Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relativity 101: Near speed of light travel

  1. Sep 14, 2012 #1
    I thought I read that if you were in a ship near the speed of light, all the stars would appear to be in front of you. The closer to c you are, the more everything will be collapsed to a cone facing forward. Is that right?

    Thinking about it a little from the non-moving frame, it seems like there would be fewer visible stars from forward since photons from stars would have to "lead" the ship by so much that they would always end up coming in nearly from behind. I'm not sure how to think about this in the ship frame though. I think the universe would appear compressed in the direction of flight, but I'm not sure what to do with that.
  2. jcsd
  3. Sep 14, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

  4. Sep 14, 2012 #3
    Here's a construct that might be helpful.

    Imagine a pinhole camera facing straight ahead.

    A photon enters at a 45 deg. angle. As it travels to the film plane, the camera is moving forward so it actually intersects the film closer to the center than it would if the camera was not moving. So it appears in the image as if it was coming from an angle closer to straight ahead.
    The same effect takes place with photons from positions behind , except the effect is reversed. The motion of the camera while the photon moves from the aperture to the film means the point it hits will be farther from the center than the actual angle so it will appear to be coming from a position more towards the front of the system.
    This will of course also take place within an eye ;-)
    Last edited: Sep 14, 2012
  5. Sep 15, 2012 #4


    User Avatar
    Science Advisor
    Gold Member

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook