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3:01 PM
Tom Lehrer recently celebrated his 90th birthday. I must admit I hadn't realised he was still alive.
 
oh yes
He's still kicking
 
these guys typoed a $\varrho$ as $d$
 
a $\varrho$ was a famous philosopher wasn't he?
In other news:
 
wot
 
3:11 PM
that's not news!
 
Frittatas with peppers and chorizo!
 
@JohnRennie Hmm.
 
All my jokes are silly. I am serious only about lunch and other matters of global importance.
 
Food? Did I hear a mention of food?
 
3:33 PM
If you're not going to bother to say what your issue is...
 
@JohnRennie Ibn Rushd
 
@Pieter using the Arabic name kind of spoils the joke, though if we're being honest there wasn't that much of a joke there to spoil on the first place :-)
 
@0celo7 simplest and most potentially easily memorable derivation of Schwarzschild yet, overleaf.com/15547425zdrppjdychkv , any ideas to make it simpler and more memorable?
 
ugh
 
The trick is setting $r = C(r)$, then a lot of the equations look far more uniform at each step
 
3:47 PM
"$r = C(r)$"
somebody lend me a tide pod please
 
What
 
@BalarkaSen I think you mean $r = C(r)$
After you with the Tide pod
 
@bolbteppa Oh, do you mean, $C$ is the identity function?
In that case I take back my tide pod
 
To derive Schwarzschild you begin from $ds^2 = A(r)^2 dt^2 - B(r)^2 dr^2 - r^2 d \theta^2 - r^2 \sin^2(\theta) d \phi^2$ and want to find $A(r)$ and $B(r)$ explicitly, if you work it out the equations at each step look far more uniform if you assume $r = C(r)$ temporarily
 
>you begin from
He doesn't even prove the Birkhoff theorem first
 
3:52 PM
Tide Pods are a line of laundry detergent pod from Procter & Gamble's Tide brand, which has sold the pods since 2012. Tide Pods could be deadly if ingested, and as a result, the Center for Disease Control and Prevention has labeled Tide Pods as a health risk. There have been numerous media reports discussing how children and those with dementia could endanger their health or life by eating the pods. Some victims have ingested the detergent pods after mistaking them for candy. In late December 2017, Tide Pods became the center of an Internet meme popularized on Twitter, which involves a dare to...
ouch...
 
"Tide Pod challenge" has to be one of the dumbest things I've heard of
I'm a bit skeptical about how widespread it ever actually was---it's the sort of thing that could easily get inflated by media---but that doesn't make the idea itself less stupid.
 
'one child was admitted to the hospital every day as a result of eating Tide Pods'
wtf
 
natural selection
 
@Semiclassical A lot of popular troll channels ate tide pods on camera
@slereah Ohbbffft
 
It's alright, I can say it
 
3:55 PM
@BalarkaSen eh, I count that as part of 'social media'
 
I don't think anyone eating a tidepod is gonna end up on a physics channel
 
@Semiclassical There's also the "Tide Pod chan"
 
How does that look like candy
 
Though the example which is both more tragic and even dumber than Tide Pod's is this: popularmechanics.com/technology/apps/a27900/…
Which is also a local story
basically, young husband and wife pair were trying to get Youtube famous, so the husband had the brilliant idea of having his wife shoot a Desert Eagle at him with a thick encyclopedia in the way
The thought being "oh lol it'll stop the bullet". It didn't.
 
Sigh.
 
4:00 PM
Yeah. He didn't survive, and last month: "Monalisa Perez was sentenced to 90 days in jail for the accidental shooting of her boyfriend as part of a YouTube stunt, to be served in 10-day stints over the next three years."
 
How did Schwarzschild lead to this
 
Oh, and she was pregnant at the time with their second child.
So....yeah.
 
That's terrible tbh
 
Agreed.
I'm glad the sentence wasn't any harsher tbh.
 
Although less welcome is the news that I will have to stop drinking to do it. You win some and you lose some I guess.
 
4:10 PM
I tasted a tide pod, had to spit it out
completely vile
 
@0celo7 well, they're detergent so they taste like soap.
That taste, by the way, is the surfactants destroying the cell membranes on all the cells in your mouth.
 
