Inside a Black Hole: Rest Frame & Singularity

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Discussion Overview

The discussion revolves around the nature of crossing the event horizon of a black hole, particularly whether one can consider themselves at rest and if the singularity can be thought of as approaching them. Participants explore the implications of being inside the event horizon and the characteristics of the singularity in relation to spacetime geometry.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that crossing the event horizon does not necessitate a change in frame of reference, suggesting that one can still consider themselves to be moving.
  • Others argue that once inside the horizon, the singularity cannot be thought of as approaching, as it is a future event rather than a spatial location.
  • One participant emphasizes that the singularity is a moment in time, questioning how it can possess spatial attributes.
  • Another participant clarifies that the properties associated with the singularity are related to the spacetime geometry rather than the singularity itself being a moment in time.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the singularity and its relationship to spacetime, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

There are limitations in the discussion regarding the definitions of time and space in the context of black holes, as well as the implications of spacetime geometry on the properties of the singularity.

tionis
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Once I cross the event horizon of a BH, is it valid to say that I'm at rest and the singularity comes up to meet me?
 
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The fact of having crossed the event horizon makes no difference other than that from there you can only go deeper into the black hole.
At some time in the fairly near future you will inevitably encounter whatever the singularity is.
You can consider your self to be moving (which makes sense because you considered yourself to be moving before you got to the horizon.),
or you can consider that center of the black hole is moving towards you, which is equally valid.
However there is no good reason why crossing the horizon implies a need to switch to a different frame of reference.
 
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tionis said:
Once I cross the event horizon of a BH, is it valid to say that I'm at rest and the singularity comes up to meet me?
No.
If you are in freefall, then it is always valid to consider yourself at rest and this works both inside and outside the horizon. However, once inside the horizon there is no way of thinking about the singularity approaching you, or looking towards it or away from it, or being a greater or lesser distance from it. The singularity is in your future, the same way that on Sunday night Monday morning is in your future.
 
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tionis said:
Once I cross the event horizon of a BH, is it valid to say that I'm at rest and the singularity comes up to meet me?
The singularity is a moment in time, not a location in space. It would be a little strange to say "Friday comes up to meet me".

Edit: what Nugatory said
 
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It is a moment in time, true, but we assign this moment in time shapes, like a ring, and spaghettification powers etc. I still don't understand how a moment in time can have all those attributes.
 
tionis said:
we assign this moment in time shapes, like a ring, and spaghettification powers etc.

Those properties aren't assigned to a moment in time. They are assigned to the spacetime geometry. (Actually, in Kerr spacetime, the ring singularity is timelike, not spacelike, so it isn't a moment of time anyway, it can be seen as a ring in space. But the ring by itself still doesn't have all the properties you are talking about; they are still properties of the spacetime geometry.)
 
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