tag:blogger.com,1999:blog-22973357.post944513194262326967..comments2020-08-08T09:17:08.654-04:00Comments on Sabine Hossenfelder: Backreaction: Why do some scientists believe that our universe is a hologram?Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger61125tag:blogger.com,1999:blog-22973357.post-17743598601912920642019-10-02T13:27:44.916-04:002019-10-02T13:27:44.916-04:00To get some more mileage out of the PDE analogy an...To get some more mileage out of the PDE analogy and to connect to entropy and action let us look at Penrose’s illustration of the boundary conditions – the <a href="https://books.google.de/books?id=VWTNCwAAQBAJ&pg=PA488" rel="nofollow">blister here</a>. S is the action and δS=0 gives the classical equations of motion, projecting out solutions not on mass shell.<br />In QM, or better QFT just Reimondhttps://www.blogger.com/profile/04669340425105889539noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-19249277656738471472019-09-26T01:49:05.035-04:002019-09-26T01:49:05.035-04:00Fred Harmand4:27 AM, September 24, 2019
" yo...Fred Harmand4:27 AM, September 24, 2019<br /><br />" you raise a good point when you are saying "there are infinitely (in fact, aleph 1) different positions inside a box, "<br /><br />Congratulations on solving the Continuum Hypothesis. You are assuming that Aleph_1 is the cardinality of the Reals. This famously depends on the axioms chosen. Also, the Reals aren't real and Steven Evanshttps://www.blogger.com/profile/13898046706669437332noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74061631739777761412019-09-24T04:27:38.535-04:002019-09-24T04:27:38.535-04:00Ivan, you raise a good point when you are saying &...Ivan, you raise a good point when you are saying "there are infinitely (in fact, aleph 1) different positions inside a box, and so infinitely many microstates, and the logarithm of infinity is not defined." In reality, you can't know the particles position with infinite accuracy according to the Heisenberg uncertainty principle. Any microstate is function of a cell of uncertainty Fred Harmandhttps://www.blogger.com/profile/06831232686070504655noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5093665677676300042019-09-23T13:07:07.134-04:002019-09-23T13:07:07.134-04:00Our world is probably a solution to PDEs – the phy...Our world is probably a solution to PDEs – the physical laws. To numerically solve/integrate PDEs we start from initial conditions and take tiny steps as e.g. shown <a href="https://www.youtube.com/watch?v=p_di4Zn4wz4&list=PLZHQObOWTQDNPOjrT6KVlfJuKtYTftqH6&index=2&t=23m1s" rel="nofollow">here with an ODE</a>. The time it takes to determine the next step depends on the required Reimondhttps://www.blogger.com/profile/04669340425105889539noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58599650065823094442019-09-21T16:36:46.312-04:002019-09-21T16:36:46.312-04:00Correction (Fourth paragraph, first sentence.): &q...Correction (Fourth paragraph, first sentence.): "sounds" should be "sound"Wind Towelhttps://www.blogger.com/profile/14370187229537168223noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-8003090121110258992019-09-20T06:47:18.699-04:002019-09-20T06:47:18.699-04:00I was making a joke
🙂I was making a joke <br />🙂Greg Feildhttps://www.blogger.com/profile/11893021846714172269noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18099273569272729622019-09-19T21:54:23.849-04:002019-09-19T21:54:23.849-04:00@Greg Feild
Maybe letting the free market decide ...@Greg Feild<br /><br />Maybe letting the free market decide what is science and what is science is where science is going wrong? Time was when it was scientists that decided that through discussion, debate and experiment. Moziburhttps://www.blogger.com/profile/11836761141351221660noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-7123836738818669242019-09-19T21:52:20.461-04:002019-09-19T21:52:20.461-04:00I did pick up one his Carrolls books on GR and the...I did pick up one his Carrolls books on GR and the only thing I remember from it is when he introduces tensors and points out the distinction between covariant and contravariant tensors and says that is old-fashioned and obsolete terminology. Except of course it isn't. Covariance and contravariance is a basic distinction in category theory. It justs goes to show what different backgrounds Moziburhttps://www.blogger.com/profile/11836761141351221660noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79604258334135766372019-09-19T21:39:58.238-04:002019-09-19T21:39:58.238-04:00I want to add I'm not a nay-sayer to string th...I want to add I'm not a nay-sayer to string theory, just to over-blown and hyperbolic claims. I think thats not un-natural. Personally, the point when I got some physics of string theory, after having worked a little through Beckers and Schwartz book, is actually going back to the history of the subject and realising that they began with the Veneziano amplitude which actually fitted with *Moziburhttps://www.blogger.com/profile/11836761141351221660noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-47449858727961280522019-09-19T21:36:41.332-04:002019-09-19T21:36:41.332-04:00> I take it you may be coming from a math backg...> I take it you may be coming from a math background?<br /><br />Hehe yeah I kind of gave my game away when I unloaded the cardinals on you people... I got degrees in CS and math logic, and I am extremely interested in physics lately, but I am also very easily confused by the sheer weirdness of it.<br /><br />> In classical statistical mechanics, you choose (arbitrarily) your smallest<br />Ivan Zaigralinhttps://www.blogger.com/profile/08309409136799098584noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18204333533291771582019-09-19T21:21:49.894-04:002019-09-19T21:21:49.894-04:00All this supposes that extra dimensions are actual...All this supposes that extra dimensions are actually there, as with super-symmetry and super-strings. When Dirac predicted the positron it was found within a decade. Can you remind me just how long we've been waiting for either direct or indirect evidence of any of these phenomena? Perhaps if physicists who want to speculate about such concepts prefaced their musings with the word 'Moziburhttps://www.blogger.com/profile/11836761141351221660noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3705642299291283262019-09-19T21:09:00.546-04:002019-09-19T21:09:00.546-04:00The holographic principle is a bit of a misnomer a...The holographic principle is a bit of a misnomer actually. After all, in a real hologram you still need a three dimensional space for the picture to appear in! As a name it is rather like the Dirac sea which involves no actual sea, and here, no actual hologram.Moziburhttps://www.blogger.com/profile/11836761141351221660noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-35300609730995723422019-09-19T07:36:19.159-04:002019-09-19T07:36:19.159-04:00bud rap is right (about mathematicism), as usual. ...bud rap is right (about mathematicism), as usual. <br /><br />I explain everything in my book <br />"Mind Boggling Exploding Swirly Stuff From the Multiverse"<br /><br />Free upon request ..Greg Feildhttps://www.blogger.com/profile/11893021846714172269noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67670722446330276192019-09-18T16:46:14.311-04:002019-09-18T16:46:14.311-04:00Yes, he does go from from disagreement to claiming...Yes, he does go from from disagreement to claiming that Carroll is an idiot doing a disservice to science -- but concludes that he should be ignored. I admit though, that in a different context (say,"The Sopranos") the phrase "think hard about what they can do to deal with this situation" might be a bit ... sinister. Check out xkcd.com/1483/ ;-) I think Woit meant "Jim Shillidayhttps://www.blogger.com/profile/10544709134684735232noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73229926918940041462019-09-18T14:26:47.820-04:002019-09-18T14:26:47.820-04:00The idea that mathematics is connected to physics ...<i>The idea that mathematics is connected to physics runs deep and goes back to the ancient Greeks.</i><br /><br />That idea is the philosophical stance called mathematicism and it does indeed run deep in modern theoretical physics. Philosophical stances are only beliefs however, and do not constitute a sound basis for doing science. In fact, it is my explicitly stated criticism that bud raphttps://www.blogger.com/profile/06948881286545517324noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-34656174805644876282019-09-18T14:02:04.920-04:002019-09-18T14:02:04.920-04:00Yep, thanks, and I guess no matter how long the sp...Yep, thanks, and I guess no matter how long the spaceship is, it will be 2d by then. Appreciate it.<br /><br />BTW, about the nay-sayers.... No surprise they'd be here; the owner of this blog is a world-class nay-sayer, and we love her for it. I guess it all depends on what someone's saying nay to.Jim Shillidayhttps://www.blogger.com/profile/10544709134684735232noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-47110509181133193732019-09-18T11:10:43.058-04:002019-09-18T11:10:43.058-04:00Given that time is reversible in QFT, and so in th...Given that time is reversible in QFT, and so in theory you can extrapolate any state at t=0 to all times prior and subsequent, in that sense the four-dimensional history and future of the universe can be reduced to the three-dimensional present moment where time is not a variable. At least, for those who believe in the block universe.<br /><br />Is the above related in any way to the holographic Scotthttps://www.blogger.com/profile/16914985126761335721noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83103924208351360302019-09-18T10:22:39.337-04:002019-09-18T10:22:39.337-04:00"Personally I think that the motivations for ..."Personally I think that the motivations for the holographic principle are not particularly strong and in any case we’ll not be able to test this hypothesis in the coming centuries. Therefore writing papers about it is a waste of time."<br /><br />I completely agree with you, Sabine. For this statement however, you don't need to be a theoretical physicist. Just "common sense&Soulmanhttps://www.blogger.com/profile/08884551782946824614noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-27622766213756825882019-09-18T07:03:29.564-04:002019-09-18T07:03:29.564-04:00Ivan,
In classical statistical mechanics, you cho...Ivan,<br /><br />In classical statistical mechanics, you choose (arbitrarily) your smallest size interval and stick with it. There will always be an arbitrary constant difference between your and some other guy's entropy, but it does not matter.<br /><br />In quantum mechanics, the states are discrete as long as you are in a finite box. You do not need to choose an arbitrary smallest lengthPhysicistDavehttps://www.blogger.com/profile/11111405959451703182noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-41595646304819592762019-09-18T06:41:16.506-04:002019-09-18T06:41:16.506-04:00The idea that mathematics is connected to physics ...The idea that mathematics is connected to physics runs deep and goes back to the ancient Greeks. The understanding of physics, or astronomy, required measurements. In the ancient world this was often just theodolite measurements of planets against the sky. The changes in these quantities are some sort of "map" between one set of numbers to another. This was made more firm with Galileo Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-1980924702456331742019-09-18T05:51:47.553-04:002019-09-18T05:51:47.553-04:00If Alice sends a photon to Bob when she is behind ...If Alice sends a photon to Bob when she is behind the horizon and Bob is not then Bob will cross the horizon before receiving the photon. Bob will notice nothing peculiar about this situation. Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-69621054095547733992019-09-18T05:06:09.124-04:002019-09-18T05:06:09.124-04:00Jim: he would if he could. See his subsequent post...Jim: he would if he could. See his subsequent post:<br /><br />https://www.math.columbia.edu/~woit/wordpress/?p=11277<br /><br />John Duffieldhttps://www.blogger.com/profile/02867342924571644602noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51509966461365425912019-09-18T03:55:12.535-04:002019-09-18T03:55:12.535-04:00@Bud rap
I forgotted saying that in my hierarchie,...@Bud rap<br />I forgotted saying that in my hierarchie, (1) and (2) and (3) have to be applied necessarily. They are not optionnal. And that mathematical consistency can bee included in logical consistency. So putting this one on level (0) or (2) is not fondamental, but you are right for putting it at level (2) <br /><br />742/5000<br />As for the necessity of using mathematics, the history of Jean-Paulhttps://www.blogger.com/profile/14622097958803312521noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83966589017120003772019-09-18T01:30:19.661-04:002019-09-18T01:30:19.661-04:00Arnold,
The holographic principle is about degree...Arnold,<br /><br />The holographic principle is about degrees of freedom. Thus, I guess what is missing in your analogy with partial differential equations (PDEs) in d+1 dim and boundary conditions in d dim is the additional condition of a maximal resolution. Since almost all PDEs only can be solved numerically anyway this translates into the maximal resolution of the dynamical mesh (BTW a Reimondhttps://www.blogger.com/profile/04669340425105889539noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-72524848317331759782019-09-18T01:29:42.090-04:002019-09-18T01:29:42.090-04:00Happy anniversary.Happy anniversary.martenhttps://www.blogger.com/profile/02423871089614417690noreply@blogger.com