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The doppler effect on light (red and blue shifts)

  1. Mar 25, 2009 #1
    what does the doppler effect mean for an individual photon? for instance in a blue shift do the photons actually have more energy if they were originally a lower frequency?
  2. jcsd
  3. Mar 25, 2009 #2


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    The doppler effect is only true for the observer and it's point of view. Let's say that a red light photon is observed by a standing observer. A different observer that is in relative motion from the first one in the direction of the light source will observe a slightly blueshifted light, a more energetical ray ( orange yellow green etc ) in accordance with it's speed relative to the "red light standing observer". If the second observer were to move along the direction of the light he would see a less energetical ray ( infrared microwave etc). It's not a complicated thing to understand, because it all comes down to the energy that can e extracted from a wave particle system.

    A baseball flying towards you would transfer a certain amount of energy if it hits you. if you move towards it you will receive more energy if you move along it's direction you will receive less.

    Let's say a highly energetic particle is moving towards the earth. From our point of view that particle has a fixed amount of energy and a fixed speed. The particle on the other hand would see a object of huge mass traveling close to the speed of light towards it. There is no point in finding out what energy our earth would have if it was traveling at near light speed, because the particle would never be able to extract more energy than it itself has, out of the system. Photons are energy waves so they will change in accordance with the system of observation, their wavelength that is.
  4. Mar 25, 2009 #3

    Meir Achuz

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    The answer to your question is yes.
  5. Mar 25, 2009 #4
    thanks guys :biggrin:
  6. Mar 25, 2009 #5
    I think that is misleading. The ball transfers more or less energy to you because its speed relative to you at impact is higher or lower. that is no true for light, it always hits you at c, but it has more or less energy because of the doppler shift.
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