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I had bazzar thought on relativity

  1. Apr 29, 2003 #1
    if you have a train in moiton in reference to stionary embankment.and the train is 20 ft long.if you have 5 points along the embankment abcde.between ac=ce,ac and ce is 20 ft.so when you speed the train up to a certain point as the front of the train reaches c the train fits between ac.then as the back end of the train reaches c.the train fits between ce.but if its fast enough.to the stationary observer,the both the trains front and back are at c at the same time,giving the train no length.but on the train if the observer was in the middle.when the front of the train is at c he's at b.when the back of the train is at e,he's at d.so to the observer on the train he 20 ft of length when to the stationary observer the train has no length.
  2. jcsd
  3. Apr 29, 2003 #2


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    How so? You have not proven this claim, it could only be true if the speed of the train were c.

    You need to specify where and when observations are made. Relativity makes it necessary to specify the full 4 spacetime coordinates of any event, this means you must establish a fixed reference frame for your measurements.
  4. Apr 29, 2003 #3


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    Since a train can't travel at C, the hypothetical implications of a train traveling at C are meaningless. Sorry.
  5. Apr 30, 2003 #4
    what if you take a ball tied to a string,and spin it around in a circle.how fast does it take to spin it to the point where no matter what,when you pass something in the balls path,its going to hit it.a couple thousand rpm's or so should do it.thus the ball is at all points at any given time.if you'd like to prove that one wrong,I'm listening.
  6. Apr 30, 2003 #5


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    Consider a WWI fighter such as the Sopwith Camel or Fokker DR1, they had a sycronized machine gun that was timed to fire through the spinning propeller. No matter what the speed of the propeller the bullets would pass through the spinning blades without hitting.

    Consider this, then reconsider your statment.
  7. Apr 30, 2003 #6
    Also, try hitting an electron in a particle accelerator with a ball, haha.
  8. Apr 30, 2003 #7
    so what your saying that if you can have a beam of light timed to pass through the path of the train,or say a spaceship passing by a spacestation to get away from the contradiction.a beam of light stationary from the spacestation perpendicular to the spaceship flying bye,would reflect the beam of light.but how much reflection of the light would determine what length the spaceship was by the duration of reflection.but the gravitational field given off by the ship at close to light,dilating time and shinking the ship,would curve the path of the reflecting light,giving us a different position of where the ship was when you tried to test the length of the ship by the duration of relection,making it hard to know exactly the length because you could'nt determine position.by the reflecting light.
  9. Apr 30, 2003 #8
    What if train is a photon (say, visible light photon 20 m long)?
  10. Apr 30, 2003 #9
    Light already travels at c.
    Last edited by a moderator: Apr 30, 2003
  11. Apr 30, 2003 #10
    There is no such thing as a 20 foot long photon.
  12. May 1, 2003 #11
    What do you mean? Take a laser beam (say, from a good long-long cavity He-Ne laser) and cut it by 67 nsec shutter, then you get x = ct = 20 m photons out of the shutter.
  13. May 2, 2003 #12
    It is a 20m stream of photons, not just one.
  14. May 2, 2003 #13
    No, you start with longer than 20 m photons already (say, from good laser with big and well silvered cavity). Then you chop 20-m chunks out of them. After shutter all your photons gotta have then 20 m length (their wave function is exactly 20 m long).
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