@ACuriousMind please, don't be hard with him, it's a Chinese - (do you see the red ties?). Let @DavidZ handle the issue. Do they know English? Is he able to read Wikipedia? Please, leave this! You don't know the conditions there (I assume so). China is big. There are regions of terrible poverty. Don't be hard.
@Sofia If they don't know English, they won't understand any answer here, either. If they know English, they can read Wikipedia and ask a more specific question. I'm not harsh, I treat them like anyone else.
@ACuriousMind Please, be a bit moderate, show some heart. Let DavidZ handle the issue, he works there, if I understand correctly. What you hurry? Please!
so sof, you say you want the answer to the measurement problem (aka "wavfn collapse"), did you know there is one in the soliton/ fluid mechanics picture?
@0celo7 hey man, I got a quick question maybe you can help me figure out. physics.stackexchange.com/questions/166937/… I can't tell if I did the problem wrong or the book is wrong.
The problem is I've never handled units like these before and am not sure how to do dimensional analysis for it.
No! I wondered about that. I didn't see one in the book for the equation they listed. But I went ahead anyways and tried the substitution and I got close. I'm not sure what the tilde was supposed to represent.
Double checking right now
He says they mean the same thing on 26, the previous page.
Well, assume only $\hbar$ $m$ and $\omega$ have units, I got $m\sqrt{s}$ for his equation. It should just be $m$.
I would guess the book is right because my equation makes it look like I have to end up with $\sqrt{m}$ which isn't sensible. At least theirs gets meters to the power of 1.
@StanShunpike Don't use SI units when doing dimensional analysis. Use capital letters that stand for the dimensions, not the units. For instance, for position, write $[x]=L$ or for velocity $[v]=LT^{-1}$.
@ACuriousMind After symmetry breaking we get something like $$|D_\mu\phi|^2\sim \frac{1}{2}A^2_\mu v^2-\frac{1}{2g^2}(\partial_\mu A^\nu)^2$$ I've never quite understood how we get $m_A^2=g^2v^2$ from this.
@0celo7 Gauge theory is a conventional mess, factors of i and g are all over the place. Nevertheless, where did you find that? How's the covariant derivative defined that you divide by $g$ instead of multiplying be it?
If you do that, you have to extract a $\frac{1}{g^2}$ from every term that contains the gauge field so that it becomes a prefactor in front of all the gauge dependent terms, and then, again, you get the mass term as desired
@0celo7 By intuition ;) If you take the limit $g \to 0$, the mass should vanish, because, if the field doesn't couple to the Higgs, the Higgs cannot grant it mass
If the mass doesn't depend on the $g$, that would mean the limit isn't smooth (not even really possible), so you don't have a well-defined theory
@ACuriousMind When we write $\phi=\frac{1}{\sqrt{2}}(v+\sigma(x)+i\pi(x))$, $v$ is the expectation value and $\pi$ is the Goldstone boson. What is $\sigma$ called? $\phi$ is the actual Higgs field, right?
@0celo7 Uh...I guess so? It's the polarisation that's normally declared unphysical by imposing the gauge symmetry upon the Hilbert space (by Gupta-Bleuler, BRST, whatever).
@0celo7 No idea, never worked with it. But I think it simply falls out of the theorem about the classification of Lie groups as a particular Dynkin diagram/root system (don't ask, I can't explain that!)
I know people who work with electroweak or strong theories every day but have no clue about the group theory of SU(N). One really doesn't need to understand every detail.
He likes to rock the t-shirts with the Lie group on it. E8 is a Lie group right?
user54412
"I had gotten lucky by investing my graduate stipend in a little company many thought was going out of business (AAPL), so I decided to go to Maui, learn to windsurf, and work on physics on my own." (Wikipedia on Lisi leaving academia)
@ACuriousMind I think that's the stand I'm going to take (not knowing every detail). I did learn quite a bit of CFT already. I think I'll read the stuff about group geometry, cohomology and spin bundles in Fecko, then Dine's SUSY book and then some lecture notes on complex geometry. Perhaps that will prepare me.
