tag:blogger.com,1999:blog-22973357.post306993327614212282..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Astrophysicist discovers yet another way to screw yourself over when modifying Einstein’s theorySabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger59125tag:blogger.com,1999:blog-22973357.post-7080797772542053002018-12-11T09:21:47.676-05:002018-12-11T09:21:47.676-05:00Hi dada,
Thanks so much for your interesting comm...Hi dada,<br /><br />Thanks so much for your interesting comment! I wrote a song about people like you:<br /><br />https://www.youtube.com/watch?v=4cJIW5FTbRo<br /><br />Enjoy :)Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33688968281274455952018-12-11T07:59:56.519-05:002018-12-11T07:59:56.519-05:00Sabine: I am not qualified to enter the technical ...Sabine: I am not qualified to enter the technical debate in a useful way, but what it appears clearly from your blog and replies, is that you make abundant use of subjective, arrogant and dismissive statements, despite declaring ignorance on certain points. The whole style is far from the respectful and rational discourse expected from an accomplished scientist. <br />Each time you use arrogant dadahttps://www.blogger.com/profile/10456028063036996693noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18341588118172028672017-12-04T12:56:46.450-05:002017-12-04T12:56:46.450-05:00Oups !Oups !F henry-couannierhttps://www.blogger.com/profile/13933350696243790692noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-34078814539824469122017-12-04T07:04:56.522-05:002017-12-04T07:04:56.522-05:00Frederic,
But it's the same equation! Yes, if...Frederic,<br /><br />But it's the same equation! Yes, if you had a *different* modified equation, then you could do that (though I don't recommend it, but let's leave this aside for a moment). But it's not. It's the same equation! Look, to see what I mean just take lambda = constant and the rest will be the usual equations. And that's a perfectly fine and allowed solution.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11371560903312547512017-12-04T06:39:50.569-05:002017-12-04T06:39:50.569-05:00SH : "But you can also make the ansatz
l(t) ...SH : "But you can also make the ansatz<br /><br />l(t) dt^2 - l(t)*a(t)^2 (dr^2 + d\Omega^2) <br /><br />which will give you a different equation for a(t) which also depends on l(t). You can then go and fix l(t) to whatever you want, but you'll still describe the same space-time (unless you change the matter content of course)."<br /><br />That's not at all the game he is F henry-couannierhttps://www.blogger.com/profile/13933350696243790692noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67805680259115098472017-12-04T03:47:26.370-05:002017-12-04T03:47:26.370-05:00Frederic,
I have been very specific above. How mu...Frederic,<br /><br />I have been very specific above. How much more specific do you need it? You can of course put such a factor in front of the FRW metric but that's merely a reparameterization of the metric. No problem with that, but also no new physics. That's just the same physics in a funny gauge. As I emphasized above, that's because this is not an independent equation. It Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-27470302192523750592017-12-04T03:29:09.915-05:002017-12-04T03:29:09.915-05:00Hi sabine ,
I understand it's a dangerous gam...Hi sabine ,<br /><br />I understand it's a dangerous game when you have equations which do not follow from a lagrangien. Here at first glance we have an extra dof which is lambda but there is also an extra equation which is just lambda(tau)~ 1/tau (equation 17). It does not follow from a lagrangien yet i'm ready to accept it because it directly follows from the new principles of this F henry-couannierhttps://www.blogger.com/profile/13933350696243790692noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58807155765495231792017-12-04T00:35:59.492-05:002017-12-04T00:35:59.492-05:00Frederic,
You don't necessarily need a Lagran...Frederic,<br /><br />You don't necessarily need a Lagrangian to get a consistent set of equations, but it's a sufficient condition. If you don't have a Lagrangian you have to do some other check to make sure you have at least enough equations/constraints to fix your degrees of freedom. At the very least you should count them. And tell us what the degrees of freedom are! Having said Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-91682557557583546292017-12-03T16:14:27.136-05:002017-12-03T16:14:27.136-05:00I suspect the only kind of equation that SH or JB ...I suspect the only kind of equation that SH or JB would consider as an acceptable one for a field is one that is derived from the extremisation of an action for this field ... it's kind of nowadays theoretical physics dogma<br /><br />I'm sorry but i still don't understand why you absolutely exclude the possibility that some degrees of freedom could satisfy equations which would be F henry-couannierhttps://www.blogger.com/profile/13933350696243790692noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-8101609985805797002017-12-02T07:24:56.847-05:002017-12-02T07:24:56.847-05:00Eusa,
No, not a problem. But I can't see any ...Eusa,<br /><br />No, not a problem. But I can't see any such term in Maeder's paper. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-39780255823007133682017-12-02T07:03:23.305-05:002017-12-02T07:03:23.305-05:00"if you do that, the additional field will al..."if you do that, the additional field will also contribute to the stress-energy."<br /><br />Is that a problem, necessarily?Eusahttps://www.blogger.com/profile/14114706429392111062noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-27686603052842787222017-12-01T18:34:45.745-05:002017-12-01T18:34:45.745-05:00I think I get it. The same equation is used twice ...I think I get it. The same equation is used twice to close the system <b>but</b> one instance of it is restricted by the scale invariance of empty space. So, they are not really twice the same equation, more like one for space with matter which is not scale invariant, and the other for empty space which is scale invariant. It is this additional hypothesis which enables this. This <i>looks</i> SpearheadBThttps://www.blogger.com/profile/00542670324878174458noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-82701594867850641322017-12-01T11:50:00.410-05:002017-12-01T11:50:00.410-05:00Sabine Hossenfelder wrote: "If you put a fact...Sabine Hossenfelder wrote: "If you put a factor 1/t^2 in front of the Minkowski metric, you get empty de Sitter space, ie a space with a cosmological constant."<br /><br />OK. Aha. Maybe. I only know the description from Hawking and Ellis, there they go to Minkowski R5 and there de Sitter space is the hyperboloid. It is also that the last time I listened to a class in GR was 30 years nad0815https://www.blogger.com/profile/15640373035677970013noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75924749837891483992017-12-01T10:24:29.394-05:002017-12-01T10:24:29.394-05:00Andre,
I did not say that eq (24) is general rela...Andre,<br /><br />I did not say that eq (24) is general relativity in strange coordinates. I don't even know what sense this statement makes. What I said is that if eq (24) is a gauge, then your "modified" Friedmann equations (27,28) are the usual ones (or they are just wrong, which is also an option, frankly I didn't check).<br /><br />I don't know what you think all caps Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-41210636124181149802017-12-01T09:42:29.913-05:002017-12-01T09:42:29.913-05:00Sabine,
S.H.: You can, of course, as I already s...Sabine,<br /> <br />S.H.: You can, of course, as I already said above, use (24) as a gauge condition <br />on the metric. Nothing wrong with that, but then you merely have general <br />relativity in strange coordinates<br /><br />A.M.: Equation (24), which is the supplementary equation, is not general <br />relativity in strange coordinates (!), this is just the relation between the energy Andre Maederhttps://www.blogger.com/profile/10447069250691469263noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-21923381080852811782017-12-01T09:06:31.527-05:002017-12-01T09:06:31.527-05:00PS: And if you do that, the additional field will ...PS: And if you do that, the additional field will also contribute to the stress-energy. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-72832238531706538682017-12-01T09:05:17.297-05:002017-12-01T09:05:17.297-05:00nad,
If you put a factor 1/t^2 in front of the Mi...nad,<br /><br />If you put a factor 1/t^2 in front of the Minkowski metric, you get empty de Sitter space, ie a space with a cosmological constant. This means empty de Sitter space is conformally flat, which is hardly news. I believe he just wants to put the same factor in front of the FRW metric, but for FRW this merely amounts to redefining the time-coordinate, and this ansatz will in general Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-7525722023735580372017-12-01T06:30:58.478-05:002017-12-01T06:30:58.478-05:00Kim,
