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

Can you move fast enough towards light so that it has a period of 0?

  1. Nov 20, 2012 #1
    at what speed must i be moving towards a beam of light in order for the wavelength to have a period of 0?

    would it be the speed of light? would it need to be greater than the speed of light? if so, what period would it be at if i were movign at the speed of light?

    i mean, maybe the question is dumb, and the answer is obvious that it would be the speed of light, but with relativity, the answer seldom turns out to be obvious i find.
  2. jcsd
  3. Nov 21, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yes. The Doppler shift factor is [(1-v/c)/(1+v/c)]1/2, which only equals zero for v=c. Since you can't move at v=c, this never happens.
  4. Nov 21, 2012 #3
    ya.. but light does.

    it's almost kind of predictable that would be the case, and yet, an interesting thought.

    and predictably i guess again, as v→-c it goes to infinity.

    here's a related question. how do we know whether or not there's a bunch of stuff in outer space that's moving away, or towards us, by rates of speed that would yield a period, as of yet, undetected by us? or detected by us, and yet, unrecognized.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook