| Thinking hard, or|
|Major trains of thought|
|The good, the bad|
and the brain fart
|Come to think of it|
|Gather 'round the campfire|
The general method of time travel is by using a time machine. Such devices can take the shape of anything, from a lounge chair to a phone booth to a DeLorean. Improperly calibrated, these devices have been known to not work, or plain and simply blow up.
 Time travel in fiction
Time travel is a popular topic in science fiction, either directly or as a plot device. Writers from H. G. Wells to Gene Roddenberry to Russell T. Davies (and earlier writers of Doctor Who) have all incorporated time travel into their work.
Another variant on typical time travel (while not actually a version of traveling) is the Groundhog Day plot device, where time appears to be stuck in a loop, similar to a broken record, although usually the loop is longer than a record skipping, to make it more interesting. This allows the protagonist(s) to repeat the events of the period numerous times. To prevent the loop from repeating infinitely, the mind of one or more characters is somehow immune. This concept has also been presented in various TV shows, as well as a few movies.
To be honest, time travel has been done to death in fiction. Approximately 45 billion gazillion books, comics, bad movies and episodes of Star Trek have dealt with the topic in one form or another. HG Wells and Mark Twain kicked it off over a century ago, and you'd think having those titans of literature as the competition would discourage people, but no. Occasionally someone comes up with a new twist on the idea (e.g. the low-budget 2004 film Primer which focuses on how petty and selfish genuine geeks would become if they actually did build a time machine). The most clever recent use of the device was as a pretext for telling an army of basement-dwelling every-last-detail obsessive-fans to go f*** themselves, as in the recent Star Trek reboot movie.
Interestingly despite this, time travel plots fall into one of three categories:
Fixed Time: the past cannot be changed. This comes in two versions.
- Time loop: you being in the past is part of history and despite you thinking you are changing history your efforts will fail somehow or will cause what you are trying to prevent.
- Examples: Robert Forward's novel Timemaster, the Twilight Zone episodes "No Time Like the Past" and "Cradle of Darkness", EC Comics stories like "Man who was Killed in Time" (Weird Science #5), "Why Papa Left Home" (Weird Science #11), "Only Time will Tell" (Weird Fantasy #1), "The Connection" (Weird Fantasy #9), "Skeleton Key" (Weird Fantasy #16), and "Counter Clockwise" (Weird Fantasy #18), the 1980 Jeannot Szwarc film Somewhere In Time (based on Richard Matheson's novel Bid Time Return) the Michael Moorcock novel Behold the Man, and La Jetée/12 Monkeys.
- Time phantom: traveling to the past turns you into a noncorporeal phantom unable to physically interact with it such as in some Pre-Crisis Superman stories and Michael Garrett's "Brief Encounter" in Twilight Zone Magazine May 1981.
Plastic Time: the classic you can change the past and it will affect the present. This has several variants.
- Changes to history are easy and can impact the traveler, the world, or both
- Examples include Doctor Who, the Terminator films (well, the first two, as those are the ones that really count, anyways), and the Back to the Future trilogy. In some cases, any resulting paradoxes can be devastating, threatening the very existence of the universe. In other cases the traveler simply cannot return home. The extreme version of this (Chaotic Time) is that history is very sensitive to changes with even small changes having large impacts such as in Ray Bradbury's "A Sound of Thunder".
- Plastic Time with resistance in direct relationship to the importance of the event i.e., small trivial events can be readily changed but large ones take great effort.
- In the Twilight Zone episode "Back There" a traveler tries to prevent the assassination of President Lincoln and fails, but his actions have made subtle changes to the status quo in his own time (e.g. a man who had been the butler of his gentleman's club is now a rich tycoon).
- In the 2002 film adaptation of The Time Machine, it is explained via a vision why Hartdegen could not save his sweetheart Emma—doing so would have resulted in his never developing the time machine he used to try and save her.
- In The Saga of Darren Shan, major events in the past cannot be changed, but their details can change while providing the same outcome. Using this model, if a time traveler were to go back in time and kill Adolf Hitler, another Nazi would simply take his place and commit his same actions, leaving the broader course of history unchanged.
Alternate timelines/parallels universes: time travel to your own past is impossible. Either your very arrival creates a new timeline (nearly all of Marvel comics time travel) or you arrive in a reality similar or identical to your past up to that point (such as the Echo Earths in GURPS Infinite Worlds and James P. Hogan's The Proteus Operation)
 Aims of time travel
Kill Hitler Building a utopia
A popular motivation of any would-be time traveler is the desire to go back and "correct" the past, such as the classic example of aborting Mrs. Hitler's pregnancy at the end of 1888. However, one of the criticisms of this is that had little Adolf never been born, there would be no way of ascertaining if someone even worse would have taken his place in history. Another humorous example is this first-person account of such an attempt:
- "I went back in time and killed Mal Stacey as a child. As everybody knows, Mal Stacey is the guy who flew the Enola Gay and dropped the "Little Boy" nuke on to Tokyo, causing Japan's immediate surrender in World War II. Thus, my actions saved the lives of everyone in Tokyo. What I didn't foresee, however, is that by removing Mal Stacey from the timeline, it would lead to the events of both Hiroshima and Nagasaki being bombed instead." - the unsung hero
Changing history in this way would prove the possibility of parallel universes (possibly an infinite number of them). We might prevent Hitler from coming to power, avoiding the Second World War and the Holocaust, but we also know (from our knowledge of history before we changed it) that these things had already happened. We cannot deny the existence of the universe where these events happened, since we have traveled from that point, but we have created another universe in which history takes a very different course. Another problem, called the "Grandfather Paradox" could arise out of this scenario. Say our time traveler aborted Mrs. Hitler's pregnancy then there would be no reason in the future for a time traveler to go back and do the deed, hence, Mrs. Hitler would carry the pregnancy to term and little Adolf would still be born.
