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Time Distortion

  1. Jul 14, 2004 #1
    Please be aware that before replying to this message that I will be transferring your replies into another forum (of sorts)

    Suppose Tom and Jerry get together. They decide that they will devise a simple time measuring device. Each has a tennis ball and both Tom and Jerry (no pun intended) decide that a second will be defined as throwing the tennis ball 5 feet into the air and then the tennis ball will fall back down 5 feet. Therefore ---- 1 second = 10 feet of vertical movement (we won’t consider velocity of the tennis balls as a factor for simplistic reasons). As both stand there with no relative motion between them they agree that a second = 10 feet of vertical motion. Now Jerry gets into the back of a pickup truck going past Tom at ten feet per (tennis ball) second. All that Jerry sees is vertical movement when looking at his ball and so does Tom, when looking at his own ball. When Tom looks at Jerry’s ball going by at ten feet per second he sees both vertical and horizontal movement. Jerry’s clock as compared to Tom’s shows that Jerry’s tennis ball has traveled 20 feet. 10 feet vertically and ten feet horizontally. Jerry’s clock relative to Tom’s ticks slower.

    (at this point shouldn’t the above scenario be viva versa?)

    As I was trying to figure out how to explain this I found a problem with time distortion that I once stumbled across. It would seem to me that Jerry would see Tom’s clock slowing down and Tom would see Jerry’s clock is slowing down. So the time distortion would cancel each other out and both Jerry and Tom would march on into the future at the same rate but I know this isn’t the case so we will ask the BBS.

    Physics BBS: I know time distortion doesn’t cancel each other but I ran into the above problem can anyone set me straight?
  2. jcsd
  3. Jul 14, 2004 #2
    There is no need to devise a new time measuring device to reach this conclusion. Both Tom and Jerry would consider themselves at rest, and the other one moving hence the other's clock runs slower. The situation is completely symmetrical. Each would also see himself marching into the future at a normal rate as he always sees himself at rest. There is no paradox here, what is your question? If Jerry attempts to communicate his age to Tom, various SR effects would contrive to make Tom receive Jerry's messages in such a way as to be consistent with the age Tom would assign to Jerry anyway.
  4. Jul 14, 2004 #3
    To Zeframe

    Thanks for the reply. I see what your are saying and that is what I am reading in a book. You lost me at "sr effects" because I don't know what SR means. What about the famous situation of a twin brother taking a speeding trip into space and coming back to meet his twin brother who has aged more? If both see the other's clocks running slower and their own running "normally" how does the accelerating aging come into play or does this have to do with the tansmission of information like I think you said at the end of the reply?

    Thank RAD
  5. Jul 14, 2004 #4
    Heh. SR = special relativity; we use it a lot around here. By "various SR effects" I mean things like length contraction and/or time dilation, which would be necessary for a complete treatment if one sends light signals to the other.

    There has been plenty of discussion about the twin scenario at this forum; there is one particularly concise and well-written post that treats it entirely within an SR framework:


    A note of warning: there are some people in theory development who have made a huge ruckus in trying to disprove SR. If you are trying to further your own SR knowledge, that is NOT a good place to do so in general. If you're not convinced that SR correctly describes the physical world, refer to the thread "Experimental support for SR" in this section.
  6. Jul 15, 2004 #5
    To Zframe C

    Oh by the way Z- I like your name, very creative and even applicable as to what we are talking about now. Yesterday I figured out that the acronym "SR" stood for special relativity. I understand about length contraction. It has been about 7 years since I read a fundamental book on how to understand relativity. I will check out the link you provided and I need to read back over some things. It seems at this point that time distortion cannot be because of the symmetry described yesterday. I will probably get back to you on this. I know clocks tick slower in in orbit above the Earth because they need to take time distortion into account when synchronizing atomic clocks between Earth and the satellites
    Thanks for your help Z talk to ya later
  7. Jul 15, 2004 #6
    Anytime. Send me a message if you'd like me to answer more q's as I also hang in other areas of the forum.
  8. Jul 15, 2004 #7
    Zefram c, don't forget that when Jerry bring the truck back to Tom, both will agree that Jerry has aged less than Tom since Jerry is entering Tom's reference frame. Just a little detail I thought needed to be pointed out. And RAD, just so no one in another thread corrects you in less polite way, I just want to mention that "time dilation" is the proper term, not time distortion. And I agree with Z about being careful where you try and find more about SR, the problem with the people making the ruckus is that a lot of them seem to do because they're too close minded to accept a world outside common experience and so any attempts to try and convert them result in them doing the equivalent of plugging their ears and yelling, "I'm not listening"...sorry, it just annoys me a little bit. What was I saying again? Oh yeah, just be careful where you try and get help. Feel free to send my PM too if you have any questions.
  9. Jul 15, 2004 #8
    Agreed, I think I missed the part about Jerry bringing the truck back. In that case, it's a fairly classical twin experiment.
  10. Jul 15, 2004 #9
    Time dilation

    Lastone: Thanks for replying. This is what I want to get at. If both systems are symmetrical than why does one age slower than the other? What is this with entering the others frame of reference? Thanks
  11. Jul 15, 2004 #10
    The classic Twin Paradox. In essence, the symmetry breaks down because SR handles acceleration badly and so in order for Jerry to reach speeds that time dilation becomes apparent at, he has to accelerate and then deccelerate to come to rest with Tom. Using the equations of General Relativity, you can show exactly how the symmetry breaks down and why the equations of SR seem to hold for only one observer. At it's most basic, Jerry returning to Tom's reference frame is what does the trick, since Tom never accelerated relative to spacetime (yes, there is something of an almost absolute nature in relativity). You can still use SR's equations, but with the assumption that Jerry will come to rest relative to Tom you can only use them with respect to Jerry. The same goes for length contraction. I'm sorry I can't give a more complete response, I'm in a bit of hurry...I promise when I can really write the response that such a problem deserves I'll make a second post. Nonetheless, hope that helps.
  12. Jul 16, 2004 #11
    Just to clarify - the time dilation experiment doesn't work with tennis balls - the conclusions derived from the light clock experiment depend upon the assumption that the other observer is bound by the constancy of the photon velocity - and therefore he concludes the difference in time passage between himself and the other frame is due to the increased path length of the photon which is hypothesized to travel at c in both frames.

