tag:blogger.com,1999:blog-22973357.post5768244731689381255..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Black holes and the Planck lengthSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger24125tag:blogger.com,1999:blog-22973357.post-45365334670001978072013-04-25T20:42:11.839-04:002013-04-25T20:42:11.839-04:00Bee, I think that your take on this is essentially...Bee, I think that your take on this is essentially correct. However, I want to point out a situation where it looks problematical (altho I have seen good-enough-looking justifications.) That is the apparent "event horizon" for an accelerating observer, O. (In Born coordinates, it's where the required acceleration for "rigidity" becomes infinite.) Well you get trouble if Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-52629109900761624322013-04-22T13:24:33.398-04:002013-04-22T13:24:33.398-04:00Could this have been more simply stated by observi...Could this have been more simply stated by observing that any coordinate transformation will also transform the event horizon. Thus if a mass extends beyond its Schwarzchild radius in the frame at rest with the centre of mass, then the mass will also extend beyond the Schwarzchild radius under any Lorentz transformation.<br /><br />I apologize if this is a re-comment, I think blogspot ate my lastAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-87213621920105692562013-04-22T13:23:07.713-04:002013-04-22T13:23:07.713-04:00Could this have been more simply stated by observi...Could this have been more simply stated by observing that any coordinate transformation will also transform the event horizon. Thus if a mass extends beyond its Schwarzchild radius in the frame at rest with the centre of mass, then the mass will also extend beyond the Schwarzchild radius under any Lorentz transformation.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-91634050719797044642013-04-10T05:02:47.149-04:002013-04-10T05:02:47.149-04:00Hi Arun,
I guess so, yes. Best,
B.Hi Arun,<br /><br />I guess so, yes. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74079442356083810692013-04-10T05:01:49.191-04:002013-04-10T05:01:49.191-04:00Robert:
I deleted your comment. There is really ...Robert: <br /><br />I deleted your comment. There is really no need to hand out insults for no reason whatsoever. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-72238800027023161942013-04-10T04:58:48.540-04:002013-04-10T04:58:48.540-04:00Hi Giotis,
My comment really wasn't so much a...Hi Giotis,<br /><br />My comment really wasn't so much about Hogan's sentence in particular, but about the role of the Planck length in this kind of arguments more generally. It just came to my mind when I read Hogan's paper. Here's another example, from <a href="http://arxiv.org/pdf/0905.4803v7.pdf" rel="nofollow">arxiv:0905.4803</a>: <br /><br />"[W]ell-separated particles Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-48177084481901312202013-04-10T04:46:13.894-04:002013-04-10T04:46:13.894-04:00Hi Erik,
These lecture notes make a good starting...Hi Erik,<br /><br /><a href="http://www.aei.mpg.de/~rezzolla/lnotes/mondragone/collapse.pdf" rel="nofollow">These lecture notes make a good starting point.</a> Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-21588110942167555302013-04-09T21:15:22.715-04:002013-04-09T21:15:22.715-04:00I believe that black holes are characterized by a ...I believe that black holes are characterized by a curvature singularity where the weyl curvature diverges to infinity. In an extreme case of the Kerr metric, describing rotating black holes, admits a naked singularity with no event horizon. I believe it is when the angular momentum contribution in larger than the mass. They are not thought to physically exist due to collapse issues and thus WVUnicyclehttps://www.blogger.com/profile/09742530943506487085noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-50987529760135272592013-04-09T19:54:53.291-04:002013-04-09T19:54:53.291-04:00BTW This [url=http://arxiv.org/ftp/arxiv/papers/09...BTW This [url=http://arxiv.org/ftp/arxiv/papers/0910/0910.1084.pdf]Felber's study[/url] is closely related to the Hogan's proposal too. Just compare the outcome of all these seemingly unrelated models: for object moving faster than 70% c Felber predict push speed, which exerts to massive bodies, Wayne predicts drag for such an object and Hogan predicts the emanation of "holographic Zephirhttps://www.blogger.com/profile/06010623752049244967noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20299089089440195612013-04-09T19:24:56.368-04:002013-04-09T19:24:56.368-04:00The thinking of formal physicists like the Bee is ...The thinking of formal physicists like the Bee is similar to attitude of people, who are believing, that the space-time is curved and path of light is straight even at the moment, when they're already wildly ENCIRCLING the black hole together with light around event photon sphere. Of course, they've truth from their perspective, but this perspective is not experimentally testable from Zephirhttps://www.blogger.com/profile/06010623752049244967noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75715508278513606942013-04-09T19:03:04.808-04:002013-04-09T19:03:04.808-04:00/*one expects quantum gravitational effects to bec.../*one expects quantum gravitational effects to become strong, not at distances close by the Planck length, but at curvatures close to one over Planck length squared*/<br /><br />The human observer scale is exactly in the middle of dimensional scales/curvatures/energy densities of quantum mechanics and general relativity, which means, the realm of quantum gravity is just the human observer scale (Zephirhttps://www.blogger.com/profile/06010623752049244967noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-70935400754036774992013-04-09T18:53:50.834-04:002013-04-09T18:53:50.834-04:00Hogan is closer with his holographic model to AWT,...Hogan is closer with his holographic model to AWT, than most of other physicists - I mean phenomenologically - from logical perspective the holography is <br />crippled model anyway. Of course Hogan's theory is hyperdimensional, so it MUST violate general relativity - not to say about special relativity. In AWT the holographic noise not only exists, but it's equivalent with CMBR noise. InZephirhttps://www.blogger.com/profile/06010623752049244967noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-69936613005747920252013-04-09T13:26:23.769-04:002013-04-09T13:26:23.769-04:00Reading this article, I came to realise that I hav...Reading this article, I came to realise that I have actually only done some calculations in GR given a Schwarzschild-like metric. Come to think of it, I have never seen anything like the dynamical process of the gravitation collapse of a bunch of matter to form a black hole. Does anyone know any proper references?Erikhttps://www.blogger.com/profile/14629571445007334997noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-8048440342492361522013-04-09T10:05:07.156-04:002013-04-09T10:05:07.156-04:00Thanks, Bee!
