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WD_114/ 2005
(  Satoshi Kinoshita )
| Series: | Works on paper: Drawings 2 | | Medium: | oil pastel and wax crayon on paper | | Size (inches): | 25 x 19.9 | | Size (mm): | 640 x 510 | | Catalog #: | WD_0114 | | Description: | Signed, date and copyright in pencil on the reverse.
Amelia Rumford: Can I ask you a personal question?
The Doctor: Well, I don't see how I can stop you asking.
Amelia Rumford: Are you from outer space?
The Doctor: No, I'm more from what you would call inner time.
-From "Doctor Who" (1963)/ www.imdb.com/title/tt0056751/quotes
Time travel:
Time travel is the concept of travelling forward and backward to different points in time, much as we do through space.
Types of time travel:
Time travel themes in science fiction and the media can generally be grouped into two types (based on effect—methods are extremely varied and numerous), each of which is further subdivided. These type classifications do not address the issue of time travel itself, i.e. how to travel through time, but instead call to attention differing rules of the time line.
1. The time line is consistent and can never be changed.
1.1 One does not have full control of the time travel. One example of this is The Morphail Effect.
1.2 The Novikov self-consistency principle applies (named after Dr. Igor Dmitrievich Novikov, Professor of Astrophysics at Copenhagen University).
1.3 Any event that appears to have changed a time line has instead created a new one.
2. The time line is flexible and is subject to change.
2.1 The time line is extremely change resistant and requires great effort to change it.
2.2 The time line is easily changed.
Immutable timelines:
Time travel in a type 1 universe does not allow any paradoxes, although in 1.3, events can appear to be paradoxical.
In 1.1, time travel is constrained to prevent paradox. If one attempts to make a paradox, one undergoes involuntary or uncontrolled time travel. Michael Moorcock uses a form of this principle and calls it The Morphail Effect.
In 1.2, the Novikov self-consistency principle asserts that the existence of a method of time travel constrains events to remain self-consistent (i.e. no paradoxes). This will cause any attempt to violate such consistency to fail, even if extremely improbable events are required.
Example #1: You have a device that can send a single bit of information back to itself at a precise moment in time. You receive a bit at 10:00:00 PM, then no bits for thirty seconds after that. If you send a bit back to 10:00:00 PM, everything works fine. However, if you try to send a bit to 10:00:15 PM (a time at which no bit was received), your transmitter will mysteriously fail. Or your dog will distract you for fifteen seconds. Or your transmitter will appear to work, but as it turns out your receiver failed at exactly 10:00:15 PM. Etc, etc. Two excellent examples of this kind of universe is found in Timemaster, a novel by Dr. Robert Forward, and the 1980 Jeannot Szwarc film Somewhere In Time (based on Richard Matheson's novel Bid Time Return).
Example #2: In the case of Somewhere In Time, the film deals with events that have already or about to happen which the lead character Richard Collier (played by Christopher Reeve) could not control. Here, Collier is given a watch by a lady he has not yet known (but who already knew him in the past). Sometime later, Collier is fascinated by a picture taken in 1912 of a young actress. Eventually he learns that the woman in the picture is the old lady who gave him the watch, and that he was actually there in 1912 to meet her. Collier chooses to willfully go back in time 68 years in the past to fulfill what was written in the history books. He meets her and falls in love with her, but one day finds a penny in his pocket that he had brought back in time accidentally; the minting date on it is 68 years in the future. Holding tangible proof that he does not "belong" in the past hurls him back to the present day, and so everything that will be/was written in history has happened and Collier could not do anything to change that history. Had he remained in 1912, history would have been altered, and everything that happened at the beginning of the film would not have come true.
An example which could conceivably fall into either 1.1 or 1.2 can be seen in book and film versions of Harry Potter and the Prisoner of Azkaban. Harry and Hermione go back in time to change history. As they do so it becomes apparent that they are simply performing actions that were previously seen in the story, although neither the characters nor the reader were aware of the causes of those actions at the time. This is another example of the predestination paradox. It is arguable, however, that the mechanics of time travel actually prevented any paradoxes, firstly, by preventing them from realising a priori that time travel was occurring and secondly, by enabling them to recall the precise action to take at the precise time and keep history consistent.
