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Can gravity red shift?

  1. Sep 6, 2007 #1
    Can gravity be red-shifted? I've never seen this addressed directly, but I don't see how it couldn't be. If gravity isn't affected by the expansion of the universe, why isn't it? If it is red shifted, would this dimunition of gravity be like a repulsive force?
  2. jcsd
  3. Sep 6, 2007 #2


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    I've never seen it addressed either, but it's an interesting thought. The thing to keep in mind is that gravity is a space-time distortion rather than an EM radiation. While the Doppler shift applies to both EM and mechanical vibrations such as sound, I don't know how it would apply to space-time.
    Last edited: Sep 6, 2007
  4. Sep 6, 2007 #3
    It seems to me that if gravity can radiate from complete gravitational collapse (a black hole singularity) while electromagnetism (light) cannot, then gravity does not affect itself as much as it does light. Also, the interaction between curvature and mass (E/c2) indicates that spacetime geometry influences light, but not necessarily gravity.

    I seem to remember the cosmologist Tom van Flandern arguing a related, alternative viewpoint.

    Great question, Bob3141592.
  5. Sep 7, 2007 #4
    The question ‘can gravity be red-shifted?’ sounds incorrect to me…I would assume that gravitational –waves- could be red-shifted, but not gravity itself. This would be due to the fact that gravity waves (should, according to GR) propagate at C, so a recessional velocity would shift the frequency of the gravity waves to a lower frequency.

    The two concepts of ‘red shift’ and ‘gravity’ are related of course - for example, if we shine a spotlight from the Earth to a satellite, the light from the spotlight will be red-shifted by the gravitational field of the Earth: http://en.wikipedia.org/wiki/Gravitational_redshift

    But gravitational mass can be considered analogous to an electrical charge (in the weak field limit anyway), and a static field condition like that doesn’t radiate unless accelerated, so the Doppler effect wouldn’t be applicable to a non-accelerated gravitational mass, imo.

    It sounds like you're looking for a gravitational model to explain 'dark energy.' That seems like an interesting theoretical direction to persue. A few years ago I read a couple of papers dating back to the 40's or 50's which suggested that the gravitational field drops to zero at a finite distance from a mass, and beyond that distance gravity could become slightly negative. I don't know if that model holds up in the light of the far more detailed observations we have today, but the idea keeps rattling around in the back of my head.
    Last edited: Sep 7, 2007
  6. Jun 24, 2008 #5
    The question was: "Can gravity red shift?"
    My answer is: YES!


    My Long and Detailed Answer is:

    -The Pound-Rebka experiment and later experiments confirmed that the frequency of light and sound--and anything possessing frequency--will be red shifted as observed from a higher elevation within a gravitational field; and blue shifted as observed from a lower elevation.

    -The ONLY way that can work, is if the natural rate of time is different for identical "clocks" held at different elevations within a gravitational field.

    -The magnitude of Shift ( dE / E ) -- "E" for "energy or frequency" -- is directly proportional to difference in gravitational potential between two positions: ( d(gh) / c^2 ).

    -For example, if the Red Shift was 50% ( d(gh) = 50% c^2 ), then a 10 MHz (10 million waves per second) signal would be measured to be 5 MHz (5 million waves per second) as observed from the higher elevation.

    -If the observer had a signal multiplier - emitting 2 waves for every 1 wave detected; then for ever 5 million waves detected, the multiplier would send back 10 million waves.

    -If another observer was placed down at the original signal source, then he would receive a return signal of 20 MHz - because for every 10 million waves originally emitted, 20 million waves were returned.

    -That's a Blue Shift of 100% !!! ( d(gh) = 100% c^2 ).

    If the Magnitude in the observed Frequency SHIFT is Directly Proportional to the difference in gravitational potential between two positions, then the calculated difference in potential between two positions is Directly Proportional to the Magnitude in the observed Frequency SHIFT. [if a = b, then b = a]

    -Notice that for the same two positions, the observed Blue Shift is greater in magnitude--as observed from below... than the observed Red Shift--as observed from above.

