Time Dilation and Length Contraction near the Event Horizon of a BH

Click For Summary

Discussion Overview

The discussion revolves around the effects of time dilation and length contraction experienced by observers near the event horizon of a black hole. Participants explore the implications of these relativistic effects for both free-falling observers and those hovering at a distance, considering both theoretical and experimental perspectives.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that a clock falling towards a black hole would appear to be slowed down, potentially appearing frozen in time.
  • Questions arise regarding whether a free-falling observer experiences length contraction and how this might affect their perception of the universe.
  • Some participants argue that time dilation and length contraction are not experienced by the observer themselves but are measured relative to other objects.
  • There is interest in how gravitational effects might lead to length contraction, with some participants expressing skepticism about claims made without thought experiments.
  • A proposal for an experiment is suggested to observe length contraction from the perspective of distant observers, involving rulers placed radially away from a gravitating body.
  • Concerns are raised about the challenges of measuring lengths in a gravitational field and how this might differ from measurements in flat spacetime.

Areas of Agreement / Disagreement

Participants express a range of views on the experiences of free-falling versus stationary observers, with no consensus on how length contraction manifests in the context of black holes. The discussion remains unresolved regarding the implications of these relativistic effects.

Contextual Notes

Participants note the complexity of measuring relativistic effects in gravitational fields and the potential for different interpretations based on the observer's frame of reference. There are also references to the limitations of existing thought experiments and the need for further analysis.

  • #31
zonde said:
What is mainstream terminology if one is describing such transformation?
I don't think there is any. That is the problem. Gravitational time dilation is well defined for static spacetimes, but not gravitational length contraction. Both you and PAllen have suggested reasonable definitions, but since neither is standard it would be good for the OP to weigh in and describe what they are referring to in their question.

zonde said:
Hmm, where did you get this?
Sorry about misunderstanding. I was (overly) focusing on 1 simply because that was the one you mentioned in association with length contraction.
 
Last edited:
Physics news on Phys.org
  • #32
DaleSpam said:
I don't think there is any. That is the problem. Gravitational time dilation is well defined for static spacetimes, but not gravitational length contraction.
When two observers are next to each other we can speak about pure SR effects in order to compare what they see. SR holds locally and there is no need to speak about any GR effects.
 
  • #33
zonde said:
When two observers are next to each other we can speak about pure SR effects in order to compare what they see. SR holds locally and there is no need to speak about any GR effects.
Right, but the OP is interested in GR effects.
 
  • #34
DaleSpam said:
Right, but the OP is interested in GR effects.
Well, right. But posts #6 and #8 seemed to say that it might be good to start with differences between what is seen by hovering observer and what is seen by falling observer.

At least we can assume that one of them is more "natural" observer and then we can find out what the other one is seeing. And yes, I was explaining it from perspective that more "natural" observer is hovering observer as we generally are that type of observers.
 

Similar threads

  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 45 ·
2
Replies
45
Views
6K
  • · Replies 63 ·
3
Replies
63
Views
6K
  • · Replies 64 ·
3
Replies
64
Views
6K
Replies
4
Views
1K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 51 ·
2
Replies
51
Views
5K
  • · Replies 34 ·
2
Replies
34
Views
3K
  • · Replies 16 ·
Replies
16
Views
5K
  • · Replies 13 ·
Replies
13
Views
2K