tag:blogger.com,1999:blog-22973357.post2661404410356503008..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Inflation: Status UpdateSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger46125tag:blogger.com,1999:blog-22973357.post-34136941251309900282019-03-22T01:43:27.429-04:002019-03-22T01:43:27.429-04:00Lawrence,
As is stressed in the paper, there are ...Lawrence,<br /><br />As is stressed in the paper, there are scenarios of inflation that do not give rise to a multiverse.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-76406729212321855912019-03-21T20:05:15.942-04:002019-03-21T20:05:15.942-04:00The multiverse, which is a term BTW that I dislike...The multiverse, which is a term BTW that I dislike, is something that comes out of inflation. These low energy vacuum regions or pocket worlds may have different vacua and thus different gauge and particle physics. For a number of reasons I question this, and think they may only differ according to attractors or endpoints in their RG flows. Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-63439139449045910132019-03-19T03:12:12.807-04:002019-03-19T03:12:12.807-04:00Paddy,
You can do exponential expansion with a co...Paddy,<br /><br />You can do exponential expansion with a constant. Not only is this not a quantum field, it's not a field. But my point is a much weaker one than what you seem to think. I am merely saying that it's an unnecessary assumption and hence should not be made. It is sufficient to say "there was a phase of almost exponential expansion and it ended". And scientists Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-81729467216715747412019-03-18T19:08:29.695-04:002019-03-18T19:08:29.695-04:00No problems with any of this. For what it's wo...No problems with any of this. For what it's worth I am moderately sceptical about current cosmological theory but I think less so than you. That is, I think the evidence in favour of GR is indeed good enough that it is sensible to talk about the early universe (we agree on that, perhaps). I absolutely agree that the inflationary explanation for flatness is more complicated (per Roger Penrose)Paddyhttps://www.blogger.com/profile/04491442182062182693noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5021867534790137262019-03-18T00:40:46.618-04:002019-03-18T00:40:46.618-04:00Hi Paddy,
Sorry, I think you are right, I don'...Hi Paddy,<br /><br />Sorry, I think you are right, I don't understand your point. I agree with what you say in that if the only thing you care about is consistency with observation, then you could stop the time evolution according to GR & SM at some density higher than what we have tested already, continue it with whatever else you want, and just put in an initial condition that works. <Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-61225890698850689362019-03-17T22:46:20.070-04:002019-03-17T22:46:20.070-04:00Sabine,
Not sure you understand my point. Sure,...Sabine,<br /> Not sure you understand my point. Sure, throw out GR if you like, but the only reason you thought an exponential expansion was needed was by using GR to extrapolate the expansion backwards in time far earlier than is supported by any actual evidence. (High quality evidence supporting GR as a good approximation does not exist for epochs prior to recombination... poor quality Paddyhttps://www.blogger.com/profile/04491442182062182693noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-13107438105963399872019-03-17T14:50:36.022-04:002019-03-17T14:50:36.022-04:00Is there any progress on understandimg dark energy...Is there any progress on understandimg dark energy? The last I heard, they were questioning the underlying data from Perlmutter and Riess...mhhttps://www.blogger.com/profile/03582678489140510042noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-32258293871008519012019-03-17T02:07:53.869-04:002019-03-17T02:07:53.869-04:00Hi Paddy,
Sorry for being unclear. I did mean exp...Hi Paddy,<br /><br />Sorry for being unclear. I did mean expansion. Let me explain: Your statement assumes the validity of GR to begin with, which may not be correct. It may be a modification of gravity, it may be a completely different theory, the source may not be a field, it may be some emergent something, and so on. <br /><br />Let me add that I am personally happy to think of inflation as anSabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-50349562011343773142019-03-16T10:55:08.959-04:002019-03-16T10:55:08.959-04:00Sabine, you wrote:
"But of course inflation ...Sabine, you wrote:<br /><br />"But of course inflation works by postulating an exponential suppression that comes from the dynamical law. And not only this, it furthermore introduces a field which is strictly speaking unnecessary to get the exponential expansion."<br /><br />Did you mean to write "suppression" rather than "expansion" as the final word here? OtherwisePaddyhttps://www.blogger.com/profile/04491442182062182693noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-4361782225178698702019-03-14T13:58:11.349-04:002019-03-14T13:58:11.349-04:00Interconnectedness is “certainly” interconnectedne...Interconnectedness is “certainly” interconnectedness—regardless of UV or IR regime, decay rates notwithstanding. Just ask Bohr, who’s not burdened with having to forget QCD(QFT(QED)). (If unavailable, LS might do).Emmette Davidsonhttps://www.blogger.com/profile/15566381168125492666noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-89848873702246418232019-03-14T09:56:05.247-04:002019-03-14T09:56:05.247-04:00You are right in part by saying locality in QFT is...You are right in part by saying locality in QFT is different from Bell type of locality with his inequalities, but it is not really apples and oranges. It might better be oranges and grapefruits. When we do P = p + iA to make momentum covariant the commutator of the gauge potentials is<br /><br />[A^a_μ, A^b_ν] = C^{ab}_cε_{μν}^σA^c_σ.<br /><br />The field tensor F_{νμ} = ∂_μA_ν - ∂_νA_μ + g[A_μ,Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-12051643557537424802019-03-13T18:49:14.875-04:002019-03-13T18:49:14.875-04:00Interesting to see the report on the work by Xi Do...Interesting to see the report on the work by Xi Dong and Eva Silverstein. This is essentially what I am saying. They do not seem to go further as I do with symmetry protected topological states and an the like. Dang, that is one problem with this. If you really get a good idea you most often know it is a good idea because somebody else does it. <br /><br />The holographic screen reduces a Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-68554986584987043792019-03-13T08:42:30.393-04:002019-03-13T08:42:30.393-04:00PhysicistDave,
It's an interesting question t...PhysicistDave,<br /><br />It's an interesting question that Ford studied 25 years ago. <a href="https://arxiv.org/abs/gr-qc/9410047" rel="nofollow">Paper is here</a>. Somewhat depressingly, it turns out the effect is far too small to be observable. There are other types of space-time fluctuations that produce larger effects, but those are not as well motivated. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-82849338805170541492019-03-13T05:06:16.968-04:002019-03-13T05:06:16.968-04:00Lawrence,
You wrote, "This gets us to the ma...Lawrence,<br /><br />You wrote, "This gets us to the matter of quantum gravitation as a field theory with the metric or curvature as the field that defines the light cone and in QFT the light cone sets these field amplitude conditions. Quantum gravitation is then very nonlocal."<br /><br />So, what happens to the light cone in quantum gravity? Does it get smeared out and thereby wreck PhysicistDavehttps://www.blogger.com/profile/11111405959451703182noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-85401155682978099842019-03-13T02:35:29.186-04:002019-03-13T02:35:29.186-04:00Phillip,
I think we discussed this before. It is ...Phillip,<br /><br />I think we discussed this before. It is correct that this statement depends on the choice of constants and initial values. But if you know that, then you don't need the extra explanation, so it's superfluous to mention.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-80909081096673976242019-03-13T02:33:48.523-04:002019-03-13T02:33:48.523-04:00Phillip,
I believe we have discussed this before....Phillip,<br /><br />I believe we have discussed this before. Let me therefore just say that this refers to a statement that you find in the paper which I am summarizing. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-89156617398844589812019-03-12T23:13:19.720-04:002019-03-12T23:13:19.720-04:00There’s a video in which KThorne and possibly LSus...There’s a video in which KThorne and possibly LSuskind et al. explore this very thing. To paraphrase from my jumbled recollection, LC’s “asymptotic observer” is Bob, and as you say the “huge radius” is to afford Alice a gentle fall per “the FLRW metric.” According to LS’s crystal ball (beta model: AdS/CFT(FLRW(GR))), Bob, who stays far away in flat space (to satisfy ADM safety protocols), over Emmette Davidsonhttps://www.blogger.com/profile/15566381168125492666noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-50078227054467304642019-03-12T10:11:10.586-04:002019-03-12T10:11:10.586-04:00"This is most obvious when it comes to the so...