The h Bar

@JohnRennie It's not, cf. discussion thread

user215373

this is completely about food or cooking science

user215373

you can see its example ques @JohnRennie

Well, cooking science is already covered by Seasoned Advice. Growing food is covered by Gardening & Landscaping and perhaps also other. What exactly are the topics here that don't fit into the other sites?

12:31 PM

By all means give it a go. After all, what do I know? I predicted the wrong result for the EU referendum.

what about raising cattle

@Dr.ZOMBOOS One example question is not nearly enough to get an idea what this site is supposed to be about.

user215373

not funny @ACuriousMind

@Dr.ZOMBOOS I don't think that was meant as a joke or to be facetious.

@Slereah I...think that's not yet covered

@Dr.ZOMBOOS It's not supposed to be funny, I meant everything I said in earnest.

user215373

12:34 PM

well i am vegetarian @ACuriousMind

Everyone can come up with reasons why an idea won't work. You should ignore us and charge ahead anyway. It's just that, well, it won't work ...

@Dr.ZOMBOOS What has that to do with anything?

@Dr.ZOMBOOS Did you reply to the wrong comment? Did you mean to reply to Slereah's comment about cattle?

Oh

@Dr.ZOMBOOS why not vegan

12:35 PM

But vegetarians also would raise cattle for milk, no? It's vegans who wouldn't raise cattle at all.

@Dr.ZOMBOOS Ignore what we're saying here. Clearly this crowd isn't in support of it, but you don't need our support. Go ahead with the site proposal and if it works out, great. If it doesn't make it past beta, then at least you tried.

I tried a vegan diet but I found the vegans a bit too chewy.

2

Vegans can drink human milk

If given voluntarily

@JohnRennie #rekt

The old jokes are the best

user215373

12:37 PM

here is the second example ques

user215373

we are not taking here about jokes

@Dr.ZOMBOOS I fear you are interpreting our good natured joking as a genuine interest in your proposed site

@Dr.ZOMBOOS what has that got to do with the validity of a cattle-raising question on the proposed site. Theoretically not everyone who uses the site will be vegetarian. Even if they are, cattle raising is still a part of food production. Not covering it simply because one is a vegetarian is like sticking one's fingers in one's ears and loudly shouting "If I don't agree with it, it doesn't exist!"

user215373

ok mr @JohnRennie

@Dr.ZOMBOOS that's Dr. John Rennie :-)

12:39 PM

Soapmaker @JohnRennie

user215373

a bit crazy

user215373

you are right @Jim

Not many people have a PhD in making soap :-)

@JohnRennie i need some soap

i smell bad

0celo7 has no nose.

How does he smell?

Terrible! :-)

user116211

12:42 PM

@0celo7 dude, use deo ;P

@MAFIA36790 too fat, can't reach

Anyway you should under no circumstances use soap as it's exceedingly bad for the skin.

@JohnRennie ...huh?

user215373

lol

@JohnRennie lolwat

12:43 PM

☐ Not REKT
☑ REKT
☑ REKTangle
☑ SHREKT
☑ REKT-it Ralph
☑ Total REKTall
☑ The Lord of the REKT
☑ The Usual SusREKTs
☑ North by NorthREKT
☑ REKT to the Future
☑ Once Upon a Time in the REKT
☑ The Good, the Bad, and the REKT
☑ LawREKT of Arabia
☑ Tyrannosaurus REKT
☑ eREKTile dysfunction

2

@ACuriousMind Are you familiar with stability in the smooth homotopy sense?

and transversality

Use shower gel. Shower gel is made with a surfactant called sodium lauryl ether suphate that is just as good as soap but much less dmaaging to skin.

@Jim the last one is not funny; it's a serious matter >:(

@0celo7 not at all

@0celo7 I think the second last makes up for it though

12:44 PM

@Jim not when your T Rex has a defect

@Jim that is excellent. I shall keep a permalink for future reference :-)

@ACuriousMind I used to think you were a geometer

@JohnRennie :)

We now have a star board that is utterly unrelated to physics :-)

Business as usual, then.

user215373

12:47 PM

i got the third ques too

@JohnRennie not so, it has chat.stackexchange.com/transcript/message/30570651#30570651 on it

@0celo7 I was a geometer once, then I took an arrow to the knee.

@ACuriousMind An algebraic arrow?

user215373

area51.stackexchange.com/proposals/100599/foody-friends/…

user215373

here i got the third one

12:47 PM

@ACuriousMind that reminds me, I need to check on GTX 1080 cards

skyrim on ultra with gfx mods > life

4

Secret Societies

Proposed Q&A site for people to ask questions and speculate about secret societies and their activities.

Currently in definition.

A much better proposal

nope, not out yet

@Slereah "Proposed Q&A site [...] to [...] speculate" Yeah, I'm sure that will go well

"It was da joos right?"

@Slereah I typically blame them, yes.

user116211

12:56 PM

@JohnRennie: I didn't considered that though:

user116211

13

A: Must the UK leave the EU?

According to The Guardian, the referendum is not legally binding, and the final decision lies with Parliament.

user116211

although of course, parliament would be going to respect the referendum's decision.

1:13 PM

@JohnRennie How does it feel not being European any more

@0celo7 I'm pretty sure Englanders never really thought of themselves as part of Europe

Y'know

I should really learn the two big CTC theorems

Tipler and Hawking

I tried reading Hawking but

Oh my stars

There were measures involved

1:33 PM

@Slereah The Geroch theorem involves Borel measures

The horror

borel measures are easy

More like boring measure

what is boring about measures?

general relativity is more boring than measure theory ;-P

A measure is just like

Substraction and addition

snore

1:40 PM

?

Well Borel measure on intervals is just $\mu [a,b] = b-a$

@yuggib some GR uses measure theory :o

and $\mu A \cup B = \mu A + \mu B$

p. boring

Is a Borel measure a functor?

A monoidal one at that?

mb

1:41 PM

@Slereah you clearly know nothing about measures ;-P

@0celo7 no

Yeah pretty much

What else is there

@yuggib why not

It maps some topological space into a vector space

@0celo7 it doesn't

what does it do to homs

@yuggib bah what do you know

I know the definition of a measure ;-P

and it is definitely not the one slereah wrote

1:48 PM

what is even a measure

Am I a measure

What is the measure of a man

a map from a $\sigma$-algebra to (positive) numbers

i.e. a specific element of $\mu\in (\mathbb{R}_+)^{\Sigma(X)}$, where $\mu(\varnothing)=0$

and $\mu(\bigcup_{j\in\mathbb{N}}s_j)=\sum_{j\in\mathbb{N}}\mu(s_j)$, with $^{\forall} j\in\mathbb{N}$, $s_j\in \Sigma(X)$ mutually disjoint

Basically what I said :p

nah

the point is of having a sigma algebra

Isn't the set of intervals of R the sigma algebra

Or close to that

I don't think I have ever felt European because that isn't the way I categorise myself.
To the extent that I categorise myself at all it would be as a scientist i.e. part of the group who care how the world works. Were I to meet an Outer Mongolian interested in GR I suspect I would feel more at home talking to them than to a European who believed in astrology.

1:54 PM

and of course in general you have to substitute $\mathbb{R}_+$ with $[0,+\infty]$, the one-point compactification of the positive reals

Are there any mongolian GR scientist

@Slereah the sigma algebra is a rather rich structure

What is the one for $R$

I've just received an e-mail from a Romanian girl inviting me to look at the naked photos of her that she's kindly sent as a self extracting zip. Now that we are leaving the EU do you think she'll stop sending me pictures?

Sorry, she will get deported back to Romania

1:58 PM

Damn, I'll have to get my trojans somewhere else.

@JohnRennie self-extracting zips are just for convenience

no harm intended

She put them in a nice .exe file

@JohnRennie o.o

What's a self extracting zip and how do you know you have one

without extracting it

When the attachment has a name like pervyphotos.zip.exe that's usually a clue :-)

heh

2:01 PM

pervyphotos.dll

Pichi Wuana

2:48 PM

Why in a forces diagram, the arrow's force of the dynamometer that holds an object, is upward?

user215373

HI

3:05 PM

Hey, I'm starting a facebook Quantum Field Theory in a Nutshell study group. Feel free to join us! facebook.com/groups/1403821159635442

8

(And I'd appreciate a star on that so that more people can see it ;) )

@NeuroFuzzy >facebook

HISS

Alyosha

Does anyone know of examples of symplectic toric manifolds in physics?
I'm reading about Delzant's theorem, but have not convinced myself fully that symplectic toric manifolds are interesting enough for the theorem to be nice.

user116211

3:21 PM

@Slereah Is Lumo on Facebook?

@NeuroFuzzy no, it's a garbage book.

One of two reasons I don't want to be a physicist.

3:45 PM

@0celo7 Anthony Zee's Quantum Field Theory in a Nutshell is one of the two reasons you don't want to be a physicist.

@NeuroFuzzy Yes.

What other book would I be talking about?

I read it as a junior and decided physics was not the right career for me

@0celo7 Huh.

@0celo7 I'll still take the advice of my quantum mechanics teachers & TAs and read it :)

user116211

@0celo7 Is that a bad book?

@NeuroFuzzy No rigor, he expects you to know representation theory, literally says virtual particles are real, doesn't even mention LSZ.

@0celo7 I mean, you should know the spin representations and all that undergraduate stuff before going into it, yeah.

user116211

3:53 PM

@0celo7: So, which book are you going to recommend on QFT?

user116211

ah! I checked Zee's book is not in the standard recommended course.

user116211

We have Peskin and Schroeder in the recommended book list.

user116211

And for advanced courses, Weinberg's three books.

user116211

And here is Lubos' recommendation.

user116211

> Anthony Zee is Mark Srednicki's colleague from UCSB. His book is really cute, has a funny cover, and offers some intuitive physical concepts that are not explained elsewhere, much like some cute stories from the history of physics

4:19 PM

@NeuroFuzzy What?

In what undergrad QM class do you calculate tensor products in SO(10)

FrancescoS

4:37 PM

Hi guys! The coefficients of an effective field theory coming form an integration of an heavy field are always reals?

LucasTizma

Hello! Weird/unconventional question, but is there a classification or study of physical motion such as dust motes in the air or particulate matter in a liquid? The seemingly random, "floaty" physics that these particles exhibit where they seem to be moving around slowly and aimlessly?

I'm a UI engineer, and I'm exploring new physics-related motion characteristics, so I'm trying to figure out what this type of motion could be classified as (and how to simulate it via simplified physics equations).

Simple spring physics to drive animations became really popular, probably because the equations for spring-damping physics is easy and playful. But I'm interested in exploring new concepts for motions that replicate subtler physics that we experience.

@LucasTizma isn't it just brownian motion

Stochastic, more generally

LucasTizma

I don't know. Is it? :) I'm not familiar enough with physics, sadly...

I'll look that up! The worst part of being ignorant about this is that I don't know what anything is called. I can usually piece my way through understanding it once I know it has a name. :D

5:31 PM

@ChrisWhite If you're a grad student and a prof takes you off his research group, what do you do?

Are you done forever?

user54412

Uh, depends on the department. But if the department doesn't step in to help, then yeah probably done forever.

Step in to help?

user54412

By finding someone else to advise you.

user54412

You could always apply to a different school or something, but in practice I doubt anyone has the fortitude to do that.

By "take off" I mean "fired for not doing enough research"

"not answering emails"

user54412

5:34 PM

No one who has been a grad student would ever apply a second time to grad school.

@ChrisWhite ...what?

Is this only in the sciences?

My mother has three graduate degrees.

user54412

I'm lazy and using "grad school" to mean "PhD"

Oh.

@ChrisWhite Well this grad student had not yet taken the quals...I think.

@NeuroFuzzy My point is that you need way more group theory than you get in any QM book.

Maybe not Sakurai first edition.

user54412

Honestly, most grad students are just barely committed to school. Vanishingly few would try to continue after a setback like that. Especially if they were in a half-decent STEM program, since they undoubtedly could make many times more money by just giving up on the whole degree.

@MAFIA36790 None.

QFT is the second reason why I decided to not be a physicist.

@ChrisWhite Well, it could be happening to a grad student in my group.

I was just wondering what's going to happen to him.

5:47 PM

Thee is no barrier to finding a new advisor and trying again. (Well,if you make a big enough impression your name would get around and there would be a social barrier to trying again in a closely related field, so make that "no formal barrier".)

But grad school involves a fair number of sacrifices, and many people would think twice about taking them on board again.

It might make sense if the problem the first time 'round was an event that happened to this hypothetical student, but not if what happened is the students personality is not well suited to the work that needs doing.

user54412

@dmckee Especially as one gets older. "I'll just live in a closet and eat ramen and not even think about starting a family" doesn't work at age 25 as well as at age 21.

Two PhD students in my group are married, one has two kids

Reminds me of KK

rip

@ChrisWhite Is the Ramen meme even real?

user54412

Even as a postdoc, I won't be able to afford anything more than a couch in the Bay Area. I don't really understand how grad students live there.

@0celo7 During the poorest part of my grad-school experience I got about half my calories in that form.

user54412

@0celo7 I've actually never had the microwave stuff. But I've known people who have. Including one who developed scurvy because he ate nothing else.

5:57 PM

This was before I got my assistantship, but I knew others in the same place beause they had chosen swankier digs than mine.

@ChrisWhite Jesus Christ.

I lived in a place with plain cinder-block walls.

@dmckee Ok I live like that now.

But no Ramen

I should run Raman on some Ramen

@ChrisWhite There is a reason I had vegetables and eggs with my ramen. I was worrying about defficency diseases.

The grad students around here don't seem to starve like you guys.

Maybe go to schools in cheaper areas?

5:59 PM

@0celo7 Have you read it? Where does he "literally say virtual particles are real"?

@Bass He literally says "the vacuum is a boiling soup of quantum fluctuations"

maybe boiling sea

It wasn't until my second postdoc that ramen seemed like a good idea again.

Why would I attack a book I haven't read

@0celo7 What's that to do with virtual particles?

You and @NeuroFuzzy just can't help but attack me

6:01 PM

But that was when I started going to Japan and had some experience with the real thing. These days I'm almost over by ramenphobia.

@Bass He's talking about virtual particles there.

user54412

@dmckee My problem is I've had the good stuff, both in Japan and in the really Asian parts of socal. I don't think I can go to the cheap stuff after that.

vacuum -> vacuum loop diagrams

@0celo7 I think it deals more with "vacuum fluctuations" than with virtual particles.

Don't take the "boiling sea" too literally. He keeps this sort-of-ironic style throughout the book.

That's not my main issue with the book, anyway

6:02 PM

I don't really like that style most of the time..

@0celo7 Where did I attack you?

@Bass "Have you read it?"

No, I'm just attacking a book I haven't read...

@0celo7 That was a genuine question. I think you have told us at least one time that you don't like and don't know QFT, so I didn't expect you to read whole books about it..

@Bass I've read Zee, Weinberg 1&2 and Srednicki.

@0celo7 Maybe you read a part of it and didn't like it. Happened to me with many books.

I despise QFT.

6:04 PM

@0celo7 Why read thousands of pages on it if you despise it?

Not all of Srednicki.

@Bass I wanted to like it.

I wanted to like string theory, too.

Read quite a bit about it.

@0celo7 I see. Maybe Weinberg is the wrong choice if you don't know what $|0\rangle$ is :P

@Bass I know what fucking $|0\rangle$ is.

@0celo7 What's your main issue with the book? Don't get me wrong, I have my own issues with the book, but I don't consider it to be "garbage".

@Bass I like literally nothing about it.

Anubhav Goel

6:09 PM

In interference using electrons in double slit experiment, we cannot use light source, as it disturbs apparatus. But, can't we simply move screen towards and away from screen, to know where they previously were and where they moved next second.

?

@0celo7 That's the "main issue"? Okay then :)

@Bass The first chapter is fine.

@0celo7 The first chapter contains the "boiling sea" :P

The second chapter is garbage, he doesn't explain the Lorentz group well at all.

Sorry, the first part.

6:11 PM

And without the Lorentz group everything else falls apart.

@0celo7 But you're coming from GR, the Lorentz group should not be a problem for you?

@Bass GR needs 0 facts about the Lorentz group.

(Not if you're doing spinorial stuff but that's different.)

And Zee is so unrigorous you can go read a math book about stuff and then be confused by Zee.

The book I like most is Maggiore's A Modern Introduction to QFT. Very short, but you get some overview of what's going on, then you can use P&S or whatever for the details.

I have an overview.

@0celo7 That's true, but deliberate. The point of the book is more intuition than mathematical rigor.

@0celo7 Maggiore's chapter 2 is about the Lorentz reps behind QFT, I liked that very much.

6:14 PM

I couldn't give less of a shit about intuition.

@0celo7 Then why do you read Zee?

And QFT is the worst subject for the "intuition" approach

@Bass I loved his GR book.

Favorite physics book. Period.

@0celo7 Huh. Well, I'll pick up the group theory I need as I go along, 'cause I'm planning to study through his Group Theory for Physicists book too!

@0celo7 It's also the one where most students struggle to get at least a tiny bit of intuition.

@NeuroFuzzy Then you might do alright.

Although remember the saying

6:16 PM

@0celo7 Which is full of hard mathematical rigor, yep :P

May 5 at 15:40, by ACuriousMind

nononononononononono, do not learn group theory from physicists! :P

@Bass I should rephrase.

The intuition approach works well in GR where the calculations aren't that bad

@0celo7 I appreciate your advice though!

Interesting...

But Zee tries to make multi-page calculations intuitive

@NeuroFuzzy I might read Fulton & Harris or some other Lie algebra book and go back to Zee one day.

After my graduate QM class next year, to boot

@0celo7 so the suggestion would be to learn representation theory from mathematicians, right?

I've heard lots of warnings to NOT take the math department group theory/lie theory courses with the expectation that they'll be useful for physics

@NeuroFuzzy ...I think so. The "group theory" in QFT is really representation theory.

Oh a straight group theory class will not be useful, no.

We have a lie groups course here that literally does nothing but geometry and topology.

So something like that would not be useful for physics.

You'd have to check the syllabus @NeuroFuzzy and ask @ACuriousMind if it's useful.

(and if your teachers like Zee then it might explain why they say the math courses would not be useful :P)

6:24 PM

@0celo7 I'm sure it's not haha. Best case I could do a reading course.

@NeuroFuzzy I think it depends on how far you want to go. If you want to understand very advanced QFT, you need to have a very solid understand on what's going on mathematically, and this you won't get in a simple "maths for physicists" course. But for a beginner's course in QFT, you're better off with a course that's tailored to what you need for the beginning, and that's "math for physicists".

@NeuroFuzzy I'm doing a reading course on differential topology right now and am working my ass off

Speaking of, why is Hirsch taking so long to arrive

@Bass And speaking of rigorous GR, Sachs & Wu is the most ridiculous book ever.

The exercises are stupidly hard.

@Bass Just curious, the most advanced Lie theory I know of is, eg, "a lie algebra is a left invariant vector field on a manifold", and then you look at the homology/cohomology of the manifold. Is this what you mean by advanced understanding of the mathematics?

@NeuroFuzzy What do homology and cohomology tell you about lie algebras?

IDK, but it's a set you can make and it contains a lot of buzz words I know.

6:35 PM

@NeuroFuzzy Well I'm no expert, but I think that's relatively basic, since some authors define the lie algebra as the set of left-invariant vector fields.

...how else do you define it?

Besides the tangent space at the identity

@NeuroFuzzy lol what

And (co-)homology is a global property of the manifold, whereas the Lie algebra is a local property, so I doubt there's much connection between them, but really, you should ask ACM or Danu about this.

@0celo7 isn't that how you're supposed to do physics?