Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Black hole falling time for external observer

  1. Sep 17, 2011 #1
    It is well know that it takes pi*m time to go from rest at the surface of a Schwarzschild black to the singularity. How much time does an external observer at infinity experience then in that time? How do I show it?
  2. jcsd
  3. Sep 18, 2011 #2


    User Avatar
    Science Advisor

    Hm, well in the first place you cannot "start from rest" from the Schwarzschild surface, since it is a null surface. Only an outward going null geodesic can be at rest there, and any timelike curve will cross it with a nonzero inward velocity.

    The external time has already gone to plus infinity when you reach the Schwarschild surface. The inside is a different coordinate patch, in which the radial coordinate r has become the timelike coordinate. So whatever "time" it takes to fall from the horizon to the singularity, there is no way to correspond it to external time.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook