Timeline for Intuitively, why do attempts to delay hitting a black hole singularity cause you to reach it faster?
Current License: CC BY-SA 4.0
19 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Mar 5 at 2:53 | comment | added | Attila Janos Kovacs | Careful analyses show that very specific conditions must be met for geodesics to end up in the singularity; the vast majority of possible geodesic and other orbits avoid the ring singularity.Why is it so common that all incident bodies are necessarily destroyed in the singularity? In the Schwarzschild spacetime, that's really the case. But the Kerr spacetime, the rotating black hole, is radically different. It is known since the late 1960s. Here is one of the key papers, that revealed how geodesics approach and avoid the singularity. luth.obspm.fr/~luthier/carter/trav/Carter68.pdf | |
| Mar 5 at 2:48 | comment | added | Attila Janos Kovacs | In the case of realistic, rotating black holes, it is not at all true that all incident bodies and light rays necessarily end up in the singularity. That's a common, widespread misrepresentation. Most geodesic orbits do not meet the singularity. Neither timelike geodesics nor lightlike geodesics. Translated into concrete terms, this means that if a test body or spacecraft enters the event horizon, it is not at all necessarily destined to enter the singularities and be destroyed. It depends on the properties of Kerr spacetime (and Kerr-Newman ), on what kind of geodesics they form. | |
| Apr 6, 2019 at 22:29 | history | edited | tparker | CC BY-SA 4.0 |
deleted 633 characters in body
|
| Oct 5, 2018 at 17:13 | comment | added | Colin MacLaurin | I want to tweak one of my comments above, which was an unnecessary technicality but it's already written. It is possible for a timelike observer to have $dr/d\tau=0$ at $r=2M$, but only specifically at the bifurcate horizon. However this is not "at rest", as is clarified by a Penrose diagram, or by the fact there is no timelike Killing vector field there. | |
| Sep 6, 2018 at 0:29 | answer | added | safesphere | timeline score: 2 | |
| Sep 4, 2018 at 21:31 | vote | accept | tparker | ||
| Sep 4, 2018 at 21:16 | comment | added | Colin MacLaurin | To see the horizon is a null hypersurface, consider the hypersurface $r=\textrm{const}$. This has normal or gradient, expressed as a 1-form: $dr$. In components, this is $(0,1,0,0)$ typically, so has norm-squared $g^{rr}=1-2M/r$, evaluating in say Eddington-Finkelstein or Gullstrand-Painleve coordinates. At $r=2M$ this is zero, so the normal is a null vector, i.e. $r=2M$ is a null hypersurface. | |
| Sep 4, 2018 at 21:11 | comment | added | Colin MacLaurin | (Those $t$'s look like the Schwarzschild $t$-coordinate, which is not defined at the horizon.) Ben Crowell is certainly correct that massive objects can't be at rest at the horizon, but it's only a limiting case. There is a slight exception for the analytically extended spacetime, at the "bifurcate horizon" as I mention below, although it may be dubious to term this case as "at rest". As for the question, choose coordinates such as Gullstrand-Painleve which are regular at the horizon, and investigate. | |
| Sep 4, 2018 at 2:52 | vote | accept | tparker | ||
| Sep 4, 2018 at 2:52 | |||||
| Sep 4, 2018 at 2:51 | answer | added | tparker | timeline score: 4 | |
| Sep 3, 2018 at 0:50 | history | edited | tparker | CC BY-SA 4.0 |
added 47 characters in body
|
| Sep 3, 2018 at 0:24 | comment | added | user4552 | But this cannot occur if the free fall begins at rest at the horizon, which I'll assume to be the case. This doesn't actually work as a fix. A massive object can't be at rest at the horizon -- we can only consider this as a limiting case. A trajectory with $dr/dt=0$ at the horizon is lightlike. | |
| Sep 2, 2018 at 20:24 | history | edited | tparker | CC BY-SA 4.0 |
added 456 characters in body
|
| Sep 2, 2018 at 20:15 | history | edited | Qmechanic♦ |
edited tags
|
|
| Sep 1, 2018 at 22:37 | vote | accept | tparker | ||
| Sep 2, 2018 at 18:21 | |||||
| Sep 1, 2018 at 21:01 | history | tweeted | twitter.com/StackPhysics/status/1035996201856974848 | ||
| Sep 1, 2018 at 19:11 | answer | added | Dale | timeline score: 27 | |
| Sep 1, 2018 at 19:00 | answer | added | J. Murray | timeline score: 7 | |
| Sep 1, 2018 at 18:44 | history | asked | tparker | CC BY-SA 4.0 |