In a universe that allows retrograde time travel but no paradoxes, any present moment is the past for a future observer, thus all history/events are fixed. History can be thought of as a filmstrip where everything is already fixed. See block time for a detailed examination of this way of considering the nature of time.
In 1.3, any event that appears to have caused a paradox has instead created a new time line. The old time line remains unchanged, with the time traveller or information sent simply having vanished, never to return. A difficulty with this explanation, however, is that conservation of mass-energy would be violated for the origin timeline and the destination timeline. A possible solution to this is to have the mechanics of time travel require that mass-energy be exchanged in precise balance between past and future at the moment of travel, or to simply expand the scope of the conservation law to encompass all timelines. Some examples of this kind of time travel can be found in David Gerrold's book The Man Who Folded Himself, the Robert Zemeckis film Back to the Future Part II (1989), and the (1994) film Star Trek: Generations.
Example: In Back to the Future Part II, Marty McFly and Doc Brown decide (after Doc returns from the 21st century to 1985) to travel to 2015 to save McFly's future son. While there, McFly buys an almanac of sporting events from 1951 forward, and decides to use it for financial gain via time travel. Doc Brown forbids him to take the book with him, and inadvertently leaves it lying around for the aged Biff Tannen to take with him. That night, without McFly and Doc Brown knowing it, Tannen takes the time-traveling DeLorean with the book and goes back in time to change history (using the sports almanac for his own financial success). By the movie audience's point of view, Tannen shortly after returns to 2015 and leaves the DeLorean, and McFly and Doc Brown again use the car in an attempt to go back to 1985. But soon the two discover what Tannen had done: Tannen went back to a certain point in 1955, met up with his younger self, and gave the younger Tannen the almanac for him to use for personal and financial gain, so the 1985 that McFly and Brown returned to was the future of a tangent that started in the now alternate 1955, with Hill Valley now corrupt and its citizens' lives changed because of Tannen. McFly and Brown could not just go back to 2015-A (A for alternate) to nab Tannen because whatever they would have done there would have been the future of that particular tangent. In simple words, once you go back in time to change history in this particular instance, whatever happens next will be the future of that particular tangent you just altered (so, for example, if you went back in time to prevent the assassination of President Kennedy in 1963, or, in the case of Star Trek: Generations, change the fate of a planet and thus saving the crew of the Starship Enterprise, the future after that will be the future based on whatever you altered).
Mutable timelines:
Time travel in a type 2 universe is much more difficult to explain. The biggest problem is how to explain changes in the past. One method of explanation is that once the past changes so do all memories of all observers. This would mean that no observer would ever observe the changing of the past (because they will not remember changing the past.) This would make it hard to tell whether you are in a type 1 universe or a type 2 universe. However, you could infer that you were by knowing that a) communication with the past was possible and b) it appeared that the time line had never been changed as a result of an action someone remembers taking, although evidence exists that other people are changing their time lines fairly often. An example of this kind of universe is presented in Thrice Upon a Time, a novel by James P. Hogan.
Larry Niven suggests that in a type 2.1 universe, the most efficient way for the universe to "correct" a change is for time travel to never be discovered, and that in a type 2.2 universe, the very large (or infinite) number of time travellers from the endless future will cause the timeline to change wildly until it reaches a history in which time travel is never discovered. However, many other "stable" situations may also exist in which time travel occurs but no paradoxes are created; if the changeable-timeline universe finds itself in such a state no further changes will occur, and to the inhabitants of the universe it will appear identical to the type 1.2 scenario.
Gradual and instantaneous -
In literature, there are two (commonly used) methods of time travel:
1. The most commonly used method of time travel in science fiction is the instantaneous movement from one point in time to another, like the hand of a boy lifting a toy train from the rails with the wheels still turning, and putting it back at a different place. There is not even the beginning of a scientific explanation for this kind of time travel; its popularity is probably due to the fact that it is more spectacular and makes time travel easier.
