This question already has an answer here:

Prior to a black hole reaching sufficient (size ) to stop radiating light (due to excessive gravity ) would the speed of radiation of light slow smoothly down to zero (as the hole draws closer to the critical size)


marked as duplicate by Qmechanic May 16 '18 at 20:02

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 1
    $\begingroup$ have a lool at the answer here physics.stackexchange.com/q/145110 to get a feel of what is happening with the speed of light in general relativity $\endgroup$ – anna v May 16 '18 at 17:48
  • $\begingroup$ I'm interested in the smoothness of the velocity change in the question.... $\endgroup$ – RaSullivan May 17 '18 at 19:40

The local speed of light, as measured in the coordinates of any inertial observer, is always the same. There is no change during the formation of a black hole.

The coordinate velocity of the speed of light could change during formation of a black hole, depending on what coordinates you're using. This is of little interest, because you can always make a coordinate velocity be whatever you like, by choosing the necessary coordinates. This is true regardless of whether there is a black hole or a gravitational field.


Not the answer you're looking for? Browse other questions tagged or ask your own question.