tag:blogger.com,1999:blog-22973357.post8988065184223007755..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Does the Universe have higher dimensions? Part 2Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger81125tag:blogger.com,1999:blog-22973357.post-62333151410011734702021-05-30T01:08:04.741-04:002021-05-30T01:08:04.741-04:00Hi shm,
Yes, thanks for pointing out. I never rea...Hi shm,<br /><br />Yes, thanks for pointing out. I never really looked into this, now I am wiser :) Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11870325988979108772021-05-30T00:21:27.684-04:002021-05-30T00:21:27.684-04:00It is for sure complicated …
You may also like: AN...It is for sure complicated …<br />You may also like: AN EMBEDDING FOR GENERAL RELATIVITY AND ITS IMPLICATIONS FOR NEW PHYSICS - https://arxiv.org/ftp/arxiv/papers/0705/0705.0067.pdf. Embedding of GR solutions in a 5D Einsteinian spacetime (or flat per https://arxiv.org/ftp/arxiv/papers/1011/1011.0214.pdf)). So solutions of GR also seem to support just N+1 dimensions. I assume it is a local shm_physhttps://www.blogger.com/profile/04244964622679107960noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-14641944196775176392021-05-29T22:48:00.721-04:002021-05-29T22:48:00.721-04:00Yes I know about the string the 10 (Supersymmetry ...Yes I know about the string the 10 (Supersymmetry and / or conformality)/ 26 (bosonic / closed strings). I was really interested in the coincidence (as well as the KK extension to SM that would also be 10 (per part 1), or 8 if the extra dimensions could be shared or 7 if local embeddings at each point was sufficient, ...).<br /><br />Ok I appreciate the answers.<br /><br />Thanks<br /><br />S<br shm_physhttps://www.blogger.com/profile/04244964622679107960noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5996287163687919402021-05-27T06:14:14.931-04:002021-05-27T06:14:14.931-04:00Your question is a bit odd. The closest interpreta...Your question is a bit odd. The closest interpretation and possible answer I can think are that de Sitter spacetime in 4-dimensions has topology M^3×ℝ, for M^3 = S^3, a three sphere for positive curvature or M^3 = ℝ^3 Euclidean space if this is flat. These spaces foliate spacetime along a real number line. Anti-de Sitter spacetime is M^3×S^1, where the S^1 is time. Time is on a circle. There are Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-48273391883501202312021-05-27T06:10:28.967-04:002021-05-27T06:10:28.967-04:00Sorry, I got confused about what we are talking ab...Sorry, I got confused about what we are talking about. The thing is, I actually decided to *not* include the comment about the embedding space in this video. I only just saw that I accidentally left it in the transcript. The comment will appear in the video coming up on Saturday, alas without the remark about the numerical coincidence. I'll add a note in the info below the video that actuallySabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20639820350015346672021-05-27T06:03:48.829-04:002021-05-27T06:03:48.829-04:00For spacetime that is orientable our spacetime can...For spacetime that is orientable our spacetime can be embedded in 5 dimensions. This is what de Sitter worked, where he looked at a metric<br /><br />s^2 = t^2 + u^2 - x^2 - y^2 - z^2,<br /><br />a flat 5-dimensional spacetime. For the signature of u positive the constraint equation on this, setting s = constant gives a hyperboloid exterior to a light cone, or de Sitter space. For the signature Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-48440755233691335822021-05-27T05:45:16.833-04:002021-05-27T05:45:16.833-04:00Yes it is Whitney. Yes it is Whitney. Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33997746360904370022021-05-27T02:18:56.239-04:002021-05-27T02:18:56.239-04:00Hi again,
I just coincidentally saw that Stephani...Hi again,<br /><br />I just coincidentally saw that Stephani's textbook actually pre-dates the theorem. So quite possibly he didn't know of it. Ie, I guess that 8 is actually the correct number. (Though of course if you can embed it into 8 you can also embed it into 10...) Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-48502276162194699062021-05-27T02:13:00.153-04:002021-05-27T02:13:00.153-04:00Well space-time isn't Euclidean. The 10 is fro...Well space-time isn't Euclidean. The 10 is from <a href="https://www.amazon.de/-/en/Hans-Stephani/dp/3326000839" rel="nofollow">Stephani's GR textbook</a>. It isn't further explained in the book, but I think it can't be more than 10 just because the metric has only 10 independent components in 4 dimensions. Having said that, as Lawrence points out, it is certainly the case that Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-69998216070619432192021-05-26T22:15:41.383-04:002021-05-26T22:15:41.383-04:00Still one more question. Whitney's theorem req...Still one more question. Whitney's theorem requires generically 2N => 8 dimensions for global embedding of a 4D spacetime. Sabine mentioned 10 D. I am still missing two... Any additional hint? Thanksshm_physhttps://www.blogger.com/profile/04244964622679107960noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-32518281285310526382021-05-26T21:39:24.687-04:002021-05-26T21:39:24.687-04:00Ah. I think Lawrence rather meant the Whitney Theo...Ah. I think Lawrence rather meant the Whitney Theorem? shm_physhttps://www.blogger.com/profile/04244964622679107960noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-68872377227672808742021-05-26T05:59:04.307-04:002021-05-26T05:59:04.307-04:00Embedding of manifolds is strange. In general, by ...Embedding of manifolds is strange. In general, by the Whitehead theorem a manifold of N dimensions is only guaranteed to embed in a manifold of 2N dimensions. A manifold of N dimensions only embeds in one of N+1 dimensions if there are some conditions met, such as orientability. <br /><br />A torus is in one embedding a donut, really dough-naught, and we can map that to a square area. These then Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-63677960882728113222021-05-25T23:21:47.884-04:002021-05-25T23:21:47.884-04:00I'm talking about global embeddings.I'm talking about global embeddings. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-6121399575252317202021-05-25T13:56:42.004-04:002021-05-25T13:56:42.004-04:00Isn't Campbell theorem telling s that a 4D spa...Isn't Campbell theorem telling s that a 4D spacetime/manifold can be embedded in a 5D flat or Einsteinian universe? Why do we need 10 D for this?shm_physhttps://www.blogger.com/profile/04244964622679107960noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-64848408403460924172021-04-27T08:58:53.883-04:002021-04-27T08:58:53.883-04:00Fantastic. :)Fantastic. :)C Thompsonhttps://www.blogger.com/profile/01723392308309671498noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-4518040425407331652021-04-26T07:38:53.279-04:002021-04-26T07:38:53.279-04:00@C Thompson,
I found the perfect website to uploa...@C Thompson,<br /><br />I found the perfect website to upload my short story called “WritersCafe”. It’s 53 pages long (double-spaced). I’ve got considerable editing to do, but as soon as that is finished and I upload the story to the site, I’ll provide the URL.<br />David Schroederhttps://www.blogger.com/profile/18048116250413347228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-78248838807628510772021-04-25T22:45:44.917-04:002021-04-25T22:45:44.917-04:00It's called the cosmological constant because ...It's called the cosmological constant because it's constant. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-7606721229852535452021-04-25T22:40:54.929-04:002021-04-25T22:40:54.929-04:00I don't know what this means, sorry.I don't know what this means, sorry. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-53699040795618638652021-04-25T10:59:56.115-04:002021-04-25T10:59:56.115-04:00Hello Sabine, I have a question, I may be naive, I...Hello Sabine, I have a question, I may be naive, I am not a specialist; My question is -Can a closed temporal magnitude linked to the three spatial dimensions plus time be used to describe many closed spatial quantities? ; I mean, If I add another time dimension; but closed, could it eliminate the excess of spatial dimensions? , varying that time closed interval could accommodate any closed Luishttps://www.blogger.com/profile/05491803947570764962noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-12701028596266916482021-04-24T23:53:38.579-04:002021-04-24T23:53:38.579-04:00Oh I see, I didn't realize that's what you...Oh I see, I didn't realize that's what you meant, partly, I think, as I was in a morning fog having gone to bed late. I do have one story that's at a link on my personal website. But it's against the rules to post links to personal websites, so I'll have to somehow obtain your email or vice versa. Alternatively, I could upload the story to some website for viewing. I'David Schroederhttps://www.blogger.com/profile/18048116250413347228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-15539531756455765242021-04-24T14:01:50.270-04:002021-04-24T14:01:50.270-04:00One interesting point that isn't emphasised en...One interesting point that isn't emphasised enough in string theory is that the Calabi-Yau manifolds they compactify the theories on are actually vacuum solutions to 6d GR with vanishing cosmological force. I find that much more comprehensible physically speaking than just the bare name, Calabi-Yau manifold. <br /><br /> I'm saying force rather than constant as it seems a bit odd to name Moziburhttps://www.blogger.com/profile/11836761141351221660noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-17040687164469275822021-04-24T10:26:41.712-04:002021-04-24T10:26:41.712-04:00Hi David, I meant, that to would be a great name f...Hi David, I meant, that to would be a great name for a band or a track or album. If you publish any writing online, I'd like to read it if you don't mind.C Thompsonhttps://www.blogger.com/profile/01723392308309671498noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-89545845624863607032021-04-24T07:39:56.419-04:002021-04-24T07:39:56.419-04:00@Topolino, Thank you for your kind words and very ...@Topolino, Thank you for your kind words and very thoughtful suggestion. I very much like that idea. Currently the concepts in the paper are not buttressed by a mathematical analysis that would evaluate the model against real world data. I'm going to do my best to rectify that deficiency before submitting the paper to a professional journal. It would be wonderful to have feedback from David Schroederhttps://www.blogger.com/profile/18048116250413347228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-66850528169534984602021-04-24T02:40:40.425-04:002021-04-24T02:40:40.425-04:00@David Schroeder
Hi David, your 'nobium bullet...@David Schroeder<br />Hi David, your 'nobium bullet' sounds like a great scenario for a story. <br />'Nobium Bullet' is also a name for a music group or album. :)C Thompsonhttps://www.blogger.com/profile/01723392308309671498noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-61303961236464213172021-04-24T00:57:10.906-04:002021-04-24T00:57:10.906-04:00Dear David Schroeder,
Thank you very much for the...Dear David Schroeder,<br /><br />Thank you very much for the comments. I cannot say much,<br />except two things:<br />1. Negative densities can be found easily in quantum mechanical systems. <br /><br />2. I would like to suggest that, if you really think that your idea is important and you want a truly professional feed-back, send the manuscript to a professional journal. You do not need to payTopolinohttps://www.blogger.com/profile/04005531267023248797noreply@blogger.com