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A Hypothetical Question

  1. Nov 6, 2004 #1
    Imagine, now a situation in which light is used to propel an object forward, just as light is used to propel electrons, imagine that very dense light is used or a hugh intensity laser is used to propel a whole lot of mass forward directly, now since light imaprts its energy to the mass, wouldn't the light lose its energy and hence slow down?

    Now another situation in which light is projected without any of it (atleast most of it) allowed to escape in a straight line and a body is kept in front of it. Now, since light is moving at the velocity of light either of the three things must happen, one either the mass should also move at the speed of light so that light and mass can keep their hands of each other and the light has somewhere to go along with the mass or two the light must flow slower than the its own constant velocity so as to allow the mass not to flow at a velocity slower than the velocity of light or three the light must go somewhere, but where?

    Also consider this, if u stipulate that the light imparts some energy and then dissipates away, i doubt that that would happen, because now the mass has some velocity, but not the velocity of light so the light still coming would accelrate it further, then further and further untill the mass is moving at the velocity of light which is not allowed!

    So where does this lead us?

    (P.S please don't go too hard on me if i am wrong, which i proably am..... ;))
  2. jcsd
  3. Nov 6, 2004 #2


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    When light interacts with massive body it is adsorbed. Then after some delay, electro magnetic energy will be readmitted, perhaps at a different energy, but it will be traveling at c. So no light is not "slowed" down or "dissipated". It is adsorbed and emitted.
  4. Nov 6, 2004 #3


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    Rather than flood my response with all that's wrong in your question, I will pick apart only ONE, and you can go on from there and see why the rest of your understanding about light is faulty.

    Light can lose energy WITHOUT slowing down. This is because energy of a photon is defined as h*nu, where nu is the frequency. So all it needs to do is change its frequency or wavelength, and it's energy is different. Look at Compton scattering. But just by changing its frequency, doesn't mean it slows down, because in vacuum, there is no dispersion of light's velocity with it's wavelenth. All wavelength/frequency travels at the same velocity!

  5. Nov 21, 2004 #4
    thx for clearing that up and sorry for my own delayed responce....
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