tag:blogger.com,1999:blog-22973357.post1764511794857912093..comments2020-04-06T23:20:22.713-04:00Comments on Sabine Hossenfelder: Backreaction: Hawking radiation is not produced at the black hole horizon.Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger96125tag:blogger.com,1999:blog-22973357.post-68041686706346430012020-02-02T21:09:39.834-05:002020-02-02T21:09:39.834-05:00Anonymous? So you haven't the bollocks to reve...Anonymous? So you haven't the bollocks to reveal yourself, yet whine about Ms. Hossenfelder and her astute observations? I find you to be lacking in any credibility and your claims are just a pedantic attempt to discredit a better thinker and scientist than you pretend to be. Cogitushttps://www.blogger.com/profile/04816887802060150420noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-59613401989616878122019-10-15T15:32:52.850-04:002019-10-15T15:32:52.850-04:00The height at which the radiation is nominally cre...The height at which the radiation is nominally created is supposed to be observer-dependent. If you are a very, very long way away, the radiation might indeed be calculated as apparently coming from ~r=3M, but if you are //at// r=3M, the radiation will seem to be coming from between r=3M and r=2M. If you are at r=2.1m, the radiation will appear to you to be be originating at somewhere between r=ErkDemon (Eric Baird)https://www.blogger.com/profile/00430413494529535159noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-14475403096944593642019-10-15T15:17:20.206-04:002019-10-15T15:17:20.206-04:00Consider a burst of outward-aimed light emitted by...Consider a burst of outward-aimed light emitted by an infalling object at the precise moment that it passes through r=2M. <br />With a Wheeler back hole, that light is supposed to remain frozen into the horizon, so if you are outside r=2M, you don't see it. Temperature=0.<br />However, if you let yourself fall into the hole, and pass inwards at speed through r=2M, then you are passing throughErkDemon (Eric Baird)https://www.blogger.com/profile/00430413494529535159noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-86212318590311585512019-09-20T09:15:01.824-04:002019-09-20T09:15:01.824-04:00Sabine, thank you so much for this post.
I love ho...Sabine, thank you so much for this post.<br />I love how you follow Einstein's idea of "things should be made as simple as possible, but not any simpler".Whykahttps://www.blogger.com/profile/07233045343665247409noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58954328103700911362019-04-02T08:16:36.221-04:002019-04-02T08:16:36.221-04:00Hi Peter,
Yes, instead of taking one large thermo...Hi Peter,<br /><br />Yes, instead of taking one large thermometer, you can take a lot of small ones. This decreases the chances of it becoming excited, but then you can rely on statistics. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73075058920033078492019-04-02T08:05:42.611-04:002019-04-02T08:05:42.611-04:00@Sabine: I realize that I'm much too late for ...@Sabine: I realize that I'm much too late for this discussion, but wouldn't a free-falling thermometer be in the vicinity of the horizon for much too short a time to interact with Hawking quanta? Thus, it would only be able to provide an upper bound for the temperature (one that is quite a bit higher than the real temperature). Although I suppose you could send $10^{10}$ "Peter Shorhttps://www.blogger.com/profile/13823970640202949073noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-9213830689289639062018-03-26T04:05:52.243-04:002018-03-26T04:05:52.243-04:00baronm1100,
It can be vice versa: external observ...baronm1100,<br /><br />It can be vice versa: external observers see no Hawking radiation but infalling bodies really see full of it that could be the extra cause with the degeneration pressure so that no event horizon ever formed. I see the value of Mersini-Houghton's work.Eusahttps://www.blogger.com/profile/14114706429392111062noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-76457709911802592792018-03-22T09:33:40.274-04:002018-03-22T09:33:40.274-04:00Sabine,
that's a great post!
