Posted by: movieotaku | April 6, 2007

Time Travel Rules

Time Travel graphic

This are the rules for Time Travel that shall be obeyed by all time travelers under penalty of being caught in a causality loop until the end of the time…

The rules for Time Travel seem to have been written down somewhere and SF Television has been using and abusing for all that time. Now, the $64,000 questions are a) is there such a thing as time travel? and b) do these time travel rules mean anything?

The Rules

1. You Cannot Assassinate Your Own Grandfather, Or Else…

One of the most famous arguments against time travel was the problem of temporal paradoxes. What happens if you kill one of your ancestors? If someone else did it, then the line that bore you would cease to exist and so would you. But if you did it to yourself, you would cease to exist thus undoing your murder which would bring you back into existence where you would travel back in time to kill your ancestor, etc. A paradox.

1a) … You Will Fade Into Oblivion Unless You Fix It.

The Back To The Future answer to this question was you faded out of existence unless you fixed the paradox.

1b) … Or you will instantly pop out of existence.

This was one of the more popular ones, especially when you did this to someone else.

2. If You Meet Your Future Self And Touch, *BOOM!*

Writers got this idea from the Pauli exclusion principle which, really simply put, said no two particles can occupy the same time and space. Fortunately, this does not mean if you met yourself that the Universe would spontaneously implode, explode, or you’d explode, or God would come down from Heaven and slap you silly. If you shook hands with your future self, probably the only thing that would happen is you’d notice how clammy your own palms are.

3. The Time Travelers and Those They Left Behind Will Remember The Old History When Everything Changes

When Time Travelers change history, they and their support crew back in the “present” time remember the old history and know history changed. I wonder how this works? Magic time protection aura? Isaac Asimov’s classic novel Eternity, Inc. actually does use a time protection aura.

4. If Changing History or Creating a Paradox is Forbidden, Then Everything You Do To Change History Will Fail

This one may be true. Kip Thorne is a CalTech physicist who set the scientific community ablaze when he came up with a credible method for making a time machine. After he published his seminal paper on time travel, a number of respectable physicists came out of the closet (so to speak) with their ideas. One avenue of research found that the laws of physics, as we know them, won’t allow you to create a paradox, any attempt to do so will be foiled. The other option is a branch in the quantum universes. The moment you change history, a new branch of history is created where you’ve killed your grandfather, but you can still exist because you come from a parallel universe where no one ever killed your grandfather.

This site for the PBS program Nova has the best quick-start guide to time travel I’ve come across.

Advice for Writers

If you want to be an SF writer, or if you already are one, please do a little research before you write your next Time Travel opus. Take the time to come up with clear, consistent rules for time travel for your universe and stick to them. If you would like some recommended readings or viewings, you can’t go wrong with the following:

  • Isaac Asimov. Eternity, Inc.
  • Robert Heinlein. Door Into Summer.


  1. I would also recommend “Imagining the Tenth Dimension” by Rob Bryanton. It’s more of a philosophical look at the concepts of string theory, but it’s got an interesting viewpoint on time travel.

  2. A good time travel Sci-Fi movie I’d strongly suggest is Primer:

    Although it might have some problems, the actual act of time travelling presented there is simmilar to Kip Thorne’s machine – you cannot travel back to a time where the time machine you use wasn’t build and turned on. This solves a few problems .. but creates new ones, of course 😉

  3. I came across a couple of interesting hypotheses regarding time travel.

    First is if time is mutable, and time travel is possible, then the universe should have balanced out to its most stable state: one where time travel never was or ever will be invented and/or used. Very convenient I think. Then again it’s basically untestable.

    The other is that any time travel would have to involve artificial manipulation of space-time. Building a wormhole for instance. The thing here is that you cannot travel before the point in space-time the space-time warp was built, because you’re only looping time in on itself.

  4. If you go back into the past and kill one of your ancestors before they had a child, then you MUST go back into the past and kill that ancestor before they had a child. To do otherwise would cause even worse problems.

