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A few questions on time

  1. Jul 7, 2009 #1
    Hello,

    If a human could travel at .9999c would their perception of time (in their own frame) be the same as the perception of time of a stationary observer (in their frame)?
     
  2. jcsd
  3. Jul 7, 2009 #2

    malawi_glenn

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    yes of course
     
  4. Jul 7, 2009 #3
    That's what I thought, but how is this known?
     
  5. Jul 7, 2009 #4
    Time ticks by at a constant rate. At different speeds, the perceptions of the two times would be different. But in their own frame of reference they would be the same. If this wasn't true, then the equations on relativity would be incorrect. Since the majority of scientists trust the data from all of the experiments done on relativity, I think that we can believe that time would tick by the same at any speed in reference to someone going at that speed.

    I know this isn't quite what you're looking for, but unless we send something that can take readings while going 0.999c, then I think we'll just have to trust science.
     
  6. Jul 7, 2009 #5

    DaveC426913

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    We have ample data of such things.

    Particles with a known decay rate, when accelerated to near light speed, show a time dilation (i.e. live longer) exactly in accordance with SR.

    Extremely accurate atomic clocks flown on jetliners high in the atmo (where gravity is weaker) have shown a dilation of time exactly in accordance with SR.

    GPS satellite data takes SR into account when measuring distances. If SR were wrong, the GPS data would be wrong.
     
  7. Jul 7, 2009 #6

    I'm not questioning SR time dilation, though.
     
  8. Jul 7, 2009 #7

    malawi_glenn

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    what are you then asking about? you asked how observers would notice time when travelling at high speeds...
     
  9. Jul 7, 2009 #8
    How is it known the observers (or travelers) mental perception of time is "in sync" with all other time dilation effects?
     
  10. Jul 7, 2009 #9

    malawi_glenn

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    the Mind is not a subject of physics, but if one has the view that the mind is just particles and forces described in principle by physical law, then it should be "in sync".

    And let us just play here, HOW would he notice things different, if the mind was detached from the physics: if the observer moving was raising his arm, would he thinking "gosh, what a long time it takes to raise my arm" ??
     
  11. Jul 7, 2009 #10
    I have no idea... Maybe their movement would seem restricted?

    I was also curious if the travelers size would increase with velocity relative to the observer, and if that could change their perception of time as well.
     
  12. Jul 7, 2009 #11
    Depending on what direction the traveler was going and relative to the observer, the traveler would get skinnier if he/she was going directly forward or backward, shorter if he/she were going up or down (relative to him/her), or a combination if in some other direction. However, the traveler wouldn't change in his/her reference point.

    Also, the traveler would appear to be moving slowly (from the observer's reference). As to what that traveler would experience would be nothing more than if he/she weren't moving at all.
     
  13. Jul 7, 2009 #12

    JesseM

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    But whether you realize it or not, you're questioning the first postulate of relativity which says all laws of physics work the same in all inertial frames, and that along with the second postulate that light moves at c in all inertial frames is what all the predictions of relativity (including time dilation) are derived from. It's also possible to show that any law of physics will respect these postulates as long as its equations when expressed in one inertial frame have a mathematical property called "Lorentz invariance" (meaning the equation is unchanged under the Lorentz transformation which relates different SR frames), and if you look at all the most fundamental laws of physics with good experimental support that are known today, they do all have Lorentz-invariant equations.
     
    Last edited: Jul 7, 2009
  14. Jul 7, 2009 #13
    Again, I'm talking about human time perception, and this probably isn't the appropriate place to discuss it unless SR talks about it specifically.
     
  15. Jul 7, 2009 #14

    JesseM

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    Unless you think human time perception isn't based on events happening in the physical brain which obey the laws of physics, then the first postulate should apply to human time perception too.
     
  16. Jul 7, 2009 #15
    Maybe if you gave an specific problem related to your question we can be more helpful?
     
  17. Jul 7, 2009 #16

    DaveC426913

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    ALL things are affected.

    you need to realize that you are right this very moment undergoing time dilation due to relativity. Do you notice anything out of the ordinary?
     
  18. Jul 7, 2009 #17

    Heh.. No, but I could argue that there's nothing to compare the feeling of my frames "time dilation" to.... We've all pretty much evolved in it.
     
  19. Jul 7, 2009 #18

    DaveC426913

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    If there is no way to detect something then how can one say exists at all?

    We're talkin' invisible, intangible, backyard elves here...
     
  20. Jul 7, 2009 #19
    Right, I guess that's why someone mentioned this is more of philosophy discussion... How could you measure a personal experience traveling at .9999c?
     
  21. Jul 7, 2009 #20

    DaveC426913

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    No. Nonono.

    You are travelling at .9999c right now.


    The whole point of relativity is that it's relative. There is no experiment you can do that can say that you are not moving at .9999c right now. Your velocity is only relative to a point of reference of your choice. You might choose the Earth as your frame of refence, but there is no way you can claim that the Earth is not moving at relativistic velocities.

    And it's not that you "can't tell" if you've moving; it's that there is no such thing as an objective frame of reference. It is all relative.
     
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