Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How time Travel work ?

  1. May 18, 2009 #1
    How time Travel work ????

    ok i know some of the basic about speed of light...
    You can't get to the speed of light ...
    You can't reach the speed of light cause According to Einstein's special theory of relativity, and E= MC ^2 objects gain mass as they accelerate to greater and greater speeds. Now, to get an object to move faster, you need to give it some sort of push. An object that has more mass needs a bigger push than an object with less mass. If an object reached the speed of light, it would have an infinite amount of mass and need an infinite amount of push, or acceleration, to keep it moving. No rocket engine, no matter how powerful, could do this. In fact, as far as we know, nothing can exceed the speed of light.

    And i know how it work
    Imagine you're standing on Earth holding a clock. Your friend is in a rocket zooming past you at nearly 186,000 miles per second. Your friend is also holding a clock. If you could see your friend's clock, you'd notice that it seems to be moving a lot more slowly than yours. Your friend, on the other hand, thinks the clock in the rocket is moving just fine, while your clock on the ground seems to be moving very fast.

    Test it out ???
    Atomic clocks are extremely accurate clocks that can measure tiny amounts of time—billionths of a second. In 1971, scientists used these clocks to test Einstein's ideas. One atomic clock was set up on the ground, while another was sent around the world on a jet traveling at 600 mph. At the start, both clocks showed exactly the same time.

    What happened when the clock flown around the world returned to the spot where the other clock was? As Einstein had predicted in a general way, the clocks no longer showed the same time—the clock on the jet was behind by a few billionths of a second. Why such a small difference? Well, 600 mph is fast but still just the tiniest fraction of the speed of light. To see any significant differences in time, you'd have to be traveling many millions of miles an hour faster.

    If you are moving time will slow down, even you in earth or out of space
    but my big big question is, how Speed of light (C) or speed have anything to do with time ? what is time ? i mean How time slow down ?? How time can slow down when travel ?hope u guy can explain for me
    Last edited: May 18, 2009
  2. jcsd
  3. May 18, 2009 #2


    User Avatar
    Homework Helper

    Re: How time Travel work ????

    Slow. Not fast. You think your friend's clock is moving slowly, and your friend thinks your clock is moving slowly. (Weird, I know. But that's the only way to be consistent - it could just as well be you moving and your friend who is at rest.)

    Hmmm... that's kind of like asking "why is relativity true." Because people did the experiments and found that it is. Other than that, you're getting into the territory of philosophy.

    It might be a little misleading for you to think about it as time slowing down; in a sense, time dilation (the effect you're talking about) is a transformation that happens when you change velocities. Things happening at a velocity different from yours always seem slower than they would if you were traveling along with them. Mathematically, it's a shear effect, a "hyperbolic rotation" (one could say), and it makes sense if you accept the math, but if you're not already at least somewhat familiar with that (the math) it probably wouldn't do you much good to see that explanation in detail.
  4. May 18, 2009 #3
    Re: How time Travel work ????

    NO like i say my friend stay on earth, will see my clock (if he can ) going faster
    and i will see his clock (if i can) going slower than normal

    i know that, when a person travel his time is not slowing down, but relate to other people who at rest, his time is slow than the people who at rest

    like this story:
    Al's parents decide to send him to summer camp in the Alpha-3 star system, which is 25 light-years away (a light-year is the distance light travels in a year). Bert doesn't want to go and stays home on Earth. So Al sets out on his own. Wanting him to get there as quickly as possible, his parents pay extra and send him at 99.99 percent the speed of light.

    The trip to the star and back takes 50 years. What happens when Al returns? His twin brother is now 60 years old, but Al is only 10 and a half. How can this be? Al was away for 50 years but only aged by half a year. Has Al just discovered the fountain of youth?

    Not at all. Al's trip into space lasted only a half year for him, but on Earth 50 years passed. Does this mean that Al can live forever? Nope. He may have aged by only half a year in the time it took 50 years to pass on Earth, but he also only lived half a year. And since time can slow down but never goes backwards, there's no way he could grow younger.

