The h Bar

obe

00:05

I barely did it.

Let me work through it more first.

0celo7

post results

obe

(dumb hs work I had to do)

FenderLesPaul

@0celo7 yeah at like 9:30?

0celo7

ok

user54412

@DanielSank So today I joined the Important People™ weekly astrophysics lunch. At one point the open discussion veered toward cosmology, and how measurements of curvature may improve in the next few years. One Important Person™ then pointed out that such measurements can distinguish between inflation models, so I asked pointedly what measurements would people accept that argue against inflation.

2

user54412

00:10

I don't think I'll be joining their ranks of Importance any time soon.

DanielSank

@0celo7 Nothing. It was the title that caused the reaction.

@ChrisWhite I think I'm missing part of the story. What was their response to your pointed question?

0celo7

00:26

@DanielSank you referenced my lie Algebra comment

DanielSank

@0celo7 It was a misclick.

user54412

@DanielSank Reading between the lines, something like "does this kid doubt inflation?"

DanielSank

@ChrisWhite Heh. Yay scientific method.

user54412

I didn't get to go into it more, but I really wanted to after hearing that measurements confirming the flatness of the universe would further prove inflation, and that measurements confirming the non-flatness of the universe would prove other models of inflation.

DanielSank

@ChrisWhite I'd encourage you to politely not back down.

If a theory is not falsifiable we're all in trouble.

user54412

00:37

@DanielSank btw I'll be visiting UCSB in about a month (not sure on the exact dates yet). Maybe I'll bump into you.

DanielSank

@ChrisWhite Dude! Forget "bumping into" me, let's get beers or whatever!

KITP conference?

user54412

More informal meetings, with the subtext of "plz hire me"

DanielSank

@ChrisWhite Haha, nice.

In that case you had better give me a call.

user54412

Ok I will :)

DanielSank

I mean, I don't want to impose on you, but if you'd like to see my lab, go for dinner, go to the beach, or anything else, I really hope you'll contact me.

I know all the best places to eat.

0celo7

00:50

@ChrisWhite I'll hire you

DanielSank

@ChrisWhite what profs are you meeting?

user54412

@DanielSank Mostly Omer Blaes and whoever he's working with.

DanielSank

@ChrisWhite Haha, nice. He taught my grad quantum course. Have you met him?

dmckee

I never look at people's profiles unless they've been misbehaving so I miss all kind of stuff.

user54412

@DanielSank Never in person, but I've met several of his former students.

dmckee

00:57

I did my undergraduate work at You Can Study Buzzed.

Worked in Phil Lubin's lab for a while.

How are things in sunny Golleta county?

DanielSank

@dmckee How was that?

@dmckee Awesome!

It's sooooooo nice outside.

dmckee

I assume you're whethering the drought a little better than the rest of the state.

DanielSank

@dmckee It hasn't affected us at all.

dmckee

@DanielSank It was hard. I thought I was smart while I was in High School.

DanielSank

@dmckee Gosh, it seems like half the undergrad student body goes through his lab.

dmckee

00:58

UCSB disabused me of that notion.

DanielSank

@dmckee Heheh, that's probably a good thing in the end.

dmckee

Then I thought I was pretty smart. Grad school fixed that.

At the time Phil was letting undergrads who could program just kinda hang about if they wanted to sit up nights and work on RAAP.

So I did.

We got lucky one week and imaged a MACHO lensing event in the 18th magnitude.

DanielSank

@dmckee I have no idea what that means :P

dmckee

If some cold Jupiter wander in front of a star in a globular cluster and you can see the star's brightness grow then dim again over 3-10 days.

On account of gravitational lensing.

DanielSank

Ah. Cool!

dmckee

01:02

It's how the MACHO density was established and they were ruled out as a significant contributer to the Missing Mass Problem (as it was called then).

Anyway most of the happen down around magnitude 20-26.

And we couldn't get the scope to track long enough to get much below 19th magnitude.

Good times.

DanielSank

You astro folks and your weird-@$$ intensity scales.

dmckee

That was my one foray into astro. I'm in particle now. Well, actually, I'm mostly in Intro Physics for Non-majors now.

I guess magnitude made sense when you were just classifying the naked-eye stars into six or seven brightness categories.

user54412

^ Learning that is what finally made magnitude make some small amount of sense to me.

user54412

"These are the first brightest stars, these are the second tier of bright stars, these are the third tier, ..."

user54412

turns out for faint point sources the human eye's intensity resolution discretizes something like 2.5 log_10(I)

dmckee

01:08

And then people quantified it and we have the back-asswards logarithmic scale to deal with until the end of time.

DanielSank

@ChrisWhite Yeah, but the fact that we haven't switched to something with dimensions of photons/time, i.e. power, boggles the mind of the modern scientist.

HDE 226868

01:23

I can only imagine how bad it must be on Stack Overflow.

user54412

42

A: Can we raise the bar for reputation for late answers to enter the review queue?

TL;DR: As of today (September 29, 2015) the maximum reputation for having an author's late answer enqueued has been raised from 10 to 50. As for further increase to 100: Queue growth Review queues lose effectiveness if posts aren't regularly (and accurately) cleared. A queue such as close ...

HDE 226868

@ChrisWhite Yeah, I had seen that.

user54412

At least they're old late answers (I think) -- it's not like we're getting 400 a week.

user54412

Oh hey, I only have 8 progress on this badge...

HDE 226868

I've gotten a bunch from 2011.

0celo7

02:38

@obe problem set?

obe

Dude I'm so screwed.

I think I'll get an extension.

Lose 5% (who cares I'm not getting a credit).

0celo7

why are you screwed

obe

AP english expects 3 essays of 1500 words this week.

0celo7

lolwat

obe

sigh

0celo7

02:44

Do you need help with the problem set

obe

I do.

0celo7

Ok

Join the ts server

dmckee

04:04

@obe Once you get writing you'd be surprised how fast 1500 words passes. Making them well considered words with literary merit (if that is desired) is harder.

DanielSank

06:43

Why does the late answer queue have 355 items in it? This seems wrong.

@DavidZ I really don't think this question should be classified as engineering.

Slereah

10:41

So does anyone know how to prove that the action of a scalar field is always positive definite

Secret

11:31

FIRST ANSWER EVER!

PS I have a preference on answering questions that allows me to describe it with a diagram

and I only answer a question if I am so confident that I would not screw it up, because I am a perfectionist

this is why I ask questions more than answering question in the SE network, because it is rare for me to be really sure about something due to my tendency to overthink

Ghost

nice answer!

Secret

Example of overthinking:
Given that $\lambda(x)$ specify the linear charge density along the x axis, can $\lambda$ be a piecemeal function such that it describe a broken line system like this?

Ghost

i wrote an answer as well, much simpler topic though...lol

Slereah

11:48

Well it's just a function

It can be discontinuous

Ghost

not too sure of my answer, the question is pretty brief...

Secret

More overthinking examples:
$\rho(t)=\lambda(x(t))\delta(y(t))\delta(z(t))$
and the list goes on and on...

naively speaking, assuming x,y,z are continuous functions, the above expression describes a point charge moving in 3D space and its charge density will vary in a predictable way with x

rigorously speaking, I suspect I might have broken a property of dirac delta distribution in my above decription, but since I have not formally learnt distributions in a mathematical context, I am not sure what I have violated

The reason I felt I have broke something is that if what I said above is valid then

$\rho(t)=f(\mathbf{r(t)})\delta(\mathbf{r(t)})$ would be enough to describe a moving point charge in space (ignoring Lienard Wiechard potentials), but this expression looks weird to me...

ACuriousMind

12:07

@Slereah What do you mean? I don't think e.g. a $\phi^3$ action is always positive.

Secret

Sorry typo: $\rho(t)=f(\mathbf{r(t)})\delta(\mathbf{\mathbf{x}-r(t)})$

Ghost

@ACuriousMind - cool nickname!

0celo7

Good morning

Ghost

good evening

ACuriousMind

good afternoon

skill patrol

12:15

good night

0celo7

It's morning....

ACuriousMind

No, it's 2pm :P

Ghost

no, it's 10pm

Secret

and $\rho(t)=\lambda(x(t))\delta(y(t))\delta(z(t))$ is actually describing a weird process:

A charge distribution that describe a point charge which blink out of existence whenever y and z not 0, otherwise its magnitude varies in a predictable way in the x direction

0celo7

8AM

Get your shit together man

Ghost

12:17

LMAO

i will, in 10 hours time

Secret

I might do a continuity equation check on that later to see if it obeys it

skill patrol

Is your health back to 100% @0celo7?

Ghost

Just fixed a weird grammatic typo on my answer... got to stop wrting answers when tired

Slereah

@ACuriousMind Well let's say for a free scalar field, anyway

0celo7

@skillpatrol 90%

Slereah

12:22

Apparently it's a Thing for path integrals

The action must be positive for the integral to converge

0celo7

Some residual coughing and mucus

ACuriousMind

@Slereah Well, there are only squares in that action - how could it not be positive?

0celo7

Minkowski

Slereah

@ACuriousMind : Well because it is $\ddot\phi^2 - \Delta \phi$

Ghost

@0celo7 that is never fun

ACuriousMind

12:24

Ah

Slereah

Also since the integration happens on every fields and not just on shell ones, I can't use the solution to show it I suspect

Or did I misunderstand the nature of that requirement

ACuriousMind

Do you have a reference for the "action has to be positive" requirement?

Slereah

It is mentionned in passing in "Euclidian gravity"

ACuriousMind

The only requirement containing positivity I can remember right now is "reflection positivity", which is something different

Slereah

Because apparently one of the big problem of QG in path integrals is that the action has to be always positive

And he goes on to say that scalar fields have a positive action

spinor fields are negative, unless they anticommute

and so on

(and the gravitational action can be arbitrarily negative)

Ghost

12:26

hmmmm silicon optical properties... why am I reading about this at 10:30pm?

0celo7

Because lasers?

ACuriousMind

@Slereah: Might it be that the Euclidean action has to be positive?

Slereah

Well yes

that is the crux of the thing

ACuriousMind

But then there is no minus, the action is just $\phi\Delta\phi$, right?

Slereah

Oh right

Derp

I am dum

Plz put a dunce cap on my head

0celo7

12:29

Lol

ACuriousMind

::folds dunce cap::

Slereah

<:(

Ghost

@0celo7 yes, yes indeed

Slereah

You know, one thing I wonder is

How did people do interferometry before lasers

Ghost

how did they spell it

Slereah

12:32

In class you always see that it's a monochromatic coherent wave etc in the assumption

But Michelson Morley was just a lamp

How does that influence the results

0celo7

What is interferometry again

Slereah

lasers and mirrors and shit

Interference between EM waves forming patterns

ACuriousMind

@Slereah Didn't they have things like sodium vapor lamps which also are pretty monochromatic?

0celo7

Very informative

Slereah

Monochromatic but what about the phase, tho

0celo7

12:34

ACM has some experimental knowledge

Secret

probably it has to be quite intense to show any weak interference pattern that is present as a white lamp is not completely incoherent, right?

ACuriousMind

Ah, the coherence

Dunno about the coherence.

0celo7

< knows nothing about lasers

ACuriousMind

You could ask that on the main site if it isn't explained in the Wiki articles

0celo7

Wow I really know nothing

Secret

12:35

The reason I have this thought is because I recall our teacher told us that Young first done his double slit experiment with white light only

and I suppose a similar principle applies

0celo7

I thought you could do double slit with sunlight

Slereah

but then how

Secret

It's hard, but possible. I forgot the coherence factor of sunlight on average however...

Slereah

Like what is the exact derivation of interference for thermal radiation

0

Q: Is it possible to produce coherent light with a thermal source?