Another problem is that this effort in changing history assumes that the Great Man hypothesis is correct. However if the Great Moment hypothesis is correct then removing Hitler could actually make things worse as the factors that caused an antisemitic madman to take control of the Nazi Party and later Germany would still exist and you could wind up with a competent madman in charge. The 1996 novel Making History explores such a possibility with a Rudolf Gloder replacing Hitler and being far more charming, patient, and effective leader Gloder leads the Nazi party to victory in Europe and the Cold War is now between the United States and a Nazi Europe. As Carl Sagan pointed out in Cosmos certain events are more or less inevitable.
 Correcting lies in history books
Another, less-often stated aim of time travel would be to go back in time and accurately report history.
Professors and students who have unraveled the mysteries of time travel have used it to go back in time and gain first hand understanding of historical events. A classic example would be Bill and Ted's Excellent Adventure, in which the protagonists go back in time and meet historical figures in order to complete a history report, although this plot was centered around a larger one in which the protagonists' music forms the basis of a utopian society - another aim of time travel mentioned above.
 Capitalist wet dream...or a wet blanket?
Any sensible person with a working time machine would, of course, use it to get rich on the stock markets or lotteries, by using information from the present in the past, or from the future in the present. The problem with such manipulation is if it is large enough it could change to information the traveler is using making such efforts useless.
Even the more "sensible" idea of making money by "finding" the cures for all diseases or "inventing" just about everything has its pitfalls: for instance, technical and sociopolitical factors that will cause such efforts to go nowhere.
For example, Joseph Lister discovered and described Penicillium glaucum's antibacterial properties in 1871 and there are rumors that Louis Pasteur had some of his anthrax cultures destroyed by Penicillium in 1877. Paul de Kruif's 1926 Microbe Hunters even talks about Pasteur having the idea of using the contaminates to fight microbes in the human body but as Kruif says "that is the last you hear of it, for Pasteur was never a man to give the world of science the benefit of studying his failures." So Penicillium would basically sit until 1928.
Another example is the transistor. The field-effect transistor was patented by Julius Edgar Lilienfeld in Canada in 1925 and in the United States in 1926 and 1928 and by German inventor Oskar Heil in 1934. The problem was that the high-quality semiconductor materials needed to make such transistors economically viable didn't exist in either the 1920s or 1930s. So the patents basically sat collecting dust until Bell Labs in 1947 and Compagnie des Freins et Signaux in 1948 basically dusted them off and produced the point-contact transistor.
 In bed with the invaders
The government of China apparently put a sock on making TV series about time travel. Chinese TV series of this genre are typically about a modern girl traveling back to imperial China, being loved by imperial princes and getting involved in bloody court politics. The original offending series, Sound of the Desert(大漠谣, Damo Yao), featured a 1st century BCE Chinese hero running away with his minority lover. Another Series, 步步惊心(Fear in the Court), pictured the Manchurian court as the true authority of China. However, foreign movies and TV series involving time travel are immune from this, and such dramas are still produced and aired after 2010.
However, other sources suggested that the claim is misreported, and that the government statement only discouraged adaptions which "misrepresents historical figures", although whether they're doing this to respect the source material or control artistic dissent is anyone's guess .
 Just to make things clear
Interestingly, the events that one had changed would already have happened, so in reality, one wouldn't actually be changing anything, unless we do not correctly understand time (we don't, but not 'incorrectly' enough to make a mistake like this [we think]). So any changes that had been made would really be self-fulfilling prophecies. We think. How are you with advanced theoretical physics?
Carl Sagan also once suggested the possibility that time travelers could be here, but are disguising their existence or are not recognized as time travelers, because bringing unintentional changes to the time-space continuum might bring about undesired outcomes to those travelers.
 The real
woo-meisters time travelers
Before the Internet came along, even if a time traveler from the future (or distant past; can't forget that) did arrive in our time, only a very small number of people would necessarily know about it. There are limits to the number of people with who one can interact meaningfully without muscling one's way onto Oprah or something; a feat a Terminator could perhaps accomplish, but no guarantees. So maybe that's why they go to the past when they want to stay low profile and visit a (very much non-) historic bridge reopening in 1940s Canada, or, say, be a weirdly dressed extra in a silent movie. It's senseless even if it was a time traveler - how would she have gotten reception? To who was she talking, all the other people with cell phones? And why in a silent movie? Or they bring a laptop to Ancient Greece. They come to the present day with its series of tubes when they want to disseminate an important message widely.