@0celo7 While, at some point, you should learn about bundles, I've not seen a single bundle in introductory string theory. It's very relevant for non-perturbative ordinary QFT, though.
@ChrisWhite Yeah ikr, mine would be lucky to be considered a scrawl. I actually read a story about a con-artist who impersonated being a doctor. For an entire year, he wrote on patients files just scribbling not actually writing anything. No one ever asked him what he wrote.
@0celo7 What do u usually put in place for Joules?
Like if I use L for meters, what do I use instead of J?
Random aside: I've started to catalog awesome science/math/other papers/talks/whatever that I've come across. Things that are really forward-thinking (even if only in retrospect), novel, insightful, or beautiful. Anyone have personal suggestions to add to such a list?
I can't stand bundles. I haven't been able to find something easy introducing them, but they come up everywhere when I read and I can't make heads or tails of them.
I meant my own, but there's also a typed version from the same course two years ago or so. They won't satisfy you, I think, and they occasionally refer to assignment solutions you (and I) don't have, but here: thphys.uni-heidelberg.de/~weigand/Skript-strings11-12/…
They're not meant to be simply read or worked through, though.
I'm thinking I'll read the notes to supplement BBS, because I have that one in print. Thus I can read notes on my tablet while having the book in front of me.
@StanShunpike Well, the basics of most topics I learn in lectures, and then I mostly just seek out whatever I find interesting on the net. I then find some paper or blog post or whatever, see different things I don't understand/know, and go search for them. Sooner or later, I'll arrive at math or physics I already know, and then I work backwards.
@ACuriousMind That's interesting. I have found that works for math and physics. I learned half of my math doing just what you described via internet. In contrast, when I studied neuropsychology a few years ago, it didn't work at all. Books were the only way to find info.
think lisi has some real talent. the deep theories can take years to deconstruct/ analyze. but theres also a bit too much media hype, maybe some of it at his own "behest"...
from the sciencedaily article, somewhat in his defense...
> Although his paper was not peer-reviewed, and Lisi himself told the Daily Telegraph that the theory was still in development and he gave a "low" likelihood to the prediction, the idea was widely reported in the media, under attention-grabbing headlines like "Surfer dude stuns physicists with theory of everything."
which reminds me of a famous quote by einstein (lisi apparently has significantly more reserve)...
@ACuriousMind What about practice problems? My method of study for my (run-of-the-mill) quantum class right now is to scan through quantum textbooks for problems which I can't solve at first.
@NeuroFuzzy I've started to do that and it's definitely made me learn a lot faster. My uncle is a mathematician and he always says you need to do proofs to learn stuff.
> In 1919, Sir Arthur Eddington led expeditions to Brazil and to the island of Principe, aiming to observe solar eclipses and thereby test an experimental prediction of Einstein's novel theory of General Relativity. A journalist asked Einstein what he would do if Eddington's observations failed to match his theory. Einstein famously replied: "Then I would feel sorry for the good Lord. The theory is correct."
@NeuroFuzzy Well, if I weren't a student that has to deal with exercise problems anyway, I'd probably start seeking some of my own, but I don't really have the desire to solve explicit problems in addition to what I already have to do.
But I find most practice problems rather unenlightening. My ability to manipulate symbols doesn't really need training anymore.
agreed, "entertaining" stuff. its too bad lisi doesnt blog(?) dont know what the current state/ status of his theory is. the 2010 "refutation" sounds pretty definitive :|
sometimes eg with complicated math proofs, some part is "salvageable"... and the rest can be turned into "conjecture"...
@ACuriousMind haha maybe I just have easier classes/homework/more free time! 3rd year undergrad physics and most of what I'm doing doesn't feel very sophisticated.
interesting, smolin is a lisi fan at least in 2007. trying to remember does smolin blog?
> "Although he cultivates a bit of a surfer-guy image its clear he has put enormous effort and time into working the complexities of this structure out over several years," Prof Smolin tells The Telegraph.
@vzn the interplay between math and physics research is interesting. Obviously, with string theory, there has been a lot of math developing. But, for example, my uncle is a mathematician and basically shows no interest in physics whatsoever.
The most damning thing about Lisi is he didn't know basic Lie theory stuff, that E_8 has an SU(5) x SU(5) subgroup, I mean that's damning, this motls.blogspot.com/2007/11/exceptionally-simple-theory-of.html cheers me up every single time I look at it lol
@NeuroFuzzy That is very possible. I've noticed that most other curricula lag at least a year behind what we can do here. 3rd year undergrad was something like (all sorts of) QFT&CFT&QCD+Algebraic Topology&Differential Geometry for me
@ACuriousMind That makes sense. I dunno why they don't do it earlier at other places. The GR class I took this quarter was the only undergrad one offered and seemed very subpar to me. I'm sure the graduate ones are fine but they should offer undergrad ones earlier covering the topics you mentioned.
was skimming motls damning critique. one wrinkle in all this. according to the telegraph article, Lisi has a phd. wonder, from where? what was his phd thesis? have encountered this phenomenon of phd cranks, which is seemingly quite different than the typical uneducated crank. phd cranks are a breed apart...
We don't have this division into "undergraduate" and "graduate" versions of topics - if you do quantum mechanics, then you to quantum mechanics, and if you do relativity, then you do relativity, and so on. They don't "dumb down" topics so that "even undergraduates" can do them. If you don't want to do the heavy stuff, there's plenty of applied courses that are less math/exercise heavy, but then cover a broader range of applications.
@bolbteppa lolol I can't find anything that explains how they work! I get tangent bundles fine. But fiber bundles I can't make heads or tails of. Okay, let me try and see if I understand it. So as I understand, a vector bundle has a total space E that is a product between and open neighborhood and R^k and the projection π maps this product space onto some topological space. So the fiber is like the inverse map or something like that. Is that correct?
@StanShunpike I get your point, I found it confusing until I read this pdf duffell.org/chapter_4.pdf and internalized the pictures, it's the only thing that actually helped me, now I think of a cylinder as a way to remember wtf is going on :)
bolb, think of the educational system as a filtering system. phd is the top filter. and then there are phds from very elite schools, presumably even more rigorous a filter. and what pops out of the filter? a small percent of bonafied cranks. so, "wtf"?!?
Is Max Tegmark the guy who is arguing against penrose and hameroff's claim that quantum gravity is acting on microtubules in neurons and facilitating computation in the brain?
@ACuriousMind ahh interesting. Well I don't want to talk more about comparisons because then I get annoyed and anxious! But that would explain why I'd lean more heavily on books! It's not so bad since university here will still put you around awesome faculty.
have studied P vs NP area for many yrs, there is a big list of crank papers maintained by a mathematician woegeorgi, and quite a few on the list have phds... seems, quite the phenomenon.... actually crank physics probably significantly outnumber the TCS "proofs"...
@StanShunpike yeah it is, if you like it and would like to post a summary of it here sometime to ensure you get it it'd really help refreshing my memory and give me an alternative perspective, no prob if not :)
@vzn haha interesting
@vzn what do you think of the "My connection of everything = connection for gravity + weak force + strong force + electromagnetism + electron + neutrino + up-quark + down-quark + other-generations" argument?
bolb re the physicsforum thread, very interesting/ current. lisi says hes still working on it. this is interesting, it sounds like someone else credible is pointing in the same direction
> Do you have an opinion about the SU(8) papers of Stephen Adler? It looks like he succeded in squezing in the SM, including the three generations, into this group. Opening a path to E(8).
Stephen Louis Adler (born November 30, 1939) is an American physicist specializing in elementary particles and field theory.
== Biography ==
Adler was born in New York City. He received an A.B. degree at Harvard University in 1961, where he was a Putnam Fellow, and a Ph.D. from Princeton University in 1964. He is the son of Irving Adler and Ruth Adler and older brother of Peggy Adler.
Adler was elected a Fellow of the American Academy of Arts and Sciences in 1974. He became a member of the Institute for Advanced Study in 1966, becoming a full Professor of Theoretical Physics in 1969, and was named...
