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Time travel

  1. May 20, 2009 #1
    I was wondering the feasbility of time travel. Has it been proven not possible? Has it been proven theortically possible?

    I have always been interested in time travel, even if it seems like science fiction, but was wondering from scientist, professors, etc, if it has been an 'unsolved' problem per se of theortical physics.

    Does anyone happen to know the name of the paradox where one is his own father, mother, self? It's a paradox of time travel with a bartender...who had an operation, and then loops through time and is his own mother, father, brother and sister!
  2. jcsd
  3. May 21, 2009 #2


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    Grandfather paradox. Time travel is mathematically possible but remains a practical impossibility. You need a very exotic type of matter to pull off the feat and nothing resembling this kind of matter has been detected.
  4. May 21, 2009 #3
    Being mathematically representable doesn't imply a physical possibility.
  5. May 21, 2009 #4
    Well at least time travel to the future appears possible....since time is relative. (It is right? I like learning about physics and math but I'm not a physist)

    If you were in a spaceship and travelled at 2/3rd the speed of light and somehow didn't get crush into oblivion with the gravtational forces that implies, for 10 years, speed away from the earth. Come back to the earth, the earth being much older than you. Is this possible?
  6. May 21, 2009 #5

    George Jones

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    Yes, this is theoretically possible. For a more dramatic effect, consider moving away from the Earth for 10 years with 99% the speed of light, and then returning to Earth with the same speed. The person who makes the trip ages 20 years, while the people on earth age 140 years.

    For more on time travel, see


    if you want, I could try and explain some of the technical terms.
  7. May 21, 2009 #6
    Wow, that is fasinating. Is it true that scientist have been able to accelerate photons at 99% the speed of light? Of course, elemental particles like this I'm sure behave differently than large bodies such as humans...I wonder if we will ever be able to go that fast. Still, it makes you think. That would be a pretty cool thing to do...

    Sure, go ahead and try to explain more technical. I've always enjoyed math classes and going to college soon, I plan to take some more just for fun. Not sure I'd enjoy it as a career, but I do love thinking about thought provoking stuff, philopshy type stuff.

    I've always wanted to do calculus. I read several books on anti derivatives (integrals), partial derivatives, etc. It's a goal of mine one day to do calculus...that's why I want to go and take some more math classes.

    As I've heard it gets much harder on higher ed classes..the problems seem to get alot harder, and I heard it can take weeks to solve a problem!

    As far as I have gotten into algebra and snagged everytime was rearranging algebraic formulations in different formats, like factoring. I could not get past the first chapter in a very down to earth algebra book, because it had factoring type stuff, really simple stuff. I did very well in algebra I in high school, but I switched to a charter school and never had to get into factoring. I would love to take trigonmetry and math fasinates me...perhaps I could learn some here.
  8. May 21, 2009 #7
    "Is it true that scientist have been able to accelerate photons at 99% the speed of light?"

    the photon will always travel at the speed of light in a vacuum this is the fundemental of Quantum physics, that time not the speed of light is the variable.
  9. May 22, 2009 #8


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    I think time travel into the past is impossible because of the logical paradoxes it implies. The simplest is the telegram paradox (a basic case of the grandfather paradox). Make a telegraph machine that can send a message into yesterday. Send a message to yourself yesterday reading "if you receive this, do not send this message tomorrow".
  10. May 22, 2009 #9


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    All You Zombies— by Robert Heinlein. Wikipedia has a page on it.
  11. May 22, 2009 #10

    George Jones

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    BadFish, you might be interested in an excellent, non-technical reference on time travel, the second edition (make sure that it's the second edition) of Time Machines: Time Travel in Physics, Metaphysics, and Science Fiction by Paul Nahin. This is a wonderful book that is written for the educated layperson.


    Physicist (and relativist) Kip Thorne wrote a foreword for the second edition of this book, and here's a quote from this foreword: "It now is not only the most complete documentation of time travel in science fiction; it is also the most thorough review of serious scientific literature on the subject - a review that, remarkably, is scientifically accurate and at the same time largely accessible to a broad audience of nonspecialists."
    I think you mean protons. The new Large Hadron Collide should be able to accelerate protons to a speed of about 99.999999% the speed of light.
    Last edited by a moderator: Apr 24, 2017
  12. May 22, 2009 #11


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    Also "The Man Who Folded Himself" by David Gerrold.
  13. May 22, 2009 #12
    Ah, but nature does not have to obey what we consider logical. Imagine trying to explain quantum mechanics to a nineteenth century physicist, for example.

    Hawking, famous for his bets, has said that we would not bet against the existence of time travel, because his opponent might have seen the future and know the answer.

    And since we're mentioning time travel stories, Haldeman's The Accidental Time Traveler is a worthwhile read. The most interesting way to turn a mediocre physicist into a super-genius is to send him back in time a hundred years.
  14. May 23, 2009 #13
    While we're mentioning Hawking, doesn't he go on to say something to the effect of time travel and faster than light travel are essentially the same? It might not be the same concept of "time travel" you were imagining though. My memory may be wrong on this, but I thought he described it by using two worlds separated by, for instance, several light years. If you can travel faster than light, you could observe the events on one world, travel to the other world, and "know" the future of the other world, as any information of these events could not have travelled between the two worlds.
  15. May 24, 2009 #14


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    Futurama had an interesting take on the grandfather paradox in the episode "Roswell that Ends Well". While Fry does inadvertently kill his father's mother's husband (in an attempt to keep him safe, and avoid succumbing to the grandfather paradox), he ends up being his own grandfather after sleeping with his grandmother!

    I read an an analysis many years ago regarding what percentage of genes were inherited by the various people leading / coming from Fry, but there was a fatal flaw, as there are chromosomes that come out of nowhere, and discrete genes (e.g. Y-chromosome are inherited only from father to son, and thus grandfather to grandson--which leads right back to himself!)

    Not as bad as an entire being popping out of nowhere as in All you Zombies though.
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