I know it's hard to swallow for some peo...Kim,<br /><br />I know it's hard to swallow for some people, but mathematical consistency has turned out a very strong predictor of a theory's success. It adds to this that if you have a theory that no one except for its inventor can use to make predictions, that doesn't live up to the scientific standard. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-80769384518526525492017-12-01T06:25:37.900-05:002017-12-01T06:25:37.900-05:00Andre,
I am not interpreting your equations at al...Andre,<br /><br />I am not interpreting your equations at all, I am merely saying you don't have enough. <br /><br />Now you say it's eq (24), but this follows from (20) which follows from (7). It's still not an additional equation to fix your additional degrees of freedom. <br /><br />You can, of course, as I already said above, use (24) as a gauge condition on the metric. Nothing Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67000465309633379912017-12-01T05:04:46.545-05:002017-12-01T05:04:46.545-05:00What about letting the "nature" decide ?...What about letting the "nature" decide ?<br />Experts of the field have concluded... Mader's proposal is "not new theory theory" or is "mathematically" wrong. For J.B. et al. it's useless to read "his later papers, with their more complicated errors".<br /><br />Ok ! you're probably right (aren't your experts ?). J.B. if you take the time toAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-86146773083830479372017-12-01T05:01:06.741-05:002017-12-01T05:01:06.741-05:00Sabine Hossenfelder wrote:
"What do you mean ...Sabine Hossenfelder wrote:<br />"What do you mean by scale invariant? Certainly you do not mean scale invariant in the usual way if you have matter added?"<br /><br /><br />I also still don't understand what he means with "scale invariant theory/model".<br />Maybe a GR model with those scale factor lambda conditions.<br /><br />Scale invariant tensors seem to be tensors, nad0815https://www.blogger.com/profile/15640373035677970013noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-45404410079145916402017-12-01T04:27:38.567-05:002017-12-01T04:27:38.567-05:00Sabine,
Quoting you: ..." It is also only fu...Sabine,<br /><br />Quoting you: ..." It is also only fulfilled when the metric has certain <br />properties which are not fulfilled in general."<br /><br />Thus, your statement implies that the properties of the empty space should not<br />be expressed with a metric which is that for the empty space, and as a <br />consequence, it should change according to the physical context Andre Maederhttps://www.blogger.com/profile/10447069250691469263noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-91943984516967242932017-12-01T03:09:25.722-05:002017-12-01T03:09:25.722-05:00Andre,
Your recent reply just contains useless wo...Andre,<br /><br />Your recent reply just contains useless words. You still haven't answered my question what's the missing equation. <br /><br />Of course \Lambda is relevant if you want to solve the equations. I am telling you merely that its presence is entirely irrelevant to the question whether your theory makes sense even on a basic level. <br /><br /><i>"Expressing this Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-66120920425770312442017-12-01T02:59:56.826-05:002017-12-01T02:59:56.826-05:00Sabine
Once again, I tell you that the parameter ...Sabine<br /><br />Once again, I tell you that the parameter \Lambda about which you don't care<br />is essential. In General Relativity, it is a free parameter. However, in the <br />scale invariant theory, \Lambda is no longer a free parameter, as you are <br />saying. Its specific meaning, as the density of the empty space (which I repeatedly mentioned), imposes a supplementary Andre Maederhttps://www.blogger.com/profile/10447069250691469263noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-78614168980869472512017-11-30T15:25:56.654-05:002017-11-30T15:25:56.654-05:00Sabine wrote:
But that's just saying that de...Sabine wrote:<br /><br /><i><br />But that's just saying that de Sitter space is conformally flat.<br /></i><br /><br />Right! I was trying to say, very politely, that in this paper Maeder not really doing anything interesting. Perhaps I was being too polite. I'll restate my comment a bit less politely, and also less technically, so nonexperts can understand it a bit better.<br /><br /John Baezhttps://www.blogger.com/profile/11573268162105600948noreply@blogger.com