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Length contraction?

  1. Jun 7, 2009 #1
    Ok, I do understand what it is, that things get shorter the faster you go.. But I just want to know why they do?? If anyone could explain to me...
    Someone told me it was just an illusion because our eyes couldn't keep up but I think that person was wrong, so thank you to anyone that can help :)
  2. jcsd
  3. Jun 7, 2009 #2
    No, it's not <illusion>. The short answer is "it's about time" and how do you measure the length of a moving object. The answer is that you must measure both ends at the "same time". That's the key.
    But at the same time, relative to who? Since two events happen at the same time relative to one frame, do not happen at the same time relative to another frame, if there is relative motion between them.
  4. Jun 8, 2009 #3


    Staff: Mentor

    You are correct. Relativistic effects are what remain after accounting for the finite speed of light. So, basically, you correct for any optical illusions and you get relativity.

    Well, science is notoriously bad at answering "why" questions. But essentially all of special relativity can be summarized by the spacetime interval formula (in units where c=1):

    ds² = -dt² + dx² + dy² + dz²

    Where ds is the interval between two events, dt is the time between the two events, and dx dy dz are the x y and z distances between them. Basically, what this says is that time is just another type of distance, and that the geometry of the universe is Minkowski geometry rather than Euclidean geometry. Essentially everything in relativity follows from this concept.
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