    But my question is how it work? why?
  5. May 18, 2009 #4


    User Avatar
    Homework Helper

    Re: How time Travel work ????

    NO your friend will see your clock moving slower than his and you will see your friend's clock moving slower than yours. I don't know where you're getting the information that your friend will see your clock moving faster than his, but it is absolutely wrong. (Assuming that both you and your friend correct for the Doppler shift, of course)
  6. May 19, 2009 #5
  7. May 20, 2009 #6
    Re: How time Travel work ????

    dannyPhysics: diazona is not wrong. Your friend flying past the Earth is the equivalent of your friend at rest in space while the Earth "flies past him". They are equivalent. Replace the Earth with another spaceship and you will see.

    The time differential actually occurs from the acceleration/deceleration of your friend in space. In other words, he accelerates to fly by, then he must decelerate to stop and turn around to come back to Earth so that you may compare clocks. This is different from "just moving by another object quickly".
  8. May 21, 2009 #7
    Re: How time Travel work ????

    ^^ thank but u guy not answer my question ^^
  9. May 21, 2009 #8


    User Avatar
    Homework Helper

    Re: How time Travel work ????

    The speed of light is the same in every inertial frame. So lets say we have two observes one flying in a space ship the other stationary on earth. The space ship fires a light pulse, what do the observes see? The observer on earth will see the pulse of light travel at c, not c+v_spaceship. The observer in the space ship will also see the pulse travel away from him with speed c. For this to add up, time has to be dilated and space has to be contracted.
    Last edited: May 21, 2009
  10. May 21, 2009 #9


    User Avatar
    Staff Emeritus
    Science Advisor

    Re: How time Travel work ????

    Your questions have been answered but you refuse to accept them! What reason do you have to keep saying "NO"? If you believe you already know the answers, why did you ask?

    The fact that you titled this "How time Travel work?" but asked questions that have nothing to do with "time travel" (answer: it doesn't work!) suggests to me that you are not clear on what questions you want to ask.
  11. May 21, 2009 #10
    Re: How time Travel work ????

    dannyPhysics: Are you asking WHY time dilation occurs at all, or simply why does time dilation occur as it relates to the speed of light? Relativity DESCRIBES reality but it does not EXPLAIN it, unfortunately.

    I have a couple of personal theories on why time dilation occurs, but they are not even half-baked at this point so I won't be subjecting them to forum criticism just yet. :)
  12. May 21, 2009 #11


    User Avatar

    Re: How time Travel work ????

    No-one can really explain to you the nature of time, but they can discribe our observations of time in our experineces, because of mathamatics based on the constancy of light. It makes sense, both logically and mathamatically, and while proving the constancy of light is a difficult feat, all experimental data regarding time dilation helps prove the correctness of Einstein's theory.
  13. May 21, 2009 #12
    Re: How time Travel work ????

    Slow down. This,
    is not true.

    This scenario compares only two clocks in relative motion. This is not the usual experiment. Instead you have substituted two clocks in relative motion. The observations are symmetric in your scenario. An approching clock appears to be running faster. A receding clock appears to be running slower.
  14. May 21, 2009 #13


    User Avatar
    Science Advisor

    Re: How time Travel work ????

    "Einstein began his analysis .... by giving operational definitions ... consistent with the principle of relativity and with the validity of Maxwell's equations ... [emphasis mine]" http://books.google.com/books?id=ggPXQAeeRLgC&printsec=frontcover#PPA58,M1
  15. May 22, 2009 #14
    Re: How time Travel work ????

    here I thought I was going to see someones plans for a flux capacitor, darn!
    well this just simply a consequence of relativity, a phenomenon, only God knows what time is and why velocity affects it.
  16. May 22, 2009 #15


    User Avatar
    Homework Helper

    Re: How time Travel work ????

    No, the web page is wrong. Otherwise I'm sure someone would have pointed it out on this thread.

    Thanks for pointing out the site, though, I think I'm going to call their attention to it...
  17. May 23, 2009 #16
    Re: How time Travel work ????

    Good grief. who on this thread has been right about anything. I see misinterpretation on misinterpretation. Where's the reset button?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook