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7:00 PM
Although...
It's only timelike for small enough $\tau_0$
So it's probably not as trivial as looking at the diagram
 
Well the small enough $t_0$ means you're chosing a small normal neighborhood
you need to use continuity of the derivative of $\eta$ there
It's clearly timelike for $\tau=0$, so it's timelike in some neighborhood
you need your $\tau_0$ small enough so you're in there
 
Can anyone guide me through this question in Ashcroft and Mermin: physicsforums.com/threads/…
 
7:22 PM
What measurements can you perform on the metric, anyway
Given some interferometer, can you measure every component of the metric?
Sounds like a thing that would be in MTW
 
"Eötvös, Pekar and Fekete checked to an accuracy of 5 parts in $10^9$ that the earth imparts the same acceleration to wood, platinium, copper, asbestos, water, magnalium (90% Al, 10% Mg), copper sulphate and tallow. Renner checked ammonium fluoride, and an alloy of 30% Mg, 70% Cu."
GR experiments involve a lot of finding objects to throw
 
@Slereah How do you type in "ö"?
 
With my keyboard
There's a ¨ key
 
7:41 PM
huh, I thought you were German...
dunno why
that wardrobe pin thing reminds me of american beauty
 
@AccidentalFourierTransform I not, I am from .hu but I live in .de . Slereah I don't know, I've thought he is from .us .
 
he's from France
 
@AccidentalFourierTransform hu-HU and de-DE both contains "ö" but in different places :-) But, en-US doesn't. fr, I don't know.
 
close enough though :-P
 
Whät?
Of cöurse we have umlauts
 
7:47 PM
in English you sometimes use umlauts in poetry, right?
 
@AccidentalFourierTransform I'll show you my umlaut
 
@AccidentalFourierTransform Not that I've seen, but we use them for rock bands apparently.
 
Apr 20 at 17:38, by AccidentalFourierTransform
A metal umlaut (also known as röck döts) is a diacritic that is sometimes used gratuitously or decoratively over letters in the names of hard rock or heavy metal bands—for example those of Blue Öyster Cult, Queensrÿche, Motörhead, The Accüsed and Mötley Crüe. Among English speakers, the use of umlaut marks and other diacritics with a blackletter style typeface is a form of foreign branding intended to give a band's logo a Teutonic quality—connoting stereotypes of boldness and brutality presumably associated with Germanic and Nordic cultures. Its use has also been attributed to a desire for a "gothic...
I thought that umlauts were used like "hey, I know that this word doesn't quite fit here, but if you stretch the pronunciation a bit, the metrics kinda work"
 
Hi
 
Wikipedia defines proper acceleration as the acceleration measured by an accelerometer; at the same time, an accelerometer is defined as a device that measures proper acceleration. From what I understood, proper acceleration is the acceleration not due to gravity, that is not caused by gravity. But are we talking about Newton's gravity or Einstein's?
 
good question
 
@AccidentalFourierTransform A slant rhyme?
 
hmm i dont know
you should know about these things, not me
but I thought that umlauts were about the metric, not the rhyme
we need @JohnRennie
 
Oh, well then I don't know
I never took advanced classes like that
 
7:58 PM
@nbro yes, it's the acceleration by a force (not gravity)
 
@Avantgarde Does it mean that we're in the Einstein's context of gravity, since gravity in Newton's one would be a force?
 
oh no
who gives a shit if gravity is a force or not
 
@nbro yes.
 
@0celouvskyopoulo7 what? it's very important to know and understand the nature of gravity, I would say...
 
what what?
"Force" is a made-up human word.
Force is not even defined in the context of general relativity, so applying "force" in that context is rather pointless.
Whether gravity is a force or not has zero to do with the "nature of gravity"
Although that's a made-up phrase as well, so who knows.
 
8:03 PM
Some old physics textbooks have umlauts
in "coördinates"
 
why physics?
all people used to write like that
 
Yeah
Lovecraft writes like that, too
Like Aëroport
 
@Slereah that's a diairesis, not an umlaut
 
> There is a constant $C=C(n,p,q,\delta,C_1,\lambda)$
 
8:04 PM
that's not constant at all!
 
well, $\frac{\partial}{\partial \mathfrak h}C=0$, so it is a constant
 
@0celouvskyopoulo7 well, the point was to distinguish between being in the context of Einstein's theories or Newton's one of gravity
 
@nbro And they are completely different. To quibble about gravity being a force or not is stupid, what even is a force?
 
the covariant derivative along the path?
 
@0celouvskyopoulo7 an influence that deviates an object from going on a geodesic
 
8:06 PM
@0celouvskyopoulo7 Stupid? Last time I studied physics was in the second year of high school
 
@Slereah That definition fails for extended objects.
 
@0celouvskyopoulo7 does it
 
whats the force acting on yo mamma
 
They don't exactly travel on geodesics.
 
well yes
 
8:07 PM
@0celouvskyopoulo7 force often appears in Newton's formulas, so a vague idea of it at least exists...
 
Due to
i n t e r n a l f o r c e s
 
whatever happened to @BenNiehoff? havent seen him in a while
 
@nbro are you asking about whether force is a pseudoforce or real force?
 
His addiction to proprietary malware got the best of him
 
Because if General relativity is correct, then it's a pseudoforce. But if you consider non-inertial frames of reference, then it's absolutely a force that exists.
 
8:11 PM
lol, what's a pseudoforce now
 
@Phase my only question, right now, is this: chat.stackexchange.com/transcript/message/37394829#37394829
 
A force that vanishes with co-ordinate transformation
like centrifugal
Well, not transformation
just choice of frame
"In relativity theory, proper acceleration[1] is the physical acceleration (i.e., measurable acceleration as by an accelerometer) experienced by an object. It is thus acceleration relative to a free-fall, or inertial, observer who is momentarily at rest relative to the object being measured. Gravitation therefore does not cause proper acceleration, since gravity acts upon the inertial observer that any proper acceleration must depart from (accelerate from).
A corollary is that all inertial observers always have a proper acceleration of zero."
-Wiki
Bip bam boom there you go
 
Mister Wiki Pedia, physicist
 
@Slereah that's Dr to you
Pedia is his middle name, his last name is Felia
 
Guess it works.
@Phase Inappropriate.
@Slereah what's an ultraspherical function?
 
8:14 PM
Insisting on the "doctor" tends to be a bit gauche I find
I do not know
 
@0celouvskyopoulo7 I can't tell when you're joking or not so I'm just gonna ignore it
 
A very spherical function, I assume
 
I never joke.
 
@Slereah Oh I see. Would you like a can of Mr Pepper?
 
Apparently they are related to Gegenbauer Polynomial
@Phase Mister Pibb only, please
You know who's the classiest supervillain?
 
8:15 PM
@Slereah is that some kind of sub-european drink?
 
Mister Freeze has an actual doctorate, and unlike most, he goes by Mister
@Phase It's an American one
 
Him and Mister Fantastic can stroke each others humbleness'
America sucks
 
Mister Pibb is one of the better known bottom of the barrel cola in the US
 
UK rules
fight me
 
Wy even get discount coke
it's not like coke is expensive
 
8:17 PM
Over here we call that "diet coke"
anyone who likes diet coke honestly can't be human
 
I think the scale is like
Coke, Pepsi, Dr Pepper, Mister Pibb
 
Coke zero, fine. Diet coke? To the other side of the wall
 
Hm, what else in between
 
Excuse me what? Dr Pepper is top tier.
It goes like this
 
@Phase I like Diet Coke.
@Slereah Pepper is not a Coke ripoff...
 
8:18 PM
Dr Pepepr, Pepsi, Co- @0celouvskyopoulo7 no you don't
 
Yeah I do.
 
no one likes diet coke
 
Prove me wrong?
 
that's a lie
 
I like it.
 
8:18 PM
 
dr Bob
 
All the various Dr Pepper knock offs
Dr. Choice sounds like an abortionist
 
What bijective correspondence maps Dr. K to Dr. pepper?
 
Dr. Perfect is probably a character on some soap opera
 
8:19 PM
"Real Dr." is quite ironic
 
@AccidentalFourierTransform he's a pastic surgeon
 
and there was an actual Dr. Becker, right?
Becker is an American sitcom that ran from 1998 to 2004 on CBS. Set in the New York City borough of The Bronx, the show starred Ted Danson as John Becker, a misanthropic doctor who operates a small practice and is constantly annoyed by his patients, co-workers, friends, and practically everything and everybody else in his world. Despite everything, his patients and friends are loyal because Becker genuinely cares about them. The series was produced by Paramount Network Television. == PremiseEdit == The show revolved around Becker and the things that annoyed him, although the supporting cast also...
 
Dr. Shaw sounds like one of those american TV shows where people go on air to talk about dramatic trailer trash drama with a 'professional'
 
In France we have Breizh Cola
It's a breton cola
 
Breton
 
8:21 PM
I remember seeing "human cola" in the store, which I assume is some kind of Soylent Green thing
 
dr chill prescribes certain plants for his treatments
 
Dr. Right is my future husband
 
Ok so, this is a chat full of bright intellectuals and people like me, so I'm sure we can solve this conundrum: Pick 3 fizzy drinks, [top tier, middle, worst]
 
While Dr. A+ is what all asian dads want their sons to be
 
8:23 PM
@Slereah and if their kids fail, they regress into Dr. Choice
 
So, let me see if I understood correctly what proper acceleration actually is. We're first of all in Einstein's context. We have frames of reference (inertial and non). Proper acceleration is measured by an observer in free-fall or by an observer in an inertial frame, i.e. a frame of reference which is not accelerating. Proper acceleration is not due to gravity, because gravity acts upon the inertial observer as well as upon the objects being measured...
 
soft drinks taste like shit to me tbh
 
$$|x-y|^{2-n}=|x|^{2-n}\sum_{j\ge 0}P_j^\lambda\left(\frac{x\cdot y}{|x||y|}\right)\left(\frac{|y|}{|x|}\right)^j$$
wot
 
the americans torrent
 
8:24 PM
Also the question is
What do you call carbonated soft drinks
 
Cola, soda or pop
 
Any serious person here?
 
they're in Abramowitz
 
Yep, that was on my clipboard before lel
 
8:25 PM
@Slereah soda
 
@nbro Nope
 
@0celouvskyopoulo7 all functions are in Abramowitz
 
piracy is wrong mofo
 
@BernardoMeurer you can't actually answer for everyone
 
@nbro You'd be surprised
 
8:26 PM
ok
 
He's right though
 
bye
 
@nbro bye
 
thats the generating function of the Legendre (Gegenbauer?) polynomials, right?
 
though really
None of that really matters
I don't like any of the colas
 
8:27 PM
@nbro I'm serious
 
I'm more of a fruit dranks guy
 
about soda
 
@Phase got a Pepper doctorate in sodas
 
the best drink is pizza
 
@Slereah could you help me with this topology thing? It's about the Axiom of Dr. Choice
 
8:28 PM
I can try
 
@AccidentalFourierTransform Gegenbauer
They're like Legendre but worse
where do you know them from?
 
It's about if you're given a set of Dr. pepper derivatives, that you can choose any of them, but they all taste like garbage
 
is Dr Choice equivalent to Zevia's Lemma?
@0celouvskyopoulo7 i needed them for my master thesis
 
Only Zorn's lemon drink
 
You just had to hijack my joke
and make it far better than mine
 
8:30 PM
@0celouvskyopoulo7 I was playing around with higher dimensional spherical harmonics
 
Btw
@nbro
You're wrong about what an inertial frame of reference is
A freely falling frame in a gravitational field is AFAIK an inertial frame
 
@AccidentalFourierTransform hmm, well they show up in integral kernels for elliptic operators on weighted Sobolev spaces...
So same reason why spherical harmonics show up in for regular PDE, I guess
who knows
 
if the wight is the measure on $S^n$, then I guess it is a natural object to use
 
uhhhhh
it's not
it's $1+r^2$ with some crazy exponent
 
8:42 PM
@dmckee Are you around?
 
crickets
 
is there general relativistic chemistry
 
@0celo did you manage to fix MMA in the end?
 
@Slereah Often but not always. See nytimes.com/2014/11/02/opinion/sunday/… for an important alternate perspective.
Being a while guy with enough physical presence to settle a room I've never felt the need to insist on a title even in the classroom, but that a sign of my having it easy.
 
"But they are mostly men, and almost all white, and they have that luxury."
wew
 
8:53 PM
Oh god
I couldn't hear you over all my Dr Choice privilege
 
Being pushy about titles outside the context where they matter is often a sign of some kind of personal insecurity or neediness.
 
Especially if you're german
Germans have tons of titles
 
I had a secondary school teacher who used to get really shitty when they wouldn't call them "dr"
 
That said, my school is a place where most students use titles for their instructors most of the time.
 
despite the fact they only just got their doctorate and kids forget
 
8:54 PM
@AccidentalFourierTransform mostly
@dmckee I had a professor who ended emails with "Dr. B"
he wrote out his name, of course
I've had two professors who did that, at least
 
I only have a master degree
Feel free to call me master Lereah
 
@Slereah Prof. Dr. habil. Dr. h.c. mult. ? :D
 
@Slereah I'm not into S&M thanks
 
@Sanya that kind of stuff, yes
 
We have a couple of professors here with difficult (for rural Americans) names from other parts of the world. One goes by "Dr [firstname]", and the other by is often "Dr. [initial]", though I have heard that he doesn't like that very much.
 
8:57 PM
@dmckee Yeah, one prof has one of those awful polish names so I can understand
 
@Slereah My school has a non-trivalal population of instructors without terminal degrees. They are called "Prof. [so-and-so]", which kinda inverts the usual sense that professor is more senior than a mere doctor.
 
Fascists!
 
What happened??
 
I guess
Dr Choice doesn't visit the h bar
 
@dmckee ::pokes::
 
9:07 PM
::squirms:: Quit that!
I'm grading so you only get half my attention.
Grades are due on Monday morning.
 
Jee
Papa bless
D. What do I do when a professor hates my guts?
 
for (var paper in papers) {
    paper.grade = random.choice('A', 'B', 'C', 'D', 'E', 'F');
}
 
And I mean that, he mocks me to my face, and not in a friendly way
 
"Another series of experiments, called "ether-drift experiments", places stringent limits on any unknown, long-range vector field that couples directly to mass energy."
 
@ArtOfCode I think you have to import stairs for that.
 
9:09 PM
What theory even has a vector field directly couples to mass energy?
 
@dmckee that'd be a new one for JavaScript
 
Javascript is a mess
 
what would it even be, $D(V_\mu) = f(T_{\mu\nu})$?
 
Mostly, yeah
 
@BernardoMeurer The first thing is to try to avoid him. The second is to bring it to the attention of the department head. Or if it is the department head someone from the office of academic affairs.
They may also be an official grievance policy in the student handbook.
 
9:10 PM
@dmckee Avoiding isn't possible, he's my lab professor, he personally reviews my work every week
 
@ArtOfCode I just assume that all simplified code was meant to by python and proceed on that assumption.
 
I guess I can talk to the head guy, he's weird though, we see
 
"Among all bodies of physical law none have ever been found that is simpler or more beautiful than Einstein's geometric theory of gravity."
How does one measure beauty
 
@dmckee well in that case
 
@BernardoMeurer On that front all you can try to do is be so good he has to admit it.
No fun, but it will help you in the long run.
 
9:12 PM
for paper in papers:
    paper.grade = random.choice('A', 'B', 'C', 'D', 'E', 'F')
 
@dmckee He took points away from me because I used getline() in a way so that all the arrays are allocated automatically to the perfect size, instead of doing some realloc() brouhaha (which is what he expected us to do)
I mean expect as in, thought we were going to, not explicitely told us to
 
@BernardoMeurer hint, from what I'm finding at university: try to do what professors expect, even if you know it's not the right way. They like taking marks away for not doing exactly what the spec says.
And sometimes even for what the spec doesn't say.
 
@Slereah what are u reading?
 
@Slereah With a IFLS article that claims everything in physics is beautiful
 
Hmmm ... getline isn't part of the standard c library (and hasn't been part of the POSIX standard for terrible long ... maybe a decade now), so he may feel that it is cheating in some way.
 
9:14 PM
I'm trying! But the guy takes points from me for anything! I implemented a way to do ops on a linked list without ever needed to go over the whole list by using a nicer struct and he took points from me because it wasn't "like everyone else did it"
 
Of course, I love getline.
 
@0celouvskyopoulo7 MTW
 
You could always code your own implementation and use that.
 
He didn't even know about getline() and how if you pass it a NULL pointer it allocates for you
 
@BernardoMeurer How are these freshman classes
 
9:15 PM
@BernardoMeurer also what I've found: think dumb. That sounds kinda harsh, but if your programming abilities are beyond everyone else in your class, try to think as they would and code accordingly
2
 
This is the equivalent of someone talking about bifunctors on $\infty$ categories
 
@ArtOfCode I can do that, sure, but it's hard when what he expects is really vague, so all I do is optimize for speed
@0celouvskyopoulo7 This is basic stuff programming-wise IMO
 
@BernardoMeurer SO, providing your own implementation with a copious documentation comment at the front solves your problem and shows him that you know how to deal with alloc class function.
 
Yep. I guess you've tried asking him to be more specific in his requirements?
 
@ArtOfCode ::nods::
 
9:16 PM
"Birkhoff's theory predicts the same redshift, perihelion shift, deflection, and time-delay as general relativity. But it requires that the pressure inside gravitating bodies equal the total density of mass-energy; and as a consequence, it demands that sound waves travel with the speed of light."
This sounds like a major issue
 
@dmckee That'll show him!
 
@ArtOfCode And I am afraid that there is something to that. I had a prof like that, too.
 
I was on the brink of delivering my assignments in inline assembly just to spite him
 
"Not until the work of Will was it realized that Whitehead's theory predicts a time-dependance for the ebb and flow of ocean tides that is completely contradicted by everyday experience."
 
@dmckee Aye, I've got one at the moment too. Refused to let me use static in a Java assignment a couple months ago because the course hadn't taught it yet.
 
9:17 PM
my thermo prof took off points for not writing down exactly the equation from the formula sheet
 
ther's a lot of weird gravity theories
 
Writing down 1st law wasn't good enough, had to write down the whole damn thing, then cross of things
 
Also refused to let me use abstract classes, but to be fair those are year 3 at least.
 
@ArtOfCode I had to build a goddamn graphical game without structs lol
 
@ArtOfCode wait what
how old are you
 
9:18 PM
@0celouvskyopoulo7 5
obviously
 
I was doing some serious pointer magic-fuckery to pull that off
 
@BernardoMeurer ouch
 
Sorry this site is forbidden to people under 13
We'll have to ban you
 
@Slereah waaaah, mommy he's being mean to me
 
@dmckee I'd liket to report an underage user.
 
9:19 PM
/s
 
@ArtOfCode I implemented 2048 in SDL2 in pure C without any structs, all in a single file, and with no extra libraries (apart from SDL and standard stuff)
It was hell
SINGLE FILE
We couldn't make our own header files
 
MTW says that outside of Cartan's theory, only metric theories of gravity work
I'm not sure I agree
 
what was Cartan's theory?
 
@dmckee Why are header files in C the way they are? Why do I have a .c and a .h? Why not write all the code in the .h already?
 
