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Homework Help: Observed light at light speeds.

  1. Oct 17, 2004 #1
    My first post on this forum, so please be gentle :smile:

    I have a paper I have to write on ANYTHING physics related for my physics class. First, a little info on my class. I go to ITT tech, so it may be considered 12 grade instea of 13 and up. Anyway, for my paper, I decided to create a hypothetical situation and investigate the physics involved. My situation is this. You are in a craft capable of achieving 99.99% of c. If fyour destination was a close by nebula, and you were able to observe the nebula during the trip, how woul it appear.

    I have been to many forums pertaining to physics, and sites that deal with the speed of light. When I go to forums, I get 20 different answers from people who have as much knowledge about physics as me(tiny bit). I have rea books and aske questions till I am blue in the face, but I cant get a straight answer for anything. PLEASE HELP :confused:
  2. jcsd
  3. Oct 17, 2004 #2
    I think tou can answer this question yourself, just check every color that you can see from that close nebula and then use the doppler effect and see if you can get any different colors or even maybe some desappear.Don't forget to use the doppler effect applied to the theory of relativity and if you don't agree with this you can always try to refute the theory of relativity which I don't know what to say.
  4. Oct 17, 2004 #3
    I unerstand about the color shift in the spectrum, but I was wonering more along the lines of the perception of time while observing the light from the nebula. Would it appear to be like watching a movie on fast forward? I ask this because if you were travelling at 99.99% of c, then the relative speed of the light coming towards you would be 199.99% of c. If you are seeing the light this fast, does time appear to speed up when the light is observed?
  5. Oct 17, 2004 #4
    Relativistic velocity is not a simple addition operation: it's actually something a little more complicated that is outlined in detail at http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/veltran.html . However, you need to just understand basically that there's no way you can alter those equations so that you travel faster than the speed of light. Also remember that the doppler shift due to high velocities only affects light waves moving with a directional component parallel to your velocity. This means that light coming at you from the side will not appear shifted. As you focus your vision more and more toward the front of you (the direction your vessel is headed) there will be a larger blue shift and probably if you're going that fast many colors would be shifted enough so that they would not be visible but rather exist in a form of radiation that would kill you. Fun :)

    P.S. welcome to PF

    Edit: I just realized I didn't really answer your question. Your perceived time will be that everything else slows down (time dilation).
    Last edited by a moderator: Oct 17, 2004
  6. Oct 17, 2004 #5
    ouch. So let me see if I have this straight. The speed is such that the light is intensified ito radiation? If there were a way to observe this phenomenon without being fried, you wouldnt observe anything because the light has shifted out of the visible spectrum?

    Sorry, must have been responing while you were editing. :smile:
    Last edited: Oct 17, 2004
  7. Oct 17, 2004 #6
    I think being fried while moving at 0.99C is the least of your problems considering that means that 99.99% of your mass has converted to energy, haha. Yeah you're correct though you wouldn't really be able to observe anything that wasn't within about 1 degree from 90 degrees from your movement.
  8. Oct 17, 2004 #7
    Thanks for all your help guys, I really appreciate it. :biggrin: I have one more question, and I will leave you alone...for now :smile: Is there a formula that represents you viewing this shift of light as it disappears when you reach Vmax?
  9. Oct 17, 2004 #8
    Yeah. You can derive it from the formula for length dilation [tex]L = \frac{L_0}{\gamma}[/tex] where [tex]\gamma = \frac{1}\sqrt{1-\frac{v^2}{c^2} }[/tex]
    Last edited by a moderator: Oct 17, 2004
  10. Oct 17, 2004 #9
    Thankyouthankyouthankyou :smile: You have no iea how long I have been searching for this (3 weeks!). My professor would only tell me to use the net. Im glad I found this site, I can tell its going to be an invaluable resource for me.
  11. Oct 17, 2004 #10
    No problem :) Always good to give back to these boards when I have taken so much. However just one note on the formula above. Just remember that the dilation is only in the direction of the velocity so the less of a component the light has parallel to your velocity the less the squeeze of the waves.
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