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Why should radiation lead to loss in mass @ Black holes?

  1. Sep 19, 2011 #1
    According to theory of black hole radiation, black holes are expected to emit a thermal spectrum of radiation, and thereby loss mass, owing to the E=mc2 equation. Well, everything was clear to me till I got to the last point. why should there be loss only in mass?? couldn't the mass be same and velocity change, in order to satisfy the above equation?? Let me know if am going anywhere wrong and what does the "c" represent to in this case? I mean...velocity of what??
  2. jcsd
  3. Sep 19, 2011 #2


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    c is the speed of light - it doesn't change.
  4. Sep 19, 2011 #3
    From the little I understand, the following is a drastic oversimplification, and is somewhat untrue, but it is a good way to visualize the process.

    As you might have heard, at the quantum level, you can have particles pop out of the vacuum (a particle-anti particle pair), and then quickly combine and dissipate. This does not violate the Law of the conservation of Energy because of how fast that process happened, and in the end when they disappeared the total energy was the same as before (also an oversimplification, but take my word). Another thing you need to know is that anti-particles and particles both have positive mass and energy.

    Now imagine one of these particle - anti-particle pairs appeared right on the edge of an event horizon in a black hole, now they broke free, but when they tried to recombine one of the particles was in the event horizon, and one was not. Because of this, they could not recombine and even out the total energy. But because physics says that can't happen, the way you explain the increase of total energy (represented by the particle which didn't fall into the black hole), is that the particle that did fall in had a negative energy, and when that negative energy entered the black hole it reduced the total mass of the black hole.
  5. Sep 20, 2011 #4
    LOL am soo sorry for the question....I was into some thing...m really sorry...such a stupid question !! Don't know what made me think its SOME velocity at that time thankz anyways :)
  6. Sep 20, 2011 #5
    This is not what my doubt was !! but the interesting thing is you have provided an even better point....never heard this before....thx for that :)
  7. Sep 20, 2011 #6
    No problem, I read the title of the topic and assumed what you were asking without reading the body in enough detail, whoops :)
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