# Tag Info

Accepted

### Why does rotation make black holes smaller?

First, let us note that “horizon radius” (at least when talking about black holes without spherical symmetry) is a coordinate dependent term, so it is better to use coordinate independent measure of ...
• 15k

### Why does rotation make black holes smaller?

isaacg asked: "Why does faster rotation shrink the outer event horizon?" It doesn't. In terms of the irreducible mass $\rm \mathcal{M}$ and the cartesian radius $\rm R=\sqrt{x^2+y^2+z^2}$ ...
• 10.4k

### How can the distance to the event horizon, as measured by a tape attached to a falling mass, be reconciled with the mass passing through it?

The answer you linked is about dangling a measuring tape above a black hole, not letting it fall freely. The end of the tape never crosses the event horizon, and its speed, relative to static ...
• 24.2k
Accepted

### Schwarzschild line element in Eddington-Finkelstein coordinates

What your are encountering here is a core feature of general relativity: time is inherently, and fundamentally a local quantity. While each observer will have an unambiguously defined local proper ...
• 10k
Accepted

### No hair theorem and Klein-Gordon equation

… what am I missing? You are missing the meaning of (various) no-hair theorems. Those theorems are talking about equilibrium configurations corresponding to end points of gravitational collapse and ...
• 15k
Accepted

### Does the current size of the cosmological sound horizon play a relevant role in the universe?

The sound horizon is the same today as at recombination. Before the time of recombination, the universe was full of free protons and electrons. Due to the electric charges of these particles, ...
• 2,648