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Lorentz Contraction

  1. Oct 12, 2003 #1

    pmb

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    I don't recall seeing this derivation anywhere but its probably somewhere in the relativity literature since most things are.

    A poster at sci.physics.relativity posted what he thought was proof that the Lorentz contraction doesn't exist. See the Fig. 1 in Lorentz Contraction - Version 2 -- www.geocities.com/physics_world/sr/lorentz_contraction_2.htm

    Here is the poster's claim
    (note: He got the angle of the mirror wrong)

    I requested a proof of his claim. In fact I repeated the request many times but he refused to post a proof.

    It was kind of fun to write this up so I posted it on the web. It turned out to be another way to derive the Lorentz contraction relation.

    In my derivation all that is assumed is the Lorentz transformation.

    So the person thought he found proof that there is no Lorentz contraction when in fact all he did was to find another derivation and he didn't even know it! :-D

    Ya gotta love that! :-)

    Pete
     
  2. jcsd
  3. Oct 12, 2003 #2

    jcsd

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    Yes I've seen it before, though not in a textbook, it's actually quite a good way of demonstrating length contraction.
     
  4. Oct 12, 2003 #3
    Obviously one needs to derive the velocity transformation rules first.
    Why does that poster say the following?

    If length contraction was actually physical, the beam would not strike the detector in any frame.

    Was the poster assuming the X-Y orientation of the mirror was the same in S and S'? So there was no contraction of the X component of the mirror width?
     
  5. Oct 12, 2003 #4

    pmb

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    Yes. If you take a look right above Eq. (1) I provide a link to that derivation.
    I'm not sure. I guess he thinks that the layout is exactly the same in the frame in which the layout is moving and that the only thing different is the length of the rod and thus the emitter-detector disatance. I kept asking him to back that claim up but he refused to. In fact I think I asked him to provide a proof almost every single day. All I got was insults - as usual! :-)

    I don't recall. The thread is called "Length contraction doesn't occur period." - check it out if you have the time.

    Pete
     
  6. Oct 12, 2003 #5

    pmb

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    Excellant!! If you recall where you've seen that can you let me know?

    Thanks

    Pete
     
  7. Oct 12, 2003 #6

    jcsd

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    I'm pretty sure that a simlair example is in Brian Greene's elegant universe.
     
  8. Oct 12, 2003 #7

    pmb

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    Thank you.

    Pete
     
  9. Oct 12, 2003 #8
    Pete,

    Are you going to send that poster a link to your new second Lorentz contraction derivation after you publish it?
    Or just leave the growler lie?

    quart
     
  10. Oct 12, 2003 #9

    pmb

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    I posted the link in a new thread and I posted the link to him directly in the old thread.

    But you know how the internet is. They love to divert attention away from the physics. One jerkoff notice that I made an error in my original Lorentz contraction page at

    http://www.geocities.com/physics_world/sr/lorentz_contraction.htm

    At the bottom I showed that lengths perpendicular to motion do not contract. But I made an error in three places an instead of writing "
    perpendicular" I wrote "Parallel" . However it was very clear what I was writing about since I gave a diagram and clearly wrong

    However someone was unable to prove me wrong in another thread and they made some very dumb comments. So to hide their embarassment they wrote
    I responded with the most obvious answer
    Oy! :-)

    In fact that thread was interesting. I should post that one too. It's on relativistic mass as an invariant. See thread I'm starting on this for details

    Pete
     
  11. Oct 12, 2003 #10

    pmb

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    FYI - the standard derivation is here

    http://www.geocities.com/physics_world/sr/lorentz_contraction.htm


    Do you recall that nut that was tossed out for flaming tom? He was the one who couldn't understand that a scalar was a tensor of ranks zero? Well that same nutcase now claims that anyone who posts such a derivation as in the link above is plagerizing him.

    So many nuts on the inernet. Where do they all come from?

    Pete
     
  12. Oct 13, 2003 #11

    pmb

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    Well this was rather humerous. Here is the response from that person
    I had, of course, explained this to him before and he ignored it.

    I explained that in each frame the photons coming out of the laser are aligned parallel to the y'-axis in S' and are also aligned parallel to the y-axis in S. While the photons move in the y' direction they do not move in the y direction.

    I've posted this diagram to explain

    http://www.geocities.com/physics_world/sr/sr23-im-04.gif

    However I think his moton says it all. Seems that he doesn't like to reason since he thinks he'll miss the truth! LOL

    Pete
     
  13. Oct 13, 2003 #12
    Watch out for this kind of trap:

    you agree all frames...will see...vertically
    in line
    .

    Terrell rotation
     
  14. Oct 13, 2003 #13

    pmb

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    Yep. That one caught me for a moment. But so long as particles are "simultaneously" measured to have the same x-component on one frame then they will "simultaneously" have the same x-component in all other frames in standard configuration with the first.

    Pete
     
  15. Nov 7, 2003 #14

    You forgot to account for error of parallax.
     
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