I was asked the same by my friend. I said that gravitational attraction also occurs for high energy particles . My friend said photon is not so very high energy particle which I found on net. He said some of light gains mass after event horizon and gets pulled. I said that the space time is bent due to huge mass of the black hole. So light has to take bigger curved paths so the light does not come back. Why does not light gets exactly come back from black hole ?


1 Answer 1


It sounds like you're asking for an elementary explanation, so ...

A black hole is a region of space where all possible paths a particle can take - the technical term is "geodesics" - are constrained to be within that region. In empty space, geodesics can be whatever you want them to be, but once you're in a black hole, all the geodesics remain within the black hole. There are images out there that might help understand this intuitively, such as this one. Light cannot get out of the black hole because it also moves on a geodesic, and as mentioned above, all the geodesics remain within the black hole.

Some other misconceptions:

  1. Gravitational attraction occurs for all particles, not just high energy particles.
  2. Light is not a "very high energy particle". It's an electromagnetic wave (and a stream of photons).
  3. Light does not have mass. It doesn't "gain mass" after the event horizon.
  • $\begingroup$ For the second misconception I had to say photon. In the question. Though I agree with light is not made of high energy particles. $\endgroup$ Sep 14, 2018 at 1:33
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    $\begingroup$ To be sure, "all possible paths a particle can take" includes non-geodesics. And, in at least the Schwarzschild geometry, all world lines within the horizon, geodesics or other, end on the central singularity. $\endgroup$ Sep 14, 2018 at 3:24

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