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

Localization by the doppler effect

  1. Nov 22, 2006 #1


    User Avatar
    Science Advisor

    I have heard that if one is hypothetically placed in a box completely solid, whith a shield that leaves everything that would have entered a normal box, like light, or neutrinos, out of it. If you sent that in a certain speed, with nothing affecting it, just traversing through space, the person inside it could not in any way find out where he is, or what speed he is going in.
    Or something similiarly, i don't explain it that good.

    Anyway, my question is, that you COULD find out what your speed is, if you originally know what for example what frquenzies glowing hydrogen gas sent out. Then you measure the frequenzie of it in all directions. Let's say (i don't know anything about it, just as an example) normal hydrogen gas sent out light in frequenzies of 5, then the doppler effect would have made the frequenzy higher the way the box is moving. if the box is moving half the speed of light, the frequenzy would be doubled, since the light waves are compressed. on the opposite side the light frequenzy would be halfed.

    so theoretically wouldn't they say something about what speed, or at least what direction they are moving in? Or have i misunderstood the doppler effect?
  2. jcsd
  3. Nov 22, 2006 #2


    User Avatar
    Science Advisor

    The H gas frequencies as seen by the receiver moving with the source would not see any Doppler shift. Doppler shift is seen by a receiver moving relative to the source.
  4. Nov 22, 2006 #3
    doppler and velocity measurement

    You can measure other's velocity using radar echo. Experiments confined in a given inertial reference frame do not offer infoirmation about its velocity.
  5. Nov 24, 2006 #4
    The Doppler effect would apply only to light coming in from outside the box. -- But you defined your box as being shielded form allowing entry of anything outside, not even the MBR.

    To ask your question in a different way, for those not in such a box: Could the MBR (Microwave Background Radiation) define a "Preferred Reference Frame" to base measurements from as the classical Newton would have wanted?
    My expectation is NO; due to 'Hubble Expansion'
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook