The h Bar

12:05 AM

@StanShunpike I think these are mostly new one-time users, and they usually ask questions beginning "I have heard that..." or "Physics says that..." where what follows after "that" is either incomprehensible or plainly wrong.

Stan Shunpike

@ACuriousMind Yes, I have seen these. They are quite fruitless. My usual policy is -1 and flag.

ACuriousMind

@StanShunpike Right thing to do, still, they feel as if they are becoming more common

Maybe I'm just getting grumpier, though

Stan Shunpike

I have heard more complaints about them in chat certainly from several users.

Whether this reflects an increase in the number I don't know. Some of the questions I have seen have been cesspool-like in the discourse they bring about. The person really has no serious interest in learning and things just deteriorate from there.

dmckee

12:23 AM

Not sure it really more, it could just be that the usual number have been more obnoxious than usual. Or the sequence of conference, finals, closing on a house in the last month could just have stretched my nerves too far.

Stan Shunpike

I doubt that would have caused multiple users to complain about it. Its not just you.

I personally find the questions and ensuing discussions a nuisance. But it seems there is little to be done. There's no magical "this user is going to be a problem" test to give each user

My economics professor told me today about one of the "Fermi stories" which are well known on campus.

ACuriousMind

@StanShunpike What kind of stories are these? Stories about Fermi?

Stan Shunpike

He said Fermi used to take his students on walks during class and just point to stuff and explain the physics on the walk. For the midterm or final, he would go to some predetermined location, point to some phenomenon, and ask them to model it right on the spot.

There was a particular example my professor gave. I don't remember the details, but it sounded like a very unusual class lol.

Needless to say, it sounds like you would need some talent to take that course.

ACuriousMind

lol, was that a special "Fermi class" or did he do that in "ordinary" courses?

Icosahedron

like what types of phenomenon?

Stan Shunpike

12:38 AM

A good question, I should ask. I can't imagine ordinary physics students attempting that, at least not here. People complain just about taking multivariable smh lol

Something involving snow, temperature I don't recall exactly as I was learning econ at the time.

This comes up sometimes in class because I like to make analogies or comparison to physics when related math comes up

And sometimes this leads to an unexpected tangent by my professor on topics that he happens to know something about.

ACuriousMind

Oh, comparing to physics does not actually get you blank stares? :D

Stan Shunpike

It often gets me "so, why don't you want to be a physicist again?" lol

"Isn't that your major?"

Icosahedron

you don't?

Stan Shunpike

Nah, I'm the physics loving economist.

ACuriousMind

@StanShunpike Hehe, I think you've got your share of that here, too

Stan Shunpike

12:41 AM

LOL true enough

I never noticed that

ACuriousMind

@StanShunpike The composing physics-loving economist ;) (and I feel I've forgotten one of your polymath features)

Stan Shunpike

I lose track lol. Too busy learning!

ACuriousMind

It's so rare for people to show an interest in physics at the level of actual theories rather than pop-sci that everyone assume someone with such an interest/knowledge must be a physicist, I guess.

Icosahedron

@ACuriousMind ..astronaut in space.

@ACuriousMind i'm 11 and I understand string theory.

Stan Shunpike

Yeah, I hate that people get such a substandard education in it. People will gladly take chemistry instead of a physics course and I'm always baffled by why schools don't ask them to get a "theoretical minimum" as Susskind likes to say

Icosahedron

12:45 AM

whatever we don't want outsiders.

Stan Shunpike

I feel like many stupid questions could be avoided if people took the time to get a basic education in how our physical world works!

Icosahedron

you don't know how it works? $ $<--->$ $

Stan Shunpike

Well, I know newtons laws. Some people don't even learn that. That leads to questions like....is gravity a force like pushing a balloon underwater or whatever nonsense that question had

ACuriousMind

@StanShunpike Many stupid questions about X could be avoided if people took the time to get a basic education in X ;)

But the case X = "physical world" seems somewhat...important, yes

Icosahedron

we can altogether end this site and link to a page of textbooks on every topic.

0celo7

12:49 AM

@Icosahedron I think you're serious

Icosahedron

srs

ACuriousMind

@Icosahedron We've had the "irony on the internet"-discussion before, haven't we?

Icosahedron

ocelot is too serious about everything I comment.

ACuriousMind

lol, I don't think he's serious

0celo7

I don't know how many times I have to say this. If you're not being serious, use an emoticon unless you know the other person knows you're kidding.

Marcel

12:52 AM

@ACuriousMind no rlly, I'm aware that you are two distinct guys ;)

Icosahedron

can we decide on a universal emoticon of sarcasm of the $\hbar$?

0celo7

:P or ;)

The former is more common.

Of course, we could make a really intricate one.

Icosahedron

do it then.

ACuriousMind

(\/) (°,,,°) (\/)

Why not Zoidberg?

@Marcel Heh, it's not clear to everyone. I had one confused user ask me once if I did change my name back and forth when we both commented on their post

0celo7

$$\int_\mathcal{M}\operatorname{ch}\left(\bigotimes_r(-1)^rE_r\right)\frac{ \operatorname{Td}(TM^\mathbb{C})}{e(TM)}$$

ACuriousMind

12:55 AM

@0celo7 If that's an emoticon for you, I don't want to experience your emotions. :P

2

0celo7

RHS of Atiyah-Singer theorem is now the sarcasm emoticon

Icosahedron

$$\int_\mathcal{M}\operatorname{ch}\left(\bigotimes_r(-1)^rE_r\right)\frac{ \operatorname{Td}what a brilliant idea. (TM^\mathbb{C})}{e(TM)}$$

0celo7

ooh, let me try

@ACuriousMind Urs Schreiber is literally Satan

huh, guess I really meant that

We should just use random equations or :P

Icosahedron

what about a * asterisk.

Icosahedron

it's definitely not as reasonable as an equation*

ACuriousMind

12:59 AM

@Icosahedron That'd look like there's a footnote missing, also, it clashes with the italics markup

user54412

20

Q: Site graduated! New design launched

As you can see the new design just went live. Which means this site has been officially launched! Congratulations! Thank you for your valuable design feedback. If you see any CSS/styling bugs, please start a new post and tag it with "design" and "bug." We have also updated the site's Twitter pr...

ACuriousMind

@ChrisWhite Ninja'd

0celo7

@Icosahedron That's a great idea $$\left(p\cdot\Gamma+\frac{\sqrt{8}}{\ell_s}\sum_{n=1}^\infty(\alpha_{-n}\cdot d_n+d_{-n}\cdot\alpha_n)\right)|\phi\rangle=0$$

ACuriousMind

...wait, Chemistry was in beta still?

Icosahedron

and we still don't have the new profile page...

0celo7

1:01 AM

@ACuriousMind +10 for name of Eq.

Icosahedron

I literally wrote 8 hours of exams today.

ACuriousMind

@0celo7 It's from string theory, and it looks faintly familiar, but I don't know what it is.

0celo7

@ACuriousMind Eq. (6.83) in Weigand. It's the Dirac equation for superstrings, aka the Dirac-Ramond Equation.

Learning about the GSO projection right now. Not that interesting, just a whole bunch of representation theory.

Marcel

@Icosahedron why would you do this?

ACuriousMind

@Marcel Why, what else do you do for fun? :)

dmckee

1:07 AM

@Marcel My graduate school comps were like that. For two days.

ACuriousMind

"comps"=?

dmckee

Those were two of my four smartest days ever. The other were the orals fro the same test and my defense.

@ACuriousMind Comprehensive exam. The one you have to pass to be allowed to propose your dissertation topic. Not all school have them.

user54412

I think most schools call them quals

Marcel

@dmckee I hope mine does not :D

dmckee

Covers all of the graduate "core" courses. Mechanics, E&M, quantum, math methods, thermal physics.

Icosahedron

1:09 AM

@Marcel I had two exams on the same day.

user54412

(though they're "generals" here)

dmckee

@ChrisWhite My school also had quals. Those covered your undergraduate stuff and had to be passed within one year of matriculating.

The quals only took one day.

ACuriousMind

Hm...we do not have anything comparable, I think

user54412

@dmckee Quals, comps, and defenses. Ouch.

Marcel

@Icosahedron everything going well?

dmckee

1:11 AM

@ChrisWhite It does enforce a minimum standard on the students, though. Everyone there was reasonably well informed and at least moderately flexible.

And you could get copies of previous versions of the exams to study.

0celo7

@ACuriousMind I know that the spin groups are the covers of the rotation groups, but how is a representation of the spin group different from a rep of the rotation group?

dmckee

It made you discover and shore up any deficiencies in you education.

ACuriousMind

@0celo7 The linear reps of the spin group are the projective reps of the rotation group, but only "half" of the linear reps of the spin group are also linear reps of the rotation group

0celo7

@ACuriousMind Linear rep?

Marcel

@0celo7 I thinks reps are only taken for simply connected groups, but don't pin me down on that.

you construct them by the lie-algebra relations and therefore effectivly use the universal covering reps (simply connected)

ACuriousMind

1:15 AM

@0celo7 Uh...usually just called a rep. linear reps are maps $G\to\mathrm{GL}(V)$, while projective reps are maps $G\to\mathrm{PGL}(V)$, where $\mathrm{PGL}$ is the projective linear group

0celo7

Are the spin and rotation groups simply connected?

I can't recall either way

ACuriousMind

@0celo7 The spin groups are, the rotation groups aren't

Marcel

^this

0celo7

@ACuriousMind Right, is the cover of a non simply connected group simply connected?

ACuriousMind

The definition of a universal cover is that it is the cover that is simply connected,

Marcel

1:17 AM

@0celo7 there is a unique one which is simply connected

ACuriousMind

All simply connected covers are isomorphic

Hence the "universal"

And it is a fact that all reps of a Lie group are induced from reps of its universal cover

But not all reps of the cover descend to rep of the covered groups, only to projective reps

0celo7

Ok, so in the RNS superstring why do we say that the fermionic modes are reps of the spin group and not the rotation group?

Unless I'm being really retarded and there are no spinors in SO(whatever)

ACuriousMind

@0celo7 Because quantum mechanics deals with projective representations (upon the space of rays). Spinors are never an actual linear rep of the group - the whole "you have to rotate them twice to get back to where you started" is just a stupid way of saying the rep is only projective.

But since linear reps are easier to deal with, it is easier to formulate every projective rep just as a linear rep of the universal cover

Additionally, since you are usually on the level of the Lie algebra, which is the same for all covers, you might not even see the difference

0celo7

The rotation gives a sign is related to the division by Z_2 in the projective linear group?

That sentence makes no sense.

Icosahedron

@Marcel Sort of, you?

ACuriousMind

1:23 AM

@0celo7 Sorta. Covers as well as projective reps are closely related to central extensions.

0celo7

@ACuriousMind Projective means "up to a phase", right?

ACuriousMind

@0celo7 Essentially, yes

0celo7

BBS is a little frugal with explaining the group theory. Is Weigand any better?

ACuriousMind

@0celo7 Nope

Almost no physicist ever explains this stuff :/

And I doubt most know it, even :P

0celo7

Lol, Weigand doesn't even bother with spin groups

He calls all of it SO(8)

Stan Shunpike

1:25 AM

are the requirements to go to being a full site arbitrary?

I mean like they don't even have a chat room requirement I feel like chat is an important part of the site. it's sorely missing on the econ Stack Exchange

0celo7

@ACuriousMind Appendix 8.5 in BLT: Dirac Matrices and Spinors in $d$ Dimensions

I know what tomorrow's reading will be!

ACuriousMind

@StanShunpike They have a lot of metrics they look at, but I think the actual requirements are a) fluid and b) secret.

user54412

For example, I'm sure the powers that be ask themselves "Is there any chance we'll be embarrassed to have this site on the network down the road?" on a case-by-case basis.

0celo7

@ACuriousMind Appendices 5.A and 5.B in GSW: Properties of SO(2n) / The spin(8) Clifford algebra

ACuriousMind

@StanShunpike E.g. MO chat is almost always totally dead, chat is not vital

0celo7

1:29 AM

Be prepared for a wave of questions.

ACuriousMind

@0celo7 Oh god, be prepared of a lot of "I don't know"s or answers where I hide behind group theory instead of actually calculating anything ;)

0celo7

@ACuriousMind Help me Björn, you're my only hope

ACuriousMind

@0celo7 Perhaps you need A New Hope<sup>TM</sup>.

I hate you, chat :(

0celo7

BLT is an interesting book. Some parts are excellently detailed, others get bogged down by details and randomly say "one can show". I think they got tired/bored or the editor told them to keep it shy of 800 pages.

user54412

™

0celo7

1:37 AM

For instance, I got really bored in the section on open string CFTs. They quoted the main result and did a lot of work on random stuff.

ACuriousMind

@ChrisWhite Using unicode is cheating ;)

user54412

Does anyone else find the whole idea of unicode/utf/etc. a little weird -- like they are conflating character encoding with alignment and decoration of those characters?

0celo7

@ChrisWhite Does Computer Modern have good kerning?

user54412

@0celo7 For text, it never struck me as being particularly bad, but I'm no graphic designer. Also, I try not to use it too much.

ACuriousMind

@ChrisWhite Yes, I feel unicode is weird. Being able to print all the variations of symbols and decorations by simply having a giant table full of them certainly works, but it's terribly inelegant.

0celo7

1:39 AM

@ChrisWhite Why don't you use it much?

user54412

@0celo7 Of course, if you count all the manual kerning latex requires for math to look good against CM, then it's pretty bad.

0celo7

Requires? Manual kerning?

user54412

@0celo7 I just don't like the letters -- there's something... thin... about them.

ACuriousMind

There is this one guy on TeX.SE who does every imaginable symbol in pdfliteral. Others load unicode or pictures, he has a bunch of seemingly random numbers inside pdfliteral and produces a beautiful image^^

user54412

@0celo7 All the \! and \, and such

0celo7

1:42 AM

@ChrisWhite So you agree that the beta is flimsy??

@ACuriousMind I've seen the symplectic group with stuff like (2,1). What does that mean? The symplectic group has nothing to do with the metric.

user54412

@0celo7 yeah

0celo7

@ACuriousMind Wiki says, for instance, $\mathrm{Spin}(4,1)\cong\mathrm{Sp}(1,1)$

ACuriousMind

@0celo7 $\mathrm{Sp}(n)$ may not be the symplectic group, but the group of symplectic unitary matrices $\mathrm{Sp}(n) = \mathrm{U}(2n) \cap \mathrm{SymplecticGroup}(2n)$ (yes, notation is stupid here). Now, you may instead of $\mathrm{U}(2n)$ preserving the usual Hermitian product as the first group take the group of matrices preserving the mixed signature version of that, giving $\mathrm{Sp}(p,n-p)$ for $p$ minuses.

0celo7

Cool

user54412

2:00 AM

@0celo7 Okay, here's a pdf with about 20 fonts and some sample math for each. I challenge you to find a good beta.

Icosahedron

@ACuriousMind Do you know the transrapid?

ACuriousMind

@Icosahedron Yes, why?

Icosahedron

Is the transrapid 09 still in beta in germany?

ACuriousMind

@Icosahedron Uh...I'm not 100% certain, but I think we gave up on the transrapid after some ugly accidents and general planning mistakes.

Icosahedron

I remember that.

ACuriousMind

2:03 AM

So, I think the beta failed

0celo7

@ChrisWhite Figure 2 is disgusting

Icosahedron

@0celo7 It looks like microsoft word.

0celo7

@ChrisWhite Do you like any of these fonts better than the first?

user54412

Of those I prefer txfonts for math (Figure 15), but I slightly prefer Palatino over Times for text.

user54412

And I've never found a font I'm happy with for $\sum$

0celo7

2:12 AM

@ChrisWhite The original sigma is so awesome!!

user54412

Probably because I don't want the two angled strokes to have different weights, yet everyone insists on making the top one heavier.

0celo7

I got LaTeX because the summation sign on Wiki looks so cool

I like 15 except for the integral and the sum

user54412

Yeah, the integral there is a bit wonky

user54412

I feel like variable-weight diagonal strokes make sense for N, M, and W, but not for Sigma, or even Y

0celo7

Oooh I like 16

Nope, that partial derivative is messed up

user54412

2:16 AM

I just don't get $\partial$ -- it's like someone tried to make a sexy d, but forgot we already had $\delta$ for exactly that purpose.

0celo7

Does it bother you that some people write the partial derivatives of $L$ in the Euler-Lagrange equations with $\delta$s?

user54412

mmm, maybe not? is there a charitable interpretation for that choice?

Waffle's Crazy Peanut

I wonder whether the SE team might redesign old sites, at least because I feel jealous of Chem.SE

0celo7

I know Zee and Kaku do that. They use $\partial$ for everything else.

user54412

I know my analytical mechanics book made heavy use of both $\partial$ and $\delta$, but in a self-consistent way.

0celo7

2:23 AM

In computer modern, the following bother me: $\Lambda, \gamma, \Psi, \beta$.

NeuroFuzzy

And here I am, typing up stuff with default latex everything

0celo7

Lambda should be wider. Gamma should be less thin and straight. Beta is flimsy. Psi looks retarded.

@NeuroFuzzy I use default, too. I would change it if I knew how.

user54412

@Waffle'sCrazyPeanut You know, we originally had a light-chalk-on-blackboard style, but the community revolted and demanded a light background.

0celo7

@NeuroFuzzy You'd better me \mathrm'ing stuff.

NeuroFuzzy

Heheh on this site I don't bother but in my documents I do!\

Waffle's Crazy Peanut

2:25 AM

@ChrisWhite Yeah, that would've been much better. I'm sorta getting bored of this blue-ish thing -_-

NeuroFuzzy

should you use \mathrm or \mbox for text subscript? Like $v_{\mathrm{matter}}$ or $v_{\mbox{matter}}$?

Waffle's Crazy Peanut

It's nice, but it doesn't have much artworks (because we're old)

0celo7

Oh god, the first one.

NeuroFuzzy

Oh.

0celo7

@ChrisWhite Your ruling?

NeuroFuzzy

2:28 AM

find -> replace, mbox -> mathrm

fixed!

user54412

@0celo7 ?

NeuroFuzzy

wow that does look better.

0celo7

@ChrisWhite Small text subsrcipts are better, right?

Howcan

@0celo7 Personally I find the smaller text subscripts easier to read. Especially if there were multiple lines, I think they'd fit more.

NeuroFuzzy

I dislike these last chapters of griffiths a lot.

0celo7

2:31 AM

Plus, say you have a descriptive subscript and an index

user54412

@0celo7 Certainly. I had to make a test document to see what mbox even does in that case.

0celo7

It would look strange for one to be full size and the other small

@NeuroFuzzy Why? (Haven't read it.)

0celo7

2:58 AM

@ACuriousMind Speaking of Geodude...

NeuroFuzzy

3:57 AM

@0celo7 Oh, well it's just that all the interesting formulas you can derive in electrodynamics -- doing symmetry stuff with the d'alembertian, worrying about advanced/retarded potentials, doing anything with field lagrangians/modern physics, etc. are either not done or the formulas are handed to you. And then you go about applying them to a bunch of different situations with a whole lot of algebra and calculus. It really focuses on writing pages of simple calculus.

I'm just tired of it. bolbteppa has it right, the way L&L tackles it is more sensible for someone wanting to do theoretical physics.

Or maybe any book that school forces me to spend so much time on will look rotten to me. The world may never know.

Stan Shunpike

4:33 AM

@NeuroFuzzy it doesn't sound like you've had a good class this quarter.

Stan Shunpike

4:44 AM

I thought electrodynamics was supposed to be a beautiful subject.

But I guess the way it is being taught, you are missing much of the beauty

In that it sounds like you are doing some very boring aspects of it

@0celo7 wtf is that creepy / weird cartoon?

DanielSank

Hi, everybody.

Stan Shunpike

Hey DS! What's new in the world of quantum computing?

NeuroFuzzy

5:39 AM

@StanShunpike the "spending too much time on one book" thing might be more likely.

Stan Shunpike

5:54 AM

@NeuroFuzzy I can see that. although I've had books that I spent lots of time with and really enjoyed it

but maybe it depends on the course

Danu

6:26 AM

@0celo7 I'm not necessarily talking about group structure

But I guess you weren't either

Stan Shunpike

6:37 AM

@ACuriousMind so what resources do you like for learning thermodyanmics?

This is cool

72

Q: Why is gold golden?

Bulk gold has a very characteristic warm yellow shine to it, whereas almost all other metals have a grey or silvery color. Where does this come from? I have heard that this property arises from relativistic effects, and I assume that it has to do with some distinct electronic transition energies...

inorganic-chemistry computational-chemistry theoretical-chemistry

Joshua Lin

8:19 AM

could anyone help me with a quick question?

http://imgur.com/gallery/cO8rHsl/new

apparently there is a peak max and an antipeak, but I can never seem to find them :(

Danu

@JoshuaLin Sorry, but this is not a homework solving site

Joshua Lin

yea I know, but like I've got zero clue who to ask about it so I was wondering if I could get a hint

Danu

I also don't know much about circuits at all. I'd think you probably just need to set up some (system of) differential equation(s)

0celo7

10:06 AM

@StanShunpike /vp/

0celo7

12:09 PM

@Danu Interesting historical tidbit: In 1829, Jacobi proved what he called "a rather obscure formula" that strongly implies the GSO projection of the RNS superstring is necessary for spacetime supersymmetry.

I wonder who actually remembered that paper when doing string theory research.

ACuriousMind

@StanShunpike I don't like learning thermodynamics. :P

0celo7

12:31 PM

@ACuriousMind The urge to learn string theory finally hit me, I can feel the pull of Hawking & Ellis slipping!

Marcel

@0celo7 you are lost in wonderland then

0celo7

@Marcel not even mad

How do I sum the half integers? Is it just half of zeta(-1)?

Oh no, that has integer contributions from even numbers

Marcel

@0celo7 you don't sum all integers to -1/12. You can however do some analytical continuation of the zeta function on domains for which the series definition isn't defined. the values on that domain have nothing to do with the sum howerver.

0celo7

@Marcel I know that, I'm being heuristic

The exercise wants me to calculate the NS normal ordering constant and I ran into a divergent sum of 1/2+n where n is an integer.

I should regulate the sum and cancel the infinite part with a cosmological constant, but I'm wondering if there's a cool number theory way of skipping straight to the answer.

Marcel

12:46 PM

dunno. but i'd say its 1/2*zeta(0) + zeta(-1)

0celo7

I thought divergent sums don't associate like that

Marcel

y sure. but that's what string theorists do

and in fact you do that in QFT too

you get something that blows up. forget about its derivation and just analytical continue it on a finite value

0celo7

Yes you use that technique from QFT a to regularize the divergent sums that appear in the zero mode of the energy momentum tensor in string theory

Alternatively, you can introduce a counterterm

Marcel

there are several other examples

0celo7

I'm sure, but I'm only 148 pages in

Marcel

12:52 PM

take for instance some feynman propagator

it's integral usually blows up

0celo7

Oh in QFT

Marcel

however analytical continuation is possible

0celo7

Complex momentum, right?

Marcel

yeah. something that's know under wick rotation

actually this is just analytical continuation

good thing bout that that most of the time this continuation is unique, giving some "rigor" in that approach

0celo7

Lack of rigor in QFT doesn't bother me too much

Marcel

12:59 PM

yeah. but don't try to find some inner reasoning behind renormalization that holds in every case. I think there is none. However I'd be glad if somebody proofs me wrong ^^

ACuriousMind

1:15 PM

@Marcel Have you read Arnold Neumaier's "Renormalization without infinities"? I think his explanation of renormalization as a generic reparametrization to decrease the sensitivity of the theory to small perturbations of the parameters in the range we are interested in makes a lot of sense, works in all cases, and is essentially the Wilsonian approach lucidly explained.

Marcel

I read about the abstract and the the simple two state system. As far as I understand what he says is: "Renormalization can be described by a reparametrization and limiting process"
but this is just essentially analytical continuation.
he claims that eliminating those sensitivity is physical, this is well ... a claim

ACuriousMind

@Marcel He does not claim that there is anything "physical" about it because you do not change the theory. All renormalization does is set the parameters such that your perturbation theory doesn't blow up quickly at that scale.

Marcel

As far as I understand for him the theory is "QFT + renormalization" because if you don't need renormalization, it doesn't change the outcome if you still apply it

sure u can argue like that

ADG

1:47 PM

help i.stack.imgur.com/oIdg5.jpg

2

ACuriousJim

Attention all! This month's name has been chosen, posts have been edited and the voting for next month's name begins now. Don't forget you can always suggest new names too. And in line with the circumstances of this month's winner, you can also suggest new profile pics with the name

Other people should be happy that now they won't have to worry about pinging me when they want to ping @ACuriousMind

Marcel

@ACuriousMind: I think this all comes down to the usuall: "the parameters in our theory are not the ones we observer because we only observer effective parameters and therefore renormalization shifts infinities away from observability"

Icosahedron

Can anyone explain this?

What does the notation on the left mean?

Marcel

@Icosahedron the scalar product of <v| and a|v>

ACuriousMind

@Icosahedron I thought you know Dirac notation?

Icosahedron

1:58 PM

wait so it's just dirac notation

o.o

0celo7

Of course it's Dirac notation.

ACuriousJim

@ADG what have you tried already?

Icosahedron

but it's not qm.

Marcel

@Icosahedron well. scalar products are common in several context

0celo7

You asked me yesterday if you can use Dirac notation for random linear algebra and I said yes.

Icosahedron

2:03 PM

pretend that I didn't ask that question today.

Stan Shunpike

Even I knew that dirac notation was used that way

I wish his name was pronounced "der rock"

I think it sounds much cooler than "der rack"

Icosahedron

it's because I learned dirac notation with only 2 vectors not 3, so I thought it was different.

0celo7

Dirac notation is with 2 vectors.

Stan Shunpike

nods head

Icosahedron

I meant 3 arguments

0celo7

2:09 PM

I don't know what you're talking about.

Icosahedron

ok forget about it.

Stan Shunpike

Lol alrighty then

0celo7

What three arguments?

You're using poor terminology.

@StanShunpike String theory excitement finally hit me today!

@ACuriousMind BBS omits the wedge on forms when discussing the GSO superstring D:

Stan Shunpike

@0celo7 oooo. Why?

0celo7

@StanShunpike It just hit me.

ACuriousMind

2:15 PM

@0celo7 Oh god, I hate people who do that.

0celo7

I meant GS superstring

But still, it's heresy.

Stan Shunpike

Lol @ACuriousMind pet peeve?

0celo7

@ACuriousMind I just noticed that b followed by j has poor kerning in Computer Modern.

ACuriousMind

@StanShunpike Yeah. I can't count the times where I've screamed "WTF, you can't multiply them like that" at a formula only to realize later that that was meant to be a wedge product

@0celo7 lol. Note that I'd only care about a capital B followed by a minuscle j, though.

0celo7

You want your name to have exquisite kerning?

Stan Shunpike

2:19 PM

Oh, I feel you on that. I hate that kind of thing. I used to feel that way about the Einstein summation convention. Then I tried writing out some of the sums myself and I realized why it is useful. But bad notation is just a nuisance and confusing.

Marcel

@ACuriousMind: I'm not all the way through that whole document. But what i get is: reparametrization does not change physics. Ok that's cool as it can be described by some unitary transformation. However: is there physical quantities that are invariant under that limiting process used for renormalization. Like, energies are apperently changing ....

so renormalization is not a pure invariance statement

ACuriousMind

@0celo7 I have never written another word containing b followed by j, I think.

0celo7

Subject is pretty common.

ACuriousMind

...how did you notice that bad kerning, anyway?

0celo7

From BBS: "A key formula in this subject is an identity satisfied by a Majorana..."

Hmm, maybe j in general has poor kerning.

Stan Shunpike

2:24 PM

@ACuriousMind So random story. I am taking this psych course. And we studied eyewitness testimony, which I am sure you can imagine is quite unreliable.

Anyways, the authors of this one paper did an experiment where they showed people pictures of a car accident. They then said, when the car hit the wall, did the windows smash? 14% said yes. Then they said when the car smashed into the wall, did the windows smash? And 32% reported yes.

So by changing the question wording, people just believed something different.

ACuriousMind

@StanShunpike ...wat

Stan Shunpike

Yeah, it makes testimony seem...not just unscientific...but completely unreliable

And capable of being nontrivially biased by lawyers or police during interrogation

ACuriousMind

@Marcel As I understand it, the full non-perturbative results (which are inaccessible, sadly) would not care for renormalization at all (precisely because reparametrization is a symmetry), all renormalization does outside perturbation theory is make it possible to take certain limits of models. Basically, renormalization just sets up the perturbation theory right.

@StanShunpike Yeah, that'd indicate you cannot actually believe any personal testimony as fact.

Or even anywhere near fact

Danu

@StanShunpike This effect is also huge in professional judges, when making decisions about criminal cases.