  5. Maybe I’m naive, but if you went back one year into the past wouldn’t you find yourself sitting in space waiting for the Earth to come along? Or if you only went back a few seconds, would the Earth come up and smack you silly while your were still unbuckling yourself from your time machine?

    • I think you are right.
      A perfect time machine would have to take into account the precise location of everything including the stars and the galaxies and the planet you are on.
      Mind you if you could invent a time machine they you could also just use it as an instant way to travel long distances like teleportation as long as you had precicse co-ordinates for the place of origin and the destination.

  6. Time is a straight line , a one way line forever moving forward to infinity . Once set in motion upon a timeline one can not go back nor jump ahead , although eistein theories prove a SIMULATION TO WHAT SOME MIGHT THINK IS TIME TRAVEL BUT IT IS STILL A FAR CRY FROM IT ! Have fun speculating about it but rest assured timetravel never has been possible never will be possible and today isnt possible . It took the earth four billion years to evolve a species capable of limited space travel no where near the light speeds needed for intersteller travel . Now how many more billion years do you think it would be before we even got close to breaking the time barrier ? Time travel is based upon every indivdual millisecond in history to have a consistent loop to itself , cant happen ! For if you were to travel back in time to a time period that didnt have time travel instantly you would be sourrrounded by billions upon trillions of your future selfs arriving a few milliseconds from the next .

  7. I see another problem with time travel. Let’s suppose that we want to go back 1000 years ago. There is not only the problem to the time travel itself, but the problem of reachong the destination: the Earth-1000-years-ago was not at the same place of the Universe than is today. So, I imagine that a time travel is also a space travel… as many space as long the backtime is. Then, if you want to see dinosaurs, you will also need a space ship capable of light-year travelling.

  8. I like how conservation of mass/energy is ignored. Does matter from projected across time affected the composition of the universe?

  9. Fundamental physics concepts

    Temporal encroachment is an action that affects the perception of time or that affects the ability to take action in the future. Temporal means related to the measurement or passing of time and encroachment is an intrusion, usually unwelcome, into the space of another.

    The space that temporal encroachment refers to is temporal space, the temporal “space” or “territory” upon which others attach significance.

    Spatial empathy is an informal term used to describe the awareness of an individual to the proximity, activities and comfort of people surrounding them.

    It is closely related to the notion of personal space, the concept that an individual has ownership of their immediate surroundings; and for others to invade this space represents an infringement on their privacy.

  10. Time travel is definitely possible. It just that those who write about it have never experienced it.

  11. Who is to say that time travel Hasn’t already been invented but not disclosed.

    Who would know?

    If somebody went back and changed history then everybody else would just remember the new history and therefore not know that anything had changed and also discount the theory or possibility of time travel based on the principle that if it existed then people would notice.

    Of all the movies I ever watched or books I’ve ever read the only one to get me really thinking is the Matrix and the question of De Ja vu.
    Although the movie explained it in relation to the story, Who has never experienced it?
    Could it not be a universal self correction, A minor time-hicup? Or simply a feeling that you’ve done this or been a place before you actually had done or been.

    I aggree with others that in order to time-travel you would also have to master spacial travel.

    • that is d best question i hav read!

  12. Factual wise if you travel faster than light to another planet and observe back on earth what is happening in real time, you will be viewing the history of Earth ie. seeing yourself preparing to get into the rocket.

    Time is a scale marks of changing events. If there is such an environment and object that remain the same forever, Time is useless on such a case or rather time is undefined in relative to outside world.

    Hence Time Travel is proven can exist by observation / viewing only … that is why you “can’t” change anything, not that it will cause anything different but the viewer is just incapable of changing anything in the show he is watching. The show has already been made.

    On the other hand, every night I dream about my past and how I would do things differently and how everyone else would also react differently … as far as the dream goes, I time travel to my past and I have changed my future. If waking up not doing anything about that, then it will just be a dream. But if I apply some changes to my current world then perhaps I will change my future. Who would say I was just dreaming then ?

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