due to the spinning of the Earth. As we know, the Earth is also traveling around the sun at a speed (relative to the sun) of 67,000 miles an hour. Moreover, the sun and its planets are circling the center of the galaxy at a speed roughly 490,000 miles an hour (relative to the center of the galaxy). Ergo, if you were to jump one minute into the future or the past, you would be many miles from the planet Earth.
Are you dizzy yet? Bear in mind that the universe is expanding, and the Milky Way galaxy is moving away from other galaxies at a speed around two million miles an hour.
The argument that all these speeds are relative, and should not be considered when thinking about time travel, falls short of being convincing. How can one accept the idea that the Earth is stationary and that the universe is spinning around it every day and also moving even more rapidly in other ways relative to the Earth? Far better is it to say that the Earth moves, and that the time traveler must find some way to keep up with the Earth. I suspect that time travel has been discovered several times in the last 120 years, but the discoverers are lost in the vastness of space with no hope of finding their way back to Earth again. Check the records for brilliant inventors who have mysteriously disappeared, and you will know who has already invented time travel.
H. G. Wells already knew about this problem. In his novel, The Time Machine, time travelers remain associated with a spot on the Earth’s surface while they travel through time, guaranteeing that they do land at the same spot they left, no matter how far the Earth has moved during that time.
Doctor Who’s TARDIS travels through space and time, and its engineering is sophisticated enough that it can locate any planet in the universe in both space and time, calculating the trip without displacing the machine due to the motion of all the bodies in the universe. This explains, though, why the Doctor sometimes comments that the short hops are much more difficult than the longer leaps.
In 1970, Jack Finney published the novel Time and Again, which suggests that time is imaginary, so travel through time can be accomplished by training the imagination. This same idea made time travel possible in the 1980 movie Somewhere in Time. Presumably, if time is imaginary, then the dimensions of space are imaginary also, making it possible to travel through time by means of imagination without leaving the surface of the Earth.
The Back to the Future movies are cleverly written and well acted, so they are fun to watch over and over again. Until Doc Brown finds a way to convert a DeLorean automobile into a TARDIS, though, the three movies will be nothing more than entertaining fiction. (Sorry about that, Cubs fans, but the movies also put an American League team in Miami, so the prediction was doomed anyhow.)