tag:blogger.com,1999:blog-22973357.post8142654645222879506..comments2021-07-30T15:23:00.163-04:00Comments on Sabine Hossenfelder: Backreaction: What does the universe expand into? Do we expand with it?Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger98125tag:blogger.com,1999:blog-22973357.post-18051200343030815692021-07-20T06:40:16.547-04:002021-07-20T06:40:16.547-04:00Hi, shouldn't universe expansion have a "...Hi, shouldn't universe expansion have a "visible" effect on subatomic particles arround us? Theoretically their wave function fills the universe so it will strech with it in some places even with speeds FTL.Catalinhttps://www.blogger.com/profile/06192244112905762189noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-63298631799040445182021-06-27T23:17:39.903-04:002021-06-27T23:17:39.903-04:00If you could ride a photon you'd be dead and w...If you could ride a photon you'd be dead and wouldn't see anything. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-85939899223049910712021-06-27T12:58:12.587-04:002021-06-27T12:58:12.587-04:00Dr. Sabine
I read that if you could ride a photon ...Dr. Sabine<br />I read that if you could ride a photon <br />you would see past, present, and future simultaenously<br />Is that so?<br />Could you relate that to the block universe and superdeterminism?Pubbli Webbhttps://www.blogger.com/profile/12908734155063692762noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3783309315702714592021-06-16T10:45:09.162-04:002021-06-16T10:45:09.162-04:00(a) Please see the info below the video.
(b) Depen...(a) Please see the info below the video.<br />(b) Depends on the exact assumptions. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5885942829045425572021-06-16T09:11:45.762-04:002021-06-16T09:11:45.762-04:00I think your 10-dimensional embedding manifold is ...I think your 10-dimensional embedding manifold is a bit higher than needed. I recall from my GR courses that the flat embedding space for an n-dimensional manifold requires at most 2n dimensions; see https://en.wikipedia.org/wiki/Whitney_embedding_theorem.Jolyonhttps://www.blogger.com/profile/06924808323646484281noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-9592549476183340092021-06-10T15:56:02.004-04:002021-06-10T15:56:02.004-04:00It expands into the same thing that it expanded ou...It expands into the same thing that it expanded out of, the Quantum Void. But since the Quantum Void is non-physical, the universe expands into nothing.Mr. Jonathan Camphttps://www.blogger.com/profile/06001639663507984948noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-26428341077309339822021-06-09T10:46:28.758-04:002021-06-09T10:46:28.758-04:00drl,
You can of course introduce a length by defi...drl,<br /><br />You can of course introduce a length by defining a scale, but there's no reason to use any of those scales, and there is still no reason to use any particular coordinate system in GR. Look, the only thing I am saying is that you can take FRW in the standard comoving coordinates, make a coordinate transformation, and get a non-orthogonal metric with flat subspaces. That's Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-63304852414117537022021-06-09T09:43:21.684-04:002021-06-09T09:43:21.684-04:00C'mon Sabine - I've been doing such things...C'mon Sabine - I've been doing such things for a very long time now. Again - Riemmanian geometry has an arbitrary global length standard. That is not a matter of coordinates at all, it is a matter of structure. This shrinking vs. expanding issue is just a demonstration of that. To make it concrete, one needs a way of breaking that global symmetry. Weyl geometry (among others) works. (It drlhttps://www.blogger.com/profile/05424774416249451584noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-45823565150854461552021-06-09T09:26:49.564-04:002021-06-09T09:26:49.564-04:00"One, it is not at all a matter of convention...<i>"One, it is not at all a matter of convention to say expansion ~ shrinking modulo coordinates. One can imagine"</i><br /><br />I suggest you don't "imagine" but do the math. There are many ways to "imagine" coordinate transformations wrongly. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-62918281401681014812021-06-09T08:09:21.274-04:002021-06-09T08:09:21.274-04:00OK I'm a little late to this but I would like ...OK I'm a little late to this but I would like to point out a couple of things.<br /><br />One, it is not at all a matter of convention to say expansion ~ shrinking modulo coordinates. One can imagine a physical field that acts on say the electron mass, which ultimately defines the size of things. The radius of the hydrogen atom goes like the inverse of the electron mass. So such a (scalar) drlhttps://www.blogger.com/profile/05424774416249451584noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-42283640057931282042021-06-07T10:35:58.844-04:002021-06-07T10:35:58.844-04:00Sorry, but the FLRW coordinates we are usually usi...Sorry, but the FLRW coordinates we are usually using, ds^2 = dtau^2 - a^2(tau) dl^2, are those where distances are shrinking but everything remains on its place. Ilja Schmelzerhttps://www.blogger.com/profile/05344206562643658764noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3735201854632395062021-06-07T10:30:06.592-04:002021-06-07T10:30:06.592-04:00JimV, A 'datum' kinetic state as a 'lo...JimV, A 'datum' kinetic state as a 'local background' system is essential to derive ANY 'propagation speed'! There may must then be hierarchical, as found in space. As Einstein put it, (after Minkowski) in '52 there are 'endlessly'('infinitely' HM) many spaces in motion within spaces. As he said; that's 'logically unavoidable' but "not Peter Jacksonhttps://www.blogger.com/profile/13905359947213961259noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-29600336393788685392021-06-06T16:55:42.658-04:002021-06-06T16:55:42.658-04:00“Do we expand with the universe? No, we don’t. Ind...“Do we expand with the universe? No, we don’t. Indeed, it’s not only that we don’t expand, but galaxies don’t expand either. It’s because they are held together by their own gravitational pull. They are “gravitationally bound”, as physicists say. The pull that comes from the expansion is just too weak. The same goes for solar systems and planet. And atoms are held together by much stronger forcesantooneohttps://www.blogger.com/profile/12559038212417783694noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-53521779844160207232021-06-06T16:41:43.981-04:002021-06-06T16:41:43.981-04:00The notion that an embedding space is needed to de...The notion that an embedding space is needed to define a space (if indeed that is what anyone is claiming) would, it seems to me, lead to the infamous "infinite regress". Along with Zeno and Democritus, I distrust infinities. They just don't seem practical to me. (Maybe it is because I only have a finite number of neurons.)JimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-89229923935630704332021-06-06T01:40:33.719-04:002021-06-06T01:40:33.719-04:00I think that the term 'expands into' is in...I think that the term 'expands into' is in general misleading. It would be better to say: <br />- "The space-time of the universe develops" or <br />- "goes through an own process of evolution"<br />Whereas no one really knows what the result will be in the end.<br /><br />See Wikipedia --> "List of unsolved problems in physics" --> "Future of the Hubert Rhttps://www.blogger.com/profile/05706995593637353535noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20651380916517516772021-06-05T19:03:16.892-04:002021-06-05T19:03:16.892-04:00"Conformal symmetry in a way is analogous to ..."Conformal symmetry in a way is analogous to the principle of least action and the conservation of phase space volume for optical light fronts."<br />That's the part I intuitively enjoy the most (and prematurely, as I'm not sure if 1) it is what I think it is 2) I can pull it out). I think it attempts to naturally develop an intuition about TR. Particularly, because it Vadimhttps://www.blogger.com/profile/17350813784317789818noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75289758536677874062021-06-05T18:49:01.063-04:002021-06-05T18:49:01.063-04:00"You can imagine a universe with just two par..."You can imagine a universe with just two particles in it. Then, space is only defined between those two particles, they can only attract each other (there is only one degree of freedom in that system), they can't repel each other because there is no further space than the space between them."<br />To hold a particle on a circular path, a force is required that is permanently Gerd Termathehttps://www.blogger.com/profile/01718262823488014650noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33556502346027379322021-06-05T13:38:29.347-04:002021-06-05T13:38:29.347-04:00(2 of 2)
So: If the main problem with connectivit...(2 of 2)<br /><br />So: If the main problem with connectivity-only topologies is that they are exceedingly sloppy about discarding implicit labeling dimensions, why did I begin this by focusing instead on the concept of thickness and inside-outside surfaces?<br /><br />That’s an interesting one. If you scrupulously avoid dimensional sloppiness and embed your manifold properly within a Terry Bollingerhttps://www.blogger.com/profile/03915136249111338024noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-43319938603611528262021-06-05T13:36:46.334-04:002021-06-05T13:36:46.334-04:00Sabine,
Thank you for an excellent explanation of...Sabine,<br /><br />Thank you for an excellent explanation of how the universe expands and why most mathematicians and physicists view embedding spaces as redundant. Some work I did years ago kept nagging at my memory until I recalled it just today. Below I take a contrary position and explain why I would not only say that embedding spaces <i>do</i> matter, but that <i>not</i> using them is Terry Bollingerhttps://www.blogger.com/profile/03915136249111338024noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54841189658090615142021-06-05T07:40:32.554-04:002021-06-05T07:40:32.554-04:00@Dr. Hossenfelder:
I'm writing this here becau...@Dr. Hossenfelder:<br />I'm writing this here because I don't use Twitter. The article from the Wall Street Journal that you re-tweeted a few days ago about transgender women being transferred into women's prisons is misleading and transphobic.<br />Consider that anyone who goes to the effort of outing themselves as transgender, making an application to move into a women's prison C Thompsonhttps://www.blogger.com/profile/01723392308309671498noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-60170158294920103362021-06-05T02:36:02.487-04:002021-06-05T02:36:02.487-04:00This comment has been removed by the author.Mr. Jonathan Camphttps://www.blogger.com/profile/06001639663507984948noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-32313646961609136402021-06-04T15:18:37.674-04:002021-06-04T15:18:37.674-04:00Johnathan, you did not seem to read my comment ver...Johnathan, you did not seem to read my comment very well or did not understand it. I definitely did not say anything like "an infinite/eternal expanse of empty space". My comment is very similar to your starting comment, i.e.<br />You: "zero point field and the quantum void are the same things and that they are the Embedding Space that the universe expands into"<br />Me: &Peter Becherhttps://www.blogger.com/profile/04022891868017776895noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54227220576062024772021-06-04T03:15:53.441-04:002021-06-04T03:15:53.441-04:00This comment has been removed by the author.Mr. Jonathan Camphttps://www.blogger.com/profile/06001639663507984948noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-1890389979319560142021-06-03T17:06:58.712-04:002021-06-03T17:06:58.712-04:00Sabine, you say:
“There’s no embedding space. So,...Sabine, you say:<br /><br />“There’s no embedding space. So, for the sphere that’d mean, we’d have to ask how’d we find out it’s curved if we were living on the surface, maybe ants crawling around on it.<br /><br />One way to do it is to remember that in flat space the inner angles of triangles always sum to 180 degrees. In a curved space, that’s no longer the case. “<br /><br />But this result antooneohttps://www.blogger.com/profile/12559038212417783694noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-77218881216708743912021-06-03T16:44:56.535-04:002021-06-03T16:44:56.535-04:00Penrose loves conformal geometry. The group theory...Penrose loves conformal geometry. The group theory basis for twistor theory is SU(2,2) of conformal geometry. He has proposed the idea of Weyl complexity in the evolution of the universe, and now he has his CCC cosmology. Conformal geometry is nice, but the problem is that it is broken.<br /><br />Conformal symmetry in a way is analogous to the principle of least action and the conservation of Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.com