Timeline for Is it possible to fall into a black hole, then come back out?
Current License: CC BY-SA 3.0
19 events
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| Dec 10, 2023 at 3:30 | comment | added | NinjaDarth | The question of what, if anything, passes for "time reversal" in a black hole arose here in Wikczek's lectures at Shanhai U. in 2004. Curiously he balked at it (he wasn't on top of his game). The answer is that (1) time reversal is a property of the framework or theory, not the individual solutions in it (e.g. the Big Bang). (2) rather, it's the solution set that has the symmetry. (3) so the question is: what's the time reversal of a black hole. Look under White Hole, Wikipedia for a discussion. | |
| Dec 10, 2023 at 0:25 | answer | added | Attila Janos Kovacs | timeline score: 0 | |
| Jan 5, 2023 at 6:10 | comment | added | Kevin Kostlan | "Is it possible to un-smash a watermelon"? Just because you can't see the carnage of objects destroyed inside black holes doesn't mean they aren't gigantic sources of entropy. Coal goes in, ash comes out. Eggs go in, omelettes come out. Matter falls in, Hawking radio-waves (very slowly) come back out. | |
| Jan 18, 2018 at 10:00 | vote | accept | knzhou | ||
| Jan 14, 2018 at 5:13 | answer | added | The_Sympathizer | timeline score: 2 | |
| Jan 14, 2018 at 4:24 | answer | added | Bob Bee | timeline score: 3 | |
| Jan 13, 2018 at 7:38 | comment | added | knzhou | @Rococo No, my question is entirely classical, so I think it should be simpler to answer. There are none of the complications of Hawking radiation! | |
| Jan 13, 2018 at 6:50 | comment | added | Rococo | Well- this is really just a variant of the black hole information paradox, right? You want to know whether the black hole is a unitary operator, which therefore has an inverse. So does everyone else! | |
| Jan 12, 2018 at 19:30 | comment | added | Alfred Centauri | See this screenshot (via Google Books) from pg. 838 of "Gravitation": "Schwarzschild geometry is dynamic in regions $r \lt 2M$" | |
| Jan 12, 2018 at 19:21 | comment | added | Alfred Centauri | Also, I think it is the case that the geodesics that cross the black hole horizon in the future crossed the white hole horizon in the past. | |
| Jan 12, 2018 at 19:21 | comment | added | knzhou | @AlfredCentauri Can you explain a bit more what that means? | |
| Jan 12, 2018 at 19:19 | comment | added | Alfred Centauri | "Moreover, the standard Schwarzschild black hole is invariant under time reversal because it's a static spacetime." - the exterior geometry is static but within the horizon, the geometry is dynamic. | |
| Jan 12, 2018 at 18:46 | history | edited | Qmechanic♦ |
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| Jan 12, 2018 at 18:09 | answer | added | John Rennie | timeline score: 4 | |
| Jan 12, 2018 at 18:04 | history | edited | knzhou | CC BY-SA 3.0 |
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| Jan 12, 2018 at 18:00 | answer | added | Acccumulation | timeline score: 0 | |
| Jan 12, 2018 at 17:45 | comment | added | safesphere | Didn't you answer your own question by describing the Schwarzschild spacetime? In the frame of a remote observer, objects never cross the event horizon. Thus, if an object's speed is reversed before the horizon, the object would return at any time up to infinity. So the time reversal works up to the point where time stops at the horizon. | |
| Jan 12, 2018 at 17:43 | history | edited | knzhou | CC BY-SA 3.0 |
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| Jan 12, 2018 at 17:26 | history | asked | knzhou | CC BY-SA 3.0 |
