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Gravitational Redshift

  1. Jan 21, 2004 #1
    Having only just learnt of the existance of this board I feel that I should make use of it as i spend most of my free time working on seemingly useless theories, might aswell see what others think.

    I have read a little on gravitational redshift but have never really understood the theory. My own theory does tend to break a few of the basic principals which I've been taught (for example light having zero mass). Firstly I model light as a photon which is moving away from a body (eg the sun) at the speed of light. Using newtons third law (F= ma = d(mv)/dt) and the universal law of gravitation I come up with an equation (which I wont quote here as i'm only looking for opinions on my method at the moment) which relates the gravitational force provided by the body on the photon to the mass and speed of the photon. by setting the speed of the photon as the speed of light (which remains constant) an equation for the rate of change of mass is established, using E = mc^2 and E = hf this rate of change of mass becomes a rate of change of frequency (or wavelength). This can be used to calculate the increase (or decrease) in frequency due to gravity. Using data for the sun and the earth the values of redshift are minute (which is to be expected).

    I would appreciate any feedback on this, and I am fully prepared to accept that it is complete rubbish because although I enjoy physics my knowledge isn't too good (i'm only 17, so give me some credit, lol)
  2. jcsd
  3. Jan 21, 2004 #2


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    Staff: Mentor

    Fair enough: 17 is a good age to be thinking about this stuff - old enough to understand it, young enough to question it.

    Have you looked into Einstein's relativity (besides just the equation) yet? You can't combine those equations because the "E" isn't the same kind of "E."
  4. Jan 21, 2004 #3
    I haven't got a very good grasp of the equation but my understanding was that for low speeds the area under the momentum vs speed graph was that of a triangle (1/2 mv^2) but as you near the speed of light the line straightens out (to the area of a rectangle, mv^2). If anyone could explain why this is incorrect I would be greatful.

    P.S. didn't de Broglie combine those 2 equation for something else?
  5. Jan 23, 2004 #4


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    Match with observations?

    Another aspect to consider is 'what are the results from experiments?' In your reading you will find that a) GR makes very precise, concrete, and testable predictions; and b) experiments have validated these predictions to a high level of accuracy (~1 in 10,000).

    If you choose to develop your idea, please find a way to derive unambiguous predictions - e.g. the relationship between the observable redshift, and gravitational potential. You can then use the results of experiments conducted to test GR to test your own ideas.
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