<i>"This is most obvious when it comes to the so-called “curvature problem,” or the question why the universe today is spatially almost flat. You can get this outcome without inflation, but it requires you to start with an exponentially small value of the curvature already (curvature density, to be precise). If you only look at the initial conditions, then that strongly favors inflation.&Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-27485346384411914462019-03-12T10:07:57.404-04:002019-03-12T10:07:57.404-04:00"Einstein’s theory tells us that the universe...<i>"Einstein’s theory tells us that the universe must expand."</i><br /><br />Technical point: No, it doesn't. In fact, the first relativistic cosmological model, by Einstein himself, was static. Yes, it is unstable, as pointed out be Eddington. Of course, the ideal model can be unstable and still static, because there is no way to perturb it, but it is true that it doesn't Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-72488783219072246012019-03-11T22:41:50.116-04:002019-03-11T22:41:50.116-04:00Medieval theologians debated how many angels can d...Medieval theologians debated how many angels can dance on the head of a pin. String theorists replaced the angels with Calabi-Yau manifolds.<br /><br />Who needs a Genie in the bottle when you have the multiverse? Anything you wish is in the multiverse.Enricohttps://www.blogger.com/profile/11062542721973950650noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-8596922508574439342019-03-11T10:33:19.215-04:002019-03-11T10:33:19.215-04:00Some people are looking for monopoles in an unorth...Some people are looking for monopoles in an unorthodox way :-)<br /><br />https://cerncourier.com/cms-beam-pipe-to-be-mined-for-monopoles/Magnushttps://www.blogger.com/profile/10153104775690766000noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-57580462376287013552019-03-11T07:46:45.979-04:002019-03-11T07:46:45.979-04:00Continued ---- A black hole does something odd. Th...Continued ---- A black hole does something odd. The g_{00} = 1 - 2m/r metric component is, at least for weak gravity, a bit like an index of refraction. Take a wine glass with a stem, cut off the cup part and you are left with the base and stem. Now think of this as a lens you place over pictures or look through. The regions of the scene you observe the stem is centered over are spread around in Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73052688666654979572019-03-11T07:45:27.161-04:002019-03-11T07:45:27.161-04:00As an undergraduate I started reading a text on qu...As an undergraduate I started reading a text on quantum field theory. I was rather dumb struck by this. I had taken a course in special relativity and introduction to general relativity as well as quantum mechanics. I was filled with the Einsteinian concept that space and time were transformed into each other and really were not that fundamentally different. Then upon reading QFT I was godsmackedLawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-15730201505425259232019-03-11T07:28:33.631-04:002019-03-11T07:28:33.631-04:00Thanks for the link to the blog post. Nice and cle...Thanks for the link to the blog post. Nice and clear. What I don't understand is your criticism against the inflaton field and that it is an ad-hoc construction which is unnecessary. To me it seems to be a very important link between the early universe and the creation of the elementary particles using standard field theories. I am the amateur here but it would be interesting to hear your Magnushttps://www.blogger.com/profile/10153104775690766000noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18654170973755332342019-03-11T02:24:44.143-04:002019-03-11T02:24:44.143-04:00That's right. But as I have explained in this ...That's right. But as I have explained <a href="http://backreaction.blogspot.com/2017/10/is-inflationary-universe-scientific.html" rel="nofollow">in this earlier blogpost</a>, magnetic monopoles may simply not exist, so this is a weak motivation. (In fact it is a motivation that I find is rarely mentioned these days.)Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.com