B Inside a Black Hole: Rest Frame & Singularity

  • Thread starter Thread starter tionis
  • Start date Start date
  • Tags Tags
    Frame Hole Rest
Click For Summary
Crossing the event horizon of a black hole does not necessitate a change in frame of reference, as one can still consider themselves at rest while in freefall. The singularity is not a location but rather a moment in time, making it inappropriate to say it approaches you. Once inside the horizon, the singularity becomes an inevitable future event, similar to how time progresses. The properties associated with the singularity, such as spaghettification, are attributes of the spacetime geometry rather than the singularity itself. Understanding these concepts requires recognizing the distinction between time and spatial characteristics in black hole physics.
tionis
Gold Member
Messages
459
Reaction score
67
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?
 
Physics news on Phys.org
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.
 
  • Like
Likes tionis
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.
 
  • Like
Likes tionis, PeterDonis and Dale
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
 
  • Like
Likes tionis
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.)
 
  • Like
Likes tionis
In Birkhoff’s theorem, doesn’t assuming we can use r (defined as circumference divided by ## 2 \pi ## for any given sphere) as a coordinate across the spacetime implicitly assume that the spheres must always be getting bigger in some specific direction? Is there a version of the proof that doesn’t have this limitation? I’m thinking about if we made a similar move on 2-dimensional manifolds that ought to exhibit infinite order rotational symmetry. A cylinder would clearly fit, but if we...

Similar threads

  • · Replies 22 ·
Replies
22
Views
1K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 73 ·
3
Replies
73
Views
1K
  • · Replies 57 ·
2
Replies
57
Views
4K
  • · Replies 4 ·
Replies
4
Views
1K
Replies
22
Views
1K
  • · Replies 40 ·
2
Replies
40
Views
3K
Replies
29
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 22 ·
Replies
22
Views
3K