tag:blogger.com,1999:blog-8666091.post110739858727589004..comments2021-02-05T18:38:25.974+01:00Comments on The Reference Frame: Tachyons can change topologyLuboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger28125tag:blogger.com,1999:blog-8666091.post-1107706505212851352005-02-06T17:15:00.000+01:002005-02-06T17:15:00.000+01:00Quantoken does'nt know about how to define vacuum ...Quantoken does'nt know about how to define vacuum states since he has never actually understood or even opened a quantum field theory book. His not having encountered a field theory book is not surprising really since in most bookstores the field theory books are generally not to be found on the same shelves as the coloring in books.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107627117311542962005-02-05T19:11:00.000+01:002005-02-05T19:11:00.000+01:00Hi Michael,
I don't wish to be a nuisance but if y...Hi Michael,<br />I don't wish to be a nuisance but if you could have a go at emailing the Schwinger paper again sometime it would be well appeciated.<br />Best regards<br />Steve MAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107621733242934612005-02-05T17:42:00.000+01:002005-02-05T17:42:00.000+01:00Quantoken,
The physical vacuum state is the one an...Quantoken,<br />The physical vacuum state is the one annihilated by all lowering operators of the full (interacting) quantum fields.<br /><br />Your weird comments are pathetic.<br /><br />--MichaelAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107587700870241382005-02-05T08:15:00.000+01:002005-02-05T08:15:00.000+01:00Michael said:
"an unstable vacuum state is defined...Michael said:<br />"an unstable vacuum state is defined as a state that is the legitimate physical vacuum state of a given instant in time". Bla bla bla.<br /><br />I am sorry. I am asking you to give an exactly definition of what is vacuum and what is not vacuum. You have NOT give me the definition of vacuum. Until you can define precisely what is vacuum, there is no point discussing vacuum state. I could well say that a space containing one photon is a vacuum state that is excited. You could also expand the concept and call everything an excited or unstable vacuum state. This is actually all theoretists have been saying. There are plenty of talk of various "vacuum states" but no one ever seem to mean anything about none-vacuum. Sure according to Penrose the whole universe is just one big bubble excited from a vacuum state, using "borrowed energy", as if you can borrow 10^100 Joules of energy for 1.4x10^10 years, without breaking the energy conservation law, and not even have to pay interest either :-)<br /><br />Give me a precise definition of vacuum please. Or at least give a criterial to distinguish vacuum and none-vacuum.<br /><br />QuantokenQuantokenhttps://www.blogger.com/profile/08057876770160255308noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107555509749902672005-02-04T23:18:00.000+01:002005-02-04T23:18:00.000+01:00Quantoken...
"A fool may be thought wise and intel...Quantoken...<br />"A fool may be thought wise and intelligent if he keeps his mouth shut"<br />Proverbs.17:27Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107551266423715832005-02-04T22:07:00.000+01:002005-02-04T22:07:00.000+01:00Hi Michael,
Sorry about that! I forgot that email ...Hi Michael,<br />Sorry about that! I forgot that email account gets blasted with spam everyday and rapidly fills up! I have'nt cleaned it out in a few days! Can you email to<br />smllr@titan71.fsnet.co.uk<br /><br />Many thanks! It is much appreciated.<br />Steve MAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107550497305256352005-02-04T21:54:00.000+01:002005-02-04T21:54:00.000+01:00Steve M, your hotmail account is apparently too sm...Steve M, your hotmail account is apparently too small for the paper. I tried to send it and got an error message back.<br /><br />Best, MichaelAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107550079411704322005-02-04T21:47:00.000+01:002005-02-04T21:47:00.000+01:00Quantoken,
an unstable vacuum state is defined as ...Quantoken,<br />an unstable vacuum state is defined as a state that is the legitimate physical vacuum state of a given instant in time, but evolves non-trivially under the Hamiltonian action. It will therefore look like a state containing many particles at a later time with respect to the physical vacuum of that later instant. Vacuum states of different times are typically related to one another through Bogoliubov transformations. There is nothing "funny" about this.<br /><br />There is indeed a conceptual difficulty in defining the physical vacuum in dynamic curved spaces. I recommend the papers by Leonard Parker on this issue for those who are interested. Anyway, this was not the subject of our present discussion. It also wasn't what you had in mind, Quantoken, because you didn't know it until I told you. I am explaining this to you although I know that you have no appreciation or understanding of these concepts. You are just here to heckle and I wish you weren't.<br /><br />--MichaelAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107547837335757972005-02-04T21:10:00.000+01:002005-02-04T21:10:00.000+01:00Here is a criticism of the so called Tachyon:
http...Here is a criticism of the so called Tachyon:<br />http://www.macalester.edu/astronomy/people/chrissy/Links/Tachyon.html<br /><br />QuantokenQuantokenhttps://www.blogger.com/profile/08057876770160255308noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107546799839131532005-02-04T20:53:00.000+01:002005-02-04T20:53:00.000+01:00Michael said:
"The imaginary energy density is sta...Michael said:<br />"The imaginary energy density is standard in field theories with UNSTABLE VACUUM. Look at Schwinger's pioneering paper"<br /><br />I find such wording amusing! Can you give an EXACT definition exactly what is vacuum and what is not vacuum? What do you mean "unstable" vacuum? Is "unstable vacuum" a vacuum or not a vacuum?<br /><br />If "unstable vacuum" is not a vacuum, you have been abusing the English language. If it is a kind of vacuum, then we have at least two kinds of vacuum, the usual stable kind we know, and your unstable kind. Then there could be some sort phase transition between these two kind of vacuum and it can be observed. Then, the whole thing is no longer vacuum by the very definition of vacuum!!!!<br /><br />There could only be just one kind of vacuum and that's the stable kind, by the very definition what is vacuum. Anything else is NOT called vacuum! It's not even physics. It's pure linguistics and logic!<br /><br />The "imaginary energy" is nonsense. Put it into general relativity it means we could have spacetime curvature which is imaginary. What does imaginationary curvature mean? It doesn't even have a mathematical meaning!<br /><br />QuantokenQuantokenhttps://www.blogger.com/profile/08057876770160255308noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107545436699990052005-02-04T20:30:00.000+01:002005-02-04T20:30:00.000+01:00Michael, that classic Schwinger paper has well ove...Michael, that classic Schwinger paper has well over 2000 citations. Do you know if it is available to view on the web somewhere? I simply don't have access to Physical Review that far back. Anyone with a pdf of it could email it to me at sdmedit@hotmail.com. Id like to see it but cant unless someone emails it or locates it online somewhere. The paper with the string version looks nice too. Lubos, maybe you could say a bit more about your idea of destabilising the Landscape via decays into C Yaus?<br />Regards, Steve MAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107537902547825242005-02-04T18:25:00.000+01:002005-02-04T18:25:00.000+01:00Hey Lubos,
I agree that Tom Banks' arguments over...Hey Lubos,<br /><br />I agree that Tom Banks' arguments overlap with what I am trying to say. It is my opinion that the background field equations should not just relate classical fields to each other, but should be equations relating fields and fluxes. That's what I would expect to be the natural description of quantized matter plus gravity and it seems reasonable to me that a more careful definition of the Polyakov path integral would reveal just that.<br /><br />Just to make the connection to the origin of this discussion: If I am right, don't you agree that this might have far reaching consequences for the number of stable vacua and related issues?<br /><br />The imaginary energy density is standard in field theories with unstable vacuum. Look at Schwinger's pioneering paper<br /><br />Phys. Rev. D82, #5, 664 (1951).<br /><br />This paper is so beautiful that it's a must read anyways.<br /><br />Best wishes,<br />MichaelAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107530457649015622005-02-04T16:20:00.000+01:002005-02-04T16:20:00.000+01:00FYI, perhaps no more baryonic dark matter problem?...FYI, perhaps no more baryonic dark matter problem?<br />http://www.wired.com/news/space/0,2697,66487,00.htmlAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107522290354156142005-02-04T14:04:00.000+01:002005-02-04T14:04:00.000+01:00Hi Michael,
what you write almost sounds like Tom...Hi Michael,<br /><br />what you write almost sounds like Tom Banks. I am very interested in these comments - you say that low energy effective action is not a good starting point to study vacuum decay and vacuum selection issues. Could you please be a little bit more specific what are "your"/the new rules (from string theory and quantum gravity) and especially how they differ from the effective rules?<br /><br />Concerning your last paragraph. The goal of string theory is not to be always different, but to predict physics in the unification regime. So your slogan "what would string theory be worth without gravity" has nothing to do with the question whether gravity in string theory qualitatiely changes the predictions of the instabilities from the low energy effective action, or whether it preserves some of them and which etc. String theory, when calculated properly, has a unique answer to this question - at least unique in every particular context. And we can't find this answer by ideology, I think. ;-)<br /><br />I don't know why you mention imaginary energy density (in Minkowski space?). In my viewpoint it is unphysical and I've never used a concept like that. Should I have?<br /><br />All the best<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107482833617043852005-02-04T03:07:00.000+01:002005-02-04T03:07:00.000+01:00Hey Lubos!
Am I denying the existence of the Schw...Hey Lubos!<br /><br />Am I denying the existence of the Schwinger effect? I do not think so.<br /><br />Sure, you can see Schwinger's effect in Euclidean space in certain descriptions. One can use instantons. And Schwinger reinterpreted an imaginary vacuum energy density as the pair production rate.<br /><br />Can we do the same in string theory? Of course. hep-th/9209032, e.g., studies a theory of open strings, with Chan-Paton charges at their ends, in an electric background and in a limit where gravity is decoupled. They found that the effective string action also picks up an imaginary part, and interpreted that as the string production rate following Schwinger.<br /><br />So everything is nice and dandy, right Lubos? Just turn gravity on! Now what? Are you going to couple gravity to your imaginary energy density? Gravity does not care about Schwinger's reinterpretation. Imaginary energy densities are just fatal in a theory of gravity.<br /><br />The effective string action is not the place where you want to see the effects of vacuum instability. One should expect to find this as tadpoles in the background field equations. Anyone who has studied beta function calculations knows that there are no such tadpoles in the theory obtained from standard analytical continuation.<br /><br />This problem has its origin in the issues I described in my previous posting.<br /><br />You say one has to be careful interpreting Euclidean space solutions in Minkowski space. It is simply not true that every aspect of physics in Minkowski space finds it counterpart in the Euclidean continuation. There are things that require more than being careful.<br /><br />To summarize, in field theory the situation is satisfactory. An imaginary energy may seem awkward, but there is nothing wrong with it if you have the correct interpretation in mind. In string theory we do not have an appropriate description, unless you turn gravity off. But what is string theory without gravity worth?<br /><br />Best wishes,<br />MichaelAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107470357382032482005-02-03T23:39:00.000+01:002005-02-03T23:39:00.000+01:00Dear Michael,
are you arguing that the Schwinger ...Dear Michael,<br /><br />are you arguing that the Schwinger effect does not exist? It definitely looks so.<br /><br />The Schwinger effect, or various vacuum decays etc., are easy to describe with an exact solution in the Euclidean spacetime. The Euclidean path integral is the better behaved one in which your various subtle issues about the sign of the action - and imaginary actions for spacelike paths etc. - do not arise. The Euclidean path integral is just a mathematical trick, and one must be very careful how this solution is interpreted in the Minkowski spacetime.<br /><br />The right interpretation is that there is a nucleation of a bubble whose boundary moves nearly by the speed of light. Inside the bubble, you have the "new", energetically favored vacuum - it is the same vacuum that you find near the origin of the Euclidean solution. The solution is only relevant for t>0. For t<0, you assume that the spacetime is in the unstable phase.<br /><br />The full calculation in the Euclidean language certainly does not require the spacetimes/diagrams to have a globally well-defined orientation. If it were so, a sphere could not contribute to string theory amplitudes because you can't comb a sphere.<br /><br />Moreover, the non-gravitational instantons - signs of instabilities - including the Schwinger pair production are described by the usual, causally trivial Euclidean spacetime, so you can define the orientation very easily.<br /><br />Best<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107469908177259362005-02-03T23:31:00.000+01:002005-02-03T23:31:00.000+01:00Oops, I just saw that I mangled the one formula I ...Oops, I just saw that I mangled the one formula I typed. I meant of course:<br /><br />S= \int DX \exp ( -i m \int d \tau \sqrt{\dot X^\mu \dot X_\mu} )<br /><br />DX is the path integral over all paths the particle can take, and \tau parameterizes the world line, and m is the particles mass.<br /><br />--MichaelAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107460658946378902005-02-03T20:57:00.000+01:002005-02-03T20:57:00.000+01:00Hi Lubos,
let me explain in a few words what I me...Hi Lubos,<br /><br />let me explain in a few words what I meant. When you write down the geometric action of a point particle, it involves a square root of the displacement squared along the world line, something like<br /><br />S = \int DX \sqrt{\dot X^\mu \dot X_\mu } ,<br /><br />where the dot is the derivative with respect to the world line parameter. If the metric that raises/lowers \mu is Lorentzian, then the square root is zero whenever the path becomes time-like at any point -- as it does an arbitrary number of times in a given path integral configuration -- and whenever that happens you can choose the sign of the square root as you please. Just fixing this set of signs from the out start is not an honest way of dealing with this issue.<br /><br />One can see this more clearly. Introduce a world-line einbein so that the action becomes quadratic. A moment's thought will convince you that the sign ambiguity in the original action is reflected in the question of whether the particle is moving forward or backward in its own proper time according to the einbein. If you just fix the sign, the direction can never reverse, but summing over all configurations requires the number of orientation changes along any given path to be arbitrary.<br /><br />Now if the metric that raises/lowers \mu is Euclidean, than the issue of this sign ambiguity never arises to begin with. You just loose the sense of time-orientation on the world-line. <br /><br />One can now argue that in the Euclidean version vacuum instability issues such as Schwinger's effect are simply absent. (I won't get into details here.) Vacuum instability seems to be reflected in the path integral formulation by the fact that trajectories that do not admit a sense of time-orientation, in the sense explained above, make a non-zero net contribution.