@JohnRennie i'm kidding
 
Likewise, if you're silly enough to swallow it, the cells in your throat, stomach, bowels and eventually your bung hole.
 
4:15 PM
"silly" seems like an understatement
 
Though having a sore butt is probably the least of your worries by that stage :-)
 
I can think of more enjoyable ways to get a sore butt
 
You meant eating lots of chilli? Right? :-)
:: John looks nervously around for any passing moderators ::
 
As long as no one goes into more detail, this is fine :P
 
4:18 PM
I think we should put the matter behind us
 
vzn
There's a point to be made that a neural network for food classification that can classify Tide pods as "not food" has already reached superhuman capabilities
 
24 mins ago, by bolbteppa
How did Schwarzschild lead to this
because...
38 mins ago, by Balarka Sen
somebody lend me a tide pod please
and it look so out of context thus I then googled
 
@Secret I think that was a rhetorical question :P
 
lol
 
vzn
blames BaSe o_O :P
just discussed at length with sig other, another recent horrifying tragedy in headlines involving teenager, apparently a significant risk factor o_O dailymail.co.uk/news/article-5609337/…
 
4:46 PM
@vzn I do not understand why it would be so difficult to send a gps position. I also called the alarm number once. Operator kept asking for an address. But this was on a cycling path (guy with an epileptic attack). Operators are not local, misunderstand.
 
vzn
@Pieter was looking into that story and tech (failure) played a role. he used siri to call 911 (twice!) & maybe got disconnected once (operators typically advise to stay on line afaik). the operators computer locked up at 1 pt, the operator has been suspended 1wk for mishandling the call. yes gps is increasingly integrated into cars/ phones and saves lives daily. amazing tech! but what happens if it ever fails in the satellites? yikes o_O
 
@ACuriousMind . You just answered a homework-like question, where OP had not made any effort (ideal gas)
 
@Pieter It's not a homework-like question by our standards - it does not ask for the solution of some exercise or the result of a computation, it asks a conceptual question: "Do ideal gases exist?". I agree it's not the best question ever, though...
 
@ACuriousMind yo
long time no see
 
@ACuriousMind There is a chance that the student would get this question on his exam. And the whole point of such statements is to make a students think for themselves.
 
5:03 PM
@Pieter Well, that's why I didn't explicitly explain e.g. why electron gases are particularly "good" ideal gases - they still have to identify the relevant interactions on their own, my answer just points them at what to look for. Generally, though, "this could be a question on an exam" is not something that concerns me overly - exams can be rather varied, and we judge questions here, not their askers.
 
@ACuriousMind I tend to think of the askers. For students, I often just make a comment with a question and/or a hint. For others (people working in a different field, etc) I am more willing to explain some stuff that I might expect a physics student to know.
 
5:53 PM
@Slereah what the hell does Witten's black hole have to do with black holes
 
6:06 PM
@0celo7 I don't know what Witten's black hole is
 
@Slereah his 2+1D quantum black hole?
 
The BTZ black hole?
 
6:28 PM
@Slereah no
well, maybe
$$g=\frac{dx^2+dy^2}{e^{4t}+x^2+y^2}$$
 
doesn't ring a bell
wait what is $t$
what kind of metric is it
 
solution of le Ricci flow
 
oh
no idea then
 
@Slereah ricci flow people always say that physicists call it Witten's black hole (probably because it sounds cool and Witten is like a mystical figure in geometry)
but they never give references
 
I mean I guess it is singular
But I dunno if it's related to black holes
 
6:37 PM
I would love to learn more string theory
 
you may enjoy it certainly
 
@Slereah but there's no time!
 
true
there is too much science
 
I am doing too many things rn
GR, hyperbolic PDE, GMT, Ricci flow
ahhh
 
I am studying the Dragon Ball right now
Still 50 episodes left!
 
vzn
6:44 PM
googling, maybe the "wess-zumino-witten" model journals.aps.org/prd/abstract/10.1103/PhysRevD.44.314
 
And that's not counting Dragon Ball Z
 
@Slereah u monster
so one of my professors loves BCS
but said he found S3 very confusing
I don't remember it much tbh
 
Chuck dies in a fire
Like he should
 
@Slereah um, did he really die
or is that the cliffhanger
 
@0celo7 I guess we won't know for sure until season 4
 
vzn
6:46 PM
huh also known as a cigar soliton hmmm arxiv.org/abs/1205.3043
 
Just went hardcore Java mode and spun up an API. Yaaaaaaaaaaaaaaaaaaas!!!!!!!!!!!
 
