It is a semi-fictional semi-biographical book centering around von Neumann
I am confused by the fact that (1) textbook QFT is all over "particles". fundamental fields transform under irreps of the poincare group and (2) "particles" *cease to be well-defined* when you talk about an interacting QFT!
Am I misunderstanding or misrepresenting the situation? I don't understand why people are not concerned with this state of QFT.
@SillyGoose i think you're talking at a higher level (and certainly over mine) but just curious have you read "There are no particles, there are only fields"?
Another general trait of such users is they target three more communities, at least, other than CV: Maths, MO, Physics.
Already the said user is banned at MO.
Might be wrong, but of late, these users follow the same rule book and pose as jack of all fields (physics, maths, stat/machine learning). They hardly respond to comment; answer multiple times a day in a somewhat mathgen like structure.
@User1865345 Please raise custom moderator flags on posts you suspect to be computer-generated
@SillyGoose I'm not sure what you mean by people being "not concerned" about this - every textbook account of QFT spends a bunch of time defining the asymptotic particle states in terms of the asymptotic "free" fields to derive the LSZ formula. It's well-known that the full state space of an interacting relativistic QFT is a messy object, but it's just a hard problem.
But for the prime application of relativistic QFT - the computation of scattering amplitudes or more generally n-point functions - it doesn't matter much (if at all).
@qwerty There are various workstreams you might look for - "constructive QFT" in the vein of the functional integrals of Glimm and Jaffe although I don't know of a lot of progress after their initial work there, algebraic QFT in the vein of Haag and Kastler or the more analytic approaches like Epstein-Glaser renormalization or Streater's and Wightman's Spin, Statistics and all that. I'm not really up to date on current work.
The name is because of how the operation of parallel transport can be phrased in terms of a projection to the vectors parallel to the manifold if you embed it isometrically in $\mathbb{R}^n$, see e.g. mathoverflow.net/a/387538/157071
@ACuriousMind this link is about the Levi Civita connection. it is worth asking whether @DIRAC1930 wants to know about parallel transport in general or the Levi Civita connection
I do not understand what Schwartz is trying to say in this section. (My understanding): The end result that is wanted is some operator that relates the free to interacting vacuum. I am not understanding the logic that Schwartz comes to the result.
I just found this blog post, which gives an interpretation of virtual particles I haven't seen before.
Consider a 1D system of springs and masses, where the springs are slightly nonlinear. A "real particle" is a regular $\cos(kx-\omega t)$ wavepacket moving through the line, where $\omega$ satis...
@PM2Ring lol it would be fun to add "here be dragons" labelled to certain topics, to those maps-of-physics people have made (like this one) historyofinformation.com/detail.php?id=5070
@DIRAC1930 there it's just habit - we use the same name because the formulae are the same, not because you could reduce it to any notion of "parallel" in terms of the Euclidean embedding; it's still a projection in terms of the Ehresmann formulation of a connection (i.e. as a horizontal/vertical split of the tangent space of the tangent bundle) but this does not directly relate to the embedding
@RyderRude >I find it more helpful to think of gravity as simply arising from this need to correct for how the underlying spacetime forces us to use different basis vectors at different points. In relativity theory, the physical counterpart of 'change of basis' is change of state of motion.
@RyderRude "loop quantum gravity" is certainly not the same as (or a subset of) "canonical general relativity". I would suggest you take knowledge more seriously.
@Allie I find it quite eerie that YouTube has recommended me a video of her today after you've mentioned her in the chat lol,I feel like YouTube is secretly watching what I'm doing on the internet :p
I happened to watch a video of her on why the famous billionaires all seem to talk about physics and have considered taking up physics in college. I should say it's eye opening
@TobiasFünke what books you recommend for a beginner who has studied some quantum mechanics and wants to start studying condensed matter physics,I would prefer if the exposition were clear and uncompromising when it comes to detail and rigor.
Altland and Simon (Condensed Matter Field Theory). Chaikin and Lubensky (Principles of condensed matter physics), but this one I only skimmed through for some certain chapters. The books by Nozières and/or Pines are classic. A solid solid state book is Grosso Parravicini, and I think Ashcroft Mermin is fine too and covers many topics.
@TobiasFünke Hi, i actually have a course in cm the upcoming semester(starting in jan) and it's the first ug course in cm,I have looked at it and to me it looks like solid state physics predominantly
@Arjun I normally avoid videos on science/physics (I prefer anything written, as I find it tends to be more precise and be writing for a less general audience) but that sounds intriguing...
@qwerty Hi,Even I don't watch videos on science that often since I find them to over simplify stuff to reach a greater audience and sometimes exaggerate some points to go viral,but this person seems to be sensible(atleast as of now lol),I'm planning to watch her feynman video after I study some actual physics for the day : )
@Arjun yeah I'm watching now, seems like she's not talking down or being clickbaity! I appreciate that. in incognito mode though, so that I don't get recommended more unless I search for it 😅
The upcoming sem is gon be quite heavy lol ,I'd be juggling statistical mechanics,electromangentism and str,solid state physics,quantum mechanics-2,quantum information theory and Topology :')
@Arjun I mean, her point was if these billionaires really want, they could pay to be taught physics and be on research projects. people get credit on papers for even small tasks.
@qwerty Oh boy I forgot these people are literally the best for making others do the work and get more credit than they ever deserved :') ,so yeah they can very well get published
@Arjun I know professors who barely did anything and got their names on papers their students or postdocs wrote... it's not right, but the juniors sometimes don't mind if it's a bigger name attached...
I wonder what's the least corrupt profession with the least amount of politics playing(I used to think academia was like that,but now I see how un-informed I was..)
What I meant is if anyone wants to discuss anything, they would. If you wish, you may post something but it is another thing to expect that would warrant a response (without additional context).
We also do study information geometry and it's a growing field. Although my current research area doesn't fall under it technically, I feel it could be relevant and so I have ventured there.
Maybe it's not that he didn't knew(could happen though). But I think he was under immense pressure to make complex stuff understandable to his lay audience and lost on crucial details in the process
Once again, it would behoove you to be more serious about knowledge: There is an obvious sense in which the statement is true: Sums of solutions to the Schrödinger equation are again solutions (=QM is linear) while the corresponding statement is not true for all classical equations of motion (=CM is non-linear). Now, it might be that in the given context that's not really relevant, but to act as if this is an obviously false statement is just misleading.
I wouldn't be surprised to find "wrong" statements. The point is that statements about math or physics mean "nothing" without a crystal clear definition of what exactly is meant, and this more often than not requires background knowledge, which most people definitely not have
@TobiasFünke it's good those hand wavey things are lesser in statistics community. I haven't found that staggering number of books written for lay people in stat/machine learning than that in physics.
If you wanted to show off how much smarter you are than an expert, you should have chosen the example more carefully (which given that you had infinite time just not to say something is an unforced error).
@User1865345 indeed :d but there are some books for a wider audience, discussing the basics of probability, statistics etc. a famous example is with testing in e.g. medicine and conditional probabilities (Bayes theorem)
@TobiasFünke there is, especially for audiences who have gotten proper statistical education. But since machine learning is in the market, people tend to sell easy paths especially for branches like clinical trials, epidemiology and the applied field altogether.
it is a difference if I talk 2h to lay people and explain physics in a very oversimplified manner, or if I write a scientific paper/report/book/text for an audience which understands the physics/math
@qwerty yes, most often. it depends, though. some friends majored in cs or engineering, so they also have a much better understanding of e.g. math or basic physics than most others
@RyderRude my last respond: You miss my point! If they "overlooked" something, then go to their papers/texts/books whatever. Everything else has no real scientific value, roughly speaking
@qwerty but many non-physicists are interested in things like black holes, expanding universe etc., where I also have no real knowledge, and hence I avoid these discussions haha
glad I'm not alone. although, I think, the more deeply you understand something the better your chances of explaining something clearly and simply. as Ive said before, I think to teach a subject it's kinda feels necessary to me to know it two levels deeper. although I think not everyone agrees.
@qwerty no, I don't avoid it but don't seek it out, either, since I don't enjoy going "it's more complicated than that" to every pop-sci misconception they've soaked up :P
@qwerty I am still not sure why that rich guy named it bayesian. After all, bayesian techniques are used so much everywhere that it's not special anymore. But maybe he felt deep connection.
