tag:blogger.com,1999:blog-22973357.post1087838535789317168..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: The Cosmological ConstantSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger91125tag:blogger.com,1999:blog-22973357.post-12340610001317286192008-05-27T13:06:00.000-04:002008-05-27T13:06:00.000-04:00Superb post Bee...I'll certainly refer to it in an...Superb post Bee...I'll certainly refer to it in any post on the subjectProfessor Rhttps://www.blogger.com/profile/08227006868149583276noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-55973607880665950952008-03-28T11:25:00.000-04:002008-03-28T11:25:00.000-04:00Hi Neil,I don't know, I'm just a kind of "interest...Hi Neil,<BR/><BR/>I don't know, I'm just a kind of "interested layman" in these matters. Maybe the paper by Eric Linder, <A HREF="http://dx.doi.org/10.1007/s10714-007-0550-z" REL="nofollow"> The dynamics of quintessence, the quintessence of dynamics</A>, is a starting point to address your question?<BR/><BR/>Best, Stefanstefanhttps://www.blogger.com/profile/09495628046446378453noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-87476859795883966292008-03-28T10:30:00.000-04:002008-03-28T10:30:00.000-04:00PS: Would quantization of DE field be related to "...PS: Would quantization of DE field be related to "Dilatons"? - tx.Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-1317142740182640862008-03-28T09:09:00.000-04:002008-03-28T09:09:00.000-04:00Thanks, Stefan, for the link. One thing I wonder a...Thanks, Stefan, for the link. One thing I wonder about and haven't seen much on (not saying it isn't there), is quantization of the dark energy field. What sort of "quanta" make up the DE field, and how affected by it being a scalar field? If there are quanta of DE, then doesn't Hawking radiation involve generating them too from the EH?<BR/><BR/>(Speaking of which, what re gravitons for that, andNeil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-53521141556492613262008-03-27T17:26:00.000-04:002008-03-27T17:26:00.000-04:00The February 2008 issue of General Relativity and ...The February 2008 issue of General Relativity and Gravitation is a <A HREF="http://www.springerlink.com/content/lm37485593h5/" REL="nofollow">special issue on dark energy</A>, and the articles are currently available for free. It seems this is a collection of interesting and quote digestible papers, for example on the question "<A HREF="http://dx.doi.org/10.1007/s10714-007-0547-7" REL="nofollow">stefanhttps://www.blogger.com/profile/09495628046446378453noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74157253010701253382007-11-25T15:07:00.000-05:002007-11-25T15:07:00.000-05:00You missed the most important fact about the CC in...You missed the most important fact about the CC <I>in the original context in which is was introduced</I> - namely, it represents the global length scale that Riemannian geometry allows, and as a corollary, the reducibility of the metric into 9 direction cosines (dynamical) plus 1 volume element (non-dynamical). In Riemannian geometry, directions are localized while length is not. In Weyl's Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-46750306268792397952007-11-22T19:43:00.000-05:002007-11-22T19:43:00.000-05:00Hi Neil',Sorry, our comments crossed. Yes, a circ...Hi Neil',<BR/><BR/>Sorry, our comments crossed. <BR/><BR/><I> Yes, a circle (or "curve" like a parabola) has curvature at every point if has continuous derivatives there.</I><BR/><BR/>To you too, you are confusing intrinsic with extrinsic curvature. I am talking about the curvature defined through the metric as discussed in the post above, the one that is relevant for GR. The curvature of any 1 Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20108587151723965412007-11-22T19:39:00.000-05:002007-11-22T19:39:00.000-05:00Hi Plato:I am talking about GR, the curvature of a...Hi Plato:<BR/><BR/>I am talking about GR, the curvature of a manifold, not the extrinsic curvature of an embedding in a higher dimensional space. In this context, a circle is flat. I am not impressed by the quotation from that website you give<BR/><BR/><I>"Einstein summarizes this in his Principle of Equivalence: There is no way to distinguish between the effects of acceleration and the effects Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-60992203630975957142007-11-22T19:37:00.000-05:002007-11-22T19:37:00.000-05:00Bee: Yes, a circle (or "curve" like a parabola) ha...Bee: Yes, a circle (or "curve" like a parabola) has curvature at every point if has continuous derivatives there. Not the same kind, but yes in the general sense. It is equal to d(theta)/ds, which is change in tangent angle per unit of progression along curve (and can be derived from regular Cartesian derivatives.)<BR/><BR/>Plato: This will raise eyebrows, but really, the equivalence principle isNeil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-243376743752998042007-11-22T18:37:00.000-05:002007-11-22T18:37:00.000-05:00Bee:A circle doesn't have curvature.I should have ...<B>Bee</B>:<I>A circle doesn't have curvature.</I><BR/><BR/>I should have given <A HREF="http://www.etsu.edu/physics/plntrm/relat/curv.htm" REL="nofollow">the link</A> and not the picture link.<BR/><BR/><BR/><A HREF="http://www.etsu.edu/physics/plntrm/relat/general.htm" REL="nofollow" TITLE="Relativity and Black Holes<br/>Curvature and Geometry">Einstein summarizes this in his Principle of PlatoHagelhttps://www.blogger.com/profile/00849253658526056393noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-15771802708482047292007-11-22T17:14:00.000-05:002007-11-22T17:14:00.000-05:00Dear Arun,Yeah, maybe some other time, otherwise I...Dear Arun,<BR/><BR/>Yeah, maybe some other time, otherwise I will have to advise myself to stick with the topic ;-) I see it more as a matter of time scales than of different parts. Some reactions come instantaneously, others take more time. Both should be taken into account. Best,<BR/><BR/>B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83807389108572974582007-11-22T15:34:00.000-05:002007-11-22T15:34:00.000-05:00I think you have to have a firm intent in this lif...I think you have to have a firm intent in this life but that is mostly learning and some sly moves. You can't have expectations however, that's a quantum physics no-no :)Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-7692290523746611612007-11-22T11:39:00.000-05:002007-11-22T11:39:00.000-05:00...as I think self-control is not an entirely usel...<I>...as I think self-control is not an entirely useless trait..</I><BR/><BR/>Perhaps more about this in some different time and place; but self-control implies that one part of you wants do to something and another part of you has to overrule it. If Padmanabhan is going by traditional narratives, at this point it is believed that there are no warring parts of you. :)<BR/><BR/>---------<BR/><Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-46429568214863341072007-11-22T08:40:00.000-05:002007-11-22T08:40:00.000-05:00Dear Arun,It's been a while since I read it, but o...Dear Arun,<BR/><BR/>It's been a while since I read it, but overall seen not particularly. He has some nice lines in there that I like (e.g. the one with the teeth brushing, and the one about acquiring balance on the bike). However, his conclusion ("one day you may realise that your the natural state is one without mind or thoughts!") is equally ill defined as the vacuum in QFT. It's full of Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-40907460757764995082007-11-21T21:02:00.000-05:002007-11-21T21:02:00.000-05:00Dear Bee,You mentioned it, and so I ask - does Pad...Dear Bee,<BR/><BR/>You mentioned it, and so I ask - does Padmanabhan's philosophy article resonate with you beyond the "God wants you to brush your teeth"?Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-90749808743703088562007-11-21T20:19:00.000-05:002007-11-21T20:19:00.000-05:00Hi Dr. Who,little did I suspect that the rioter wo...Hi Dr. Who,<BR/><BR/><I>little did I suspect that the rioter would be Bee herself [...] my post was aimed at declaring that the AP is irrelevant to the problem of the CC</I><BR/><BR/>Well. If I wanted to cause a riot, believe me I could do better :-) I was just trying to clarify my point of view. I don't know why the mentioning of the AP always comes with funny remarks like the A-word, or Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-49403141251351933172007-11-21T20:09:00.000-05:002007-11-21T20:09:00.000-05:00Well, I did predict that talking about explanation...Well, I did predict that talking about explanations of the CC would lead to a riot....little did I suspect that the rioter would be Bee herself! I did of course read your stuff about the AP, but as I said -- twice! -- I don't think that the AP really has anything to do with the Landscape theory of the CC. As I said -- you did read my post, right? -- what we need is a theory that can explain the Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-81174576579054177932007-11-21T17:49:00.000-05:002007-11-21T17:49:00.000-05:00"David Finkelstein showed that in Unimodular Relat..."David Finkelstein showed that in Unimodular Relativity the Cosmological Constant is an unavoidable Lagrange Multiplier..."<BR/><BR/>After reading the 78th listing in a Yahoo search for "unimodular relativity", it looks like unimodular relativity just means conventional GR with the Cosmological Constant allowed to be variable and that makes it different than conventional GR and the conventional Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-9883967500254457632007-11-21T17:29:00.000-05:002007-11-21T17:29:00.000-05:00HI Marty,thanks for the pointer. No, I was not awa...HI Marty,<BR/><BR/>thanks for the pointer. No, I was not aware of these comments by Gordon Punsch. But it seems that they to go in the very same direction as the papers by Jaffe. This would simply imply that we should stop bringing up the Casimir effect when discussing the vacuum. Hm, will have to think about it...<BR/><BR/>Best, Stefanstefanhttps://www.blogger.com/profile/09495628046446378453noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5784087662580344612007-11-21T17:18:00.000-05:002007-11-21T17:18:00.000-05:00Hi Neil',The effect of the CC on the redshift is w...Hi Neil',<BR/><BR/>The effect of the CC on the redshift is what is measured in the supernovae data. This however is not a Doppler effect and has nothing to do with the potential of the supernovae. Roughly speaking the net effect is that the light is emitted, but it has to travel through a lot of space to reach us. While it does so, the space expands and redshifts the wavelength of the light. Yes,Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5959232184403504882007-11-21T17:00:00.000-05:002007-11-21T17:00:00.000-05:00OK, point taken. So, here's a question directly ab...OK, point taken. So, here's a question directly about the CC: how does it affect red shift, if at all? I always wondered, how only Doppler type considerations could be used to get relative red shift between galaxies. Consider: If I consider myself the standard for the center of mass density, and emit light, that light has to climb up through the gravity of each sphere it keeps reaching the edge Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79701748377791291082007-11-21T16:22:00.000-05:002007-11-21T16:22:00.000-05:00Hi Stefan,May it be that the "standard" Casimir si...Hi Stefan,<BR/><BR/><I>May it be that the "standard" Casimir situation with the parallel plates is a configuration where just by some weird coincidence the force which is actually caused by the van der Waals like interaction between quantum fluctuations of charges [...]</I><BR/><BR/>This reminds me of some comments by Gordon Pusch on Usenet a while ago. At the time, at least, he maintained that Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-32664929770379270542007-11-21T16:19:00.000-05:002007-11-21T16:19:00.000-05:00Hi Neil',As much as I appreciate and encourage you...Hi Neil',<BR/><BR/>As much as I appreciate and encourage your interest in understanding GR, this is not a forum. Please post questions about Rindler space or elevators elsewhere - I am really sorry, but I just don't have time to be an "ask-the-expert" service. <BR/><BR/>I want to kindly ask you to only comment on the topic. This, I should add, would require that you read what I wrote. Generally, Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-2436746092584522142007-11-21T16:13:00.000-05:002007-11-21T16:13:00.000-05:00Folks, you can't understand the CC/dark energy etc...Folks, you can't understand the CC/dark energy etc. unless you get GR, and I'm trying to understand GR at some middle to upper-middle brow level. I heard something weird about the acceleration of bodies moving rapidly relative to distributions of mass and ask for your take. Gravitomagnetism apparently isn't the only example of unequal acceleration applying to bodies at different velocities Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-52284943222511411572007-11-21T14:48:00.000-05:002007-11-21T14:48:00.000-05:00The definition for CC related to what I've been re...The definition for CC related to what I've been reading is:<BR/><BR/>"4-form dA /\ dA - HyperVolume<BR/>In American Journal of Physics 39 (1971) 901-904, David Finkelstein showed that in Unimodular Relativity the Cosmological Constant is an unavoidable Lagrange Multiplier beloging to a constraint that expresses the existence of a Fundamental Volume Element of Spacetime Hypervolume at every point Anonymousnoreply@blogger.com