tag:blogger.com,1999:blog-22973357.post945642041132090294..comments2017-04-27T14:07:19.793-04:00Comments on Backreaction: Stephen Hawking turns 75. Congratulations! Here’s what to celebrate. Sabine Hossenfelderhttps://plus.google.com/111136225362929878171noreply@blogger.comBlogger44125tag:blogger.com,1999:blog-22973357.post-29002695929808430342017-01-12T10:22:03.440-05:002017-01-12T10:22:03.440-05:00Pendulum equations can omit the bob (swing, but no...Pendulum equations can omit the bob (swing, but not in free fall), have mass (torsion, moment of inertia), have mass and weight (spring). Pendulum equations are empirically validated.<br /><br />Exact theory (math) is not applied theory (science). All quantum gravitations are empirically sterile. SUSY is sterile or fudged (e.g., proton decay and Super-Kamiokande). Something is fundamentally Uncle Alhttp://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-30051662637683691402017-01-12T00:47:41.751-05:002017-01-12T00:47:41.751-05:00senanindya,
I have already answered these questio...senanindya,<br /><br />I have already answered these questions, but it seems you didn't read my reply. I'll do it once again but I am already getting tired of this and have no interest in continuing this fruitless exchange. <br /><br />You are asking "why does this have to be experimentally tested". Once again: It's a prediction for a physical system. You test it because Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-85941804366145587432017-01-11T19:18:56.698-05:002017-01-11T19:18:56.698-05:00"Look, just forget that Hawking ever said he ..."Look, just forget that Hawking ever said he does this calculation for black holes. Imagine he'd just have said you take a quantum field theory and put it on a background described so-and-so, then I predict there should be a radiation with properties so-and-so. That's what is being tested here"<br /><br />Which brings me to a question I have also asked several times and you havesenanindyahttp://www.blogger.com/profile/04275136786127034360noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-80233121530682277682017-01-11T07:28:35.645-05:002017-01-11T07:28:35.645-05:00senanindya,
"As far as I understand, mathema...senanindya,<br /><br />"As far as I understand, mathematical modeling in physics only makes sense with respect to some system being modelled."<br /><br />As I said, the fluid analogue is such a system.<br /><br />You write<br /><br />"If you wanted to check if the model describes System A, then checking it for System B doesn't answer your question."<br /><br />That's Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-61643691725041499252017-01-11T05:58:24.423-05:002017-01-11T05:58:24.423-05:00Bee:
1) "Sure maybe you wanted to describe so...Bee:<br />1) "Sure maybe you wanted to describe something else, so what ?"<br /><br />So everything. As far as I understand, mathematical modeling in physics only makes sense with respect to some system being modelled.<br />So "Is SHM a correct model of a pendulum ?" is a meaningful question.<br />But if I aimed to describe a pendulum and ended up describing a spring - I have senanindyahttp://www.blogger.com/profile/04275136786127034360noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79674859418799597142017-01-11T03:48:03.944-05:002017-01-11T03:48:03.944-05:00Ambi Valent,
I hope Sabine doesn't mind the b...Ambi Valent,<br /><br />I hope Sabine doesn't mind the blatant publicising, but if you have questions about physics then the Physics Stack Exchange is a place where you can have real physicists answer your questions about physics. I won't add the link because I'm not sure about the rules on putting links in comments, but a quick Google will find the site.<br /><br />The answer is thatJohn Renniehttp://www.blogger.com/profile/13013474010567496220noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-39507274370528690662017-01-11T03:13:18.230-05:002017-01-11T03:13:18.230-05:00Is a translation of the singularity theorems into ...Is a translation of the singularity theorems into plain language available somewhere?Ambi Valenthttp://www.blogger.com/profile/03488247852564879628noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-39423418265055133822017-01-11T02:59:05.560-05:002017-01-11T02:59:05.560-05:00"It seems a singularity is still just an exer...<i>"It seems a singularity is still just an exercise in mathematical physics, a mathematical curiosity with no chance of any "physical reality" ever being observed, directly or indirectly.<br /><br />Seems all we can ever observe are effects and events _outside_ the event horizon(s). What am I missing?"</i><br /><br />Following up Sabine's comment: You are confusing Phillip Helbighttp://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-57957475501629959762017-01-11T02:36:50.354-05:002017-01-11T02:36:50.354-05:00senanindya,
