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The Nature of length contraction

  1. Oct 23, 2008 #1
    Can someone please clear up the nature of length contraction

    Does the spacial dimension parallel to the motion of a moving metre stick contract (as seen by a stationary observer).


    Is contraction a purelly matter phenomenon whereby space is constant and the actual material of the metre stick contracts.

  2. jcsd
  3. Oct 23, 2008 #2


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    "The actual material of the metre stick" does not contract.
    Your measurement of the length of the stick changes if you measure each end of the stick at the same time.
  4. Oct 23, 2008 #3


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    From the point of view of an observer in motion relative to the meter stick it is space itself that contracts, not just material objects. That is, if you have two material meter sticks, with a meter gap between them (measured in a frame in which the meter sticks are constant) moving past you, you will observe the gap to be smaller than a meter just like the sticks themselves.
  5. Oct 23, 2008 #4
    To confirm HallsofIvy interpretation: a roating disk also "warps" due to space time contraction along the outer rim due to contraction of spacetime as viewed by a stationary observer.."rigid" materials are not quite so rigid as we think!!!! Space itself contracts and drags material along with it...
  6. Oct 23, 2008 #5


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    Only if it's massive, and if it is, it's warping spacetime even before it begins to rotate (but the rotation makes the geometry deviate even more from being flat). It definitely makes sense to consider a massless rotating disc as a thought experiment. If it makes you more comfortable, think of it as having mass m, and decide to let m go to zero later. This is enough to let you ignore the mass. In this thought experiment, there's no spacetime curvature.
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