A great book on this and many related effects is Kahneman - Thinking, fast and slow. He's a Nobel Prize winner (Economics) who did many experiments to expose just how bad we are at being rational :D

(or you can read his papers, I guess)

Stan Shunpike

Yeah, Kahneman is good. Won it for prospect theory IIRC

@ACuriousMind exactly!

Not anywhere near fact.

ACuriousMind

2:39 PM

@ChrisWhite Am I reading this right as that they withdrew the graduated design because people didn't like the black-on-white and just never gave us a new one?

ADG

@ACuriousMind well I have tried many things

Let cylinder move x distance to right [The COM]
then compression in right spring is x

Jim the Enchanter

@ADG I think you wanted to respond to me.

ADG

then $x=2x_2+x_3$
and let tension in right string be T that is $T=kx$

and in left be T' which is $T'+kx_3=4kx_2$
@SMF vague statement lacking context [yours]
Now $T-T'-f=ma$
and $fR=\frac12mR^2\frac aR$
so $f=\frac12 ma$
and thus:
$$T-T'=\frac32 ma$$
now find T and T' in terms of x and put it here,

then relate to $a=\omega^2x$
then Time period is $2\pi/\omega$

@JimtheEnchanter oh yes this is not working

Jim the Enchanter

You're last answer was just to prove how cool you are, right ? — Abc2000ro 6 mins ago

Stan Shunpike

@ACuriousMind why is physics like one of the last sites to get an upgrade?

Jim the Enchanter

2:44 PM

Finally somebody noticed

ACuriousMind

@DanielSank: lol, you didn't know about PO until know?

@JimtheEnchanter Heh

@StanShunpike How should I know? :D

They just hate us^^

ADG

@JimtheEnchanter ok then maybe I should go, bye.

Stan Shunpike

Its discrimination. That's what it is. Time for revolution.

Kidding but it just is weird

Like math has it, beta sites have it, so....

yuggib

3:06 PM

-2

Q: Why do people make distinction between science and philosophy?

Why do people make distinction between science and philosophy? Do they think that the great scientists that pushed the knowledge frontier further did that by magic? Don't they realize that you cannot "do science" without first thinking about what you're doing? Do they think that novelty appears o...

soft-question

the discussion is hilarious :-D

I appreciate the effort of many in convincing it, but I think it is not worth to discuss with some people...

also, it is fun but maybe obvious to note that the OP is by far the more ideologically biased of the people involved, despite his claims of the contrary...

ACuriousMind

@yuggib You mean, they have created an ideology that all current science is ideology? ;)

yuggib

@ACuriousMind exactly ;-)

gonenc

3:46 PM

@A

Shoot :) @ACuriousMind you are in Heidelberg Uni is that correct?

ACuriousMind

@gonenc Yes

gonenc

Well... I'm planning to go there for a study in physics. Would you really recommend there or would you say that LMU or any other uni is better?

I'm not from germany so I really don't know anyone else to ask to, who really studied there

ACuriousMind

@gonenc I would gladly recommend it, but depending on what you want to do, some other places might be better in that specific area. For LMU, you could ask @Danu, they're hardcore mathematical there, I don't know about the "normal" degree, though. For more "applied" physics, looking at places like Aachen would be worthwhile, I think.

Which area of physics are you specifically interested in, if any?

gonenc

@ACuriousMind I'm planning to be a theoretician, so applied physics doesn't interest me a bit.

In particular I would say QM interests me the most, though I'm still in the phase of learning it.

ACuriousMind

@gonenc Then I can really recommend Heidelberg, although, as I said, I don't want to say it's necessarily the "best". Are we talking Master or Bachelor studies here?

gonenc

3:56 PM

@ACuriousMind Since I'm not interested in applied physics, I fear that physics Heidelberg Uni is all about bio-physics etc. because of the obvious medical school

@ACuriousMind bachelor just starting :)

ACuriousMind

@gonenc No. There are biophysicists and atmospheric scientists, but the "main" topics in physics are astrophysics and QM/QFT, I would say.

There are some GR/cosmology people as well, and all sorts of other things, I think there's for almost every topic and least someone here who does it.

gonenc

@ACuriousMind that is really reassuring.

Are you going to take your masters in heidelberg too?

ACuriousMind

@gonenc So then you would consider doing your Master here?

@gonenc Yes, I am currently enrolled in an MSc here

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