Return to Answer

OP is apparently looking for 1D structures:

1. On one hand, a 3+1D Kerr black hole has a 1D ring singularity.

2. On the other hand, an event horizon has always codimension 1 in spacetime. Subtracting 1 time-direction, we would speak of the event-horizon in 3+1D as an "area". In 2+1D that becomes a "length".

OP is apparently looking for 1D structures:

1. On one hand, a 3+1D Kerr black hole has a 1D ring singularity.

2. On the other hand, an event horizon has always codimension 1 in spacetime. In 3+1D we speak of the event-horizon as a 2D area, i.e. we are implicitly suppressing 1 dimension. According to that terminology the event-horizon becomes a 1D length in 2+1D.

OP is apparently looking for 1D structures:

1. On one hand, a 3+1D Kerr black hole has a 1D ring singularity.

2. On the other hand, an event horizon has always codimension 1 in space, so in 2 spatial dimensions, it is 1-dimensional.

OP is apparently looking for 1D structures:

1. On one hand, a 3+1D Kerr black hole has a 1D ring singularity.

2. On the other hand, an event horizon has always codimension 1 in spacetime. Subtracting 1 time-direction, we would speak of the event-horizon in 3+1D as an "area". In 2+1D that becomes a "length".

OP is apparently looking for 1D structures:

1. On one hand, a 3+1D Kerr black hole has a 1D ring singularity.

2. On the other hand, an event horizon has always codimension 2, so in 2+1D it is 1-dimensional.

OP is apparently looking for 1D structures:

1. On one hand, a 3+1D Kerr black hole has a 1D ring singularity.

2. On the other hand, an event horizon has always codimension 1 in space, so in 2 spatial dimensions, it is 1-dimensional.