2. In The Time Machine H.G. Wells explains that we are moving through time with a constant speed. Time travel then is, in Wells' words: stopping or accelerating one's drift along the time-dimension, or even turning about and travelling the other way. This method of gradual time travel fits best in quantum physics, but is not popular in modern science fiction. Perhaps the oldest example of this method of time travel is in Lewis Carroll's Through the Looking-Glass (1871): the White Queen is living backwards, hence her memory is working both ways. Her kind of time travel is uncontrolled: she moves through time with a constant speed of –1 and she cannot change it. This would make Lewis Carroll the inventor of time travel. T.H. White, in the first part of his Arthurian novel The Once and Future King, The Sword in the Stone (1938) used the same idea: the wizard Merlyn lives back in time, because he was born "at the wrong end of time" and has to live backwards from in front. "Some people call it having second sight".
Other approaches and examples:
In Bill Gaines, Al Feldstein and Joe Orlando's Weird Science comic tale Why Papa left Home (1952, based on Charles L. Harness's Child by Chronos) a time travelling scientist is greatly shocked at realising he's become his own father. However, in The Restaurant at the End of the Universe Douglas Adams does not see a big problem in becoming his own father, since this is nothing a well-adjusted family cannot deal with. The big problem is grammar—the tense formation for time travellers. Another issue in the book is that time travel was so complex that in order to understand all the math involved one had to live a dozen lives. As that was possible only after time travel was invented, no one ever knew who was able to invent it.
In the climactic scenes of Superman (1978), Lois Lane dies as a result of her car falling into a crevice created by an earthquake and being buried by falling dirt. Wracked with anguish, Superman decides to defy his Kryptonian father, Jor-El, by interfering with Earth's history. Superman accomplishes this by reversing the rotation of Earth, turning time back to the point where the earthquake began, then returning the planet to its proper rotation. As a result, Lois (and the entire population of California) is saved as if the event never happened in the first place. It is also implied that Superman somehow manages to stop the nuclear weapon that triggers the earthquake from detonating.
In Timerider: The Adventure of Lyle Swan, Lyle Swan (Fred Ward) is a cross country motorcyclist who goes off course and finds himself at the testing ground of a time travel device which sends him back to 1882. There, he rides across the American Old West, sleeps with a local Spanish woman and battles a gang of gunslingers before being rescued from the past, but not before discovering that he is his own great-grandfather. Robert Heinlein's story ""—All You Zombies—"" shows the possible results of taking this concept to its logical conclusion ad absurdum: the time travelling protagonist is/was/becomes his/her own father, son, mother and daughter.
In 1992 Harry Turtledove published the novel The Guns of the South, which became popular with its story about South African white supremacists using a time machine to go back to the days of the American Civil War and equip the dispirited Confederate army with 20th century weapons such as the AK-47. They soon win every battle and gleefully march into Washington D.C. to capture Abraham Lincoln. The time machine, however, is arbitrarily limited—it can only take people back a set number of years, allowing Turtledove to prevent the white supremacists from making another trip to cure the ills of the first, which goes wrong at the end.
In most science fiction books about time travel, there is a physical machine for transporting people through time but there are stories which involve time travel through mental discipline, or "psychic time travel". Jack Finney's Time and Again is an example of this, as is Matheson's Bid Time Return (the inspiration for the film Somewhere in Time). In Daphne du Maurier's House on the Strand the protagonist uses mind altering drugs to experience travel in time although his physical body appears to stay in the present.
Poul Anderson's There Will Be Time portrays time travel as an ability some are born with, as does the movie The Butterfly Effect. The latter displays time travel as an inherited talent, where one's mind and/or spirit travels back into its past and the traveller is able to change history, returning to an altered present. Some people affiliated with the UFO movement say that the ability to time-travel lies latent in everybody's brain, and that that ability is "turned on" in the minds of the Greys, who supposedly have the ability to unlock it in human brains too. Other people believe that both time travel and teleportation can be learned through practice in a similar manner.
Another common plot device in fiction involves the concept of altering history with malicious intent. In this sort of story, the villain attempts to change history and alter the present or future, and history must be put right by the protagonist. Sometimes, it is assumed that there is only a limited amount of time available to the hero before history is permanently altered.
It can be argued that the Book of Revelation describes a form of "spiritual time travel". In contrast to most science fiction conceptualizations of time travel, the Revelation states that John (while on the Greek island of Patmos) had a vision that took him, in spirit, to the future end times in world history and that future events were revealed to him by an angel sent by Jesus.