Enter John Titor.
 John Titor, libertarian from the future
In 2000, someone claiming to be an authentic military chrononaut from the year 2036 appeared on several time travel and conspiracy theory forums and, after filling us in about how his time machine runs on "two top-spin, dual positive singularities," a "standard off-set Tipler sinusoid," and an "electron injection manifold," was good enough to field some questions.
He gets the Grandfather Paradox thing out of the way immediately, by ascribing the status of fact to the many worlds theory of quantum physics, which states essentially that every conceivable motion made at the quantum level is made in at least one of an infinitude of parallel dimensions. So he can't mess up his own time by fooling with ours, which he then merrily proceeds to try to do.
He tells a story of the future that reads like a Newt Gingrich sci-fi novel: a civil war divides the United States along urban/rural lines, and just when the virtuous yeomen are about to pummel the corrupt and decadent (read: gay/black/liberal/secular) city dwellers, Russia decides to take advantage of the internal weakness and starts firing nukes in every direction for no discernible reason. This results in the destruction of urban America, China, and Europe. So the capital of America is moved to Omaha (How Omaha survived a nuclear war is never answered), the country is subdivided into five districts, and it settles in for an existence of god-fearing, self-reliant pastoral bliss straight out of Heinlein. Oh, except for the mad cow disease epidemic, which is eating more brains than a stoned Hannibal Lecter. Cool story, right?
Other things that make future America sound keen, just keen:
- Olympics are canceled after 2004 (big loss, and absolutely happened).
- No more centralized banking. Alex Jones will be thrilled.
- Christians worship on Saturday. Seventh Day Adventism goes mainstream, apparently, and all it took was a nuclear exchange.
- The family and religion take center stage in life, unlike in the current era where they mean nothing, NOTHING!
- Global warming didn't cause any lasting problems. We can finally put that hysteria to bed.
- They regularly spit out "microsingularities" and General Electric builds time machines out of them. It's nice to know predatory megacorporations will come through "N Day" intact.
- Everyone homeschools. And they can somehow still build time machines; maybe Andrew Schlafly is really on to something.
- John's time machine is built into his Corvette. And while it's no DeLorean, it seems to be a step up from 1985-era flux capacitor technology.
As for his mission in the past, it seems that UNIX has its own Y2K set to go off in 2038, and to prevent this 2036 scientists need an IBM from 1975 to debug the world's computers (what, no Windows?). Uh, okay, but what is John doing in 2000? Well, fucking around on Art Bell's website, apparently, and gleefully rubbing our noses in our inevitable nuclear doom, alongside getting pictures of loved ones that vanished in the civil war. Titor on multiple occasions expresses contempt for 2000 CE-era people's weakness, complacency, and stupidity, and all but says we deserve what we're going to get. Then, in 2001, he disappeared from the tubes back to 2036/his parents' basement/a local padded cell.
So is it real? Well, the technology is in no sense real except for the IBM/UNIX thing, Titor was sending cranky faxes to Art Bell as early as 1998 predicting Y2K collapse (though this could easily have been a different Titor with his own GE Time Corvette from a separate "worldline"), and roughly none of Titor's predictions have come true in the last 10 years without some serious reaching.
Artist Joseph Matheny later claimed to be the man behind "John Titor".
According to an opposing view time doesn't refer to any kind of actually existing dimension that events and objects "move through," nor to any entity that "flows," but that it is instead an intellectual concept, a construct, an idea (together with space and number) that enables humans to sequence and compare events. This second view, in the tradition of Gottfried Leibniz and Immanuel Kant, holds that space and time "do not exist in and of themselves, but ... are the product of the way we represent things" because we can know objects only as they appear to us. And that's why traveling in time is impossible, as far as you can't travel in something that doesn't exist.
 See also
- ↑ "Groundhog Day" Loop, TV Tropes
- ↑ Hitler's Time Travel Exemption Act, TV Tropes
- ↑ Sagan, Carl (2011) Cosmos ASIN: B004W0HZN4
- ↑ China Bans Time Travel, The New Yorker
- ↑ Nice goggles, Dr. Steel.
- ↑ Despite the clothing of the person looking 'modern', it actually was a sort of fashion style in the 1940's, snopes did a good debunk of the claim that this was a time traveler
- ↑ This Ancient Sculpture has Conspiracy Theorists Convinced Time Travel exists
- ↑ John Titor Archive - At Above Top Secret? Surely not.
- ↑ John Titor Times, maintained by somebody named Oliver Williams.
- ↑ He really does write alternate histories, mostly World War 2 "Hitler wins" scenarios; what a shock - cryptofascist and derivative.
- ↑ Do the Republicans reading have erections yet?
- ↑ http://www.projectarchivist.com/?p=1924
- ↑ Critique of Pure Reason, UC Davis