@TobiasFünke Usually I'm at a party and someone goes "I watched a documentary about black holes/string theory/whatever last night" and then says something so wrong as a summary I can't help but correct them :P but it happens like once every 2 months or so
@TobiasFünke I had hard time teaching a non parametric course to a group of psychology graduates. I can dilute something at the expense of sacrificing many results which I am not at all happy about. But had to. Definitely not going to do for lay people.
As I said, my knowledge in e.g. GR (or even SR) is not good enough that I would like to start a discussion, i.e. I don't feel confident enough even though I might have the answer to some specific questions, or could correct some misunderstanding
@qwerty ah, well, for small talk I usually just pick the basic kind of physics I expect them to be familiar with (xkcd) and go "like that", e.g. gauge theory is about more complicated cases of being able to add constants to potentials
Social science students only need advice when to use which tool and other subsequent wisdom. After all they will only use R Or Stata to run a code and voila.
In information geometry, the Fisher information metric is a particular Riemannian metric which can be defined on a smooth statistical manifold, i.e., a smooth manifold whose points are probability measures defined on a common probability space. It can be used to calculate the informational difference between measurements.
The metric is interesting in several aspects. By Chentsov’s theorem, the Fisher information metric on statistical models is the only Riemannian metric (up to rescaling) that is invariant under sufficient statistics.
It can also be understood to be the infinitesimal form of the...
@qwerty lol i know. It’s like vector…tensor…vector. About your other comment: i haven’t seen that paper but I’ll take a lookzie now. Thank you for the reference
Whenever I discuss with students, I try to at least in one or two sentences, point out that the situation is, actually and as so often, more complicated, and either refer to literature or say we'll discuss this later
@ACuriousMind but what i mean is that the textbooks only care about (dubious choice of the word carefully) defining the LSZ reduction formula and then explaining how to compute it conveniently.
I've already referred you to e. g. Reed and Simon for a more formal account of the scattering theory setup, but beyond that I'm afraid it's mostly monographs and papers, not textbooks
Economics just seems like math :P. From my small experience in an introductory course, the content is nothing you wouldn’t expect and the nomenclature is absolutely horrible.
Hm but i think i don’t want to know more about scattering theory, i am more interested in gaining some glimpses into the interacting Hilbert space and time evolution proper. I recall that r&s discuss a rigorous way to relate asymptotic to interacting hilbert space.
There isn't really just an "advanced QFT" book except perhaps the second volume of Weinberg, there's instead dozens of different aspects you can be interested in that each have different kinds of literature
@SillyGoose :) it's probably not actually not quite what you were talking about, but tangentially I thought it was quite a nice generalist/lower level article
@SillyGoose they do, and they also discuss asymptotic completeness (that the two spaces are equal) as a property realistic QFTs are expected to have, i.e. you can express everything in terms of free particle states.
There are literally tons of bogus papers who resort to p hacking and manipulate their results.
Statistics is not a machine which provides a clear cut output.
Without going to the argument whether assumptions have been assessed beforehand, the final result can be deceptive for inferential purpose. A single p value, for example, doesn't really say much, unlike what is taught in many places.
Meta-analysis is a method of synthesis of quantitative data from multiple independent studies addressing a common research question. An important part of this method involves computing a combined effect size across all of the studies. As such, this statistical approach involves extracting effect sizes and variance measures from various studies. By combining these effect sizes the statistical power is improved and can resolve uncertainties or discrepancies found in individual studies. Meta-analyses are integral in supporting research grant proposals, shaping treatment guidelines, and influencing...
We already have multiple threads tagged as p-values that reveal lots of misunderstandings about them. Ten months ago we had a thread about psychological journal that "banned" $p$-values, now American Statistical Association (2016) says that with our analysis we "should not end with the calculatio...
@TobiasFünke @arjun there is a strict simplification and strict subset of A&M by a Steven Simon, but you'll find it easier by googling oxford solid state basics. The utility is that, because it is shorter, you can quicker finish the book and move onto something that goes into modern maths version of the same. Of course, it would not be covering as much as A&M covers.
@naturallyInconsistent I know these lecture notes, yeah these are quite good, IIRC. What do you mean with "modern math versions"? Can you name an example?