Timeline for What are some approaches to discrete space-time used in modern physics?
Current License: CC BY-SA 2.5
19 events
| when toggle format | what | by | license | comment | |
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| Apr 3, 2011 at 21:31 | comment | added | Daniel | @Deepak: don't sweat it. Living and learning… | |
| Apr 2, 2011 at 8:14 | comment | added | user346 | @Daniel my recent experience with my answer to this question on pseudoscalars in E&M has led me to realize what it feels like to be on the receiving end. In hindsight I was too aggressive in critiquing your answer and am guilty of not doing unto you as I would like to be done unto me. In any case, hopefully, we will have another opportunity to clarify these issues in a less confrontational manner. Cheers mate and apologies for my rudeness. | |
| Apr 1, 2011 at 9:12 | comment | added | Daniel | @Deepak: don't mistake your lack of knowledge for "random facts": the fact that you can't put these arguments together and understand my points says absolutely nothing about their validity (it only speaks about you). It's not my fault you don't know certain aspects of QFT: i even provided a reference that expands on some of my points (on top of giving you more references to clarify further doubts). I have been very honest and forthcoming, but can't fit in ~350 characters what i understand to be the answers you're looking for. | |
| Apr 1, 2011 at 9:04 | comment | added | user346 | @Daniel you are throwing up random terms and concepts to cover the fact that you made gross errors in your answer. Readers are free to decide, after reading my responses and yours, as to where the truth lies. I'll go troll elsewhere now ;) | |
| Apr 1, 2011 at 9:00 | comment | added | Daniel | @Deepak: "(…) they are as silly as these two." I haven't used adjectives to characterize your comments so far and i'd have appreciated you keeping this discussion at the Physics level. However, i understand your inability to do so, granted that you don't even appreciate what a 'Cauchy problem' is. So, if you want to keep on trolling, go right ahead — i have better things to do. | |
| Mar 31, 2011 at 20:38 | comment | added | user346 | if you want to call the measurement problem by wave-particle duality ... what? That's like comparing apples and oranges. What did I say that makes you think I'm equating the two? About QFT on deSitter take as look at Candelas and Raine's 36 year old paper. To quote from the abstract: The massive scalar and Dirac fields quantized on a de Sitter background geometry prove to be exactly soluble models in general-relativistic field theory. Is that what you're asking for? About your other points, they are as silly as these two. | |
| Mar 31, 2011 at 18:22 | comment | added | Daniel | As for your other points, suffices to say that QFTs over curved backgrounds are a hairball. And i would love to see you do QFT over a de Sitter background (as opposed to its more famous cousing, anti-de Sitter): can you define the Cauchy problem for a simple (bosonic, spin 0 — free scalar; or maybe even $\phi^4$) QFT over de Sitter space? If you can do this, would you be able to do very same for Gauge Theories (Yang-Mills)? Maybe our definitions of "frontier research" are slightly different... | |
| Mar 31, 2011 at 18:18 | comment | added | Daniel | @Deepak: I really don't intend into dragging this discussion, so i hope this short version of my answer will satisfy you: you can read about wave-particle duality in Penrose's tome, The Road to Reality, chapter 21, in particular in section 21.5. As for QFT, it creates and destroys wave-functions, thus clearing the confusion on the spot. Now, if you want to call the measurement problem by "wave-particle duality", that's your personal choice, but not the community's. | |
| Mar 30, 2011 at 0:36 | comment | added | user346 | tie up into a neat package. As to precisely what quantum gravity reveals about the question of wave-particle duality is something that is not yet very clear (AFAIK), but it in inevitable that it must shed new light on this (century) old paradigm. I hope that clarifies where I am coming from. I am also happy to discuss further any issues you feel are relevant. Admittedly these are complex topics which have no straightforward resolution hence their categorization as "frontier" research. | |
| Mar 30, 2011 at 0:34 | comment | added | user346 | Also see papers by Achim Kempf (link1)[arxiv.org/abs/gr-qc/9907084] (link2)[arxiv.org/abs/hep-th/0404103] (and many other papers) who has done extensive work in trying to understand the the meaning of "discrete" and "continuous" in the context of quantum gravity. The second reference also shows that the existence of a minimal length leads to a cutoff on the maximum information density in a given region. Work along these lines has by now been done independently by several groups and individuals. Point being, the discreteness of geometry and the informational aspect of nature all | |
| Mar 30, 2011 at 0:30 | comment | added | user346 | which it is constructed. For smooth manifolds QFT is the usual beast we are familiar with. For discrete manifolds - such as the graphs which describe the structure of spacetime in LQG, for instance - the notions of operators and observables in QFT have to be altered accordingly to take into account the discontinuous and discrete behavior of physical quantities. In LQG such considerations lead to the notion of a "generalized (gauge) connection" which has support only on 1D manifolds - sort of like the Wilson loops of ordinary QFT and QCD. | |
| Mar 30, 2011 at 0:25 | comment | added | user346 | No, QFT does not resolve the wave-particle duality. It cannot do so, because wave-particle duality is a central aspect of Nature. Also, if you do feel that QFT "resolves" wave-particle duality then it is incumbent upon you to explain such a bold statement. The information theoretical aspect of quantum gravity is encoded in the holographic principle, the question of black hole entropy and the covariant entropy bound - see my answer to this question. The nature of any QFT depends on the background manifold on | |
| Mar 29, 2011 at 23:54 | comment | added | Daniel | @Deepak, cont'd: with that out of the way, let me ask you this: Does QFT resolve the so-called wave-particle duality or not? What is the definition of the information theoretical aspect of the unverse? What are the domains of validity of QFT and how would this fare when compared to a possible theory of quantum gravity? Thinking about these questions will definitely lead you into what my reasoning was to answer these questions. | |
| Mar 29, 2011 at 23:50 | comment | added | Daniel | @Deepak: I know perfectly well what i'm talking about and assure you there's absolutely no misconceptions anywhere in my answer. Having said that though, you don't need to take my 'assurance' as any form of guarantee, but if you're going to make such a strong criticism, it'd be good form for you to point out the differences, the misconceptions you claim to exist. | |
| Mar 29, 2011 at 20:54 | comment | added | user346 | there is no particle-wave duality, it makes no sense to ask if spacetime is quantized or discrete, discrete spacetime would have no effect on QFT, dude, what are you are talking about? These are some serious misconceptions that you are propagating to the laymen. The informational theoretical aspect of the universe is not well-defined - seriously, have you not read any scientific literature from the past decade? Unless I'm completely misunderstanding you, this answer is riddled with gross mis-characterizations of various issues and their status in modern physics -1. | |
| Nov 16, 2010 at 6:04 | vote | accept | Amir Rezaei | ||
| Nov 15, 2010 at 15:04 | comment | added | Daniel | @Amir: i perfectly understood your question (5). If you check the link i sent, you'll see that things such as "Planck Volume" and "Planck Time" exist and are well defined (and have a numerical value, as per your wish). So, in this sense, a notion of "spacetime atom" does exist, even if it's vague. To make it precise, it will of course depend on the particular theory you have at hand. | |
| Nov 15, 2010 at 14:31 | comment | added | Amir Rezaei | @David, Thank you for your answer. Regarding question 5 I’m asking for an equivalent constant to planck's constant for time. So the question isn’t what is the unit, the question is what is the constant. If such constant exit then it has value and dimension. That is what I asked. I’ll come back to you regarding other points. | |
| Nov 15, 2010 at 14:01 | history | answered | Daniel | CC BY-SA 2.5 |