tag:blogger.com,1999:blog-22973357.post5871780294306569250..comments2021-08-22T06:05:44.372-04:00Comments on Sabine Hossenfelder: Backreaction: No foam: New constraint on space-time fluctuations rules out stochastic Planck scale dispersionSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger58125tag:blogger.com,1999:blog-22973357.post-70969612889311112182016-01-17T03:29:29.764-05:002016-01-17T03:29:29.764-05:00Sam,
Partly in response to the comments here, I w...Sam,<br /><br />Partly in response to the comments here, I wrote <a href="http://arxiv.org/abs/1504.06070" rel="nofollow">this paper</a>, in which I have stated all definitions. It is especially meant for newcomers, so please have a look, I hope it will answer your questions.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-44797314297874715502016-01-16T16:47:00.608-05:002016-01-16T16:47:00.608-05:00I know this is dated - the discussion ended a whil...I know this is dated - the discussion ended a while ago. But I'm still not sure which side of the coin I agree with regarding the triangulation of spacetime. I think the point that was argued boils down to the definition of "Lorentz invariance." Now, Lorentz covariance is well defined, but I think Lorentz invariance is not as well defined. I think the definition that should be used Anonymoushttps://www.blogger.com/profile/10231560762849861690noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-65174437214169566132015-07-23T07:12:40.175-04:002015-07-23T07:12:40.175-04:00I think this article may be of some relevance to t...I think this article may be of some relevance to the above discussion. arXiv:1502.04320<br /><br />Best,<br />DAnonymoushttps://www.blogger.com/profile/04245217592187021011noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11068932007831990662015-03-23T12:12:17.229-04:002015-03-23T12:12:17.229-04:00Arun,
You mean in terms of convergence radius? Ye...Arun,<br /><br />You mean in terms of convergence radius? Yes, could be. Interesting thought. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-86297070054913874432015-03-23T11:44:00.656-04:002015-03-23T11:44:00.656-04:00Hi Bee,
I understand what you wrote, I think. If ...Hi Bee,<br /><br />I understand what you wrote, I think. If you write up for arxiv, that would be really good, I always have a fighting chance of understanding what you write.<br /><br />I know this is a bit of a leap, perhaps over a cliff, doesn't it suggest that analyticity of functions in Minkowski space puts stronger conditions on the function than in Euclidean space? I know, e.g., Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-12899996267675038242015-03-23T02:12:44.265-04:002015-03-23T02:12:44.265-04:00Arun,
The problem, in a nutshell, is that there i...Arun,<br /><br />The problem, in a nutshell, is that there is no Lorentz-invariant way to find a "neighbor" that does not lead to a space-filling network. I think I will actually write this up at some point and put it on the arxiv.<br /><br />First, notice that the Causal Sets people have a procedure to find a "neighbor" (which leads to what they call "chains", that Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-40573822685417550182015-03-22T19:09:04.525-04:002015-03-22T19:09:04.525-04:00Thanks for the answer Bee. Much appreciated!Thanks for the answer Bee. Much appreciated!petehttps://www.blogger.com/profile/12969621709127674152noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-71479319848017135842015-03-22T16:16:19.772-04:002015-03-22T16:16:19.772-04:00Thanks, Bee, for setting me straight!
So, if I at...Thanks, Bee, for setting me straight!<br /><br />So, if I attempted to do a computation by first discretizing Minkowski space with a sprinkling, and then try, e.g., to approximate a derivative by a finite difference of values between "neighboring" points, I would find I have to deal with an infinity of "neighboring" points?<br /><br />I find it very counterintuitive that in Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-86984388815194277642015-03-21T13:35:02.322-04:002015-03-21T13:35:02.322-04:00Hi Pete,
Yes, good point, sorry for being vague. ...Hi Pete,<br /><br />Yes, good point, sorry for being vague. What I meant was "there is no evidence for space-time foam that appreciably affects the propagation of light through space."<br /><br />Regarding the vacuum energy - different foam, if you wish, it's basically the fluctuations in the other fields that contribute to the vacuum energy (or rather: should contribute). Best,<br Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-21413505054816927842015-03-21T13:05:20.227-04:002015-03-21T13:05:20.227-04:00Great article,
The one thing that I've been w...Great article,<br /><br />The one thing that I've been wondering about is the distinction between the quantum foam mentioned in this article and the vacuum energy that you discussed in the previous article. I've always assumed that "quantum foam" conveyed a similar idea as vacuum energy, independent of whether or not it affects the speed of photons at different wavelengths.<br /petehttps://www.blogger.com/profile/12969621709127674152noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-72628504345882241552015-03-21T11:29:59.255-04:002015-03-21T11:29:59.255-04:00Dear Arun,
You're misunderstanding me. There ...Dear Arun,<br /><br />You're misunderstanding me. There is a (locally countable) Lorentz-invariant sprinkling, see<br /><br />http://arxiv.org/abs/gr-qc/0605006<br /><br />The point I was making is that you cannot make this into a network (ie connect points) without making this network locally space-filling. It works for points because points are trivially already Lorentz-invariant, whereas Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75688835006035335872015-03-21T10:59:41.522-04:002015-03-21T10:59:41.522-04:00^^^ no countable sprinkling of points. I suppose ...^^^ no countable sprinkling of points. I suppose all bets are off on uncountable sets.Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-37429662113970441562015-03-21T10:58:11.352-04:002015-03-21T10:58:11.352-04:00Hi Bee,
I agree with you that there is no sprink...Hi Bee, <br /><br />I agree with you that there is no sprinkling of points in a Lorentzian space-time that looks identical in all inertial frames. That is, there is always something which distinguishes one frame from the rest.<br /><br />What I'm wondering is - is there are "fibration" of Lorentzian spacetime - a sprinkling of null geodesics that is Lorentz-invariant? <br /><br />Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-9237582544771592712015-03-21T08:57:43.297-04:002015-03-21T08:57:43.297-04:00Nemo:
A-ha-ha, you're right, I already wrote ...Nemo:<br /><br />A-ha-ha, you're right, I already wrote that. I was thinking it sounded kind of familiar...<br /><br />You don't have to quantize space and/or time. I refer by 'quantum gravity' as anything that resolves the known inconsistencies in our theories. You also shouldn't confuse the quantization of the metric with the quantization of space itself. <br /><br />Every Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23078033068000669092015-03-21T08:29:24.454-04:002015-03-21T08:29:24.454-04:00P.S.