Nice discussion! I do not see "t...senanindya,<br /><br />Nice discussion! I do not see "the case you can imagine". Indeed the derivation of Hawking radiation is not completely rigorous.<br /><br />See e.g. this paper from highly respected colleagues https://arxiv.org/abs/gr-qc/0408009<br />who conclude after a discussion of some deep conceptual issues involving ultra-high energies:<br />"However, we also Mauricehttp://www.blogger.com/profile/16375058316648610565noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-30420368073787240782017-01-11T00:46:49.970-05:002017-01-11T00:46:49.970-05:00Unknown,
Singularities were believed to appear in...Unknown,<br /><br />Singularities were believed to appear in the math, but not in solutions than can occur under realistic circumstances. The singularity theorems proved that isn't so. Indeed, singularities can be formed under quite general, physically realistic, situations. To avoid them it's hence not enough to just believe they don't occur, one has to really modify the theory. Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-16730426570062370842017-01-11T00:44:27.035-05:002017-01-11T00:44:27.035-05:00senanindya,
If your model correctly describes the...senanindya,<br /><br />If your model correctly describes the observation, then it describes the observation. If it doesn't, it doesn't. I don't understand your problem. Sure, maybe you originally wanted to describe something else. So what?<br /><br />The problem is with your sentence:<br /><br />"But wouldn't I already know that if I had done the math right ?"<br /><br /Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-71357253037295952412017-01-10T20:14:13.397-05:002017-01-10T20:14:13.397-05:00Hi Bee,
Thanks for the great post. I was ...Hi Bee,<br /> Thanks for the great post. I was following the discussion above with Andy and Maurice and John and this is what continues to confuse me at least (maybe they had similar issues)<br />Let me illustrate my confusion with an analogy (um..)<br /><br />Suppose I model the motion of a pendulum using Simple Harmonic Motion (that's like using QFT in curved space to model senanindyahttp://www.blogger.com/profile/04275136786127034360noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-63861141120885023552017-01-10T15:55:48.202-05:002017-01-10T15:55:48.202-05:00ok, I'm not a theoretical or mathematical phys...ok, I'm not a theoretical or mathematical physicist, but when I read something like:<br /><br />"... with Roger Penrose, Hawking proved that singularities form under quite general conditions in General Relativity,...<br />Before Hawking and Penrose’s work, physicists had hoped that the singularities which appeared in certain solutions to General Relativity were mathematical curiosities Unknownhttp://www.blogger.com/profile/14136922143569965933noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-29131807092800789062017-01-09T23:36:53.229-05:002017-01-09T23:36:53.229-05:00Thanks Bee for reminding us that great visionaries...Thanks Bee for reminding us that great visionaries still exist among us!<br /><br />Pfoglehttp://www.blogger.com/profile/00492537607275147704noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-52074588543612628582017-01-09T17:36:36.852-05:002017-01-09T17:36:36.852-05:00"In the 1980s, Hawking worked with Jim Hartle..."In the 1980s, Hawking worked with Jim Hartle on the no-boundary proposal according to which our universe started in a time-less state. "<br /><br />Hi Sabine,<br /><br />Do you happen to have a link handy to a decent reference/paper on this subject? Sounds fascinating, would love to learn more.<br /><br />Thanks!Evan Thomashttp://www.blogger.com/profile/02260017465845457855noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-69289154647033140012017-01-09T12:19:54.186-05:002017-01-09T12:19:54.186-05:00Thomas,