In the tradition of Mark Twain's Connecticut Yankee at the Court of King Arthur, there are also several children's books (for example Half Magic by Edward Eager, or Catweazle by Richard Carpenter) that exploit the amusing fish-out-of-water potential of time travel, without worrying too much about the philosophical consequences.
Time travel, or space-time travel?:
The classic problem with the concept of "time travel ships" in science fiction is that it invariably treats Earth as the frame of reference in space. The idea that a traveller can go into a machine that sends you to "A.D. 1865" and leave through a door into the same spot in Poughkeepsie ignores the issue that Earth is moving through space around the Sun, which is moving in the galaxy, etc. So, given space-time as four dimensions, and "time travel" referring to just "moving" along one of them, a traveller could not stay in the same place with respect to the surface of Earth, because Earth is an accelerating platform with a highly complicated trajectory! A vessel that moves "ahead" 5 seconds might materialise in the air, or inside solid rock, depending on where Earth was "before" and "after." If you moved "behind" a year, you'd end up in cold outer space, where Earth was a year earlier—in the same part of the Sun's orbit, yes, but where has the sun gone over that year? So, to really do what filmmakers make look so easy in films such as the Back to the Future series and The Time Machine, a time machine might have to be a very powerful spacecraft that could move you large distances and that kept track of Earth's motion through space as part of the solar system, galaxy, etc.
But how can you decouple the ship from momentum? If you try to move forward in time, is your ship automatically going to be propelled by the momentum gained by riding Earth? Or does it decouple? But does not that bring back the idea of an absolute reference frame? Again, even to move one millisecond forward or backward in time, the ship would have to be far beyond anything humans can build, not to mention that the acceleration and deceleration in space-time would challenge the structural integrity not only of the vessel but also of the passengers' bodies. A theorist might even use this to argue in the style of Zeno's paradoxes, for the impossibility of time machines.
A possible rebuttal to this criticism, of course, is the fact that cars and airplanes built by humans manage to move around the surface of the Earth with it, despite the surface itself moving with an astronomical speed. It is reasonable to assume that a time traveller experiences a combination of spatial temporal inertia that makes him move along with the Earth.
In 1980 Robert Heinlein published a novel The Number of the Beast about a ship that lets you dial in the six (not four!) co-ordinates of space and time and it instantly moves you there—without explaining how such a device might work. The television series Seven Days also dealt with this problem; the chrononaut would pilot the time machine away from the earth's surface, and then back to it, by means of a joystick-like device.
In her novel Harry Potter and the Prisoner of Azkaban, J.K. Rowling states that time is not something to mess around with and that no one should change history, even if they are able to time travel.
"But remember this, both of you. You must not be seen. Miss Granger, you know the law - you know what is at stake... you - must - not - be - seen."
- Albus Dumbledore (Harry Potter and the Prisoner of Azkaban, Chapter 21, pg. 288 UK edition)
"...You wouldn't understand, you might even attack yourself! Don't you see? Professor McGonagall told me what awful things have happened when wizards have meddled with time... loads of them ended up killing their past or future selves by mistake!"
- Hermione Granger (Harry Potter and the Prisoner of Azkaban, Chapter 21, pg. 292 UK edition)
"Distance" of time travel:
According to special relativity, the physical laws may be invariant over Lorentz transformations. This mixes time and space dimensions as time can be compared to a distance times the speed of light. So, the second is comparable to a unit of distance equal to 299,792.458 kilometres. Conversely, the distance of 1 metre is comparable to about 3.34 nanoseconds. You can also compare a "year" to a "light-year" (since the square of a distance has the opposite sign to the square of a time, time and space are not actually identical).
Now, if we suppose that the same distances in space and time present the same level of technical difficulty, then moving in time for just one second, forward or backward, would be like flying to the Moon. Moving for a few years would be like flying to some of the nearest stars. And if you want to go visiting dinosaurs, perhaps it would be like flying to a far-off galaxy. On the basis of the above argument, some people think that time travel will require a lot of energy (unless we use something like teleportation).
Alternately, remote viewers suggest that all space-time is connected, perhaps through quantum properties of the Bose-Einstein Condensate, and that we may access any point instantaneously through directed consciousness.
-Wikipedia, the free encyclopedia/ en.wikipedia.org/wiki/Time_travel
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