tag:blogger.com,1999:blog-22973357.post4056247905334317316..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: The Minimal Length in Quantum Gravity: An Outside ViewSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger50125tag:blogger.com,1999:blog-22973357.post-32175242024488712012009-09-19T11:33:34.230-04:002009-09-19T11:33:34.230-04:00Thanks Phil, and yes we should focus (as it were) ...Thanks Phil, and yes we should focus (as it were) on the direct, minimal length question. QM interpretation issues do matter though, because "it matters" (can't quit punning) for ML, whether a particle is "really" characterized by a de Broglie wavelength, or whether that's just a pilot wave for a little "chunk" that stays the same size (I may be Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-30561005820858201022009-09-19T10:30:03.367-04:002009-09-19T10:30:03.367-04:00One just had to know "where to begin" fo...One just had to know "<a href="http://eskesthai.blogspot.com/2009/09/macrscopic-similarities-in-microscopic.html" title="Macrscopic Similarities in a Microscopic World " rel="nofollow">where to begin</a>" for minimum length to be considered.<br /><br />In a "condense matter theorist point of view" applicability can be used, while in "thought experiment previously PlatoHagelhttps://www.blogger.com/profile/00849253658526056393noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67279897188259196352009-09-19T08:37:27.520-04:002009-09-19T08:37:27.520-04:00Hi Neil,
“That also supports my interpretation o...Hi Neil,<br /><br /><i> “That also supports my interpretation of the WDCE.” </i><br /><br />As you may or not be aware, the concept of <a href="http://plato.stanford.edu/entries/qm-bohm/#mp" rel="nofollow">decoherence</a> is actually an integral part of Bohmian Mechanics and was initially brought forth in the first of Bohm’s two landmark 1952 papers; although it was not actually called to be Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-81845551036080156762009-09-18T20:36:49.518-04:002009-09-18T20:36:49.518-04:00Phil,
Indeed you didn't confuse superpo and e...Phil,<br /><br />Indeed you didn't confuse superpo and entanglement. I can be careless in responding to mixed players. I just put out my standard quick take on the difference because, as you noted, "It appears superposition and entanglement is being looked at here as being one in the same." Your explanation is more artful anyway.<br /><br />As for the Wheeler delayed choice Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-12870561878108881892009-09-18T11:50:55.823-04:002009-09-18T11:50:55.823-04:00How would one push back perspective toward "m...How would one push back perspective toward "minimal length?"<br /><br /><a href="http://arxiv.org/abs/hep-th/0508217" title="Entanglement Interpretation of Black Hole Entropy in String Theory" rel="nofollow">Entanglement entropy</a> sets up a thought process about how we see "geometrically" once one assumes one has seen in ways that a Q<->Q measures allows.<br /><br />PlatoHagelhttps://www.blogger.com/profile/00849253658526056393noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-88267070254189722502009-09-18T06:58:40.772-04:002009-09-18T06:58:40.772-04:00Hi Neil,
I would agree that the nature of the qua...Hi Neil,<br /><br />I would agree that the nature of the quanta still has a lot to be explained, for which new models are trying to be developed. However to say “the universe just can't be represented in realistic ways” is tantamount to saying there is no reality. I would also agree that to look at any particle as a dimensionless point in itself presents as being an impossibility, whether Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-81210096161589486952009-09-17T11:51:59.746-04:002009-09-17T11:51:59.746-04:00Thanks Kris, and your site is interesting (good fo...Thanks Kris, and your site is interesting (good for people in neuroscience to dabble in physics but we on the edges of the clique must tread carefully...) But I find the "inverse mass" (reduced mass?) curious - a nucleus surely has the DB wavelength according to its total mass! I am suspicious of any process (eg increasing boundness) having a trend first in one direction, then in the Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23410304990415626282009-09-17T06:04:56.404-04:002009-09-17T06:04:56.404-04:00Hi Kris,
Just to acknowledge my goof in refering ...Hi Kris,<br /><br />Just to acknowledge my goof in refering to you as Chris instead as Kris as it should be; so sorry.<br /><br />Best,<br /><br />PhilPhil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67268599669768585252009-09-17T05:53:00.654-04:002009-09-17T05:53:00.654-04:00Hi Neil, James & Chris,
It appears superposit...Hi Neil, James & Chris,<br /><br />It appears superposition and entanglement is being looked at here as being one in the same. Superposition is when single quanta are considered as existing in more than one state simultaneously until observation, while entanglement is the interdependence of state between two or more quanta that exists regardless of spacial separation. The first is a question Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-69666043860947591362009-09-17T02:00:02.865-04:002009-09-17T02:00:02.865-04:00Hi Neil,
... anyone notice the oddity of defining...Hi Neil,<br /><br /><i>... anyone notice the oddity of defining the Compton/de Broglie wavelength in terms of the momentum of a given "particle"? What if two particles are attached in various ways, do they count as "one" or "two" etc. - just like in Galileo's Socratic question challenging Aristotelian physics about the speed of a given falling body!</i><br /><br Kris Kroghhttps://www.blogger.com/profile/07340827856086381459noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-15807880299006322632009-09-17T00:17:06.346-04:002009-09-17T00:17:06.346-04:00Hi Bee!
After reading so many opinions on minimum ...Hi Bee!<br />After reading so many opinions on minimum length, I still believe it to exist.<br /><br />The emphasis is on belief since it is a belief, as well, for those who do not believe in minimum length.<br /><br />Even though you have gone across the pond, I hope to keep seeing this blog.<br /><br />good luck!<br />jaljalhttps://www.blogger.com/profile/16969819389823705458noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-78469882036145011142009-09-16T19:29:23.986-04:002009-09-16T19:29:23.986-04:00James, it looks that the point of the Schrödinger&...James, it looks that the point of the Schrödinger's Virus experiment is to show that quantum superposition can be applied to objects as large as viruses - with a bit of added "organic" mystique. It helps to clear up where the boundary between the quantum and effectively macroscopic/classical world begins. (But "decoherence" arguments, IMHO, can't honestly do that - seeNeil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-22760424347050093122009-09-16T18:14:11.139-04:002009-09-16T18:14:11.139-04:00Niel,
I found this link which might be of interes...Niel,<br /><br />I found this link which might be of interest concerning diffraction/scattering of atoms by gratings: http://arxiv.org/pdf/quant-ph/9905090v1<br /><br />Seems that it all depends on the situation. In general you have a quantum many-body problem. However, if the incident group of particles is bound sufficiently tightly so as to be much smaller than the grating spacing (such as is Jamesnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-88893999269021571182009-09-15T22:05:09.999-04:002009-09-15T22:05:09.999-04:00Correction - I mean De Broglie wavelength, since t...Correction - I mean De Broglie wavelength, since the particle collection could be moving at any velocity (not just the 0.707 c that gives CW.)Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-42581678522808908822009-09-15T22:02:18.511-04:002009-09-15T22:02:18.511-04:00James, Bee made a perfect little posing of my ques...James, Bee made a perfect little posing of my question - "in which case[s] the Compton wavelength of a collection of particles is related to the total mass rather than each particle having its own."<br />I don't understand your answer re R^3n, I guess you mean some phase space but Compton wavelengths are "real" as per diffraction etc. BTW, look up "Schrodinger's Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-1830751497624120842009-09-15T21:44:15.908-04:002009-09-15T21:44:15.908-04:00Too many glasses of wine... of course it should ha...Too many glasses of wine... of course it should have been: 'in "real" R^3'jamesnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-90787782207391196222009-09-15T21:34:05.196-04:002009-09-15T21:34:05.196-04:00Oh OK - I misunderstood the question.
Unfortunate...Oh OK - I misunderstood the question.<br /><br />Unfortunately this other one is a bit trickier! I guess it depends on the circumstances. Presumably we have in mind some kind of scattering, and which picture is the better approximation is a question of scale, and the nature of the scattering interaction. <br /><br />Of course, if we have an n-particle system then the wavefunction doesn't Jamesnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-38601031696467548022009-09-15T09:58:05.386-04:002009-09-15T09:58:05.386-04:00James: On the risk of misinterpreting Neil, I thin...James: On the risk of misinterpreting Neil, I think his question was in which case the Compton wavelength of a collection of particles is related to the total mass rather than each particle having its own.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3526840458233053242009-09-15T09:52:41.738-04:002009-09-15T09:52:41.738-04:00Neil,
within the confines of non-relativistic QM,...Neil,<br /><br />within the confines of non-relativistic QM, I think the quantity you are looking for is the 'centre of mass', call it X.<br /><br />Given a group of particles this is defined just as in the classical case, and represents the average position of the group.<br /><br />Differentiate this twice w.r.t time and multiply by the total mass (sum of individual masses) and you get Jamesnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3087673268675823712009-09-14T14:41:37.775-04:002009-09-14T14:41:37.775-04:00Thanks Bee for reference and some explanations. By...Thanks Bee for reference and some explanations. By "odd", I meant the taking for granted of what makes a "single object." How connected or affiliated do m1, m2, .... have to be, for the quantum wavelength/s to be referenced to lambda = h/gamma*(m1, m2, ....)v separately, versus lambda = h/gamma*(m1 + m2 + m3 + ...)v as a sum?<br /><br />You refer to bound states which I have Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-88425131322341656392009-09-14T11:15:57.750-04:002009-09-14T11:15:57.750-04:00Have been thinking about your post Bee and some th...Have been thinking about your post Bee and some thoughts are being gathered <a href="http://eskesthai.blogspot.com/2009/09/where-susskind-leaves-off-seth-lloyd.html" title="Where Susskind leaves off, Seth Lloyd begins" rel="nofollow">here</a>PlatoHagelhttps://www.blogger.com/profile/00849253658526056393noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-37847524408819413422009-09-14T09:17:27.516-04:002009-09-14T09:17:27.516-04:00Hi Bee,
I will read the paper. Thanks for clarify...Hi Bee,<br /><br />I will read the paper. Thanks for clarifying.<br /><br />Best KayKay zum Feldehttps://www.blogger.com/profile/04233793196547147876noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-70915433878644101012009-09-14T09:10:17.735-04:002009-09-14T09:10:17.735-04:00Huh? I think you have completely misunderstood wha...Huh? I think you have completely misunderstood what I said. First, the uncertainty relation is not thought to be absent at high energies/small distances, but instead it should get larger, in such a way that there is no possibility to have an arbitrarily good resolution of structure which, in usual QM, you could in principle do if you only had high enough energies. Second, as I said explicitly in Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-61870891060333393082009-09-14T09:04:14.897-04:002009-09-14T09:04:14.897-04:00Hi Bee,
so the theory (Quantum Gravity) of favori...Hi Bee,<br /><br />so the theory (Quantum Gravity) of favoring a finite length should be a 'quantum theory' without an uncertainty relation ? It might be no problem that this theory has no uncertainty relation, but what is left of a quantum theory then ?<br /><br />Best KayKay zum Feldehttps://www.blogger.com/profile/04233793196547147876noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3013486923470239932009-09-14T07:22:46.539-04:002009-09-14T07:22:46.539-04:00Hi Bee,
Thanks for this paper of Garay you pointe...Hi Bee,<br /><br />Thanks for this paper of Garay you pointed out to Neil, for it does appear to be a very good synopsis of the whole subject. Perhaps from here I might get a better handle on the concept and arguments in general.<br /><br />Best,<br /><br />PhilPhil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.com