The h Bar

3:01 PM

@0celo7 I use them a lot. It makes me feel like a commentator in a sports game for some reason. Please, do tell me why you dislike them as you do.

0celo7

@Nick Because there are two missing deltas, and I have no clue what I'm doing.

Nick

@ACuriousMind: Are you a nuclear physics person?

@0celo7 Well, in geography, you can find loads of deltas. (poor joke)

0celo7

@ACuriousMind I HAVE AN IDEA

MAYBE THERE'S ONLY ONE DELTA MISSING

ACuriousMind

@Nick No, I am a quantum field theory person, I think

0celo7

@ACuriousMind You mean future GR fanatic, right?

You'll be like the GR Jesus.

Converting QFT scrubs across the land.

ACuriousMind

3:06 PM

@0celo7 If I actually start liking GR, I'll change my name to GRJesus. :D

Nick

@ACuriousMind All I have to learn about are Electronics, Optics, Nuclear Physics, Semiconductors and Communication Technology. Too bad, I have no quantum.

@ACuriousMind When you say quantum field, I'm thinking of a packet of energy (quanta) drifting in some force field.

0celo7

I can't wait for the reference, Superclassical Physics: Why Quantum Mechanics Makes Literally No Sense by @ACuriousMind .

ACuriousMind

@Nick That's...not what I do^^

Nick

@0celo7 If it makes no sense, it is only sensible that it does makes some sense, and that sense is nonsense. This is the paradox of senslessness.

0celo7

@ACuriousMind I completed the calculation. I started in light cone coordinates, switched to worldsheet coordinates and then switched back to light cone coordinates.

My hate for P.B.s is renewed.

ACuriousMind

3:11 PM

@Nick Got a philosopher there, eh?

Nick

@ACuriousMind I know. but you should know about how the layman comprehends your field.

0celo7

@ACuriousMind Do you know if P.B.s or P.B.'s is correct?

I can never remember if apostrophes are sometimes allowed or not.

ACuriousMind

@0celo7 I think the apostrophe is not correct, but I also often do it

Nick

@ACuriousMind Yes, he pops up when I'm sleepy.

ACuriousMind

Uh...no comment

0celo7

3:22 PM

Morning cat brush bounty.

Nick

@0celo7 Fuzzy logic?

0celo7

Ha

Nick

This is just not fair. I wrote a decent answers which covers all the bases and the wordless answer gets more votes.

Kyle Kanos

Life isn't fair :shrug:

Also, I would use asymmetrical rather than unsymmetrical (though the latter is indeed a word, it's just that the former is the far more common one).

ACuriousMind

Even meta.SE knows that: Life isn't fair

Nick

3:35 PM

@KyleKanos It depends on the English type. I use a mixture of Jamaican and Indian English.

Kyle Kanos

I also think that many of us "prolific" answerers would agree that our best answers are not the most up-voted answers

Nick

@KyleKanos Well, that sorta makes me feel better.

0celo7

@ACuriousMind SUSY terminology is ridiculous.

Nick

@KyleKanos Are you an optics, electronics or nuclear person?

Kyle Kanos

@ACuriousMind Somewhat curious that the guy's 2nd post is now very much upvoted.

@Nick Neither. I'm an astrophysicist.

ACuriousMind

3:37 PM

Feb 6 at 14:04, by ACuriousMind

In unrelated news, I hate it when people write stuff like sneutrinos. I always think it is a typo until I recall these stupid supersymmetry names.

@KyleKanos Apparently, life becomes fair if you complain enough :P

0celo7

@ACuriousMind In psych we were doing a crystallized intelligence experiment. We had to write as many words as possible starting with "s". I think I abused the word "super" a bit.

Kyle Kanos

start saw she single soft separate sword stellar star spunk supernova strange sequel segue sift sentence sick stick stark spark shark shank shaft sheet shear spell sport seven seventeen seventy

Is that enough?

:D

0celo7

@ACuriousMind neutrino = sneutrinoino

ACuriousMind

@0celo7 You mean, the LHC was for finding the shiggsino?

Oh god, this is ridiculous :D

Kyle Kanos

sigh I still see that there are >20 "actionable" items on the review queue

ACuriousMind

3:49 PM

@KyleKanos We were down to 9 sometime yesterday

Kyle Kanos

Lowest I saw was 11, but I can believe that.

Also, seems we can retract our too broad votes on the Mirror symmetry question. OP separated them

ACuriousMind

Yep

0celo7

@ACuriousMind When talking to non-STEM friends, always say s-particle-ino.

ACuriousMind

@0celo7 I don't think I talk about particles to my non-STEM friends that often. Though answering questions about quarks with "You mean the squarkino, right?" sounds fun.

0celo7

@ACuriousMind Talk to your chem friends about selectrino configs.

ACuriousMind

4:16 PM

Heh

tpg2114

Ooo, to answer a question here, I dug out the study guide I made for my qualifying exams. I think I've shared this before in here but it was ages ago, so I'll do it again in case anybody is interested: dropbox.com/s/mf7z4ojgk4gghrl/QualsStudyGuide.pdf?dl=0

And the usual disclaimers -- I know there are typos in it places and I have no intention of fixing them, so equations should probably be checked before using them as the only source of info

DanielSank

4:38 PM

@Danu Nah. PhD is from UCSB. Unfortunately, Schrwarzenegger was no longer the Governator at the time, so I didn't get his signature.

Sofia

@infinitesimal I forgot to tell you: I like animals and I think that people who love animals have good hearts.

ACuriousMind

@tpg2114 Just to make sure: You do realize you left your name in there?

tpg2114

@ACuriousMind Yeah, I don't really care if people know my name

ACuriousMind

Alrighty then

tpg2114

I don't generally use SE for things I wouldn't want associated with my name, so I look at it like publishing a paper or something

5

I did remove my social security number, all of my bank account information, and my entire medical history from the PDF though, just in case ;)

Physics Meta

5:01 PM

0

Q: Share question within SE users

I know that there's a way to share questions from SE in Twitter, fb, g+ etc. Is there any way to share a question to the users of SE? I can't use none of the available options because I do not have accounts in them.

feature-request

Stan Shunpike

6:14 PM

@ACuriousMInd

Okay let me try to summarize what I feel I understand based on what we discussed yesterday

So firstly, from reading Lee I know you basically build smooth manifolds first from sets, then topological spaces, then topological manifolds, and finally you get a smooth manifold eventually.

But we have this problem with smooth manifolds because we can't compare tangent spaces at different points on the manifold. This makes it hard to do calculus, which is something we want because it would let us measure curvature.

Now, from what I understood yesterday, when it comes to curvature, the thing we are interested in is the tangent bundle for the manifold. This is an affine connection because it is operating on an affine bundle, in this case a specific one called the tangent bundle.

ACuriousMind

I wouldn't say that we are doing this to measure curvature, that's just a nice byproduct. Primarily we want to do calculus on the vector fields, I'd say

Stan Shunpike

So in vector calculus, I felt like I had a nice strong grasp of what a vector field is. Ever since I started studying GR and differential geometry, I feel like I don't understand them. In particular, I don't understand the idea of a section. @bolbteppa Helped me out by giving me a PDF on fiber bundles, but I still think I am pretty weak at them.

Like is a section just a map from the tangent bundle to the manifold that projects a vector field onto it?

ACuriousMind

@StanShunpike No, a section is a map from the manifold into the tangent bundle that attaches a vector to every point

It's just the formalization of what a vector field is

Stan Shunpike

Oh, you're right. I'm misreading what they say.

So then, a section of the tangent bundle maps from the manifold into the tangent bundle?

ACuriousMind

Yes

Stan Shunpike

6:26 PM

Wow, that makes total sense with the diagram.

ACuriousMind

And a section obeys the additional restriction that, when you project back, you get the identity on the manifold

Stan Shunpike

ooooo that's cool

ACuriousMind

This is the formalization of the idea that it attaches to every point of the manifold exactly one element of the fiber

Stan Shunpike

That what attaches.....the tangent bundle attaches to every point onf the manifold exactly one element of the fiber?

ACuriousMind

The section

A section of a bundle is just a thing that attaches to every point on the manifold an element of the fiber

Hence: A section of the tangent bundle is just a vector field

(Morally, at least)

Stan Shunpike

6:35 PM

You used the example of a circle and a cylinder before. The base space B is the circle right? The total space E is the cylinder right? So is the fiber then the line element we are attaching onto the edge of the circle?

ACuriousMind

@StanShunpike Yeah. The circle is a 1-manifold, so it's tangent space is the line $\mathbb{R}$ at every point, and it's tangent bundle is an infinitely long cylinder, with the fiber $\mathbb{R}$ above every point

Stan Shunpike

Ah! I didn't get that the line was the tangent space. Wow that's very cool.

bolbteppa

@StanShunpike do you have a link to the pdf handy?

Stan Shunpike

Why is it's tangent space a line? Why couldn't it be a plane?

bolbteppa

I need to bookmark it finally haha

Stan Shunpike

6:38 PM

@bolbteppa hang on

ACuriousMind

@StanShunpike Well, the circle is one-dimensional, right?

And n-dimensional manifolds have n-dimensional tangent spaces

Intuitively, there is only one direction tangent to the circle if you embed it somewhere

Stan Shunpike

@bolbteppa duffell.org/chapter_4.pdf

@ACuriousMind true, although when I have seen it embedded on a circle, it's always like perpendicular to the edge of the circle. I would think it would have to be parallel.

bolbteppa

@StanShunpike Thanks! Okay, well intuitively the problem with defining derivatives on a manifold is that we want to be able to deal with quantities of the form $f(\vec{x} + \vec{h}) - f(\vec{x})$ yeah? The problem is that what I've written is ill-formed, because $\vec{x} + \vec{h}$ is actually in a completely different vector space, the vector space at the point a point $p + h$...

Stan Shunpike

@bolbteppa I suggest saving it on ur computer in case the link dies. That's what I did.

Didn't wanna lose that good resource!

bolbteppa

Thanks, all his pdf's are good, chapters 1, 2, 3 etc...!

ACuriousMind

6:46 PM

@StanShunpike Yes, every tangent space is parallel in the intuitive embedding. We...cannot really imagine the way the cylinder is formed from that, but if we just turn all the tangent spaces perpendicular, we can pretend we understand it ;)

Physics Meta

Recent Questions - Physics Meta Stack Exchange: Weird home page scenario: physics.SE [duplicate]

posted on March 06, 2015 by MARamezani

This question already has an answer here: The site toolbar looks broken in Chrome. How can I fix it? 1 answer This is what I observe. Watching from an ASUS laptop; an i5 intel CPU, and a chrome web browser (latest version). Well, I found an screenshot from a ph…

Stan Shunpike

Oh no! Another little trick that I wasn't aware of. So those diagrams are actually misleading?

@bolbteppa OH You're right! I never noticed that!

Wow! smart

ACuriousMind

@StanShunpike Well...misleading...they cheat a little. But it really doesn't matter in which way you turn the lines. The problem with the actually tangent lines is that they all intersect, so you cannot imagine how their "disjoint union" looks like. But when you turn them perpendicular, they don't intersect, and the cylinder emerges as the union clear as day

It's also a happy accident that the bundle actually carries the topology of the cylinder

bolbteppa

@StanShunpike that is a point Lee makes when describing Lie Derivatives in the intro to chapter 18 (the intro to every chapter of his is worth consulting at some point!)

Stan Shunpike

@ACuriousMind Is that what you meant about the fact they don't have disjoint union topology?

@bolbteppa I will make sure to do that. Lee is awesome. He's a very good writer.

ACuriousMind

6:51 PM

@StanShunpike Yes

So, one might say, while the parallel tangents are a good picture for every tangent space as such, they aren't good for the bundle, and the exact converse is true for the cylinder picture

At some point or another, you have to give up to actually fit these things into our pathetic 3D intuition.

Stan Shunpike

I don't like using my imagination frankly. It makes me more confused. But sometimes I have to to understand the basic idea of what people are talking about.

bolbteppa

@StanShunpike you should always use your intuition ;) Find out how the big words are just formalizing your intuition, never give up! :D So there are two ways to talk about derivatives on a manifold, one method (Lie derivatives) is to use a 'flow' to transport the vector in the $f(x + h)$ tangent space back to the $f(x)$ tangent space so you can compare them, another method (covariant derivatives) is to use the idea of a connection to connect the vectors in two different tangent spaces

@StanShunpike so a Lie derivative is literally just formalizing this cool baby example:
http://www.ictp-saifr.org/schoolgr/Lecture0Friedman.pdf
& the Covariant derivative is literally just formalizing this cool baby example:
http://books.google.ie/books?id=CRIjIx2ac6AC&lpg=PP1&pg=PA185#v=onepage&q&f=false

This
https://books.google.ie/books?id=miwuxaEXvOsC&lpg=PA487&ots=5kwEAh-3uh&dq=%22Riemann%20curvature%22%20symmetries%20%22lie%20derivative%22&pg=PA487#v=onepage&q=%22Riemann%20curvature%22%20symmetries%20%22lie%20derivative%22&f=false
is the more coordinate-lazy-physicist way of dealing with Lie derivatives

ducks

Stan Shunpike

Nice! I will study those. grazie amico.

You have an interesting approach

I haven't read anything yet that focuses on Lie derivative and flows as a way to understand curvature.

I've only heard the covariant derivative discussed for that.

bolbteppa

I'm just explaining what it means to take (first) derivatives on a manifold, curvatures involve second derivatives and covariant derivatives

Stan Shunpike

Ah! That's interesting though!

Cool.

I hadn't known about that.

ACuriousMind

7:02 PM

I prefer the connection approach to derivatives because it gives you arbitrary derivatives directly.

And "curvature" just appears as the obstruction to $\mathrm{d}^2 = 0$.

Stan Shunpike

So that approach gives you the best of both worlds so to speak then?

ACuriousMind

Well, Lie with its flows and vectors is probably more intuitive

Connections are more the algebraic approach than the geometric, I think

bolbteppa

@StanShunpike now look at my Lie derivative example, and look at my covariant derivative example, see how amazing they are, especially as compared with just about any book on manifolds describing these ideas, I leave it as an exercise for you to find a similar easy amazing explanation of Riemannian curvature, it should be explainable to a 1st year calculus student (assuming they followed that easy explanation of what a covariant derivative is)

Stan Shunpike

@bolbteppa Cool. thanks for info. awesome.

bolbteppa

Cool, I'll tell you where to look if you can't find it after a week or so

I looked in Wald and seen him talking about how einbein's simplify the computation of the whole Schwarzschild solution, the problem is what he gave is still insane...

Stan Shunpike

7:15 PM

Which page?

@bolbteppa

bolbteppa

Section 6.1

Stan Shunpike

Hahahaha

That's the one I began the first few pages on last night.

Are you saying it's very difficult?

lol I may not have gotten to that part yet. I was getting all confused by his hypersurface lingo and thinking I needed to get something to supplement to make sense of it. I was gonna start with Wikipedia

Jimmy360

My first comment in the h-bar!

Stan Shunpike

Welcome!

bolbteppa

Well I just haven't really read the tetrad stuff and have no idea how to compute the Riemann curvature tensor via tetrads and don't really think of connections as 1-forms yet so I need to just do a bit of work I guess

Stan Shunpike

7:24 PM

Yeah, I was about to come on here and ask about that.

I haven't heard that we needed to do that.

Tetrads sounded surprising.

But I'm still learning. I just didn't hear Weinberg mention them

So I assume if Weinberg didn't feel the need to use them, they aren't needed for an introductory understanding.

bolbteppa

No they aren't but they save you pages of calculations if you do Schwarzschild directly tbh

Stan Shunpike

Oh really? Well, then I might take the time! Lol I'm always looking for ways to save mess.

bolbteppa

For an exam I'll probably be asked to compute Schwarzschild so I'm gonna have to learn how to do it via tetrads, it looks like there's literally no thought involved tbh so it's worth it lol

Stan Shunpike

I took my first GR class this quarter and had to do pages of calculations. It was awful!

I mean, I loved it! But the calculations were tedious is all I am saying

NeuroFuzzy

@StanShunpike what kind of calculations?

Tensor index spaghetti?

Stan Shunpike

7:29 PM

YES

lol

exactly

well phrased. Tensor index spaghetti

NeuroFuzzy

ahhhh. Hey have you looked at penrose tensor notation?

Stan Shunpike

@NeuroFuzzy No, what is that? Is it handy? I'm always looking for easier ways to write stuff.

NeuroFuzzy

@StanShunpike en.wikipedia.org/wiki/…

I know absolutely no GR (Except something about, what, tangent spaces have the minkowski metric or something??) but I've had a bit of fun with tensors and that notation!