    Therefore, the calculated difference in gravitational potential is greater in magnitude as observed from below. And is less in magnitude as observed from above.

    -In Other Words: Any particular difference in gravitational potential, is Blue Shifted as calculated from below; And, Red Shifted as calculated from Above.

    View attachment 14490



    The above equation took me about 15 steps (to include all detail) to compose.
    Rule of Thumb in using my equation:
    -If the Observer is Higher, then the Difference in Potential (Delta-Phi) is Positive.
    -If the Observer is Lower, then the Difference in Potential (Delta-Phi) is Negative.

    The Numbers: 0 and 1 in the equation are Not exponents, but rather Superscripts designating the observer.
    Last edited: Jun 24, 2008
  7. Jun 24, 2008 #6

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    Gravity, as opposed to gravitational waves (which do have a frequency) is a static interaction.
  8. Jun 25, 2008 #7
    Gravitational Potential is the product of Gravitational Field (acceleration) and Distance.

    The Gravitational Potential may not have any Frequency, but does have an Amplitude or Magnitude.

    A Static Potential as calculated from a lower elevation will seem to be Greater in Magnitude; and Less in Magnitude as calculated from a higher elevation.

    This Calculation of Magnitude of Potential must be derived from the measurements of Frequency of any given Signal. Therefore, the Magnitude of a Difference in Gravitational Potential is a direct expression of the measured Shift in Frequency.

    This "appearance" of Difference in Gravitational Potential is also Shifted in Amplitude the same way the "appearance" of Signal Frequency is Shifted.

    If a Shift of a Greater Absolute Value was considered as Blue Shift; and if a Shift of a Lesser Absolute Value was considered as Red Shift, then an Increased Magnitude or Amplitude can be considered to be a Blue Shift in a sense; and a Decreased Magnitude or Amplitude as a Red Shift.

    However, if we had Gravitational "Waves", then both the Frequency and Amplitude of the Waves -- as well as any "DC Component" of Gravitation -- will be Shifted all together.


    In case you're confused, let me simplify the concept:

    1) What's really going on with all this Red-Shift Blue-Shift is nothing more than a distortion in the natural-flow-of-time (natural oscillations) of identical clocks placed at two different elevations. BTW, Atoms are Clocks too! - This creates a measurable distortion (Shift) in the Frequency of any given signal.

    2) E = h * v ...where E is Energy, h is Planck's Constant, and v is Frequency. Therefore Energy is Frequency, and Frequency is Energy. - Therefore a measurable distortion (Shift) in the Energy of any given signal.

    3) delta-E = m * g * h ...where delta-E is Difference in Gravitational Potential Energy, m is Mass, g is Gravitational Field (acceleration), and h is difference in elevation.

    Crunch everything together, and you will see that:

    1) If the "appearance" of Frequency is Red-Shifted, then the "appearance" of Energy is also Red-Shifted or Down-Shifted.

    2) If the "appearance" of Energy is Red-Shifted or Down-Shifted, then the "appearance" of a Difference in Energy is also Red-Shifted or Down-Shifted. Therefore, the "appearance" of a Difference in Gravitational Potential Energy can also be Red-Shifted or Down-Shifted.

    3) If the "appearance" of a Difference in Gravitational Potential Energy is Red-Shifted or Down-Shifted, assuming that mass is relatively constant, then the "appearance" of a Difference in Gravitational Potential (g*h) will also be Red-Shifted or Down-Shifted.

    If Gravitational Potential can "appear" to be Red-Shifted, then so can a Gravitational Field (acceleration).

    If the Gravitational Potential or Field of any given Body of Mass was Altered or Shifted in "appearance" in any way, then the over-all Gravitational Flux produced by the Body of Mass is also Altered or Shifted in "appearance". -- Every thing gravitational about it becomes altered or shifted in the same manner.

    Finally, the Flux, the Field, the Potential, the Waves -- Everything Gravitational -- therefore:
    Gravity, Period!!! ...can be Red-Shifted
    [as expressed by the Frequency-To-Energy-To-Potential-Converted Frequency Red-Shift]
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