    LastOne standing - the acceleration explanation is only one of many different ineffective attempts to avoid the SR twin and triplet paradox - the reason so many words and articles have been written about it is because there are different theories as to the entire subject
  13. Jul 16, 2004 #12
    Lastone and Yogi

    It is funny that I recognize both of your screen names. I know that I have talked to both of you before (I am new to the forum) I want to thank you both for replying. Yogi your are right. I was using tennis balls in place of a light clock. I figured that the movements were not accurate enough and the speeds are of hardly no fraction of c. I was trying to illustrate to others that when moving in respect to others there is two directions of motion. As I was doing this I came upon the symmetry of the two systems and wonders as to how a photon from the big bang has aged none. I too am in a hurry and have to go. I would like to investigate this symmetry breaking in detail but I must go. If this gets too deeply into mathematics it will lose me but now I can see as to why people would question as to one photon aging less than the other.
  14. Jul 16, 2004 #13

    I had the same problem as you with the symetry. It was "obvious" to me that because each saw the others clock as slowed down by the same amount, they were "cancelling out".

    However, two gentlemen, Chroot and Ambitwistor, spent some time one Saturday evening explaining that the proper way to assess what is going on is through the use of spacetime intervals. The two observers will end up having different, asymetrical, spacetime intervals.

    The concept of acceleration wasn't helpful at all to me. It seemed that if one accelerated, he could define himself to be at rest and view the other as accelerating. Chroot and Ambitwistor cut straight through that confusion by getting to the concept of the spacetime interval.

    I don't feel qualified to go into it myself and wouldn't be able to handle any questions that might arise, but if you can find someone who can explain the asymetry in terms of the spacetime interval, it will remove the confusion created when you come to the very logical conclusion that the two equal and opposite time dilations seem to "cancel out".

  15. Jul 16, 2004 #14
    A point I now wish I had made the time to address. While I'm not particularly adept at explaining the situation myself, an article at http://science.howstuffworks.com/relativity.htm explains it well on a page I believe is titled "Fun with Special Relativity" or something like that. It uses the relativistic doppler effect to explain the relative time intervals zooby mentioned.
  16. Jul 16, 2004 #15
    I did a little digging and found the thread where they explained this to me:

    variable speed of light - Physics Help and Math Help - Physics Forums

    I start asking questions about halfway down the first page, and if you follow from there on you can see I ask roughly the same questions as Rad, which Chroot and Ambitwistor handle expertly.

    (This thread, incidently, is of some historical signifigance to PF in that it is the very first time LaTeX was used here. Ambitwistor used it to show his equations, and Chroot was so impressed that they began working on making it a permanent feature.)

  17. Jul 16, 2004 #16
    Thanks, I've been looking for some more info myself to explain the paradox.
  18. Jul 17, 2004 #17

    I just dropped in on a busy Saturday to see what you guys had to say. I don't have time to check out the provided links at this moment. I will check all this out later. I want to thank everyone for the help on this subject and will talk to ya all later.
  19. Jul 18, 2004 #18
    New update: a few hours ago I started reading Brian Greene's "The Elegant Universe" and he tackles the twin paradox quite nicely. Also a good read if you want to learn about the details of special and general relativity as well as quantum mechanics and superstring theory.
  20. Jul 20, 2004 #19
    To Last One


    I have read "The Elegant Universe". After finishing the book I donated it to a local library which I now regret. I took out a copy of "The Elegant Universe" from a local library a week ago. I was using this book in reference to what Einstein said about 'every object in the universe is moving at the speed of light'. I think his (Greene) analogy using an auto driving into the glaring sun is what we are talking about here. That when traveling at speeds close to c you take some of the velocity moving in the time dimension and redirect to move through the space dimension. I have the book in hand if you have any details you want to refer to me in the book. I am still going over the information provided in this thread.

    Last edited: Jul 20, 2004
  21. Jul 20, 2004 #20
    While the section with the vehicle on the drag strip does a good job of showing why time slows down as you speed up, the twin paradox comes a little before that (though I don't believe he ever calls it by name). As long as you've got the book handy, p.43 is the section I'm talking about. To summarize what he says, the only way the twin that by common standards we would say is moving, he/she has to change directions, thereby accelerating in order to return to other the twin. Acceleration is also neccessary to initiate the relative motion. Since SR doesn't cover non-uniform motion, this puts it into the domain of general relativity. Spacetime itself provides a benchmark for non-uniform motion, so by accelerating one of the twins establishes himself/herself as being the one in motion. Of course there are other explanations that Greene doesn't mention but this one is simple and wide-reaching. The point is paradoxes arise from flawed logic, so no matter which method you use to explain the twin paradox, it's just a case of trying to apply SR where it doesn't belong.
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