What is the difference between SR and GR?

Discussion in 'General Science & Technology' started by Mark Turner, Jul 5, 2019.

  1. Mark Turner Registered Member

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    Thank you for the video , I find dynamical process interesting . If I watched that video a dozen times , I'd still probably not understand the kinetic energy involved .
    That's physics though ,it is complex when you start to see and hate the complexity of the physics but in a mind boggling good way .

    Thanks for sharing and giving me something to think about .
     
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  3. Mark Turner Registered Member

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    If nothing changes within the caesium itself , then how can the frequency possibly change ?

    Aren't different reference frames accountable for a difference in enthalpic condition ?

    Thanks in advance
     
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  5. paddoboy Valued Senior Member

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    Time dilation is only evident when observing the other frame. Time is always seen to advance at one second per second in one's own frame of reference. Using the twin paradox [which is not a paradox] I travel away from Earth at 99.999% c.....You see my time advancing both mechanically and biologically slower then yours.....I see your time advancing slower then mine. Here there is the "apparent paradox" Still that edict holds of time passing at one second per second within each's own frame...nothing untoward, nothing apparently different with regards to time within each's own frame. It is only when I accelerate/decelerate to return to you back on Earth that a difference in the passing of time is noticed. Although surprisingly this is not entirely the answer. The important point being that you, on Earth have only experienced one frame of reference, while I doing the actual travelling and decelerating exists in two frames. Paradox gone.The following video explains....don't be put off by the maths in the middle of the video, and go to the answer in the last couple of minutes.


    Or explained much more simply here...your question answer at the 2 minute mark......
     
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  7. James R Just this guy, you know? Staff Member

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    Mark Turner,

    The frequency doesn't change in the rest frame of the caesium, or whatever. It is only different when you compare it to a second clock in some other frame of reference. In other words, the time dilation effect is fundamentally due to what space and time are like, not due to any physical property of clocks.
     
  8. Seattle Valued Senior Member

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    4,163
    Time dilation is necessary once you determine that the speed of light is fixed and everything else is relative.

    Time has to slow down when speed approaches the speed of light because nothing can go faster. The usual thought experiments involve a stationary observer on a train station platform and another person in the train that is passing by.

    The example given is usually a light clock where it takes a second for a beam of light to bounce from the floor to the ceiling of the train. To the person in the train it appears to bounce straight up and down. To the observer it appears to bounce at an angle (due to the speed of the train). The beam of light has to travel further on the moving train but it still has to occur in one second.

    The only way to do that is for time to slow down since nothing can go faster than the speed of light. In this thought experiment the train is going at close to the speed of light.

    The same concept is involved with someone riding in the back of a truck going 100 miles an hour. This person throws a ball at 10 mph in the direction of travel. The ball therefore is now going 110 mph.

    If you do the same experiment but instead of throwing the ball, you shine a flashlight in the direction of travel. The difference is that the light won't be going 10 mph + C (speed of light). It will just be going C no matter how fast the vehicle is going.

    It's because of that "math" that we have to have time dilation. Spacetime is one thing. You have more "space", you have less "time", mathematically.
     
  9. James R Just this guy, you know? Staff Member

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    It takes longer than one second, according to the person watching the train move, because, as you say, it has to travel further, but (and this is the important point) at the same speed.
     
  10. Mark Turner Registered Member

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    Thank you for the videos .

    Isn't time dilation based on the caesium and length contraction used in the GPS systems , two separate phenomenons?

    Thanks in advance.
     
  11. Mark Turner Registered Member

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    Doesn't the shorter second measured always fit within the longer second measured ?

    Thanks in advance..
     
  12. Seattle Valued Senior Member

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    4,163
    Time dilation has nothing to do with caesium.
     
  13. Seattle Valued Senior Member

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    What does this even mean?
     
  14. Mark Turner Registered Member

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    In the light clock thought experiment the clock at relative rest will measure 1.2s by time the clock in relative motion measures 1.s because of the extra distance travelled of the angular path of light .

    To ask my question alternately , if you simultaneous rolled out two balls of string , one slower than the other , the shorter string reference frame will always fit within the longer string reference frame ?

    Thanks in advance.
     
  15. Seattle Valued Senior Member

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    So what?

    In the thought experiment case there are two different frames of reference, one going close to the speed of light and one at rest.
     
  16. exchemist Valued Senior Member

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    This is Theorist, yet again. I would not waste your time if I were you.

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  17. Mark Turner Registered Member

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    Yes , I'm aware of that .

    The speed of light is constant , the angular path the light travels in the moving reference frame is a greater distance than the light travels in the clock at rest frame . By time the moving reference frame measures 1 tick , the clock at rest measures ~1.2 / 1.3 ticks .

    Wouldn't that make 1 tick in the moving reference frame equal to ~1.2/1.3 ticks of the rest frame ?

    Thanks in advance
     
  18. Seattle Valued Senior Member

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    We've already established that. What is your point?
    Thanks in advance.
     
  19. Mark Turner Registered Member

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    If the clock at rest reference frame was expanded in distance between the mirrors , wouldn't that then be perfectly synchronised with the one in motion ?

    Thanks
     
  20. Mark Turner Registered Member

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    Hello , I'm not great at maths but this morning I have attempted to add some values to my question in case it was not understood .

    1. Clock at relative rest

    H = ~399723277m

    Tick rate = 1.3 light seconds per tick


    2. Clock in relative motion

    H= 299792458m

    Angular path distance the light travels

    d=~399723277m

    Tick rate = 1.3 light seconds per tick


    Dilation = 0t

    Is that correct because of c constant ?

    Thanks in advance
     
  21. DaveC426913 Valued Senior Member

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    12,259
    Yes.

    Yes. That is all totally correct.

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  22. Mark Turner Registered Member

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    Thank you for your reply


    Einstein was very brilliant with all his notions .
     
  23. Seattle Valued Senior Member

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    Hahaha...
     
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