Timeline for Black hole collision and the event horizon
Current License: CC BY-SA 3.0
19 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jan 17, 2012 at 2:55 | comment | added | Ron Maimon | @ThePopMachine: Physics is objective. If the same holds on the Christianity stackexchange, then I would have hope for the world. I didn't change my mind about anything, and it seems that neither did you, we just found out we were talking about the same thing from slightly different perspective, which often happens. If somebody actually changes their mind, then that's a reason to cheer, but don't hold your breath. People are usually far too stupid to do that. | |
| Jan 16, 2012 at 18:31 | comment | added | ThePopMachine | @RonMaimon: Look at that. We both started telling each other we don't know what we're talking about and in the end we agree. Maybe there is hope for the world. :) | |
| Jan 16, 2012 at 18:25 | comment | added | Ron Maimon | @ThePopMachine: Yes, this is accurate. The coarse graining is physical, and within string theory or any other quantum theory of gravity (or even in numerical relativity) the merger will complete in a finite time. But the dynamics are complicated, and hard to visualize. It will take a real simulation to answer this question fully. | |
| Jan 16, 2012 at 18:16 | comment | added | ThePopMachine | ... that nothing can escape away from the axis anyways. So there is a point where they are merged from the external point of view. I understand your point about "horrendously complicated" "smooshing", but if this persists then it is not true that blackholes "have no hair". At a certain point any such features must be so small and so thoroughly mixed that they cease to exist. | |
| Jan 16, 2012 at 18:10 | comment | added | ThePopMachine | @RonMaimon: I understand the principle of what you are saying. But this is a purely mathematical phenomenon. For example, if you have two identically sized blackholes on a direct collision course, it should be obvious that there is planar region between them where the forces/curvature balance and you could sneak by (i.e. the EHs actually flatten away from each other due to the gravity pulling away in the opposite direction). But asymptotically this would only apply to an infinitely thin plane and eventually the force toward axis between the blackholes is sufficient... | |
| Jan 16, 2012 at 8:04 | comment | added | Ron Maimon | @ThePopMachine: It is well known that both horizons smear out over the new horizons, by smooshing in thin layers, like kneading dough over and over, without ever touching. This is what makes this question interesting--- the two horizons asymptotically become one, by mixing up in a horrendously complicated way which only looks like a merger in a coarse graining. This is not my insight, it is due to either Gibbons or Horowitz or Pope, or Page, I can't remember exactly who, who used this non-meeting property to claim (incorrectly) that the Gregory Laflamme transition never happens. | |
| Jan 15, 2012 at 21:01 | comment | added | ThePopMachine | @RonMaimon: This is so ridiculous. The fact that EH is defined a certain way or that it exhibits certain properties that you might also attribute to 'objects' doesn't make it an object. The fact that the blackhole as a whole has certain properties that are indistinguishable beyond the event horizon doesn't make the event horizon itself an 'object'. Like Harry said, at a certain point in time there are two horizons and at some later time there are one. If you don't think EHs can merge (i.e. contact) then how do you think supermassive blackhole formation at the centers of galaxies works? | |
| Jan 15, 2012 at 17:41 | comment | added | Ron Maimon | @ThePopMachine: You are totally wrong. The horizon is physical, and it is defined as the boundary of communication with infinity. It is as physical as the notion of "far away", which is always perfect in model black holes. The event horizon is an object, with viscosity and electric resistance, and its physicality is not changed by the fact that things can fall through (from their own point of view). This is Susskind's black hole complementarity (and 'tHooft's holography, and Thorne and Co's Membrane paradigm, and all modern AdS/CFT), and it obsoletes all previous thoughts about black holes. | |
| Jan 15, 2012 at 16:25 | comment | added | ThePopMachine | @RonMaimon: No! "Nothing ever gets to the horizon" is just a misunderstanding on your part. It's wrong because it applies to objects and light, etc. An event horizon is not an object, just a boundary in space. It's not that different from this "paradox": point a laser pointer really far away, say at the moon. Then change the direction really fast. It's not hard to show the dot can go faster than the speed of light. Impossible, right? No! The dot is not a "thing". | |
| Jan 15, 2012 at 13:48 | answer | added | mdaoust | timeline score: 2 | |
| Dec 27, 2011 at 4:17 | comment | added | Ron Maimon | @Harry: I agree, but there it is problematic, I don't know how it works, whether one grows, or whether you can consistently view either growing, etc. If I knew, I would give an answer. The only thing I know is that you can't collide horizons, because nothing ever gets to a horizon, time stops there. You can only effectively collide horizons in a coarse-grained picture (which is more physical anyway). | |
| Dec 26, 2011 at 20:05 | comment | added | Harry Johnston | @Ron, I suspect the OP is mainly interested in the case of two black holes of similar size. | |
| Dec 26, 2011 at 12:11 | answer | added | del piero | timeline score: 0 | |
| Dec 26, 2011 at 10:24 | comment | added | Ron Maimon | @Harry Johnston: The way it happens for a small black hole going into a big one is that the big one gets a little bigger nonlocally a little before the little one hits, and the little one smears over the big horizon. There is no contact. | |
| Dec 26, 2011 at 8:42 | history | edited | David Z | CC BY-SA 3.0 |
edited tags, improved wording
|
| Dec 26, 2011 at 5:26 | history | tweeted | twitter.com/#!/StackPhysics/status/151171902629609472 | ||
| Dec 26, 2011 at 3:58 | comment | added | Harry Johnston | @Ron, that may be technically true, but at some point the system shifts from having two distinct event horizons to having a single event horizon. That point could reasonably be referred to as "contact" IMO. | |
| Dec 26, 2011 at 3:12 | comment | added | Ron Maimon | There is no contact. | |
| Dec 26, 2011 at 1:27 | history | asked | bill | CC BY-SA 3.0 |