In water the pertubations one uses aren&#...Thomas,<br /><br />In water the pertubations one uses aren't quantized, so there isn't strictly speaking a Hawking effect. Excuse me for being somewhat sketchy on that here, there are different types of analogue gravity systems, some quantized, some not, some using fluids, others solids. But yes, as I said, even with BECs the situation isn't clear and it'll take more time to sort Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-7796902896243003462017-01-09T11:31:16.456-05:002017-01-09T11:31:16.456-05:00Hawking may not have created a completely new fiel...Hawking may not have created a completely new field of science but rather worked in one. But most of the progress made in science and society in general was not made by the original innovations, but by their usage and improvement. And Hawking surely improved general relativity.<br /><br />So, happy birthday, Stephen Hawking.Ambi Valenthttp://www.blogger.com/profile/03488247852564879628noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-48664802937259136372017-01-09T10:28:36.771-05:002017-01-09T10:28:36.771-05:00Just because the long distance, classical, descrip...Just because the long distance, classical, description is the same (analogous) does not imply that the leading quantum correction is the same. The leading correction to fluid dyanmics near your bath tub drain is not quantized water waves, it is quantum kinetics of atoms and molecules. The situation is only marginally better in BEC's. There are many classical and quantum corrections to Thomas Schaeferhttp://www.blogger.com/profile/06838983632065478955noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-1130862246168372672017-01-09T07:33:42.856-05:002017-01-09T07:33:42.856-05:00Andy,
You don't prove a mathematical theorem ...Andy,<br /><br />You don't prove a mathematical theorem by making an observation. Hawking did a calculation that demonstrates particle production happens in certain background fields and the radiation has certain properties, is thermal and has correlations etc. You measure these particles, you know that the effect exists and the particles are like what Hawking predicted, that's what I'Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-52841373911072444072017-01-09T07:27:48.696-05:002017-01-09T07:27:48.696-05:00Maurice,
I'll not fight with you over the use...Maurice,<br /><br />I'll not fight with you over the use of the word 'analogy'. I have explained sufficiently often now what I mean. Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11984100163001233732017-01-09T07:24:17.860-05:002017-01-09T07:24:17.860-05:00@Sabine
I did not change the question I directly
r...@Sabine<br />I did not change the question I directly<br />responded to your statement "It is more than an analogy."<br /><br />As to your bashing of John: If it really were <br />more than an analogy (it is not in our opinion) and if it were firmly established<br />I (and I guess u also John?) would think Hawking would<br />get his Noble prize.<br /><br />That you think even this wouldMauricehttp://www.blogger.com/profile/16375058316648610565noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-24522818441386630572017-01-09T07:15:16.779-05:002017-01-09T07:15:16.779-05:00Sabine,
Perhaps something interesting might be sa...Sabine,<br /><br />Perhaps something interesting might be salvaged from this misunderstanding and wasted time. <br /><br />Now we understand that you propose that the physical fluid analogue can prove that Hawking's <i>mathematical</i> theorem calculated in the context of GR (and QFT?) is correct. Perhaps one reason why some of us misunderstood you is that it seems highly unusual to resort Andy Millerhttp://www.blogger.com/profile/15729194602104030005noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5630459911640010442017-01-09T06:38:05.857-05:002017-01-09T06:38:05.857-05:00John,
I'm not offended. I'm tired of cons...John,<br /><br />I'm not offended. I'm tired of constantly having to repeat myself. Anyways, apology accepted :o)Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58232205715092877492017-01-09T06:24:28.205-05:002017-01-09T06:24:28.205-05:00Sabine,
My apologies. I've obviously offended...Sabine,<br /><br />My apologies. I've obviously offended you and I didn't mean to. I'm a long time reader of your blog and enjoyed reading this post. My comment wasn't meant as a contradiction or to imply that anything in your post was wrong. It was just, well, a comment.John Renniehttp://www.blogger.com/profile/13013474010567496220noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-25263317798915590632017-01-09T06:20:03.039-05:002017-01-09T06:20:03.039-05:00Phillip,
Not sure what you mean. It has arguably ...Phillip,<br /><br />Not sure what you mean. It has arguably lead to a lot of effort to try and find a theory of quantum gravity that would solve the problem. A lot of papers on quantum gravity are actually about black hole evaporation. Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.com