Question about black holes and gravity

Click For Summary

Discussion Overview

The discussion revolves around the nature of black holes, specifically addressing the relationship between the event horizon, the mass of black holes, and how surrounding objects can orbit them as if they possess knowledge of this mass. The inquiry touches on concepts from general relativity and the implications of the "no hair theorem."

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions how stars orbiting a black hole can move correctly without knowing the mass of the black hole, which is thought to be hidden behind the event horizon.
  • Another participant introduces the "no hair theorem," suggesting that black holes are characterized by mass, charge, and angular momentum, although the theorem's validity may be uncertain.
  • A different participant argues that observers present before the formation of a black hole would know the mass that fell into it, implying that the mass is not a secret, and that the curvature of spacetime reflects this mass.
  • It is noted that while mass is conserved, information cannot be sent from inside the event horizon to the outside, which complicates the understanding of how mass influences external orbits.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the implications of the event horizon and the nature of black holes, with no consensus reached on the underlying questions posed.

Contextual Notes

The discussion includes assumptions about the "no hair theorem" and the nature of information conservation, which remain unresolved and depend on interpretations of general relativity.

pitoko
Messages
2
Reaction score
0
The black hole is surrounded by an event horizon. No matter which fell under the horizon will never escape, even in the form of information (in the classical theory of relativity). So why is the star orbiting a black hole moving at the correct speed and trajectory, as if they knew the mass of a black hole? Knowledge of the mass of the black hole, depends on the amount of matter inside the event horizon, and this is a secret. How nature does it do?
 
Physics news on Phys.org
Hi pitoko, welcome to PF.

Black holes have charge, angular momentum, and mass. Look up "no hair theorem". It is not clear that the "no hair theorem" is always correct and so black holes may have some more hair, but they certainly have at a minimum the charge, angular momentum, and mass.
 
Any observer who was around before the black hole formed know how much mass went in, so the mass can't be secret. The curvature of spacetime surrounding the black hole is a frozen record of how much mass went in. Note that a person inside the event horizon can't use the mass of the black hole to send information to the outside; since the mass is conserved, it's not possible to modulate the signal.
 
Thank you for your answers DaleSpam and bcrowell, you answered me exactly what I wanted to know ;)
 

Similar threads

  • · Replies 22 ·
Replies
22
Views
1K
  • · Replies 40 ·
2
Replies
40
Views
4K
  • · Replies 62 ·
3
Replies
62
Views
8K
  • · Replies 73 ·
3
Replies
73
Views
3K
  • · Replies 51 ·
2
Replies
51
Views
5K
  • · Replies 20 ·
Replies
20
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 22 ·
Replies
22
Views
4K
  • · Replies 32 ·
2
Replies
32
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K