Great. I read about Lisi back in the day, but I was still at school then, so I had no idea what that was about, and then I forgot it. Now I'm reading up on stuff, and I have no idea what the heck all the fuzz is about. To have a consistent quantum theory you need to do more than just assign some representations and draw pretty pictures!
@bolbteppa What's fascinating is the author's example of picking a point on the mobius band an moving along. It's reminds me of parallel transporting in that an action we think should produce a commuatitive result (ie returning to the same location here), doesn't and we end up at a different point.
That "my connection of everything" argument of his seems to destroy his whole argument, about adding one forms and scalars, I'm wondering how he could make such a silly claim, is there a way to justify it, I think he calls it a "superconnection" to pretend it makes sense
I am attempting to build a waterfall out of a gutter system. I currently have an awning that is 72" by 48" with 3" high (tentatively) buffers on each side to keep the water from flowing off. The awning is tilted 95 degrees downward from the side of a building. Connected to the awning I have a gut...
Mhhh, from the conclusion of Lisi's paper: "Quantum E8 theory follows the methods of quantum field theory and loop quantum gravity - though the details await future work." He literally dodges the part where it actually becomes difficult to write down a consistent theory.
Does anyone know of a good introduction to gauge covariant derivatives? As I understand from Danu, the gauge covariant derivative is directly related to the covariant derivative from Riemannian geometry. So I would like something that makes a connection (pun intended) between the two since I am familiar the the latter but not the former.
@KyleKanos I am editing an answer to that fellow, Agnivesh Singh, because he has difficulty in understanding that his question and the other one, are the same in essence. And Mr. Timaeus, dropped an answer to the former question and disappeared. His answer is correct, but incomplete. I asked him to complete his answer and I told him how, but probably he didn't see my comment.
@KyleKanos Now, what to do with the question of that Agnivesh Singh? After working on it and explaining, I wouldn't like anymore that it be deleted. And my answer is more complete than Mr. Timaeus. So, what will be?
@Sofia Closing and Deleting are two different things. Roughly speaking, only closed questions with no answers and a negative score are deleted. Even if the question is closed (which currently doesn't seem to be likely), your answer will stay.
Okay, mandatory moment of reflection. Let's all just stop what we are doing and once again consider the fact that viXra.org is something that exists and that some people seriously believe it has value outside of entertainment
General relativity was written to describe all behaviour of spacetime. And expanding universe is one small subset of the whole general class of spactimes in the phase space of general relativity.
So yes, relativity does apply to an expanding universe. At least general relativity does.
apparently, Alf has had 500 downloads of his paper on viXra, therefore it must have some validity
@ScienceFiction&Fantasy for those times when "Unclear what you're asking" isn't good enough, I think we need an "unclear what you're smoking." close reason.
From Alf: "however, as Einstein noted, Relativity was not established in expanding space."
I just answered this question that community brought up, because the question had a score of 5, and the two answers were not getting any hits and I considered they were not answering well the simple question which got these 5 votes.
Now I checked and the user who asked the question came only on...
I always wonder where the crackpots get their ideas. And how they become so convinced of them, when they either are flatly proven wrong by experiment or can't even write down a coherent mathematical statement of it.
@ACuriousMind It's not hard to see where they get the ideas from. Every physicist and his dog has their own personal theories about how the universe works and what things really are. We just have the common sense to trust the accepted theories until ours can at least pass the ego test.
What I can't understand either is how they blatantly disregard the physics they know nothing about and argue with those who know it on the basis of "I understand my theories better than accepted ones, thus mine must be right and the accepted ones must be wrong"
@ACuriousMind and @KyleKanos I think it's worthy that my answer stay, because I guess that it will spare us the effort to answer additional similar questions in the future. The case of uniformly moving charges bothers people due to the idea that non-accelerated charges don't radiate. (By the way, I also thought so in the past.)
