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Is light really affected by gravity?

  1. Oct 18, 2007 #1
    It is commonly said that objects such as black holes exert such a powerful gravitational influence, that not even light can escape.

    However, isn't it true that light is NOT affected by gravity in and of itself, but that mass/gravity curves space-time, so the trajectory of light is influenced by the curvature of space-time, and not by the gravity itself?

    And in the case of a black hole, the curvature of space-time is so great, that it literally curves back onto itself, and so once a photon has ventured close enough to become caught in the curvature, it will have no "choice" but to continue to follow the space-time continuum that leads to the center of the black hole?
  2. jcsd
  3. Oct 18, 2007 #2


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    All true except one point.

    "isn't it true that light is NOT affected by gravity in and of itself, but ... by the curvature of space-time, and not by the gravity itself?"

    Gravity IS the curvature of space-time. Like centrifugal force is a fictional force (it's actually inertia viewed from a non-inertial FoR), so too, gravity is a fictional force (it's actually curved space-time viewed from a FoR that only perceives 3 dimensions).
  4. Jan 18, 2011 #3
    Hi..i am 15 years old..and i am wondering if light is really affected by graviyt,when the sun, one of the things that i know that has a great gravitational field is unable to hold it..leting it reach the earth..bt a teacher of mine told me that light is affected in the sense that gravity can be bended by it..i just want to know more about it..
  5. Jan 19, 2011 #4
    i ment light,instead of gravity on my statement..its to be said that light has such a little mass that its difficult to say that it is affected..
  6. Jan 19, 2011 #5

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    Light is measured to be affected. See, for example, the experiments of Pound and Rebka.
  7. Jan 19, 2011 #6
    I believe the gravitational effect on light was first observed in 1919 during a solar eclipse (3 years after Eienstien predicted it) when the position of stars near the edge of the eclipsed disc of the sun were measured and found to move is a curved path aroudn the disc as the sun moved in front of them.


  8. Jan 20, 2011 #7
    the sun does not prevent its own light from escaping it b/c it is not a black hole. you are correct though that the sun is very massive, and therefore has a significant gravitational field that cannot be ignored. so while it isn't nearly massive enough to bend its own light back on itself so that it never escapes in the first place, it is massive enough to bend light somewhat. it is easier to visualize this by considering light that originated elsewhere in the universe than it does to consider the sun's own light. the above poster spoke of this definitive proof in which distant stars were observed near the limb of the sun during a solar eclipse, when in fact they should have still been hidden behind the sun. such a "visual displacement" is too small to be seen with the naked eye, but has been observed with telescopes and instrumentation. this is proof that gravity (or spacetime curvature) is responsible for the bending of light.
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