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Hypothetical; what would a rocket look like to an outside observor if

  1. Sep 11, 2005 #1
    just finishin an essay on special relativity; and iv just realised to of the sources iv used contradict each other. If a rocket is travelling near the speed of light, and it is feeling space contraction, to an outside observor will the rocket appear to be contracting (and being flattened like a ball into a pancake) or will look like its stretching to travel across the distance (ala to it, space is contracting, to outside the rockets stretching)? or is the answer completely different?

  2. jcsd
  3. Sep 11, 2005 #2


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    Staff Emeritus
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    The rocket traveling fast with respect to another observer is not "feeling" anything special (if it is going a constant speed). It's physics is just the same as when it wasn't going so fast (always, always, relative to that outside observer!). The outside observer sees it contracted in the direction of motion but not in the two perpendicular directions. Pancake like.
  4. Sep 11, 2005 #3
    Lets say one guy is in the rocket and the other on Earth. The guy in the rocker will see the Earth flatten and the guy on Earth will se the rocket falatten. This is NOT contradictory. This problem is very similar to whats known as Twins Paradox
  5. Sep 11, 2005 #4
    I thought I had read that due to the way light bounces off the rocket, it'll actually look rotated, rather than simply contracted. :confused: I haven't really read a lot about how it would actually look, though, because if that is what happens it'd just be an optical illusion, and what really happens would of course be length contraction.
  6. Sep 11, 2005 #5


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    In relativity, we must distinguish between what a single observer "sees" (using the light rays that travel from an object to his eyes) and what he "observes" (after correcting for the time that it takes for those rays to travel from the object to him).

    When we talk about length contraction etc., by default we talk about "observing" the object either as described above; or by having several observers with synchronized clocks, and using a common spatial coordinate system, each located at key points, or close enough to them that the light-propagation time is negligible. For example, to measure the length of a moving rod, we could have two observers at rest with respect to each other, position themselves such that the two ends of the rod pass next to them simultaneously, in the inertial reference frame in which the observers are at rest.

    When someone wants to describe the actual visual appearance of relativistically moving objects, he usually says very explicitly that that's what he's doing.
  7. Sep 12, 2005 #6
    This rotation rather than contraction is a result of the aberration of light (the time it takes light to reach us) and it is not quite so simple as a rotation. The rotation result is just when the object is in a direction from the observer which is perpendicular to the direction of motion. The full truth is a nonlinear transformation where things behind you also look contracted and things in front of you also appear stretched out. Try out my simulator at www.relspace.astahost.com[/URL]
    Last edited by a moderator: Apr 21, 2017
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