@0celouvskyopoulo7 Zero curvature and non-zero torsion
 
9:21 PM
how does that work?
what's the manifold
 
@BernardoMeurer Compile-time efficiency.
 
zero curvature is a strong condition on topology
well...maybe not if you're not using LC
 
@dmckee ::listens carefully::
 
Keep in mind that c was originally written to run on something with less memory and computational power than things you've run with a potato.
 
That's true, I have some tuned potatoes
But I don't get what difference it makes, having a .h and a .c as opposed to just a .h
 
9:22 PM
Compiling is hard work and you didn't want to compile the code for anything more than once if possible. Those the whole separate compilation infrastructure.
 
Well, I don't know if Cartan requires zero curvature
But the metric is independant from the matter content, anyway
 
There are some nice questions about this on programmers and stack overflow (the ones on SO are old, mind you).
@BernardoMeurer The typically header file only requires the compiler to update the symbol table, not actually build a AST and emit code.
 
Ah, I see
Cool
 
8
Q: Mathematica stuck in "running" for every calculation I attempt, kernel error

0celouvskyopoulo7I downloaded Mathematica this morning to do an implicit polar plot. I attempt to run the code Manipulate[ ContourPlot[ Evaluate@With[{r = Sqrt[x^2 + y^2], \[Theta] = ArcTan[x, y]}, {r Cos[Pi \[Theta]/(Pi - 2 chi)] - Exp[1/(r^2 Sin[Pi \[Theta]/(Pi - 2 chi)]^2- 1)] == 0, r^2 == 1}], {x, -2, 2}...

I'm at +8!
@BernardoMeurer My desk lamp is flickering, what do?
 
@0celouvskyopoulo7 More power
That's always the solution
jk
Put a capacitor on it
A bigass one
 
9:31 PM
what's that
 
0
Q: Why does the world look 3+2 dimensional instead of 2*3+2 dimensional?

Thomas KlimpelIn quantum mechanics, it is not obvious (for me) how to deduce the perceived dimensionality of the world from the (mathematical) description by high-dimensional wave functions. To simplify the problem, let us restrict the question to how the world looks like when perceived (only) with the help of...

I wanted to comment "what" but apparently you need 15 characters minimum
 
@0celouvskyopoulo7 Just plug mains into a potato and then plug the potato on your lamp
 
@Slereah see my comment.
 
rob
@Slereah Whaaaaaaaaaaat?
 
Nice ruse
 
rob
9:33 PM
59
A: Is gravity just electromagnetic attraction?

JimShort answer: No. Long answer: Nooooooooooooooooooooooooooooooooooooooooooooooooooooo. Moral of the story: Gravity and EM are two very different things that look similar to some people because they both fall off like $\frac{1}{r^2}$. Be careful what you trust. When someone makes a claim like th...

 
Guys, I don't really understand why they mention a "field of view"? I've seen it in a post* here on Stack, but I still don't understand why we consider this. Why does it matter how much we see?
* https://physics.stackexchange.com/questions/126101/why-the-electric-field-vece-is-constant-position-independent-for-an-infi
 
it refers to solid angles
 
The moral of my story is to never think you're smart enough to understand PDE
It's an impossible task
 
they are pretty shit
 
@Slereah Let's write a book on weighted Sobolev spaces
 
9:45 PM
no thx
 
what better do you have to do
 
The GR book
Another book I had in mind to do was just a big book on spin
Just explain spin from all possible angles
Because it is the worst explained thing
 
@Slereah oh okay, I've never heard of that before
oh i have actually
didn't know it was called like that
 
@0celouvskyopoulo7 No
 
9:49 PM
@Slereah It's basic GR
 
is it
 
@Slereah Since my question is referenced here already, let me just repeat my wish to get an explanation what is wrong with my question:
Why the downvotes? Seriously, it is unclear to me what is wrong with this question. Maybe I will ask on "The h Bar", perhaps somebody is willing to explain it to me. Feel free to also explain it here, then I don't have to ask. I won't take your explanation as indication that you downvoted... — Thomas Klimpel 19 mins ago
 
@Slereah "The large scale structure of Sobolev-spaces"
 

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