One question I c...Sabine,<br /><br />that's a great post!<br />One question I couldn't find an answer to:<br />Does an infalling observer notice any hawking radiation at all? Or does it effect only external observers?Anonymoushttps://www.blogger.com/profile/05919645839824482512noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33408434551907679742017-08-27T03:06:46.125-04:002017-08-27T03:06:46.125-04:00I don't understand this. What does the stress-...I don't understand this. What does the stress-energy tensor of the Hawking radiation tell us about its origin? All I need for creating regions with high local energy of radiation not originated there is a lense. And a BH is an extremely powerful lense. So, from the radiation created at the collapsing surface a lot may be catched for a longer time around the photon orbit, before flying away Ilja Schmelzerhttps://www.blogger.com/profile/05344206562643658764noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-89038281313839613712017-08-25T00:44:05.057-04:002017-08-25T00:44:05.057-04:00Ilja,
It is correct that the cause of Hawking rad...Ilja,<br /><br />It is correct that the cause of Hawking radiation is the time-dependence of the background geometry. It does not follow from this however that Hawking radiation must be created at the horizon, or a thin region around the black hole. This is simply wrong, as you can convince yourself easily. Go and look up, for example, the stress-energy-tensor of the Hawking radiation. You will Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11239542045881052022017-08-24T15:33:54.244-04:002017-08-24T15:33:54.244-04:00I disagree. If the gravitational collapse stops so...I disagree. If the gravitational collapse stops some \(10^{-100000}\) Planck lengths away from the Schwarzschild radius, Hawking radiation stops after a very short time. So, if there will be Hawking radiation after this short time, it has to be emitted from this thin region around the BH, and not at all from somewhere far away. <br /><br />See Paranjape, Padmanabhan, Radiation from collapsing Ilja Schmelzerhttps://www.blogger.com/profile/05344206562643658764noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-43341475562177379952017-01-09T23:43:50.247-05:002017-01-09T23:43:50.247-05:00Ambi Valent,
The answer to your question is '...Ambi Valent,<br /><br />The answer to your question is 'in principle, yes', but the interaction with other matter is normally not taken into account. The way that these calculations are done, one merely deals with one field that doesn't self-interact. In other words, nobody ever considers the possibility, so not much is known about it. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20184000956057244212017-01-09T17:31:28.883-05:002017-01-09T17:31:28.883-05:00Just found this. My question is a bit related to t...Just found this. My question is a bit related to the one of Steve further up, but not the same.<br /><br />If the Hawking radiation is "smeared out" over a large vicinity around the black hole, would it then be possible for a negative-energy particle to interact with other particles (matter or light) before it enters the black hole, and if so, could it "steal" energy from themAmbi Valenthttps://www.blogger.com/profile/03488247852564879628noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11921160103595529072016-11-14T06:35:08.874-05:002016-11-14T06:35:08.874-05:00"I mean, String Theory, as far as I understan...<i>"I mean, String Theory, as far as I understand, are not literally vibrating strings. It is a metaphor for a mathematical construct not meant to be taken literally."</i><br /><br />I don't know, not being a stringy person. Maybe someone who actually works in the field can comment. My impression is that they are indeed one-dimensional objects which vibrate. A similar question Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-90431696973385676612016-11-13T20:19:57.215-05:002016-11-13T20:19:57.215-05:00" still want to punch the damned book. Not be..." still want to punch the damned book. Not because I didnâ€™t understand it, but because it convinced so many other people they did understand it."<br /><br />I think that this is true for almost all popular physics books. I mean, these books almost always are without math and only use metaphors because that's the only way to explain complex ideas that are often mathematically Ufotofu9https://www.blogger.com/profile/12211994492168099117noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-16003705849796220342016-08-04T05:38:28.404-04:002016-08-04T05:38:28.404-04:00Sk,
