1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relativity question

  1. Jan 29, 2009 #1
    Suppose we have a two giant ideal springs very far apart from each other such that each spring can be used to launch a spaceship X to relativistic speeds. So a spaceship is launched using spring A to relativistic speeds, it reaches spring B which it compresses and is thus relaunched when spring B relaxes and the cycle thus continues.

    Now say there is a person inside spaceship X who shines a flashlight out of a window of the spaceship onto say a large number of solar panels lined up along the route from spring A to B. Whenever the spaceship accelerates (decelerates) he switches off the flashlight.

    Now from the perspective of the solar panels, since the spaceship X is traveling at relativistic speeds, say 1 minute of the shining of the flashlight relative to the spaceship corresponds to 10 years relative to the solar panels.
    How is a 1 minute burn of a flashlight able to generate enough energy to generate electricity for 10 years? Is it because the chemical bond strengths change at relativistic speeds?
     
  2. jcsd
  3. Jan 30, 2009 #2

    Mentz114

    User Avatar
    Gold Member

    I think everything balances up without resort to the proper times of the two observers. The energy transferred from the light to the panels is proportional to (intensity x time). Measured in each frame the energy will be the same if the transverse Doppler effect is taken into account.

    I haven't got time now to do the calculation.

    [edit]
    Naively ( light frame quantitities are primed) L is the length of the panel, t is clock time and v is the velocity of the light emitter relative to the panels.

    in the panel frame : t = L/v, I=I'*gamma
    in the light frame : t'=gamma*L/v, I'=I'

    (t*I)=(t'*I')

    Looks a bit too easy, but given that light energy is proportional to frequency, it could be right.
     
    Last edited: Jan 30, 2009
  4. Jan 31, 2009 #3
    sid: interesting question!! Good perspective!!

    Yet I did not get the spring reasoning....why not just a space ship passing by at relatvistic speed?? Does the spring continuing cycle have any effect...I don't see any.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Relativity question
  1. Relativity question. (Replies: 7)

  2. Questions on Relativity (Replies: 56)

  3. Relativity questions (Replies: 12)

  4. Relativity question (Replies: 9)

Loading...