@Cows calm
 
hehe
 
vzn
now knows more about witten black holes than 0celo7
 
I can google as well you know
 
7:00 PM
10 messages moved to Trash
 
lol
 
0_O
hm this looks better tbh
 
vzn
lol bye
apparently comparing black holes (regarded as soliton(s) by witten!) to particles (also regarded as solitons by mass cutting edge research!) is now unacceptable content here... o_O
 
I only know of Witten's dog
 
@vzn Mocking other users is inacceptable - this includes persistently replying "lol" to other users earnest messages after being asked not to, but also @0celo7's and @BalarkaSen's responses I just deleted. Next one to cross the line gets a nice suspension, apparently y'all are unable to get the hint otherwise.
 
7:05 PM
I am tempted to reply your message with a lol, but I don't want to get banned at this moment.
 
@ACuriousMind "y'all" is cultural appropriation
 
Oh, wait, I know.
@BalarkaSen lol
@ACuriousMind In your face
 
@BalarkaSen Since I specified other users, all you just did is laugh at yourself. Which, come to think of it, is a good skill to have :P
@0celo7 Since English is not my mother tongue, you might argue me speaking it at all is appropriation :P
 
@ACuriousMind can I request you stop speaking english? im offended
 
@ACuriousMind That is a sloppy answer to an epistemological question of whether I as an entity am identical to my conception of another individual, as my perception of the "other" is fundamentally based on my own perception of myself.
Your argoment is invalid my friend
 
7:28 PM
Dropping code like a boss!!
Listening to Cardi B
 
@BalarkaSen Argoments are for argonauts
 
while coding . . . .
The guy next to me is building a cpu from scratch using breadboards lolz
ha
listening to Lemon now by pharell et al
super pumped
 
@ACuriousMind I am slain.
 
Any Java experts out here? I want to know!! Show your faces!
hehe
la la la la
ok atacking direct from command line now . . .like a boss
Hot damn this song is lit. I feel like its making me write awesome code
damn Cardi B
wohoo
let me just reset gradle
then attack pom.xml
 
7:46 PM
is cringed
 
@BalarkaSen teach me JAVA
hehe
 
iunno Java but i can certainly recommend better music :p jk no pop shaming here
 
hehehe
How can you not love Cardi B - Drip feat. Migos [Official Audio]
hehe
 
I don't even know who these people are
 
Just not my kinda music :) I don't listen to pop rap too much
 
7:50 PM
lol
the Migos Cardi B combo is fire lol
:P
 
I listened to that one song by Migos which I thought was okay
But that's all
 
8:07 PM
@ACuriousMind how?
do you not go on the internet?
 
Not to the places where I would encounter contemporary rap, no :P
 
@Cows "I Like It" is much better
 
would anyone mind helping me with some regex?
it should print a list that looks something like ['matrix:[[1,0],[0,1]]', 'matrix2:[[0,1],[1,0]]']
currently, it just prints a blank list.
 
@heather Have you entered the regex and the file contents e.g. here and checked whether it actually matches what you want to search?
 
nope, let me try that. i've never seen that site, good to know about!
 
8:19 PM
It's my go-to to do anything with regexes, because I'm terrible at both writing and understanding them without running them over test strings :P
 
well, i switched it to python, and it seems to be taking too long to terminate.
which...i don't even know.
 
Hmmm?
 
oh, nvm, it finished.
it was giving a weird error.
 
When I paste your regex it parses it almost instantly (of course I don't have the test file, though)
 
it matched what i wanted it to, i think.
 