Stan Shunpike

@NeuroFuzzy That's cool! Might I recommend starting with John Lee's books if you are interested in learning the math.

I started with them about 4 months ago and I'm now reading Wald slightly uncomfortably, but nonetheless learning a lot.

I highly recommend Lee. I am not a great math wizard, so Lee was like a breath of fresh air because he writes so thoroughly and simply.

@ACuriousMind

So here are the properties of a connection as written on Wikipedia.

NeuroFuzzy

@StanShunpike Thanks. If so many people here are reading Wald maybe I should start.

ACuriousMind

7:36 PM

@StanShunpike groan. Yes. Unfortunately, that's how the diffgeo people insist on introducing it.

Stan Shunpike

@ACuriousMind Is this the wrong way? I hate it. I have no idea what it says. So if you have a better way, I'm all ears.

ACuriousMind

@StanShunpike Do you know the exterior derivative?

If you do, connections become sooo much simpler. At least, they became for me

Stan Shunpike

I am close to knowing it and I'd make an extra effort if it would simplify the connection because I hate the way it's presented.

So explain and I'll learn as I go

@bolbteppa Know anything about Topos?

@ACuriousMind By hate the way it's presented, I was referring to the affine connection not the exterior derivative.

bolbteppa

I think it's a category-theoretic way to talk about attaching families of things to other things locally

Stan Shunpike

@bolbteppa the tetrad?

bolbteppa

7:43 PM

topos

Stan Shunpike

@bolbteppa Because Danu said it was really hard. And I'm disappointed because if it is then it's probably not worth the effort to learn to read this book I have called Topos of Music

ACuriousMind

@StanShunpike Okay. Here we go. First observation: Given a $p$-form $\omega$ taking values in an $n$-dimensional vector space, we can obtain a $p+1$-form as $\mathrm{d}_A \omega(x) := \mathrm{d}\omega(x) + M(x)\omega(x)$ where $M$ is any $n\times n$ matrix-valued function.

Stan Shunpike

@ACuriousMind Alright, I follow so far.

bolbteppa

wtf... what is that book!

ACuriousMind

Oh, sorry. $M$ has to be a matrix valued $1$-form, not a function

Stan Shunpike

7:48 PM

@bolbteppa I dunno frankly. I've tried to decipher it for ages and am just as perplexed about it as when I began.

ACuriousMind

And the rule how to interpret $M(x)\omega(x)$ is to just wedge the differentials and apply the corresponding matrix components to the vector components.

If you can accept that, then I can already tell you that $M(x)$ here is what will become a connection form.

bolbteppa

Do you have a youtube video of his of music that was made by a computer program?

0celo7

@ACuriousMind Blumenhagen has a non-CFT derivation of the Virasoro algebra. Two pages of normal ordering hell. Also, I bought some tonic water. What's your preferred ratio?

Stan Shunpike

@ACuriousMind Let's suppose I can accept that lol. Continue. What is a connection form? A connection is a bilinear map according to Wikipedia right? So is that what you mean by a connection form?

ACuriousMind

@0celo7 Around 1:2, I think.

bolbteppa

7:52 PM

I think that's missing the point of what a connection is, ultimately you just want some function that acts on basis vectors so you can relate vectors in a moving basis back in terms of your original basis

ACuriousMind

@StanShunpike Yeah, forget everything you know about connections :P But I just realized I probably will mess this up if I do it on the fly. Let me write something up and get back to you.

Stan Shunpike

Okay, that's fine. I look forward to hearing about it. This sounds much more intuitive then the way I've heard it presented. Awesome!

0celo7

@ACuriousMind I did 1:2 gin:tonic with Sapphire and Canada Dry and it was yucky. Way too much tonic. I'll try 1:1 next time.