strangling = struggling :-DP.S.<br />strangling = struggling :-Dnemohttps://www.blogger.com/profile/07365330980872106443noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83201771203368235402015-03-21T08:26:12.576-04:002015-03-21T08:26:12.576-04:00I read it.
I understand why we should understand w...I read it.<br />I understand why we should understand what happen to gravity at quantum level, but what I do not understand is why to reach the goal we should quantize the space.<br />Yes, I read that there's a big problem with the singularity and the information paradox, but I'm strangling with the idea of a bended space-time that is something really very different from what we nemohttps://www.blogger.com/profile/07365330980872106443noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-77301361966095333722015-03-21T07:50:12.918-04:002015-03-21T07:50:12.918-04:00Thank you very much Sabine. I'll read it!Thank you very much Sabine. I'll read it!nemohttps://www.blogger.com/profile/07365330980872106443noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54154128423240610892015-03-21T07:37:09.521-04:002015-03-21T07:37:09.521-04:00Nemo:
h has the dimension of an action. It appear...Nemo:<br /><br />h has the dimension of an action. It appears in the path integral. You have to quantize gravity because it couples to matter which we already know is quantized, and nobody knows how to consistently couple an unquantized to a quantized theory.<br /><br />That's the short answer. This reminds me though I meant to write a blogpost about the question "why quantize gravity&Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83724730026963503282015-03-21T07:28:44.422-04:002015-03-21T07:28:44.422-04:00There's a point of QG discussions that I'v...There's a point of QG discussions that I've never really understand so, i make the question:<br /><br />As far as I understand the quantization belong by h. h has the dimension of the angular momentum. Why than it is so important to quantizy the space?<br /><br />Is the space to be quantizied or the space-time?<br /><br />I'm quite confused... <br /><br />Of course if it is not too nemohttps://www.blogger.com/profile/07365330980872106443noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-64950601492444852852015-03-21T06:10:52.509-04:002015-03-21T06:10:52.509-04:00I'm just making my own model, which features, ...I'm just making my own model, which features, among other exciting concepts, string orbit scalar intermodulation. Find me on facebook, to learn more about The Big Drag and the semiconductive quantum circuit of the fractal multiverse. peace Paul Adamson friend requests welcomeAnonymoushttps://www.blogger.com/profile/09538878851436654530noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-1727482979604207412015-03-20T10:30:40.771-04:002015-03-20T10:30:40.771-04:00vmarko:
You should go and look up "ad homine...vmarko:<br /><br />You should go and look up "ad hominem" because you don't seem to understand what it means.<br /><br />What I have told you is simply that you are wasting my time and that I would appreciate you would first look up what I said.<br /><br />"So yes, I claim that even a square lattice is in fact Lorentz invariant,"<br /><br />This is just plainly wrong, and Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-80569859819504949242015-03-20T09:31:40.768-04:002015-03-20T09:31:40.768-04:00Hi Bee,
"Before you produce more fog, please...Hi Bee,<br /><br />"Before you produce more fog, please go and look it up."<br /><br />Bee, this is uncalled for. I don't see the purpose for ad hominem in a serious discussion.<br /><br />What is happening here? I have a feeling that I have defeated your opinion on Lorentz invariance of triangulations, and now you are becoming increasingly more brash, in order to shut me up or vmarkohttps://www.blogger.com/profile/12660488689205445871noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-61315806103762979122015-03-20T09:30:29.853-04:002015-03-20T09:30:29.853-04:00Hi Bee,
"When I say "invariant", I...Hi Bee,<br /><br />"When I say "invariant", I mean "invariant", period. If you are claiming a triangulation is invariant, then ALL of its aspects must be invariant. You claimed that is possible."<br /><br />Again, the projection of the triangulation on a hypersurface is not an aspect of the triangulation, but an aspect of the hypersurface. The fact that the vmarkohttps://www.blogger.com/profile/12660488689205445871noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-71962730352001291182015-03-20T02:25:07.118-04:002015-03-20T02:25:07.118-04:00Zephir,
The photon for all we presently know does...Zephir,<br /><br />The photon for all we presently know doesn't have a rest mass. If it had a rest mass it would be rest in the rest frame. It would of course not be at rest in all frames. Besides this, you could easily have answered this question with Google and I would appreciate if you tried this first the next time. Please make a little effort before clogging my comment section with Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33439153487559634962015-03-19T20:38:43.001-04:002015-03-19T20:38:43.001-04:00Great article,
The one thing that I've been w...Great article,<br /><br />The one thing that I've been wondering about is the distinction between the quantum foam mentioned in this article and the vacuum energy that you discussed in the previous article. I've always assumed that "quantum foam" conveyed a similar idea as vacuum energy, independent of whether or not it affects the speed of photons at different wavelengths.<br petehttps://www.blogger.com/profile/12969621709127674152noreply@blogger.com