8:23 PM
@BalarkaSen have you finished evans yet
 
i think i'll have to fiddle with it a bit. thanks @ACuriousMind!
 
@heather Wait, are you sure str(open(...)) actually returns the filecontents? open(...) returns a file object, I'd be surprised if str(...) works on it like that
 
nope, not sure at all.
 
To get the file content as a single string, I'd usually do f = open(...); filetext = f.read()
 
let me see.
well, that would explain it.
filetext is not what i thought it was.
@ACuriousMind yep, that worked. now i just have to tweak the regex a little bit, it's not quite right.
 
8:58 PM
@Slereah do you understand the stability statement for the Yvonne-Geroch theorem
 
I do not
 
Ringstrom requires compactness and I don't have the patience to read everything and see why
 
9:09 PM
How do I get limits of integration for v and a here please? i.imgur.com/hQ9ZWZD.png
 
9:21 PM
@0celo7 the melon was featured on meme review
 
when
 
that's old news
 
2aheadofthecurve
 
9:43 PM
Holy hell. Soon, we'll be living in "the 20s". And eventually when people say "the 20s", they'll be referring to us, not the 1920s
 
@SirCumference are you on weed
 
No I'm just sleep deprived
 
9:59 PM
@ACuriousMind True, but however you formulate it, it is a very special connection that's tied to the metric in the end and hence not quite the same as a typical gauge field.
 
@G.Bergeron if by "typical" you mean Yang-Mills, I of course agree - but the notion of gauge fields is not limited to Yang-Mills gauge fields.
 
@ACuriousMind :p
@BalarkaSen What the hell is that?!?
 
@SirCumference i wonder if people will say the '020s' vs the '920s' or something weird like that.
 
probably just the 20-20s and 19-20s
 
10:23 PM
@ACuriousMind Unless you split the metric in background plus perturbations, I'd argue the gauge group acts on base space versus on the fibers. If by gauge group you mean ''the stuff you promote from global to local'', then yeah ok.
 
vzn
@G.Bergeron so did you study GR? have any interest in new research? ps meant magueijo earlier, got the name wrong, arguelles is a newage freak
 
@G.Bergeron I don't know what you mean by a gauge group "acting on the base". What is unique to GR is that the gauge transformations act on tangent vectors, i.e. we do not have the completely disconnect between the action of gauge transformation and that of spacetime transformations we have in Yang-Mills.
What the gauge group is depends on which formalism you're using - if using the standard Christoffels, the gauge group is $\mathrm{GL}(n)$, but if you're using the spin connection instead you have just $\mathrm{SO}(1,n-1)$, i.e. the Lorentz group.
 
@ACuriousMind It's also different in that the action is completely different
 
@0celo7 I already said this is not Yang-Mills :P
I'm not demanding that you use YM techniques and try to do GR with that, that would be pointless
 
10:39 PM
what even are Yang-Mills techniques
wick rotation?
 
Given a vector field $A_{\mu}$ take it's covariant derivative $D_{\nu} A_{\mu} = \partial_{\nu} A_{\mu} - \Gamma_{\nu \mu}^{\rho} A_{\rho}$, a quadratic invariant from $\partial_{\nu} A_{\mu}$ gives you EM, a quadratic invariant from $\Gamma_{\nu \mu}^{\rho}$ gives you GR
 
@ACuriousMind I was referring to this disconnect you're talking about: Infinitesimal transformations act on tangent space, which you can see as a fiber, but group elements act on spacetime itself, whereas yang-mills type gauge group act both infinitesimally and not on the fibers only.
By acting on the base, I was referring to the base space in a fiber bundle.
 
Maybe Einstein's theory for combining EM and GR was all about $D_{\nu} A_{\mu}$ and he never realized it
 
@G.Bergeron No, the group elements are $\mathrm{GL}(n)$ matrices acting on the tangent space. The gauge transformations of GR are not the diffeomorphisms acting on spacetime (the base), no matter how often you'll hear that non-sensical claim, but the diffeomorphism do induce gauge transformations via their Jacobians. See physics.stackexchange.com/q/346793/50583
 
@vzn I did, as in taking graduate classes, but I haven't really done any research in this direction, yet.
 
vzn
10:44 PM
@G.Bergeron any interest in new research? have a new paper have been wondering about a professional opinion for long time...
 
