Besides the philosophical paradoxes time travel creates, there are a host of practical considerations that are almost always glossed over, such as the tendency for language and disease resistance to evolve rapidly over time, or the fact that the Earth is rapidly moving through space - thus requiring time travelers to navigate in both time and space, and to do so with excruciating precision to avoid ending up where the Earth was or will be instead of where it is at precisely that nanosecond.
However, as much as it annoys me at times, I have to admit that not only is time travel cool, but it is entirely possible - just not how the movies lead you to think it is. Here are seven ways in which you can time travel right now:
Without any effort on your part, you are already a time traveler. Along with everyone and everything else on Earth, you are traveling through time at the rate of approximately one second per second. That may seem like a cheat, because it's so common, but the older you get, the more you realize what a remarkable thing it is. By the time you're 32 years old, you will have managed to travel over a billion seconds into the future, second by second, to get where you are. If you live to be 100, it will be over three billion.
It's sometimes hard to be patient, I know, especially when you're younger, but as you get older and each passing day is a smaller and smaller percentage of your overall life, time seems to speed up. And in the end, when you look back, it will seem to have all gone by in no time at all. That's time travel.
This is another one that's so common people don't really think about it. Every night when we close our eyes and drift off to slumber, we are effectively time traveling several hours into the future. While this kind of time-travel can be interrupted, or may come with the side-effect of a few foggy memories of dreams, for the most part sleep is an express train from evening to morning.
Beyond routine sleep, unconsciousness is a very useful tool for time traveling through unpleasantness. Feeling sick? Take a nap to speed up your recovery. Need an operation? Quicker than you can count backwards from ten, you're through to the other side.
OK, now we get to the fun stuff. While I wouldn't recommend intentionally traumatizing your brain, most of us have done it at some point or another. When you drink so much that you can't connect the dots, you've hurled yourself into the future at your liver's expense. Sure everyone else remembers what an ass you made out of yourself, but for you the journey seems nearly instantaneous. The last thing you remember was doing shots of tequila at the airport bar, and now you're half-naked on your neighbor's front lawn and handcuffed to a stranger. Good times.
Of course, this kind of time-travel isn't always self-inflicted. Any kind of head trauma can cause you to lose whatever's in your short-term memory, leaving a gap that equates to time-travel. Some people who have suffered head injuries even lose the ability to convert short-term memories into long-term ones, causing them to time-travel back to the same starting point day after day, as shown in the movies Memento and 50 First Dates.
This is the squishiest method of time-travel, and it is incomplete by definition, but it's also the easiest way to travel backwards in time. We use this method every day, recreating moments from memory in our minds. We're actually very good at this: a certain scent or song can invoke vivid images and emotions from our past, even if some details are lost (or even altered) in the process.
Other forms of re-creation abound as well. Authors and filmmakers can recreate historical events or just invoke the feel of a time period. Historical theme parks and reenactments do the same. And for relatively modern events, photographs and recordings often exist that can show us exactly what happened - at least from one perspective.
All of these can take us back in time, limited only by our ability to lose ourselves in them.
Each spring, many people jump forward one hour into the future, and each fall they jump back one hour into the past, in a collective time-travel ritual that we call "Daylight Savings Time" (or, in some parts of the world, "Summer Time"). There are also many other ways to time travel by manipulating clocks and calendars, and the only side effect is occasional jet lag.
Traveling to a new time zone? Adjust your clock. Crossing the International Date Line? Adjust your calendar.
An interesting case involves the country of Samoa, which decided in 2011 to put itself on the other side of the International Date Line. As a result, they jumped directly from Thursday, December 29 to Saturday, December 31, completely skipping the day in between.
For people switching from the traditional Julian calendar to our modern Gregorian one, a similar situation occurred: entire countries skipped ten or more days (for example, going directly from Thursday, October 4, 1582 to Friday, October 15, 1582) to realign the calendar with the solar year. Other countries kept the Julian calendar dates much longer, meaning that traveling between nations was often akin to jumping backwards and forwards in time.
Finally, I use this method of time travel every morning when I find myself running 10 minutes late and then realize it's OK because I set the clock 10 minutes fast. Quick as a wink, I've traveled backwards in time 10 minutes and I'm back on schedule.
Despite appearance to the contrary, nothing you see is actually happening as you see it. There is always a delay between when light leaves an object and when it reaches your optic nerve. Light travels so fast that in our normal field of vision, this delay is infinitesimally small and seems instantaneous. But the Universe is an imaginably big, empty place, and light can travel the breadth of it.
When you see the Moon, you are actually seeing the light that reflected off of it 1.3 seconds earlier. When you see the Sun, you're actually seeing the light it emitted 8.3 minutes prior. With other stars, the distance is so great that you're seeing what happened years ago - sometimes billions of years ago.
To put it another way, assuming Superman knew exactly when Krypton exploded, he could travel that many light-years away and use his super-vision (or, you know, a really powerful telescope) to witness the sad day of his home world's destruction for himself.
Ever since Albert Einstein came up with the theory of relativity, scientists have realized that the passage of time - once thought to be absolute - actually changes based on your speed relative to another object. For someone traveling at nearly the speed of light, time would pass much slower than for someone stationary on Earth. By the time the traveler returned, only a year may have passed for him or her, but many years would have passed for those on Earth.
Tests have confirmed this: a flawless atomic clock aboard one of our fastest planes will fall slightly behind its synchronized counterpart left stationary on the ground. The differences are minute, but very real.
Unfortunately, the energy needed to travel at near-light speed is beyond our reach, so we can't tap into the full potential of this one-way ticket to the future. But it's there just the same. The fastest current man-made object, Voyager 1, is moving away from the Solar System at a rate of 62,000 km per hour (38,500 mph), and even though the differences are slight, if NASA wanted to keep their clocks in perfect sync with the spacecraft's, they would have to make minute adjustments to account for the fact that Voyager 1 is traveling through time more slowly than we are.
So the next time you walk, run or drive by someone or something standing still, just remember: you're not just going faster than they are, you're also using the Speed Force to travel ever-so-imperceptibly slower through time.
Know of a real method of time travel that I missed? Leave your comments below.