ACuriousMind

Oooh, if you got sapphire you can go to 1:1 without problems. I usually...don't drink that fancy :P

Also, completely unrelated: This question managed to stump me. How the hell do you impose $\psi_R = (\psi^c)_L$ on a fermion where $\psi_L$ and $\psi_R$ transform in different representations?

bolbteppa

If you have a vector field $\vec{A} = A_i \hat{e}^i$ and take it's derivative $\partial_j \vec{A} = \partial_j A^i \hat{e}_i + A_i \partial_j \hat{e_i}$ you see we took the derivative of the basis vector too, basic calculus ignores this, but I want to express the vector $ \partial_j \hat{e_i}$ in terms of my original basis so I say $ \partial_j \hat{e_i} = \sum_k \Gamma ^k _{ij} \hat{e}_k$ and get
$\partial_j \vec{A} = \partial_j A^i \hat{e}_i + A^i \Gamma ^k _{ij} \hat{e}_k$, the $\Gamma ^k _{ij}$ are 'connection coefficients' and we're obviously gonna have to use a 1-form acting on basis…

0celo7

7:58 PM

@ACuriousMind I need to lower my standards for food and drink. I'm going to be devastated when I leave home.

bolbteppa

Messed it up a bit but that's the jist

0celo7

@ACuriousMind I've seen this explained somewhere.

Real neutrinos aren't majorana.

ACuriousMind

@0celo7 I went through my Standard Model lecture notes, but somehow we managed to not talk about it...

bolbteppa

This is mental youtube.com/watch?v=inWm1twf2Ic

0celo7

That question doesn't make sense.

ACuriousMind

8:01 PM

@0celo7 Well, that's what I thought, but everyone kinda talks about them being Majorana. All I can see is that massive sterile Majoranas generate a "Majorana mass" term for the ordinary neutrinos in the seesaw mechanism

0celo7

@ACuriousMind Who says that majorana neutrinos have to interact weakly like real ones?

ACuriousMind

@0celo7 Nobody, that's why they're called sterile :P

Stan Shunpike

@bolbteppa He looks like he just got out of bed...

0celo7

@ACuriousMind :p

ACuriousMind

But you see everyone stating that we "don't know whether neutrinos are Dirac or Majorana"

And this doesn't make sense to me now that I've gone through the seesaw mechanism about thrice

Stan Shunpike

8:03 PM

@bolbteppa Here's the problem: he doesn't provide a simple example of how u can use that stuff to make better music.

bolbteppa

That's kind of amazing how he takes two viewpoints, continuous and discrete, with the dance analogy

0celo7

@StanShunpike Protip: mathematical music theory is not for real musicians.

It's for musicians who regret not majoring in math.

Stan Shunpike

@0celo7 You said it. That's what I've figured out from chatting here.

@0celo7 See, I thought they wanted to make better music. But you're right. That's exactly what it looks like. A bunch of them just fool around with math and pretend to apply it to music.

0celo7

@ACuriousMind My his logic, any majorana fermion participates in no interactions.

Right?

Stan Shunpike

@bolbteppa You got any good resources on ODEs and / or PDEs?

ACuriousMind

8:08 PM

@0celo7 Hm, it doesn't couple to any gauge fields at least. You can write it into other terms, though

bolbteppa

I think that is absolutely amazing, they are trying to understand the structure of music and use math as a model to think about it, that's phenomenal

0celo7

@ACuriousMind What else are there but gauge fields?

ACuriousMind

@0celo7 Fermions

0celo7

@ACuriousMind Fermionic interactions? What?

ACuriousMind

You can let it couple to other fermions, that's what seesaw does if I am not misunderstanding it

0celo7

8:09 PM

Oh

Stan Shunpike

@bolbteppa It really saves a lot of time in composing.

bolbteppa

@StanShunpike if I tell you what I think about ode's you'll go crazy, think the 5 volumes on ode's by Forsyth

ACuriousMind

You write something like $m\nu_L N_R$ where $N$ is a sterile Majorana

0celo7

@ACuriousMind I have not worked on the seesaw mechanism in months.

(That's a long time for self study.)

Stan Shunpike

@bolbteppa What do you mean?

bolbteppa

8:10 PM

@StanShunpike the old book on ODE's by Ince is the most useful book probably but make sure you know what's going on in something like Boyce & DiPrima first

0celo7

@ACuriousMind Does the seesaw mechanism require a Higgs-esque symmetry breaking?

ACuriousMind

@0celo7 Yeah

Stan Shunpike

@bolbteppa Some of these music-math guys though make statements that contradict my experience composing.

ACuriousMind

There are different types, but they all have a shiggsino in some form or another

bolbteppa

Like what?

0celo7

8:14 PM

@ACuriousMind Any insights into this question? Has an SE poster proved that sneutrinoionos are Dirac?

