1. Limited time only! Sign up for a free 30min personal 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!

Angular Velocity of a source of light

  1. Apr 8, 2014 #1
    This is not schoolwork.
    Imagine that light did not have a constant speed, but behaved in the manner expected from experience. Namely, if the source of the light is rushing toward you, the light will approach you faster; if the source is rushing away from you, the light will approach you slower. This is incorrect, of course, but it's worth investigating the consequences of a non-constant speed of light because the failure to observe those consequences is evidence that the speed of light is constant. With that backdrop, consider a binary star system situated a very large distance L from Earth. Let the angular velocity of the smaller star be ω, as it orbits the larger star in a circle of radius r.
    What value of ω=v/r will result in the light emitted when the smaller star is traveling directly away from Earth reaching us at the same moment as the light emitted later, when the smaller star's orbit has it moving directly toward earth? (choose one)
    a) ω=(c/r)*sqrt((πr)/(2L+2πr))
    b) ω=(c/r)*((πr)/(2L+πr))
    c) ω=(c/r)*sqrt((πr)/(2L+πr))

    I think that the time it takes for the light emitted from the smaller star when it is traveling directly away from Earth has to be equal to the time it takes for the light emitted later plus the time it takes to complete half an orbit. So:
    t1 = t2 + t3
    L/(c-v) = L/(c+v) + pi*r/v

    How can I get the answer from this? Thank you for your help.
  2. jcsd
  3. Apr 8, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    "from experience" the speed of light in invariant - but I get what you mean:

    ... you mean, what if light obeyed Galilean relativity.

    See "Michealson-Morely experiment" for an example of this sort of calculation.

    The time is also the distance to the Earth divided by the velocity of the light.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook