tag:blogger.com,1999:blog-22973357.post7793795541250990573..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: This and ThatSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger70125tag:blogger.com,1999:blog-22973357.post-41061983813691421682009-10-16T08:36:14.317-04:002009-10-16T08:36:14.317-04:00Sorry for my previous post, I have inverted the de...Sorry for my previous post, I have inverted the definitions previously. So let me first correct myself:<br /><br />Configuration space: 6N dimensional space in which the whole system is represented by one point in that space.<br /><br />Phase space: 6 dimensional space in which the whole system is represented by N points in that space.<br /><br />So the whole system is represented by one Christinehttp://egregium.wordpress.comnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-8734562844101495012009-10-16T07:35:48.064-04:002009-10-16T07:35:48.064-04:00Hi Christine,
.....for the N particles); the so-...Hi Christine,<br /><br /><i> .....for the N particles); the so-called "configuration space" usually represents the whole system as a point in the space, and so it is a 6 dimensional space. </i><br /><br />All what you have said is of course quite true, yet in configuration space these 6 dimensions represents the space of one particle as it relates to itself, whose dimensionally Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-34502587864829656282009-10-16T07:23:22.743-04:002009-10-16T07:23:22.743-04:00I don't quite get the physical/philosophical p...<i>I don't quite get the physical/philosophical point about configuration space. </i><br /><br />Neither do I.Christinehttp://egregium.wordpress.comnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-70696880554357037982009-10-16T01:23:39.813-04:002009-10-16T01:23:39.813-04:00I don't quite get the physical/philosophical p...I don't quite get the physical/philosophical point about configuration space. When two particle histories have the same values of position and time coordinates, then in spacetime they are in contact, while in the 6 N dimensional configuration space of N particles, this is not instantly obvious. In fact, in phase space, canonical transformations can turn generalized coordinates and momenta Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-12613557638537717732009-10-15T23:23:43.484-04:002009-10-15T23:23:43.484-04:00Dear Bee,
I post this link here to add to a globa...Dear Bee,<br /><br />I post <a href="http://www.dawn.com/wps/wcm/connect/dawn-content-library/dawn/the-newspaper/columnists/irfan-husain-survival-of-the-fittest" rel="nofollow">this link here</a> to add to a global perspective of science and society.<br /><br />-Arun<br /><br />PS: if you find the reference to hypocrisy puzzling, google, or read <a href="http://www.wowessays.com/dbase/af1/nyv305.Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-21670412139886464912009-10-15T17:32:10.925-04:002009-10-15T17:32:10.925-04:00Hi Phil,
(...) science with the aid of mathemati...Hi Phil,<br /><br /><i> (...) science with the aid of mathematics has come up with another level of or degrees of freedom, which is called configuration space and is considered by most as not real, yet rather simply a creation of mind (...) </i><br /><br />Well, it is a question of experience (classically speaking for now) that if you consider at a given instant of time a system formed by Christinehttp://egregium.wordpress.comnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-24308928538469489532009-10-15T09:04:17.510-04:002009-10-15T09:04:17.510-04:00If the issue is how matter and geometry are relate...If the issue is how matter and geometry are related, there is a question: is it a mere coincidence that the number of generations is the same as the number of spatial dimensions ? Or perhaps they are related in some structural manner ?joel ricenoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-1713213272141996652009-10-15T07:18:38.173-04:002009-10-15T07:18:38.173-04:00Hi Christine,
“With time, we have proven to be a...Hi Christine,<br /><br /><i> “With time, we have proven to be able to turn a part of what we regarded as metaphysics into physics. The ultimate level at which this can lead to, if there is one at all, in terms of real understanding, is a philosophical question.” </i><br /><br />I find your comment to be both an astute observation and contemplation, which in essence is what both good science and Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-4950258192537458832009-10-15T07:11:21.664-04:002009-10-15T07:11:21.664-04:00This comment has been removed by the author.Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-21913065206647710482009-10-14T13:00:58.064-04:002009-10-14T13:00:58.064-04:00hi B.,
correction - I agree that number of dimens...hi B.,<br /><br />correction - I agree that number of dimensions mathematically should follow from something more fundamental, like algebra, but I'm not sure I would call it quantization. It's a tricky argument. An example (half-metaphor):<br /><br />our perception screen is 2-dimensional, but as kids we learn from, you might say, mathematical experimental correlations that world "isAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51004026089864614342009-10-14T08:06:58.252-04:002009-10-14T08:06:58.252-04:00What intrigues me about spatial dimensions is not ...What intrigues me about spatial dimensions is not their number per se, but the very fact that the universe admits certain independent (countable) degrees of freedom. I wonder whether a universe could be conceived without independent directions. When we answer that first, we might be able to address dimensionality. Time is another mystery of its own.<br /><br />I am 100% with Bee. We are Christinehttp://egregium.wordpress.comnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-48202429035025495632009-10-14T07:07:15.068-04:002009-10-14T07:07:15.068-04:00Arrow: There are never good reasons for believe, o...Arrow: There are never good reasons for believe, otherwise you'd know and not believe. A speculation without evidence is exactly that: a speculation without evidence. What differentiates believe and fantasies from scientific theories is testability and self-consistence. Models with extra dimensions offer both (the latter with constraints as previously mentioned, but then which of our theoriesSabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-45249470687749336052009-10-14T06:53:39.458-04:002009-10-14T06:53:39.458-04:00Giotis: "Arrow, in the brane world scenarios ...Giotis: "Arrow, in the brane world scenarios only gravity can probe the extra dimensions and gravity has been tested accurately only down to a fraction of a mm."<br /><br />Yes, but this rests on the assumption that only gravity can probe extra dimensions which I find very suspect and unappealing, it not only breaks the unity of spacetime by introducing special dimensions it also Arrownoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-72138651689368907042009-10-14T03:20:20.814-04:002009-10-14T03:20:20.814-04:00Hi Giotis,
Thanks for pointing out, I didn't ...Hi Giotis,<br /><br />Thanks for pointing out, I didn't know that. In any case, this was just an example of roughly what I was talking about. As I said I didn't look into the details of that particular paper anyway. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79808990974486614502009-10-14T03:17:39.772-04:002009-10-14T03:17:39.772-04:00Dear Arun,
Yes, maybe it's not a question we ...Dear Arun,<br /><br />Yes, maybe it's not a question we will be able to find a satisfactory answer to at all. Note however that I was explicitly asking for a mechanism, eg a mechanism such that if you start with an arbitrary # of spatial dimensions, the dynamics is such that we always ends up having 3 large and the others small. I would consider that a satisfactory explanation. At least for Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-48879332093298974102009-10-14T03:11:32.251-04:002009-10-14T03:11:32.251-04:00Hi A,
Not sure what you mean there. Yes, maybe th...Hi A,<br /><br />Not sure what you mean there. Yes, maybe the issue with dimensions has something to do with the quantization, but who knows. I personally am more sympathetic to the idea that geometric quantities of whatever sort don't make much sense at subplanckian scales. Though there's often ways to define something akin dimensionality of a manifold by other means. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-41774408143599876642009-10-14T02:32:42.219-04:002009-10-14T02:32:42.219-04:00Arrow:
The fact that we cannot explain why there...Arrow: <br /><br /><i>The fact that we cannot explain why there are 4 and not 4000 dimensions does not mean however that we should question this value, we get it from experiment and so it should be trusted. </i><br /><br />People are calculating how the existence of extra dimensions would affect our experiments and analyze the data to see if it contains indications for the existence of additionalSabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-29189070851978636962009-10-14T02:10:12.861-04:002009-10-14T02:10:12.861-04:00"If experiment indeed had excluded extra dime..."If experiment indeed had excluded extra dimensions then no one would talk about them"<br /><br />Show me the theorist who would abandon a good theory just because of something as trivial as the experimental verdict.<br /><br />Ptolemy's epicycle theory survived for 1,500 years. Now that's something to be inspired by.Thomas Larssonnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-86102275279786249382009-10-13T16:30:38.065-04:002009-10-13T16:30:38.065-04:00", we get it from experiment and so it should...", we get it from experiment and so it should be trusted."<br /><br />Arrow, in the brane world scenarios only gravity can probe the extra dimensions and gravity has been tested accurately only down to a fraction of a mm. So we could well have large extra dimensions of that order. If experiment indeed had excluded extra dimensions then no one would talk about them. If on the other hand Giotisnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11219463837768035492009-10-13T15:52:37.585-04:002009-10-13T15:52:37.585-04:00Bee: "The question I was raising is the follo...Bee: "The question I was raising is the following. Our present view of reality is that we live in a manifold with fields on it. Why does that manifold have 4 dimensions and Lorentzian signature?"<br /><br />Science can only discover how Nature operates not why it operates a particular way. Even if I could explain how the number 4 follows from such and such more fundamental principle youArrownoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-80080820791149208932009-10-13T15:23:43.673-04:002009-10-13T15:23:43.673-04:00Helling and Pollicastro strongly disputed that (he...Helling and Pollicastro strongly disputed that (hep-th/0409182 & hep-th/0610193). As a result I think Thiemann gave up the whole idea. That's why I think he never published the anticipated sequence for the LQG string in curved target space. But I'm not at all sure that this is the reason, it's just my impression.Giotisnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54116119258370055372009-10-13T15:23:37.319-04:002009-10-13T15:23:37.319-04:00hmm.
in a way I agree...
but let me explain how ...hmm.<br /><br />in a way I agree...<br /><br />but let me explain how I mean it-<br /><br />issue is deeper, and the need for quantization procedure modification is just a corollary of that.<br /><br />and in fact - the issue is with DIMENSIONS itselfs. <br /><br />so- quantization procedure should be modified as a consequence of conceptualizing dimensions.<br /><br />A.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3481130153453725452009-10-13T13:14:24.239-04:002009-10-13T13:14:24.239-04:00Hi A,
I don't know. What I am saying is that ...Hi A,<br /><br />I don't know. What I am saying is that one should consider that the quantization scheme we know does a good deal in describing Nature at relatively low energies, might not be the right thing to do at high energies. In particular, it seems to me that the need of string theory to have additional dimensions (and the problems that come with their compactification) are in the end Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20611486765046419262009-10-13T12:37:56.471-04:002009-10-13T12:37:56.471-04:00Hello bee,
strangely here I agree that main motiv...Hello bee,<br /><br />strangely here I agree that main motivations for considering extra dimensions rest on mathematical consistency. And that being related to having no good reason why we live in 3+1 world. you say something about quantization should be done? I think also , yes. but in what way do you mean that (about quantization)?<br /><br />A.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-61227335967687365772009-10-13T10:55:21.629-04:002009-10-13T10:55:21.629-04:00Oswaldo Zapata attempts to take on the myth of the...Oswaldo Zapata attempts to take on the myth of the lone creator:<br /><br /><a href="http://spinningthesuperweb.blogspot.com/2009/10/superstring-world-i-of-iv.html" rel="nofollow">http://spinningthesuperweb.blogspot.com/2009/10/superstring-world-i-of-iv.html</a>Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.com