00:00 - 20:0020:00 - 23:00

12:05 AM
@BalarkaSen I would read the shit out of [3] W. I. Brouwer. Tropical Measure Theory. Springer, 1998.

3 hours later…
3:04 AM
Sure, the spacetime there is pretty fucked, but is it warped enough to create CTCs?

1 hour later…
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.

4:40 AM
@JohnRennie haven't done a benchmark in days

5:37 AM
@Kaumudi.H check Hangouts and ping me back here ...

2 hours later…
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.

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

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

Anonymous
$P=I^2R$

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! :)

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

9:05 AM
Hello one and all! Does any one have any experience with energy conservation in the Post Newtonian regime?

1 hour later…

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)

11:19 AM
Anyone else get hit with serial downvoting?

@Blue Thanks. What I am after is something equivalent to this post
2

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!! :)

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

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

@KyleKanos Looking into it.

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?

12:43 PM
@KyleKanos nope. Obviously someone just loves you.

@Mithrandir did you watch it?

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

I did
why are there two of you

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

@0celóñe7 obviously two huge fans of LOTR

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.

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...

@Mithrandir24601 it was quite predictable

@0celóñe7 especially given some of the trailers

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

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

yep, literally impossible to spoil
@ACuriousMind the grump could guess it

1:43 PM
especially given a certain trailer...

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?

@Mithrandir24601 Always use \mathrm for group names.
So it would be $\mathrm U(d)$

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

@Mithrandir24601 So?

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

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

2:07 PM
@0celóñe7 so I've already defined a mathrm{U} :/

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?

@0celóñe7 OK, back to the way it originally was :P thanks
@0celóñe7 Is there a specific way of denoting the Haar measure then?

2:23 PM
@Mithrandir24601 not as far as I know
$m_G$ is popular but $m_{\mathrm U(d)}$ is awkward

Anonymous

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

@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

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

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

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.

Uninterested. I will pass on that...

@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

2:49 PM
@Mithrandir24601 20 different Haar measures?

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

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?

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.

@Blue see this:
10
Turkey

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

Currently in definition.

2:51 PM
I am surprised that psychology did not exists yet

@Secret it's a sham field

Isn't psychology entertained in cognitive science se?
Cognitive Sciences
For practitioners, researchers, and students in cognitive science, **psychology**, neuroscience, and psychiatry.

O I see

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

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

Anonymous
@WrichikBasu I've followed it. Done.

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

3:01 PM
lol
good meme

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

i give it a light 7 decent 8

@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.

@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.

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

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.

@Blue I thought the next one was in 2019 dec

Anonymous
Hope the skies clear up :)

in india

Anonymous

South india is over the path of totality

Anonymous
Ah, that would be near the Indian Ocean

Anonymous

3:55 PM
@Blue maybe you can visit thesouth then :p

@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

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

@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?

@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

Odd
Is it necessary though
like if you have the negation of the axiom of choice
Is it false

4:30 PM
@Blue Yes. We have spoken before.
What is that "iirc"?

"if I recall correctly"

Anonymous
^

oh.
Yes. In fact I am in it.
Currently among the top 42. They will drop 32 of us by the next week.

@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

Oh nice
Whats the duration of your camp?
@AHB do you mind sending the question papers of the camp?

Anonymous
Aha, they're live streaming it.

4:54 PM
@Blue thanks for the video!

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

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

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

what the hell is that supposed to be

@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 $A$

5:10 PM
My keyboard is doing something weird where tab is sending messages
@Mithrandir24601 how do you linearize a matrix

@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

I am again left wondering why physics is just linear algebra

@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'

5:44 PM
here in Belgium we cannot see the solar eclipse...or even the sun, for that matter

Anonymous
@BenNiehoff Heh, its eve

oh, but sunset isn't for another 1.5 hours or so
it's just cloudy ;)

this eclipse is hurting the economy

they should reschedule it!

whats this eclipse mania
whut is this shitz

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

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 :/

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

Pinhole projector works
Eyes don't
I can see why they say not to stare at it without glasses

6:39 PM
@Blue where did you find that? It seems correct in grammar.

@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).

Anonymous
@0celóñe7 Cool that :D

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 :)

Of course not... ;)

@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)

Does a proton have a radius, thus volume?
Can the proton be compressed?

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...

@DanielSank paging for cooking help

Anonymous

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 :)

@0celóñe7 Oooh - what are you cooking?

Aww :/

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

Erm... No

7:04 PM
you can turn red wine vinegar into decent red wine for cooking

@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?

@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

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

Eclipse was amazing

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

7:09 PM
Got some glasses

but you can't mask the red wine taste

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

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

Do you want the white wine taste?

@Mithrandir24601 I can make it without the wine I guess

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?

but if there's a simple solution I will do it
@Mithrandir24601 I really like wine

@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...)

how can you hate it
do you like any alcohol?

@0celóñe7 what's up?

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

7:14 PM
@DanielSank I need to come up with 1/4 cup of dry white wine for a dish

what dish though?

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

@0celóñe7 Ok.

@Mithrandir24601 lime chicken
@DanielSank I'm 19

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

7:15 PM
@DanielSank I'm in an on-campus apartment, I'm not taking the risk

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?

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

7:19 PM
Nevermind RIP

Anonymous
@DanielSank function of $x$

@DanielSank evaluated at whatever is in the subscript I bet

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

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

Anonymous

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

@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 $0<x<a$

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

@Sid yes
there are exceptions

Like?

7:36 PM
church, parents house

Anonymous

Anonymous
wtf

@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...

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

but what they wrote is strictly speaking incorrect

Anonymous
@0celóñe7 Why?

@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

@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.

@0celóñe7 Not without yeast and time.
Or expensive biochem lab equipment.

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

7:48 PM
Indeed.
Why would you need a distillery?

a winery then

ah.

@DanielSank I need bourbon too

You need to trade dollars for it.
And be older.

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

7:51 PM
lmao
this is a college town
my 70 year old dad has to show his ID

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

Anonymous
Tell someone older to buy it for you. ;)

@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)

7:55 PM
oh, it's common here too
people get caught though

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

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. =)

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

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

00:00 - 20:0020:00 - 23:00