Stan Shunpike

@bolbteppa Like Dmitri Tymoczko wrote a book called A Geometry of Music. And I watched a video of him youtube.com/watch?v=XUyx31f-U3M

@bolbteppa and he claims that our brains / minds don't really notice when we change keys

@bolbteppa and I know that's clearly false.

ACuriousMind

@0celo7 I think they have at least proved that either I am completely blind or most physicists talk complete nonsense when they say they might be Majorana

0celo7

@ACuriousMind I changed the title and tags on that question.

Stan Shunpike

@bolbteppa Every time I write a song, one of the last things I do is I go through the song and check which key it should be in. And it matters because, there are only certain keys I can switch it to that will work. For instance, it usually works to shift it by 6 steps on the piano. So if I wrote a song in C major. Then F# will work.

0celo7

@ACuriousMind Either way, I smell Stockholm.

Stan Shunpike

8:17 PM

@bolbteppa But if I shift it to say D major which is like 2 or 3 steps, it changes the way you hear the relationships between the notes. Although the song will sound the same in some sense, the degree of pleasure gets decreased because the accents are all messed up.

But he seems content to just ignore that.

ACuriousMind

::facepalm::

Stan Shunpike

@bolbteppa I don't think Tymoczko is as taleneted as Mazzola. But I also can't understand what Mazzola is saying at all.

0celo7

@ACuriousMind Think about it this way: either he proved neutrinos are Dirac or he prevented you from spreading lies and ignorance as a future lecturer.

ACuriousMind

I now think Majoranas are perfectly fine. Charge conjugation is perfectly fine. People just need to stop saying that charge conjugation "flips all quantum numbers".

0celo7

@ACuriousMind I was about to ask if all numbers are flipped.

After all, spin isn't flipped.

Stan Shunpike

8:19 PM

@bolbteppa The basic thing a music theorist needs to quantify is pleasure. And there are only 7 notes. So the question is, how should you combine them? What are the rules? But I don't see what topos has to do with answering that. And 200 pages into his book, I don't feel like he has begun to answer that question. And the book is like 1300 pages.

bolbteppa

I have thought about that question and I feel I cannot answer it, I just cannot decide if switching a song you write from, say, C to D, really matters, I think it matters if you wrote it in C then see what it'll sound like in D, but if you come back a day later and start in D it might sound worse in C, I'm just not sure...

0celo7

Why should isospin?

ACuriousMind

@0celo7 Yeah, they aren't. They can't, because you can't "flip" a representation

Stupid pop-sci with its stupid simplifications

0celo7

I know they're completely unrelated.

Don't kill me.

ACuriousMind

@0celo7 Nah, both are just specifications of representations. No worries ;)

0celo7

8:21 PM

@ACuriousMind The $\Sigma^+$ has the opposite isospin from the $\Sigma^-$ and one is not anti to the other.

Or something along those lines.

bolbteppa

@StanShunpike the tetrad calculation is explicitly done out in McMahon's Relativity demystified!

0celo7

@bolbteppa Which calculation?

Stan Shunpike

Really!?!? What an unusual place to find it!

That's great. I should read that before Wald

0celo7

@StanShunpike Carroll is enough prep for Wald in my humble opinion.

If you're having trouble with Carroll, on the other hand...

You shouldn't jump to a higher level book if you don't understand the prerequisite/lower level book.

Stan Shunpike

@0celo7 Wald is fine. I'm handling him decently. I am prepared enough I think actually.

I just have pockets of stuff I don't understand

and I like to supplement with easier things.

bolbteppa

8:24 PM

I'm not 100% sure it's really gonna simplify things anymore tbh I just want to compute the Schwarzschild metric quickly without assumptions and I think this one is dragging some in :(

MARamezani

Hi guys!

0celo7

@bolbteppa All you need is $SO(3)$ symmetry and Einstein's equations.

bolbteppa

@0celo7 yeah but writing down Einstein's equations takes ages...

MARamezani

I'm a newbie to physics. I had a question.

0celo7

@bolbteppa Straumann does it fairly quickly using tetrads.

@MARamezani State your business.

MARamezani

8:28 PM

Is physics.SE overwhelmed with homework?

