Black hole falling time for external observer

Click For Summary
SUMMARY

The discussion centers on the time experienced by an external observer at infinity when an object falls into a Schwarzschild black hole. It is established that an object cannot start from rest at the Schwarzschild surface due to its nature as a null surface. Instead, any inward trajectory will have a nonzero velocity upon crossing this surface. Furthermore, the time experienced by an external observer diverges to infinity as the object approaches the Schwarzschild surface, indicating that the internal time to fall from the horizon to the singularity cannot be directly correlated with external time.

PREREQUISITES
  • Understanding of Schwarzschild black holes
  • Familiarity with null and timelike geodesics
  • Knowledge of general relativity concepts
  • Basic grasp of coordinate systems in spacetime
NEXT STEPS
  • Study the properties of Schwarzschild solutions in general relativity
  • Learn about the implications of null surfaces in black hole physics
  • Explore the concept of time dilation in strong gravitational fields
  • Investigate the relationship between internal and external time in general relativity
USEFUL FOR

Physicists, astrophysicists, and students of general relativity who are interested in the dynamics of black holes and the nature of time in extreme gravitational fields.

keithdow
Messages
28
Reaction score
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?
 
Physics news on Phys.org
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 Schwarzschild 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.
 

Similar threads

Undergrad You can't actually enter a blackhole?
  • · Replies 40 ·
2
Replies
40
Views
4K
High School Falling into a black hole
  • · Replies 43 ·
2
Replies
43
Views
4K
High School How can a black hole absorb matter?
  • · Replies 31 ·
2
Replies
31
Views
2K
High School How do Black Holes Grow? A Far-Away Observer's Perspective
  • · Replies 67 ·
3
Replies
67
Views
6K
Undergrad Falling through the event horizon of an evaporating black hole
  • · Replies 51 ·
2
Replies
51
Views
6K
Undergrad Can light be reflected in a black hole?
  • · Replies 22 ·
Replies
22
Views
2K
High School Black Hole Observation: Outside Observer & Spherical Symmetry
  • · Replies 3 ·
Replies
3
Views
1K
Undergrad Black hole and coordinate time from the perspective of Alice outside
  • · Replies 26 ·
Replies
26
Views
3K
Undergrad Looking closely at the descent into a black hole
  • · Replies 51 ·
2
Replies
51
Views
2K
Undergrad Interpretation of (X,T) coordinates in Kruskal diagram
  • · Replies 34 ·
2
Replies
34
Views
3K