The h Bar

0celóñe7

12:05 AM

@BalarkaSen I would read the shit out of [3] W. I. Brouwer. Tropical Measure Theory. Springer, 1998.

Secret

3:04 AM

Sure, the spacetime there is pretty fucked, but is it warped enough to create CTCs?

John Rennie

4:13 AM

CTCs require either an object of infinite size (e.g. Tipler cylinder) or exotic matter. This is a theorem due to Hawking. Since colliding black holes are neither of these there are no CTCs around colliding black holes.

Mostafaııııııııııııııııııııııı

The shortest paper I've seen

(here)

0celóñe7

4:40 AM

@JohnRennie haven't done a benchmark in days

John Rennie

5:37 AM

@Kaumudi.H check Hangouts and ping me back here ...

Anonymous

7:22 AM

@JohnRennie Any idea how much power typical tv/a.c. remote IR bulbs require ? I can't find much data about it on the net.

John Rennie

@Blue Same sort of current as any other LED I'd have guessed

About 50 mA

Anonymous

@JohnRennie Aha, thanks. Also what would be the approx resistance of the filament ? I need to calculate the power required

Anonymous

$P=I^2R$

John Rennie

It's a LED, so the resistance is a function of the voltage across it. However the spec sheet says 50mA at 1.5V so the power is $P=IV$ i.e. $P = 1.5 \times 0.05$W.

Anonymous

@JohnRennie Oho. I forgot to take that function of voltage into account. Thanks a ton! :)

John Rennie

7:32 AM

@Blue aren't you supposed by doing electronics engineering at college? Don't they teach you this stuff? :-)

Anonymous

@JohnRennie They haven't started teaching electronics as yet (as such). I'm collecting information for my physics project. It was silly of me to try to find resistance of p-n diode which forms the led bulb (as it is not constant). Well, most resistances are not constant anyway. :)

Anonymous

Currently they are teaching basic math and physics along with a bit of solid state:P

Rumplestillskin

9:05 AM

Hello one and all! Does any one have any experience with energy conservation in the Post Newtonian regime?

skullpatrol

10:09 AM

There's going to be a little black spot on the sun today...

Rumplestillskin

Does any one have a reference for obtaining the energy integral from newton's second law in a rotating frame?

Anonymous

10:47 AM

@Rumplestillskin You mean rotational energy ? There are plenty. You'll find it in any college mechanics good.

Anonymous

(along with the derivation)

Kyle Kanos

11:19 AM

Anyone else get hit with serial downvoting?

Rumplestillskin

@Blue Thanks. What I am after is something equivalent to this post

2

Q: Help in an integration step in QFT by Lewis H. Ryder

There is an integration step I can not figure out and is frustrating. We start from the equality $$ \dfrac{\partial^2\phi}{\partial x^2} = \dfrac{\partial V}{\partial \phi} $$ and by integration process we are supposed to get (eq. 10.8 in the textbook): $$ \dfrac{1}{2}\left(\dfrac{\pa...

@blue Except in a rotating frame

I hope that makes sense!! :)

Kyle Kanos

I got hit with like 9 answers DV'd, only 4 were reversed

Rumplestillskin

@KyleKanos I am not. However, I do not have enough up votes for a rampage of down votes to be considered serial.

ACuriousMind

@KyleKanos Looking into it.

Pritt Balagopal

12:06 PM

Hello everyone.

I'm trying to learn NMR Spectroscopy, and I want to learn about the nucleus, it's spin states and energy levels. Can anyone suggest a good book, preferably one that's easily downloadable as a pdf to help me learn about nuclei?

Sid

12:43 PM

@KyleKanos nope. Obviously someone just loves you.

0celóñe7

@Mithrandir did you watch it?

Mithrandir

Watch what? ...unless you meant @Mithrandir24601, of course.

0celóñe7

I did

why are there two of you

ACuriousMind

We should be grateful that Mithrandir2 - Mithrandir24600 don't also visit this chat :P

Sid

@0celóñe7 obviously two huge fans of LOTR

Mithrandir

1:05 PM

@ACuriousMind I kept trying to figure out why you would subtract 24600 from 2 until I realized that that was a 'to' :P. I fail.

Mithrandir24601

1:39 PM

@0celóñe7 yeah, I watched it. Still have to watch the last 10 minutes or so, but I can guess at least some of what happens...

0celóñe7

@Mithrandir24601 it was quite predictable

Mithrandir24601

@0celóñe7 especially given some of the trailers

0celóñe7

I guess you saw the part where the thing falls in the water

Mithrandir24601

@0celóñe7 yeah, at that point, what happens next is really obvious (although I've yet to actually see the bit that happens next :P)

0celóñe7

yep, literally impossible to spoil

@ACuriousMind the grump could guess it

Mithrandir24601

1:43 PM

especially given a certain trailer...

Mithrandir24601

1:58 PM

Quick question - in terms of notation, I'm using $U$ as a unitary matrix - is using $\mathbb{U}\left( d\right)$ reasonable for the group of $d\times d$ unitaries, or am I better off just using $U\left( d\right)$?

Or something else entirely?

0celóñe7

@Mithrandir24601 Always use \mathrm for group names.

So it would be $\mathrm U(d)$

Mithrandir24601

@0celóñe7 I'd love to, but I'm actually using mathrm for superoperators and channels...

0celóñe7

@Mithrandir24601 So?

Mithrandir24601

(In this case, it's the unitary operator channel)

0celóñe7

Why does that prevent you using $\mathrm U(d)$ for unitaries?

Mithrandir24601

2:07 PM

@0celóñe7 so I've already defined a mathrm{U} :/

0celóñe7

you should reconsider that

use some fancy $\mathscr U$

$\mathrm U(d)$ is the unitary group, anything else is simply incorrect

@ACuriousMind Hmm. Could it be that the eclipse is simply cover for the Masters to do maintenance on the Sun?

Mithrandir24601

@0celóñe7 OK, back to the way it originally was :P thanks

@0celóñe7 Is there a specific way of denoting the Haar measure then?

0celóñe7

2:23 PM

@Mithrandir24601 not as far as I know

$m_G$ is popular but $m_{\mathrm U(d)}$ is awkward

Anonymous

@PrittBalagopal mehr.sharif.edu/~organic-ch/NMR.pdf

Anonymous

It's a part of the book by LG Wade.

Mithrandir24601

@0celóñe7 it is a bit, but it's what I'm using at the minute, so I guess I'll stick with it then

Thanks

0celóñe7

@Mithrandir24601 unless you're using a lot of Haar measures I don't see why plain old $m$ is bad

Mithrandir24601

@0celóñe7 Well... a couple of pages in and I've got about 20 so far :P (yes, that's almost every equation...)

Wrichik Basu

2:46 PM

Those who are interested, please support:

1

Incredible India

Proposed Q&A site for all those who are curious to know about India, her rich cultural heritage, geographical heritage, spiritual heritage and knowledge store.

Currently in definition.

Sid

Uninterested. I will pass on that...

Wrichik Basu

@Sid well, OK.

Anonymous

Umm, then people will start proposing SE site for each and every country....

Anonymous

I wonder if those SE guys will allow it

Anonymous

But well, I am supporting it for now

0celóñe7

2:49 PM

@Mithrandir24601 20 different Haar measures?

Wrichik Basu

@Blue there is a site for turkey as well. That's why I started it.

@Blue thanks :-)

Secret

36

Speculative Science

Proposed Q&A site for proposed Q&A site for people with hypothetical questions "what if" conforming to the sciences; Physics, Biology, Chemistry, Geology, etc.

Currently in definition.

Anonymous

@WrichikBasu Where? Which one?

Secret

That should remove a whole lot of what-if traffic in PSE

93

Psychology

Proposed Q&A site for anyone interested in psychology, students, professionals at all fields of psychology (Biological,Behavioral,Cognitive,Social,Psychoanalysis).

Currently in definition.

Wrichik Basu

@Blue see this:

10

Turkey

Proposed Q&A site for people living in, travelling to, or curious about Turkey

Currently in definition.

Secret

2:51 PM

I am surprised that psychology did not exists yet

0celóñe7

@Secret it's a sham field

Wrichik Basu

Isn't psychology entertained in cognitive science se?

Cognitive Sciences
For practitioners, researchers, and students in cognitive science, **psychology**, neuroscience, and psychiatry.

Secret

O I see

Mithrandir24601

@0celóñe7 depends what you mean by 'different' - about 3 Haar measures over different groups, but the functions are (mostly) different

Balarka Sen

Secret

2:54 PM

anyway, those who worry about too many what-if questions in WSE and PSE should support that speculative science SE

Anonymous

@WrichikBasu That is just a proposal. You can see that there are only 10 users who have followed it in the last 1 month. Without a large enough user base it will shut down soon. Hope you can get sufficient followers for your proposal. Good luck

Balarka Sen

@0celóñe7 I am a Freud you are mistaken about your opinion

Anonymous

@WrichikBasu I've followed it. Done.

Secret

Pretty sure if speculative science went online and healthy, it should resolve many off topic questions in PSE

0celóñe7

Fallout 4 Mod - Death Grips Guillotine "YUH" Mini Nuke Sound Mod

►

Balarka Sen

3:01 PM

lol

good meme

Wrichik Basu

@Blue thanks for that. Let's hope for the best! :-)

Balarka Sen

i give it a light 7 decent 8

Pritt Balagopal

@Blue Thanks, but I don't want to learn about NMR, I already have a book about that. I need to learn the basics of nuclear phenomenon before trying to give NMR a shot at reading.

0celóñe7

@Mithrandir24601 what do you even need Haar measure for in physics

Anonymous

@PrittBalagopal I don't think I can help much with that. This website looks good - grandinetti.org/Teaching/Chem7160. If this doesn't help then try asking someone in the Chem SE chat room.

Mithrandir24601

3:23 PM

@0celóñe7 I'm looking at noise in t-designs for randomised benchmarking of a quantum chip. T-designs happen to have a convenient definition in terms of the Haar measure, which means it's coming up quite a bit

heather

it's cloudy and raining. where i'm at, you'd probably not be able to see the eclipse =/ hopefully it clears up so i can see it.

Anonymous

Watch the live stream instead =P. BTW, here, we aren't gonna have a total solar eclipse in 17 years.

Prathyush Poduval

@Blue I thought the next one was in 2019 dec

Anonymous

Hope the skies clear up :)

Prathyush Poduval

in india

Anonymous

3:26 PM

@PrathyushPoduval timesofindia.indiatimes.com/home/science/…

Prathyush Poduval

@Blue timeanddate.com/eclipse/solar/2019-december-26

South india is over the path of totality

Anonymous

Ah, that would be near the Indian Ocean

Anonymous

Bad luck for Northies

Prathyush Poduval

3:55 PM

@Blue maybe you can visit thesouth then :p

@Blue timeanddate.com/eclipse/solar/2020-june-21 you can watchthis then

Slereah

@0celóñe7 LQG has Haar measure

Which is related to the whole gauge business, so I'm wondering if it's used in general for gauge stuff

Isn't gauge quantization related to the Haar measure?

I dunno

Mr. Xcoder

Hello everyone. I wonder if you have improvement suggestions on this answer.

Sid

@Blue TOI is the Toilet Paper of India. :P

Anonymous

@Mr.Xcoder It is not clear why a crest will be formed just outside of the trough bellow the location where the stone falls

Anonymous

4:14 PM

You might consider how surface tension causes the waves.

Anonymous

One more thing - a single stone falling should have produced only one crest and one trough.

Anonymous

But it produces several crests and troughs

Anonymous

Why is it so?

0celóñe7

@Slereah interesting application of the axiom of choice

if you have $f:E\subset \Bbb R^n\to\Bbb R^m$ Lipschitz, $m\ge 2$, then there is an extension $g:\Bbb R^n\to\Bbb R^m$ with the same Lipschitz constant

the proof needs the axiom of choice though

Slereah

Odd

Is it necessary though

like if you have the negation of the axiom of choice

Is it false

AHB

4:30 PM

@Blue Yes. We have spoken before.

What is that "iirc"?

Slereah

"if I recall correctly"

Anonymous

^

AHB

oh.

Yes. In fact I am in it.

Currently among the top 42. They will drop 32 of us by the next week.

Prathyush Poduval

@AHB Top 42 of what?

Anonymous

@AHB That sounds good. Hope you get through and enjoy solving the problems. (And not to worry even if you don't). :)

Anonymous

4:37 PM

@PrathyushPoduval Iran's Olympiad Camp for IPhO participants selection I guess

Prathyush Poduval

Oh nice

Whats the duration of your camp?

@AHB do you mind sending the question papers of the camp?

Anonymous

Watch the Solar Eclipse Live Across the US | Solar Eclipse 2017

►

Anonymous

Aha, they're live streaming it.

Wrichik Basu

4:54 PM

@Blue thanks for the video!

DukeZhou

I'm psyched I was able to score a pair of legit glasses at the last minute, even though we're only getting about 81% coverage!

cool vid

0celóñe7

@Slereah apparently it is equivalent to en.wikipedia.org/wiki/Boolean_prime_ideal_theorem

Mithrandir24601

Does anyone know the name of the property $\lvert ABC\rangle\rangle = A\otimes C^T \lvert B\rangle\rangle$ ?

0celóñe7

what the hell is that supposed to be

Mithrandir24601

@0celóñe7 Well, I've been lazy here and used '^T' as transpose

Oops - A, B and C are matrices

And $\lvert A\rangle\rangle$ is what I know as the linearisation of $A$

0celóñe7

5:10 PM

My keyboard is doing something weird where tab is sending messages

@Mithrandir24601 how do you linearize a matrix

Mithrandir24601

@0celóñe7 in this case, it's performing the operation where each row becomes a column vector, which are put together in such a way that the first row becomes the first d elements, the second row becomes the second d elements etc. Of a $d\times d$ matrix to a $d^2$ column vector

0celóñe7

I am again left wondering why physics is just linear algebra

Mithrandir24601

@0celóñe7 in this case, it's actually just a thing used in a simple 'proof' used to derive the t-design condition from what's known as 'channel twirling'

Ben Niehoff

5:44 PM

here in Belgium we cannot see the solar eclipse...or even the sun, for that matter

Anonymous

@BenNiehoff Heh, its eve

Ben Niehoff

oh, but sunset isn't for another 1.5 hours or so

it's just cloudy ;)

0celóñe7

this eclipse is hurting the economy

Ben Niehoff

they should reschedule it!

Balarka Sen

whats this eclipse mania

whut is this shitz

Ben Niehoff

5:51 PM

I dunno, nobody here gives a shit, obviously

but it's been a while since there's been a nice eclipse over the US

0celóñe7

I can see it

It's ok

Anonymous

6:10 PM

I think my question will be too trivial for the ELL site. Does this sentence sound correct: "We saw the fatal cliff more than once, from which the climber fell to his death." ? Is there any grammatical error in the quoted sentence?

Anonymous

It doesn't sound good though

Anonymous

Uh, @rob isn't around :/

vzn

← just saw eclipse (thru glasses), pretty freakin amazing, est 93% coverage around here but same light as a little cloudy. not sure whether to panic or relax. last week did seem freaky wrt world events o_O timeanddate.com/eclipse/solar-eclipse-myths.html

0celóñe7

Pinhole projector works

Eyes don't

I can see why they say not to stare at it without glasses

Wrichik Basu

6:39 PM

@Blue where did you find that? It seems correct in grammar.

Mithrandir

@Blue sounds slightly awkward to me. What's the context?

Anonymous

@WrichikBasu Have got an English test on Wednesday. :P

Anonymous

@Mithrandir Basically it is a grammar exercise. I was asked to correct the sentence (if it is incorrect).

0celóñe7

Anonymous

@0celóñe7 Cool that :D

Mithrandir24601

6:47 PM

@Blue If I was reading this in a novel based in an appropriate time period, this seems perfectly fine to me, but if I were to hear someone say it today, it would feel... I dunno... 'slightly awkward', as @Mithrandir says

Anonymous

Gosh...are you socks of each other ? :'D

Anonymous

@Mithrandir24601 Thanks for the input :)

Mithrandir

Of course not... ;)

Mithrandir24601

@Blue You're not to first to ask that though ;)

@Blue No worries, but don't expect my grammar to be perfect (although I am from the UK)

Черенки

Does a proton have a radius, thus volume?

Can the proton be compressed?

0celóñe7

6:55 PM

@BalarkaSen do you like r/surrealmemes?

Anonymous

Proton has detectable wave properties.

Anonymous

For classical models I think you can take it to be a sphere having a certain radius...

0celóñe7

@DanielSank paging for cooking help

Anonymous

@Черенки Read up Planck's density

Anonymous

More than once we saw the fatal cliff... or We more than once saw... do a better job of keeping the right pieces together. — StoneyB 5 mins ago

Anonymous

7:00 PM

Ah, this sounds better :)

Mithrandir24601

@0celóñe7 Oooh - what are you cooking?

0celóñe7

@Mithrandir24601 it's general advice

Mithrandir24601

Aww :/

0celóñe7

I can't get ahold of white wine, but I don't think white wine vinegar will exactly do the trick

Mithrandir24601

Erm... No

0celóñe7

7:04 PM

you can turn red wine vinegar into decent red wine for cooking

not sure about white

Mithrandir24601

@0celóñe7 Depending on the recipe, it can be done

But I'd generally just add more of whatever liquid you're already using

e.g. if something wants 150ml stock, 150ml white wine, I'd just go with 300ml stock (maybe a little more complicated than that, but that's the gist of what I do)

@0celóñe7 If you really want to do that, would half white wine vinegar, half water seem reasonable?

0celóñe7

@Mithrandir24601 maybe, but there might be a trick

for instance, tomato paste with red wine vinegar is a good substitute for red wine in stews and whatnot

it kind of neutralizes the vinegar

Mithrandir24601

@0celóñe7 yeah, the water doesn't neutralise the acid, but it dilutes it a bit

Sir Cumference

Eclipse was amazing

0celóñe7

@Mithrandir24601 it's not neutralizing the acid as much as masking the taste/smell

Sir Cumference

7:09 PM

Got some glasses

0celóñe7

but you can't mask the red wine taste

so it's a tricky business

Mithrandir24601

I've never used wine vinegar, so I wouldn't know how it smells :P

Phase

If I have two neutrons and have it so they collide, if they have enough energy by virtue of their motion + their mass they will form a small black hole right? If two neutrons then collide with much higher energy, does that mean that because the sum of energies are greater, the schwartzchild radius is greater and that they would form a black hole even when being further away from each other than the last pair? Also could anyone point me to a source about what one of those, if taken to be the /1

Mithrandir24601

Do you want the white wine taste?

0celóñe7

@Mithrandir24601 I can make it without the wine I guess

Phase

7:11 PM

centre of a co-ordinate frame and the other neutron is just moving relative to it, would observe as the spacetime around it changes?

0celóñe7

but if there's a simple solution I will do it

@Mithrandir24601 I really like wine

Mithrandir24601

@0celóñe7 That's a yes then :P

I, on the other hand, hate both white and red wine (to drink), so am probably not the best person to ask (although in certain foods, wine is essential...)

0celóñe7

how can you hate it

do you like any alcohol?

DanielSank

@0celóñe7 what's up?

Mithrandir24601

@0celóñe7 Some... Port, whiskey, brandy and dessert wine

0celóñe7

7:14 PM

@DanielSank I need to come up with 1/4 cup of dry white wine for a dish

Mithrandir24601

what dish though?

0celóñe7

I can't get white wine, is there some way to turn white wine vinegar into cooking wine?

DanielSank

@0celóñe7 Ok.

Go to store. Trade dollars.

0celóñe7

@Mithrandir24601 lime chicken

@DanielSank I'm 19

DanielSank

@0celóñe7 Call friend, go back to step 1.

0celóñe7

7:15 PM

@DanielSank I'm in an on-campus apartment, I'm not taking the risk

DanielSank

oh ffs

ok then just use a bit of lemon juice and/or vingar.

Waaaay less than however much wine is called for.

If I were you I'd use some white grape juice and maybe a tablespoon of vingar. Then taste it and adjust with lemon juice or whatever as you feel is appropriate.

The problem with the grape juice is that it will add sugar that you probably don't want.

That's the world you live in though.