@vzn Well, yes, hence why I am studying this in more depths now.
 
vzn
in theory salon, Aug 13 '16 at 23:01, by vzn
re Tenev/ Horstemeyer https://arxiv.org/abs/1603.07655
 
The first paragraphs of that article have me convinced that the old ether theory is real, and Einstein agreed with the ether, and that QFT backs this up
 
@ACuriousMind I'm not sure I follow you here. I mean if your theory is built out of tensor fields, well diffeomorphisms will act on these through their Jacobians, yeah. But general covariance is diffeomorphism invariance and this invariance will be reflected on the level of infinitesimal equations through their Jacobians only.
 
vzn
@bolbteppa so then youre a JD acolyte eh ("the one who shall not be named")
 
10:53 PM
@vzn is this more of your anti-science
and those high falutin' universities had me convinced Einstein got rid of the whole ether thing
 
@G.Bergeron Yes, which is nothing special to GR - most physical field theories are "diffeomorphism invariant". The special thing is that GR has the notion of a covariant derivative and the gauge fields - Christoffels - that come with it. From a really "gaugey" viewpoint, someone took an abstract $\mathrm{GL}(n)$ gauge theory (not YM, obviously) and soldered it
 
@ACuriousMind Ok, I see, you firmly take a gauge group to have a non-trivial action on the action itself. I guess I would agree. Would you agree saying, then that a crucial difference resides in that the gauge invariance of GR comes because diffeomorphism invariance of spacetime implies GL(n) invariance of tensor equations on that spacetime whereas yang-mills has this gauge group action from the outset?
 
@G.Bergeron I'm not convinced that "diffeomorphism invariance" is special to GR at all. In what sense is an ordinary field theory action (Yang-Mills, $\phi^4$, you name it) less "diffeomorphism invariant" than the E-H action?
But yes, the gauge symmetry of GR is certainly different in that it is interwoven - soldered - with the notion of tangent vector, while other gauge theories usually only act in a space completely separate from the tangent geometry
 
@ACuriousMind It is not less so, because we construct those actions out of tensor quantities.
 
@G.Bergeron Yes, so how could diffeomorphism invariance possibly imply the gauge invariance of GR if no such gauge is to be found e.g. in $\phi^4$ theory?
I might enjoy discussing this further, but alas it is 1 am here and I've got to work tomorrow, so if I stop responding, it's nothing against you ;)
 
11:06 PM
@ACuriousMind I'd say because we typically construct QFTs in flat space hence the covariant derivatives are trivial.
@ACuriousMind fair enough :p
 
@G.Bergeron I never said that our FT should be Q!
 
Well remove the Q!
 
And anyway, e.g. 2d Euclidean Yang-Mills QFT on arbitrary surfaces is a thing, the partition function is exactly solvable
So no, not all field theories live in flat space
 
Of course and one can try to do QFT in curved space-time to get some results, but at that point, are you not implying the gauge invariance of GR in as much as you are including gravitational effects?
 
@G.Bergeron No, coupling these theories to gravitational effects is another bag entirely
Note that as long as you're just using exterior derivatives, there's no need for GR's covariant derivative at all - the Christoffels just cancel in antisymmetrized covariant derivatives.
 
11:18 PM
@ACuriousMind Ok so you do not take this curvature to be dynamical, fair enough. From the point of view of GR are you not really just neglecting the reaction of spacetime to the presence of your matter field?
 
@vzn the formula 1.1 of that article is derived in Landau volume 7 using ideas from thermodynamics like free energy, maybe the old derivation used F = ma, but taking that as your starting point without a relativistic derivation that somehow does not already imply normal GR, I don't know how it makes sense beyond an interesting 'formal analogy' as they note in the paper, I could be wrong
 
@vzn In a cursory review, it is not surprising at all that a linearized GR can be seen as an elastic theory. I'm not sure how everything holds up in the non-linear regime...
 

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