Coherent light means monochromatic light and alle waves have the same phase difference. This is given for laser, where the resonator is a potential box and the outgoing waves have the same phase difference. What is about a thermal source like a bulb? The emitting surface is not smooth, the involv...

Thank goodness for SE

0celo7

I saw a YouTube vid that did it with sunlight

Slereah

12:45

hank.uoregon.edu/teaching-modules/Broadband-Interferometer/…

Secret

6

Q: Is coherent light required for interference in Young's double slit experiment?

In this Veritasium video, a home experiment is presented which appears to produce a very good double-slit interference pattern with normal sunlight. The experiment is an empty cardboard box with a visor and a placeholder for a microscope slide with two slits on one side. This is arranged with th...

photons home-experiment popular-science double-slit-experiment interference

Slereah

"I say "more or less" to emphasize the fact that it is never 100% coherent, (even from a laser), and it is never 0% coherent (even from a lightbulb or sunlight)"

Hm

Isn't it possible to create total EM noise?

Ghost

@Slereah interesting concept

0celo7

morning

you lot have issues

@StanShunpike Just looked at the hardstyle charts for the first time in multiple months. Found this awesome thing.

Great summer album!

Urgh, I'm gonna spend money again :/

Oh lord Phuture Noize released an album too

@ACuriousMind Does German Law block Beatport too?

William Budd

13:04

If I managed to stably levitate a stationary rigid object using only a bunch of simple room temperature ferromagnets, would it be news? I mean, nobody seems to have done that yet, right?

ACuriousMind

13:32

@0celo7 You mean on YouTube? Probably

0celo7

@ACuriousMind no I mean the site I just linked

ACuriousMind

@0celo7 No, it seems to work

skill patrol

why is German Law so uptight about blocking the internet?

0celo7

Fascism

ACuriousMind

@skillpatrol It's not about "blocking the internet", the reason are the messy copyright/IP laws regarding music and its performance. You are also not allowed to publicly (as in: intended for customers to hear it) play a recording of music without paying a fee.

skill patrol

13:45

I see.

ACuriousMind

So YouTube has to block video containing copyrighted music unless they want to get sued (since they don't pay that fee, among other things)

skill patrol

Right.

Makes sense.

0celo7

It doesn't make sense because there are legit music channels that are blocked in Germany.

ACuriousMind

Many people want a reform of these laws, and especially want to get rid of the authority (the GEMA) overseeing the collection of the fees and their distribution to the creators, but it is a slow process

0celo7

Legit as in endorsed by the artists and the publishing company.

I don't like piracy at all, but GEMA is ridiculous.

Blocking VEVO? Seriously?

ACuriousMind

13:49

@0celo7 Yeah, see, the obligation to enforce copyright and collect the fees is automatically granted to the GEMA in many cases - the artists can not opt out of this process.

0celo7

@ACuriousMind I know.

ACuriousMind

(Not saying this is the way it should be, but it is the way it is)

0celo7

I lived in Germany too :P

Pissed me off to high heaven when I was denied music

Not even a German :O

ACuriousMind

@0celo7 I don't think I was more than vaguely aware of the existence of GEMA in middle school :P

0celo7

@ACuriousMind I had it explained to me because a video from some microwave channel was blocked.

It had music in the background.

The person who made the video emailed everyone who complained.

David Z

13:51

@DanielSank in its earlier form, I think it was. Now, maybe. That one I wouldn't be surprised to see reopened by the community.

skill patrol

Hi @DavidZ

0celo7

Damn... Phuture Propaganda is not as good as Music Rules the Noize.

Not worth $10.

@obe problem set?

Kutski & Audiofreq - Hookshot (ft. Ragga Twins)

►

:OOOOOO

Emilio Pisanty

14:14

Anyone care to comment on physics.stackexchange.com/a/28430/8563

2

?

As far as I'm concerned it could use a couple of downvotes

Came up on the Late Answers queue

0celo7

@DanielSank homework in the title!!!!!!!!!!!!!!!

skill patrol

@0celo7 you listen to stuff like that?

0celo7

@skillpatrol yes

"stuff like that"

-.- what does that mean

skill patrol

do you like bob marley?

0celo7

who?

skill patrol

14:22

nvm

-_-

0celo7

@Pies watch the Kahn academy videos on vector calc

@Pies also watch his videos on linear algebra

@Pies then you should be ready for amazon.com/Einstein-Gravity-Nutshell-A-Zee/dp/069114558X

@skillpatrol he must not be that good if you won't tell me who he is

skill patrol

@0celo7 excuuuuse me????

0celo7

you're excused

skill patrol

he is the father of that gendre

0celo7

which is?

ACuriousMind

14:26

@EmilioPisanty I'm having trouble deciding whether it is an answer because I can't really parse what the question is asking.

0celo7

OH

reggae

skill patrol

yes

0celo7

I like reggae when it's mixd with other genres

but I'm not a big fan of the pure stuff

skill patrol

techno mixes well imo

0celo7

that's not techno...

learn your EDM genres

it's subground

skill patrol

14:29

reggae + techno + house = ?

0celo7

no

reggae + subground = that

subground is like hardstyle but different

it's a style that came out of the experimental tents at Q-base

skill patrol

ok

0celo7

started by ACTI and Kutski I think

Audiofreq makes it now too

skill patrol

I call all that xtc music ;-)

0celo7

what

skill patrol

14:33

the drug

0celo7

indeed

Damn, I have to get some music

2015 was a good year for hardstyle

I'm hearing a lot of experimental stuff in these tracks

I think -- maybe the scene is just changing

skill patrol

Perhaps.

0celo7

I don't spend time on /r/hardstyle any more

so I'm kinda out of touch

skill patrol

Subground is a mix of various music genres which consists of a sub bass on beat mixing influences from multiple electronic dance genres such has techno, hardstyle and hardtrance, characterized by a tempo around 130-135 beats per minute, just like electro tracks

Wow!

0celo7

I'm probably going to buy a 100 track compilation

Then make that my GTA playlist

:)

best way to listen to music tbh

skill patrol

14:44

High energy stuff!!!

0celo7

subground is not high energy...

you need some Angerfist in your life

170bpm headbanging = crazy

skill patrol

indeed

0celo7

Korsakoff - Unleash The beast (Angerfist Remix)

►

skill patrol

cool

Slereah

@ACuriousMind : I guess now I must find out

0celo7

14:49

can't recall the melody off the top of my head

Slereah

WHY IS THE SPINOR ACTION NEGATIVE

0celo7

I just know that's a really good track

Slereah

But positive if anticommutin'

0celo7

GRASSMANN NUMBERS

FFS

Slereah

I do not look forward to it because I don't know SO(4) spinors :p

Well yes BUT THAT'S NOT A DEMONSTRATION

It also doesn't explain the commuting case

Calm down dude

0celo7

14:51

I will not calm

you keep asking this question

Slereah

Spin(4) is SU(2)xSU(2) apparently

0celo7

I knew that

Slereah

Because saying"Grassman numbers" isn't really the proof of $S_E[\psi] < 0$

0celo7

of course it is...

Slereah

"For fermions, the mapping between Minkowski space and euclidean space is, however, not without problems"

Oh great

Problems

0celo7

14:54

fucking problems

Slereah

Do not be a Duffield @0celo7

0celo7

what does that mean

Slereah

You know what it means

0celo7

JD is a well-respected bona-fide mainstream physicist

I could only hope to be him

Slereah

Well if you continue YOU WILL BE

0celo7

14:55

::injects Evidence:: Feels good man

Slereah

"While the two fundamental spinor representations $2_{L,R} $ of the Lorentz group in four dimensions are complex, the fundamental spinors $2_{1}2_2$ are (pseudo)-real for the orthogonal group SO (4)."

The hell does pseudo real mean

0celo7

@ACuriousMind

he knows

ACuriousMind

Uh...not sure about the pseudo

Slereah

Apparently complex conjugation maps each representation into itself

mb that

ACuriousMind

That's what I'd have called "real"

Slereah

14:59

yeah it is weird

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