Anonymous

I need some QM help. On page 13 of this pdf, any idea why $[u_1(x)]_{x=a}=[u_2(x)]_{x=-b}$ should hold true?

DanielSank

Getting sugar out of juice is... hard.

@Blue What do the brackets mean?

Anonymous

I don't understand how they are applying boundary condition at $x=a$ and $x=-b$

Anonymous

They aren't even boundaries

Phase

7:19 PM

Nevermind RIP

Anonymous

@DanielSank function of $x$

0celóñe7

@DanielSank evaluated at whatever is in the subscript I bet

Anonymous

Evaluated at $x=a$ and $x=-b$

DanielSank

Why the hell wouldn't you write $u_2(-b)$?

Anonymous

7:21 PM

@DanielSank I wrote what was written in the pdf so that people can understand which part I'm referring to, quickly

0celóñe7

@BalarkaSen Interesting: there's a Sard theorem for Lipschitz functions.

@DanielSank I take it I won't be able to find unsweetened grape juice?

@Blue what are the $u_i$s?

Anonymous

$\psi(x)=u_K(x)e^{iKx}$ using Bloch theorem. $u_1$ is for when $0<x<a$

Sid

@0celóñe7 isn't drinking not allowed in the U.S. till you are 21?

0celóñe7

@Sid yes

there are exceptions

Sid

Like?

0celóñe7

7:36 PM

church, parents house

Anonymous

wtf

0celóñe7

@Blue I urge you to stop reading physics

Anonymous

Okay, the first one makes a bit of sense if I write it as $\lim_{b \rightarrow 0}\frac{\sinh(\beta b)}{\beta b}=1$

Anonymous

Phew...

0celóñe7

7:39 PM

they are using $\sinh x\sim x$ as $x\to 0$

which is what you wrote

Anonymous

Got it now

Anonymous

I'm being stupid

0celóñe7

but what they wrote is strictly speaking incorrect

Anonymous

@0celóñe7 Why?

0celóñe7

@Blue because $\sinh x\to 0$ as $x\to 0$

Anonymous

7:41 PM

@0celóñe7 That's exactly what confused me

Anonymous

I've started to dislike physicists :P

0celóñe7

@Blue what they really want is that $\sinh x=x+\mathcal O(x^2)$

and then drop the $\mathcal O(x^2)$ term

Anonymous

@0celóñe7 Yes. The Taylor approximation. I get it.

DanielSank

@0celóñe7 Not without yeast and time.

Or expensive biochem lab equipment.

0celóñe7

I wouldn't like to see the fine for setting up a distillery on campus

DanielSank

7:48 PM

Indeed.

Why would you need a distillery?

0celóñe7

a winery then

DanielSank

ah.

0celóñe7

@DanielSank I need bourbon too

DanielSank

Can't help you there.

You need to trade dollars for it.

And be older.

Sid

@DanielSank why can't he simply lie about his age?

0celóñe7

7:51 PM

lmao

this is a college town

my 70 year old dad has to show his ID

Sid

Eeks. You can't lie. Good luck getting your wine

Anonymous

Tell someone older to buy it for you. ;)

0celóñe7

@Blue while that is possible, my apartment does now allow alcohol because it's on school grounds

it's a state school

Anonymous

Wow. Quite strict it seems.

Anonymous

Here alcohol, weed, etc is quite common. (Not that I ever indulged :P)

0celóñe7

7:55 PM

oh, it's common here too

people get caught though

Sid

I haven't seen alcohol here, yet. Smoking is pretty common. The guy in the room next to me smokes

Anonymous

Fortunately I don't have to stay in a hostel :P I wouldn't want awkward roomates and wingmates

Sid

Duh. You are missing some very good time

Anonymous

I can stay comfortably in my air conditioned room XD

Anonymous

@Sid Uh, maybe. Everyone has to miss something. =)

Balarka Sen

7:59 PM

@0celóñe7 Lipschitz means exactly that it's differentiable (C^1?) almost everywhere, right? So that's not super surprising to me.

There are things like Lipschitz manifolds, which are things in between the PL and the DIFF category

0celóñe7

@BalarkaSen Not sure what $C^1$ a.e. means

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