As I ~~heard~~ read?

bolbteppa

@0celo7 Computing Christoffel symbols then computing Riemann curvature then Ricci curvature then writing down Einstein's equations is a huge job, Wald says tetrads are a shortcut but looking in McMahon it doesn't look like it, I'll look in Straumann now

0celo7

@bolbteppa Beginning of chap 4.

ACuriousMind

@MARamezani Well, overwhelmed is a bit strong. While I could do with less questions to close, I don't feel overwhelmed.

MARamezani

How serious is the condition of good users leaving?

ACuriousMind

@MARamezani I don't know of any good users that left recently.

At least, any very active good users.

MARamezani

8:31 PM

Aha. So is Stack Exchange life running smooth?

ACuriousMind

Since meta has been quite quiet, I'd say yes

MARamezani

I read some things about this and for a second I thought I got here after an apocalypse.

0celo7

@ACuriousMind You \mathrm Lie groups too?

MARamezani

-39

Q: Physics is rotting into a bad situation, a request for community manager intervention

Physics Stack Exchange is experiencing the throes of very bad days. Lots of main and key users (compared to the total number of them) have left or are leaving. Examples of the community destruction include, with the leave: Have we lost the necessary critical mass of professional physicists? I...

discussion community

ACuriousMind

@MARamezani that's one-and-a-half years old

Stan Shunpike

8:33 PM

And -39

MARamezani

I thought the language was coarse and unhelpful, but the state of the union is true.

@ACuriousMind Doesn't give the reason for it not to apply today, does it?

ACuriousMind

@0celo7 Of course

0celo7

@ACuriousMind That comment is just a comment, not a challenge.

NeuroFuzzy

Hahahah @MARamezani "You want to know what the problem with Physics.SE is?"

Oh boy!

MARamezani

@NeuroFuzzy Oh just when I thought humor was out for a sec.

bolbteppa

8:35 PM

@0celo7 omg thanks a lot I'll sit down and try that one someday soon, I think that is phenomenal I hope I don't get stuck on it!!!

MARamezani

@NeuroFuzzy Yeah sorta.

0celo7

Cheerio, real life calls. Going to get bartending lessons from my dad's buddy.

ACuriousMind

@MARamezani Uhm, I'd not apply rants from suspended users from more than a year ago to today

0celo7

Apparently this is a college skill I need.

@bolbteppa You mean Straumann?

ACuriousMind

@0celo7 Well, it can't hurt to know how to pour a drink, can it? :D

0celo7

8:37 PM

@bolbteppa I like Straumann, and I think I even convinced @ACuriousMind to read it sometime in the future.

@ACuriousMind Good point.

MARamezani

So the only "thing" I should be careful about is arrogant new users huh?

bolbteppa

That Straumann book looks pretty good I'll definitely refer to it every now and again when Landau just says something is obvious lol

MARamezani

Ones that only look for an answer to their homework....

ACuriousMind

@MARamezani Why should you be "careful" about them?

Ignore them, flag them, whatever you like...

MARamezani

Nothing... Just not to start arguments and such.

bolbteppa

8:50 PM

@StanShunpike so basically McMahon's Relativity Demystified and Straumann's General Relativity explain the derivation of the Schwarzschild solution using tetrads, with Straumann making it insanely short, but I like the derivation of the $e^a$ part of the metric given here maths.tcd.ie/~ipde/GR_Notes.pdf I doubt it'll get any simpler than this!

Stan Shunpike

@bolbteppa wow that one is great! Perfect. I will use this to supplement Wald.

bolbteppa

Though doing it using a metric including $t$ as that pdf assumes will help you prove Birkhoff's theorem and derive Straumann's equation 4.13 (e.g. solve exercise 1) so be careful

bolbteppa

9:10 PM

@StanShunpike I'm not gonna lie that music book reminds me of Lacanian topology en.wikipedia.org/wiki/Fashionable_Nonsense "spacetime of human existence"

Stan Shunpike

9:27 PM

LOL

@bolbteppa it reminds me of trying to understand my high school chemistry teacher who tried to explain spin using political parties.

Absolutely unintelligible.

Stan Shunpike

9:39 PM

Goodness, yeah the link you posted is exactly how I feel about the book. He's throwing words around and not bring clear definitions to the table as to what they mean.

ACuriousMind

@StanShunpike: Am I hallucinating or is your gravatar changin frequently?

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