Just as with colliding with a CMB ph...Thanks, Bee!<br /><br />Just as with colliding with a CMB photon, can in principle a particle collide with a graviton and produce a black hole?Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-39112285549965426982013-04-09T09:50:12.418-04:002013-04-09T09:50:12.418-04:00I've just opened the paper. The quoted text re...I've just opened the paper. The quoted text refers to figure 1 where it is clear (well not so clear) that he is talking about the Compton wavelength and its relation to Schwarzschild radius.<br /><br /> Of course he should state this clearer in his text too. So my overall impression is that this is a misunderstanding.Giotishttps://www.blogger.com/profile/03594944884584261018noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79001054296854223892013-04-09T06:36:03.145-04:002013-04-09T06:36:03.145-04:00OK, I thought I remembered him from a previous pos...OK, I thought I remembered him from a previous post here. Let's see: "Craig Hogan is Director of the Fermilab Center for Particle Astrophysics, where he is also a member of the scientific staff and the Theoretical Astrophysics Group. He is also a professor at the University of Chicago, where he is on the faculty of the Department of Astronomy and Astrophysics, the Enrico Fermi Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51304239365217946002013-04-09T05:02:03.110-04:002013-04-09T05:02:03.110-04:00Who is this Hogan guy? The statement you quoted w...Who is this Hogan guy? The statement you quoted would probably be rejected from the sci.physics.research newsgroup as "too speculative" (a euphemism for "not even wrong"). Sounds like typical crackpot stuff.<br />Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-16143012809617187362013-04-09T03:25:18.113-04:002013-04-09T03:25:18.113-04:00Hi Arun,
Since the CMB is dilute but physically p...Hi Arun,<br /><br />Since the CMB is dilute but physically present, there's a tiny but nonzero probability that your massive particle, if sufficiently fast, will hit a CMB photon and form a black hole. So then it has a horizon. But I'm not sure that's what you had in mind. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51388457883856770172013-04-09T03:08:01.726-04:002013-04-09T03:08:01.726-04:00Giotis, Amitabha,
Yes, you can. That's the es...Giotis, Amitabha,<br /><br />Yes, you can. <a href="http://backreaction.blogspot.com/2013/04/black-holes-and-planck-length.html" rel="nofollow">That's the estimate I did here</a>, one of the easiest ways to arrive at the Planck scale. I don't know what he had in mind, but whatever it was the way he expressed it is nonsense. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-45778008465755967222013-04-09T02:54:44.481-04:002013-04-09T02:54:44.481-04:00Amitabha beat me to it. The minute I saw it I thou...Amitabha beat me to it. The minute I saw it I thought that the guy has Compton wavelength in mind and its relation to Schwarzschild radius.<br /><br />Otherwise it doesn't make much sense...Giotishttps://www.blogger.com/profile/03594944884584261018noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-38749763802553572462013-04-09T02:09:28.860-04:002013-04-09T02:09:28.860-04:00You could however compare the *Compton wavelength*...You could however compare the *Compton wavelength* of a massive particle to its Schwarzschild diameter:<br /><br />\hbar/Mc and 4GM/c^2<br /><br />The mass of a particle for which these are equal is twice the usual Planck mass. A massive particle may be used as a probe of lengths comparable to (or smaller than) its Compton wavelength, but in this case that cannot be done.<br /><br />Perhaps I am Amitabhahttps://www.blogger.com/profile/17140154364941569189noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-56055038339106003912013-04-09T02:06:40.842-04:002013-04-09T02:06:40.842-04:00This comment has been removed by the author.Amitabhahttps://www.blogger.com/profile/17140154364941569189noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-57136184695377002282013-04-08T11:03:15.572-04:002013-04-08T11:03:15.572-04:00"an object in motion relative to you appears ..."<i>an object in motion relative to you appears shortened.</i>" Viewing angle interacts - Terrell rotation,<br /><br />http://en.wikipedia.org/wiki/Terrell_rotation<br />Proc. Camb. Phil. Soc., 55 137 (1958)<br />Phys. Rev. 116(4) 1041 (1959)<br /><br />"<i>not at distances close by the Planck length, but at curvatures close to one over Planck length squared.</i>" At per areaUncle Alhttps://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33099821785543379782013-04-08T10:45:50.470-04:002013-04-08T10:45:50.470-04:00Donald Moffitt's sci-fi, Crescent in the Sky, ...Donald Moffitt's sci-fi, Crescent in the Sky, A Gathering of Stars - apart from imagining an interstellar human culture where Islam predominates, also uses this "paradox".<br /><br /><a href="http://www.donaldmoffitt.com/books.html" rel="nofollow">http://www.donaldmoffitt.com/books.html</a><br /><br />One could ask - can a massive particle moving sufficiently fast relative to the Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.com