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Motion of Spectral signature

  1. Jun 18, 2008 #1
    I have a cube with a spectrometer at the center of each face. In the center of the cube is an exited glob of hydrogen. The spectral lines (signature) of the hydrogen are registered at the same frequency on all six spectrometers.
    I now set the cube in motion.
    Does the signature move up or down the spectrum on any of the spectrometers?
     
  2. jcsd
  3. Jun 18, 2008 #2

    Dale

    Staff: Mentor

    During acceleration, yes.

    During inertial motion, no.
     
  4. Jun 18, 2008 #3
    What if the cube is travelling at a constant [non-zero] velocity relative to the "glob"?

    Regards,

    Bill
     
  5. Jun 19, 2008 #4

    Dale

    Staff: Mentor

    Then, yes, but that is not how I interpreted the OP.
     
  6. Jun 19, 2008 #5
    The cube is at rest with respect to the source (hydrogen) at the center.

    So the frequency of light detected will be the same for all spectrometers?
    And an identical construct in any other inertial frame will show the same results?
     
  7. Jun 19, 2008 #6

    DrGreg

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    Science Advisor
    Gold Member

    DaleSpam is correct. For inertial motion, nothing is moving relative to anything else, so all 6 spectrometers record the same frequency.

    During acceleration, analyse this from the inertial frame in which the cube was at rest when some photons were emitted from the glob in all directions. By the time these photons reach the sides of the cube, the cube is no longer stationary in that frame. So the doppler shift formula applies. Blue shift for the rear face (moving towards the emission point). Red shift for the front face. And transverse doppler for the other four sides.
     
  8. Jun 19, 2008 #7

    Dale

    Staff: Mentor

    Yes.
     
  9. Jun 19, 2008 #8
    Then constant linear motion has no measurable effect on the properties of light?
    This seems to indicate light (EM) is nothing more than a propagating modulation of spacetime.
    A modulation that is held constant between all inertial frames via time dilation and length contraction.
     
  10. Jun 20, 2008 #9

    Dale

    Staff: Mentor

    There is the relativistic Doppler shift which is measurable. Your set up seemed expressly designed to avoid that.

    I don't know what you mean by that, but if you mean something different than Maxwell's equations or a QM description of light then it probably belongs on a different forum.
     
  11. Jun 20, 2008 #10
    Yep. That is the point of Special Relativity. Moving with constant motion results in no measurable effects that any different to be stationary.

    That is one way of looking at it, but it is not the view of Special Relativity. It is the view of Lorentz Ether theory which produces identical results to Special Relativity but unfortunately it makes the ether undectable. If the ether is undetectable then "there is no need of it" as Einstein said.
     
  12. Jun 20, 2008 #11
    I mean it in the sense of Maxwell's equations, QFT and GR. All of which express dynamics of space-time in their own "separate" way.
    Is there a forum here that permits one to question the mainstream metaphysical modeling of GR, QT and the Standard Model?

    kev, there is another way. The ether is not it.
    A very careful (first principled) study of time in all of physics makes it clear. I cannot get into it here as mentioned above.
    But if you're interested, consider this: there are only three dimensions in physics (in the universe) - space, time and mass.
    The first continuum was modeled by Einstein as space-time.
    The next includes mass in "exactly" the same relativistic structure.
     
  13. Jun 20, 2008 #12

    zonde

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    Aether is undetectable and "there is no need of it" only if Special Relativity have unlimited domain of applicability and that is clearly not the case as for any theory of physics.
    And as that is not the case aether could be detectable.
     
  14. Jun 20, 2008 #13
    Well, it can be shown that the vacuum of space is not empty. Put a rocket in an otherwise empty universe and start to accelerate hard. Accelerate relative to what? Don't worry about that. Just look behind you and notice all the radiation that is popping out of the vacuum. Clearly the vacuum of space is not empty.
     
  15. Jun 20, 2008 #14

    zonde

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    Right, probably detectable is not the right word because it all the same is only concept of physics. Probably better would be to say that it could be competitive approach to use less abstract concepts with more realistic descriptions.
     
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