The stress-energy tensor of the Hawking flux ...Sk,<br /><br />The stress-energy tensor of the Hawking flux is not a source to the background geometry. It's not a closed set of equations. The (missing) closure is known as 'backreaction'. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-25792944783540327762016-08-04T03:48:27.382-04:002016-08-04T03:48:27.382-04:00I had a question. We know that Ricci tensor around...I had a question. We know that Ricci tensor around horizon is zero, then how come we get a positive energy-momentum tensor outside horizon?Anonymoushttps://www.blogger.com/profile/14407658664492300399noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-80330483338292100412016-04-05T19:02:51.568-04:002016-04-05T19:02:51.568-04:00Thanks Sabine, Candelas paper seems to give an exp...Thanks Sabine, Candelas paper seems to give an explanation. Unknownhttps://www.blogger.com/profile/05365965162940498227noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74044987030018237992016-04-05T12:10:41.583-04:002016-04-05T12:10:41.583-04:00Unknown,
This is a good reference
http://journal...Unknown,<br /><br />This is a good reference<br /><br />http://journals.aps.org/prd/abstract/10.1103/PhysRevD.21.2185<br /><br />(and references therein) as well as this book<br /><br />http://www.cambridge.org/be/academic/subjects/physics/theoretical-physics-and-mathematical-physics/quantum-fields-curved-spaceSabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-60651639226518852112016-04-05T11:47:48.045-04:002016-04-05T11:47:48.045-04:00Dear Sabine,
thanks for your comments on this ve...Dear Sabine, <br /><br />thanks for your comments on this very interesting issue of where the radiation originates. I would like to ask you, when you mention that the stress tensor close to the horizon has been computed, can you give a reference? I would like to follow that computation closely.<br /><br />Regarding non-locality, I am not convinced. It has been computed the Unruh vacuum for a Unknownhttps://www.blogger.com/profile/05365965162940498227noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-61899460983562461772015-12-17T06:37:06.480-05:002015-12-17T06:37:06.480-05:00Helbig, I owe you a tenner. No mbh at LHC. I pay y...Helbig, I owe you a tenner. No mbh at LHC. I pay you. Can provide postal address to dnikbin@yahoo.co.uk if necessary. I send you cash.<br /><br />NikbinDarius Nikbinhttps://www.blogger.com/profile/09673611975076324091noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-8139397433482790732015-12-13T16:41:09.709-05:002015-12-13T16:41:09.709-05:00My comments concerned radially moving detectors (f...My comments concerned radially moving detectors (freely falling vs. hovering). For orbiting detectors I should defer to experts in general relativity. (I am a quantum theorist and mathematician.) But my understanding is that there are precious few closed geodesic orbits very near a black hole. An observer in a (say) circular orbit there (r < 3M) is not in free fall; there must be some Anonymoushttps://www.blogger.com/profile/15149338716070142385noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73003875717736106692015-12-12T12:44:31.396-05:002015-12-12T12:44:31.396-05:00Sabine,
I'd tend to assume that the radiat...Sabine, <br /> I'd tend to assume that the radiation seen by an orbiting observer is going to be equivalent to Zel'dovich radiation.ErkDemon (Eric Baird)https://www.blogger.com/profile/00430413494529535159noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-13025057964074184222015-12-12T12:42:00.603-05:002015-12-12T12:42:00.603-05:00Alex:
" The Unruh effect seems to occur in an...Alex:<br /><i>" The Unruh effect seems to occur in any spacetime for a particle detector with a large enough acceleration, with the clicks of the particle detector being produced from the energy it takes to accelerate the detector. While the Hawking effect occurs due to the non-static spacetime caused by an object collapsing to a black hole, with the energy to produce the particles coming ErkDemon (Eric Baird)https://www.blogger.com/profile/00430413494529535159noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-36051851903960527062015-12-12T05:51:59.714-05:002015-12-12T05:51:59.714-05:00Hi again Alex,
I vaguely seemed to recall that Un...Hi again Alex,<br /><br />I vaguely seemed to recall that Unruh mentioned the orbiting observers in his paper, and turned out I recalled correctly. <a href="http://www2.lns.mit.edu/fisherp/Unruh.pdf" rel="nofollow">Have a look at page 886, right column</a>, the paragraph that starts with "I would now like to return to the question..." which, I think, is exactly the question you asked. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.com