<br /><br />I don't have to explain to you that all these issues carry over to string theory; some issues are even much exacerbated there. In fact, it is much harder to make sense of the sense of time orientation on a world-sheet, but presumably this is important. As you know, Schwinger's effect is absent in beta-function calculations using the standard analytical continuation. After these explanations, even Peter Woit can guess why that is.<br /><br />Maybe one should supplement the Euclidean (world-sheet) metric with a Killing vector field that defines the time orientation. But how exactly do you incorporate it into the action? Worse: Such a Killing field need not exist.<br /><br />Best wishes,<br />MichaelAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107454253817036072005-02-03T19:10:00.000+01:002005-02-03T19:10:00.000+01:00but they also realized the power of using visual i...<I>but they also realized the power of using visual imagery to represent mathematical symbols.</I><B>Ciara Muldoon</B>As soon as you used the word <B>Tachyon</B>, the anti- would automatically jump on the band wagon. Nobody questions the intelligence of this anti position, just why string/Mtheory should not be so?<br /><br />We already have the amazing Randi.:) <br /><br />Dialogue to debate the essence of why this math should not be used would be more constructive, and save a laymen from having to venture into further illusions, if that is what is felt.<br /><br />There is no doubt in my mind that we need the physics to verify. Sean asks a good question in his blog about metaphors, and such leading math minds can readily say, why this vision is not a good one?<br /><br />If you are going after mirror symmetry the anti- position is not doing very well right now with no arguments to back it up.:)<br /><br />Michael might have been right about Loop, but there are intelligent people working in "all areas," that might debate the essence of these views constructively?Legacy Userhttps://www.blogger.com/profile/01554579710459395706noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107446735085915792005-02-03T17:05:00.000+01:002005-02-03T17:05:00.000+01:00This comment has been removed by a blog administrator.Quantokenhttps://www.blogger.com/profile/08057876770160255308noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107446455560318422005-02-03T17:00:00.000+01:002005-02-03T17:00:00.000+01:00This comment has been removed by a blog administrator.Quantokenhttps://www.blogger.com/profile/08057876770160255308noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107444112797186182005-02-03T16:21:00.000+01:002005-02-03T16:21:00.000+01:00Dear Matti,
what you write is very interesting bu...Dear Matti,<br /><br />what you write is very interesting but I don't have the necessary background. What is the TGD framework? References welcome.<br /><br />Best<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107443999713912312005-02-03T16:19:00.000+01:002005-02-03T16:19:00.000+01:00Dear Michael,
I enjoyed reading your comment. By ...Dear Michael,<br /><br />I enjoyed reading your comment. By the way, just to be serious: the motivation for these papers is purely a conceptual one - to understand tachyons in string theory including the non-realistic vacua. I don't think that the authors were driven by phenomenological motivation. But I agree that it is an important motivation for us.<br /><br />The Schwinger production of D-branes is something that the landscape modelers do study. It's controlled by an instanton representing the instability with respect to a spherical nucleation of a domain wall, which changes the amount of flux inside. This process itself can be kind of controlled and suppressed because the instanton's action is large. On the other hand, spontaneous topology change of a general kind is something that, I believe, has not been studied satisfactorily for the garden variety landscape vacua.<br /><br />So far I have not understood your analytical continuation stuff, but it's probably because of the limited time I had for it.<br /><br />All the best<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107443573414221832005-02-03T16:12:00.000+01:002005-02-03T16:12:00.000+01:00Peter,
if/when I had a quantitative evidence with...Peter,<br /><br />if/when I had a quantitative evidence with detailed geometry, I would probably publish it, and not just on a blog.<br /><br />This proposal is just a sketch of my general feeling that "convoluted" vacua simply won't be generated by the early cosmology, as we will once understand properly. <br /><br />I admit it is a belief to a large extent, but the idea that all convoluted vacua are comparably likely like the simple vacua - and therefore the anthropic unpredictability is the issue for the day - is also just a belief.<br /><br />Best<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1107443250042182702005-02-03T16:07:00.000+01:002005-02-03T16:07:00.000+01:00Hi Lubos,
Do you actually have any evidence for y...Hi Lubos,<br /><br />Do you actually have any evidence for your idea about destabilizing the landscape by decays into simple Calabi-Yaus, or is just your usual pure wishful thinking.<br /><br />Good to see that your commenters are sometimes as off-the wall as mine: <br /><br />"the web of dualities becomes so dense on complicated CYs that in the end most of the gazillions of vacua are just dual to one another, even if we don't see it yet" <br /><br />"That's why string theory has never been more exciting and promising than today. It is tremendously successful..."<br /><br />Pretty hilarious stuff....Peter Woithttps://www.blogger.com/profile/06232761993739122656noreply@blogger.com