@Sofia Currently there is only your close vote on it. Three people (including myself) voted to leave it open, so it's not even in the close queue anymore
@JimdalftheGrey Because the field in space changes as the particle moves on, and the changes propagate with the speed of light, but they see no reason why they should propagate with the speed of light, because the change is "not an EM wave because the charge is not accelerating" and the only thing they know to be propagating with the speed of light are EM waves.
viXra sounds bad. But academic publishing is pretty bad too. Sort of horrible, like end of science horrible. Maybe it's not so bad for Physics stuff, though.
Ok guys, this should be a fuzzy/silly question, but I have to understand why we do that (id est: the sign meaning).
Let's suppose I want to describe, as a joke, the classical state of a coffee machine that is working and our of order, or something similar like a door for example.
I can't see the...
@JimdalftheGrey why people are weird? These are beginners. We have all the time questions around this question, i.e. what kind of fields produce isolated charges in uniform movement. Is it a ridiculous issue for you?
A facepalm (sometimes also face-palm or face palm) is the physical gesture of placing one's hand flat across one's face or lowering one's face into one's hand or hands. The gesture is often exaggerated by giving the motion more force and making a slapping noise when the hand comes in contact with the face. The gesture is found in many cultures as a display of frustration, disappointment, embarrassment, horror, shock, surprise or sarcasm.
== Origins ==
According to Macmillan Dictionary, the word "facepalm" first appeared around 2006, though another source has an earliest citation of 2001....
The guy just doesn't understand the foundations of general relativity, he doesn't know the fundamental basis and is confusing examples of general relativity, namely cosmology, with the theory itself.
"This gesture is not unique to humans. A group of mandrills at the Colchester Zoo has adopted a similar gesture to signal the desire to avoid social interaction or to be left alone." lol
General relativity was written to describe all behaviour of spacetime. And expanding universe is one small subset of the whole general class of spactimes in the phase space of general relativity.
So yes, relativity does apply to an expanding universe. At least general relativity does.
I still feel like I haven't wrapped my mind around expansion. I watched a TED talk on dark matter last night and my mind just is still visually too stuck in Euclidean thinking. I keep thinking of it like space just changing length scale. It would be like suddenly a mile isn't a mile but two.
That reminds me of some discussion I've had with climate change critics....esp. the dredging up of yet-another-whack-postulate when you've dispatched the current one. Like playing whack-a-mole with infinite moles.
@Sofia That feeling you get after reading those comments; the pain, embarrassment, frustration, and exhaustion; that will give you a better definition of what it means to facepalm than anything I can describe
@Jiminion Yet somehow my score in that game is always a finite number
@ACuriousMind you, fiend, you are the one who invented the joke that I am a Victorian time-traveler. I don't even understand what it is, but it is wicked. You tell it to me in clear words!
The Victorian era of British history (and that of the British Empire) was the period of Queen Victoria's reign from 20 June 1837 until her death, on 22 January 1901. It was a long period of peace, prosperity, refined sensibilities and national self-confidence for Britain. Some scholars date the beginning of the period in terms of sensibilities and political concerns to the passage of the Reform Act 1832.
The fields of social history and literature often refer to the Victorian era as Victorianism, especially when discussing the attitudes and culture of the later two-thirds of the 19th century. The...
@ACuriousMind (don't feel offended by the word fiend, I recall it from a splendid movie, "Interview with the vampire". A very poetic and sensitive movie.)
He says he wants to modify special relativity to incorporate expanding space, I guess what he means is to take the Minkowski metric and then allow distances between points in 3-D space to grow, implying we're not in special relativity anymore, right?
Dungeons & Dragons (abbreviated as D&D or DnD) is a fantasy tabletop role-playing game (RPG) originally designed by Gary Gygax and Dave Arneson, and first published in 1974 by Tactical Studies Rules, Inc. (TSR). The game has been published by Wizards of the Coast (now a subsidiary of Hasbro) since 1997. It was derived from miniature wargames with a variation of the Chainmail game serving as the initial rule system. D&D 's publication is widely regarded as the beginning of modern role-playing games and the role-playing game industry.
D&D departs from traditional wargaming and assigns each player...