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I'm travelling in a spaceship at 0.95c. Will things outside appear to be stretched?

  1. Nov 30, 2008 #1
    An outside observer will perceive my spaceship as being shorter, but what will i see of my outside surroundings? Will they be longer?
     
  2. jcsd
  3. Nov 30, 2008 #2
    Re: I'm travelling in a spaceship at 0.95c. Will things outside appear to be stretche

    Depends what you mean by perceive. He certainly will not actually see it shorter. Only when he draws a choordinate chart he will conclude it is shorter.

    Roger Penrose and James Terrell are the folks who thought a bit deeper about length contraction than others who just parrot the dogma that it is directly observable. :smile:
     
  4. Nov 30, 2008 #3

    JesseM

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    Re: I'm travelling in a spaceship at 0.95c. Will things outside appear to be stretche

    In relativity there's a difference between what you see visually and what you measure in your own rest frame. What you see is affected by the fact that light from different events (or different parts of a single object) takes different amounts of time to reach you; the coordinates you assign to events are based on compensating for such delays, the usual method being for each observer to use a network of rulers and synchronized clocks at rest relative to himself, and defining the coordinates of events purely in terms of local measurements on this system (for example, if I see an explosion happen next to the 12-meter mark on my x-axis ruler, and the clock sitting on that mark reads 5 seconds at the moment the explosion happens next to it, then I assign that event coordinates x=12 meters, t=5 seconds in my frame).

    When people talk about length contraction, they are talking about what's measured in your frame, not what you see visually (the visual size is influenced by something called the Penrose-Terrell effect which MeJennifer mentioned). But as far as how length contracts in different frames, the effect is completely symmetrical--if you are moving at 0.95c relative to an observer on a space station, then in the station's frame your ship's length will appear shrunk, but in your frame the ship's length will be normal and the length the station will be shrunk, by exactly the same factor (keep in mind that in your frame, your ship is at rest while it is the station that is moving at 0.95c away from you, and in relativity there is no objective physical truth about how fast any object is 'really' moving, all speeds are relative to your frame of reference).
     
  5. Nov 30, 2008 #4

    Hurkyl

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    Re: I'm travelling in a spaceship at 0.95c. Will things outside appear to be stretche

    The visual effects are symmetric. The 'distortion' seen by the outside observer as he looks at your spaceship will be the same as the 'distortion' seen by you as you look outside.

    As to precisely what the distortion is, is complicated; I haven't worked it out myself. There will surely be some shortening involved, but I've heard that, visually, the distortion looks more like a rotation.
     
  6. Nov 30, 2008 #5
    Re: I'm travelling in a spaceship at 0.95c. Will things outside appear to be stretche

    Wikipedia has a decent description, in part :

    http://en.wikipedia.org/wiki/Terrell_rotation

    I had forgotton reading about this for the first time about a month or so ago and never got to post the obvious question: Is there an analogous effect for time dilation? Why?
     
  7. Nov 30, 2008 #6

    JesseM

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    Re: I'm travelling in a spaceship at 0.95c. Will things outside appear to be stretche

    I'd say the relativistic Doppler effect is the closest analogy; because of this effect, a clock moving towards you will visually appear sped up rather than slowed down, and a clock moving away from you will visually appear slowed down by a factor greater than the time dilation factor.
     
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