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3:04 AM
Does this description of tensor order on Wikipedia contradict itself?
Whoops, nevermind. 'vectors and dual vectors in the input and output'. Can't figure out how to delete message. Ignore me!
 
 
2 hours later…
5:04 AM
yesterday, by Yuvraj Singh...
How do we quantify more carefully the notion that the "curvature approaches Planck values?
@YuvrajSingh... That's a good question and I'm not sure how you would define a characteristic length scale for the curvaure.
The problem is that what you mean by a length depends on your choice of coordinates so there isn't any obvious way to define a length scale.
 
 
2 hours later…
7:28 AM
In a Feynman diagram in real space and imaginary time, we first insert a particle at a position at time t0. Then a lot of processes happens at t1, t2, t3... and then we measure the particle at tn. Is it always true that t0 < t1, t2, t3... < tn?
I think in some cases we can say tn < t0 and we call it the hole propagator. What I'm most curious about is if t1, t2, t3 has to happen in between these times
 
user434058
Which is the best book for learning tensors and tensor calculus? I am looking for a book which starts the stuff from the basics and after reading it, you would know almost everything there is to know about tensors.
 
7:44 AM
In the second configuration....How is $F_x>0?$
I do not understand how x>0 yields F_x>0 and x<0 yields F_x<0 in the second configuration
Also what to judge about stable and unstable equilibriu
equilibrium
What information would Fx>0 or Fx<0 give me ?
 
 
1 hour later…
9:05 AM
I am trying to read Krupkova's book on the jt bundle
The horror
too many bundles
 
I watched Zodiac today. It was a pretty long movie and the ending didn't surprise me that much.
 
$$\int_\Omega J^r \gamma^* \lambda = \int_\Omega J^r \gamma^* (\lambda + \eta)$$
This is apparently the formal statement that the action is invariant up to total derivative
Except $\eta$ is a contact one-form of $J^r Y$!
$$J^r \gamma^* \partial_{J^r \xi}(\lambda + \eta) = J^r \gamma^* i_{J^r \xi} d(\lambda + \eta) + J^r \gamma^* di_{J^r \xi} (\lambda + \eta)$$
The horror
 
10:01 AM
@Slereah : Olga Krupkova btw passed away last fall. RIP.
 
F
 
10:47 AM
@Slereah is this still your quest of understanding holonomies or something else?
 
11:21 AM
@ACuriousMind All is one, @ACuriousMind
Although by now I think I found a decent paper for holonomies
this one is pretty good
As you can see
All is linked
Not sure where Jesus fits in yet
Also there is something about Regge calculus in there
(the measurements form a simplicial manifold)
 
11:37 AM
Not sure whether that's a mind map or one of these conspiracy boards they make in movies :P
 
11:59 AM
The holonomy conspiracy
 
good evening all
I always wondered how did Bohr come up with his postulates lately I saw a meme in r/physicsmemes saying something about Bohr that he accidentally came up to those postulates ?
people here are of course more experienced than me can anyone tell that what intuition of Bohr led him to theses postulates ?
I tried but couldn't understand because I am @dumb as a rock
 
@dumbasarock If you're interested in actual historical developments, there's our sister site History of Science and Mathematics
 
user434058
@dumbasarock AFAIK, he saw the emission and absorption spectrum, recorded and usedthat data and used classical mechanics to arrive at $mvr=n \hbar$.
 
user434058
@ACuriousMind Why are the other sites called "sister sites", why don't we use the male counterpart, or better, just some ungendered adjective?
 
what was the reason behind choosing circular orbit ?
 
12:08 PM
@FakeMod Not sure why it's prevalent in English, but e.g. in German 'website' is grammatically female so it's the more intuitive choice for me
There's another sister site English Language & Usage you might ask about it :P
 
user434058
@dumbasarock Huh?
 
nothing, forgive me
 
Maybe websites are like boats?
 
user434058
@ACuriousMind Unfortunately, my native language doesn't have a word for "website". It is an ancient language :D
 
user434058
@dumbasarock No problem :)
 
user434058
12:10 PM
@ACuriousMind What!?
 
you @FakeMod are Indian right ?
 
@FakeMod boats are traditionally referred to as female in English
 
user434058
@dumbasarock yes.
 
user434058
@ACuriousMind Same in our language as well :)
 
I made a popular joke I thought you would understabd it
 
user434058
12:12 PM
@dumbasarock I hate Neha Dhupia, coz it's ma choice...
 
@FakeMod Then I don't understand your exasperation about me wondering whether websites are like boats :P
 
you got it
 
user434058
@ACuriousMind It was out of context for me. I thought we had dropped the talk about gender of words :)
 
how are you spending your lockdown/ quarantine though >
 
user434058
@dumbasarock This has been my routine for the last 2 years :D
 
12:14 PM
makes sense you are a JEE aspirant
what about you sir @ACuriousMind?
 
Not Indian, not a JEE aspirant, also not a knight.
 
user434058
@ACuriousMind I was wondering whether you are old enough to be called a sir just because of your age?
 
i know sir you are none of them.
I am asking what are you doing in theses days of lock-down ?
 
I don't know what you would consider "old enough" but in any case I simply don't like being called 'sir'
 
His knowledge compels me to acknowledge him as a "sir"
 
user434058
12:17 PM
@ACuriousMind That's perfectly fine. But I was subtly implying that I wanted to know your age :)
 
user434058
@dumbasarock Definitely!
 
::counts fingers:: 27, I think
 
okay so he's 27 and on stack exchange for 5 years which means he joined stack at age of 22 which is my current age.
and here I am asking "wHY bOhr gAvE hIS pOStulateS ?
 
@dumbasarock Well, since I can work from home the routine hasn't changed much. Most of my in-person RPG groups have shifted to happening online, and I finally can stay home and play video games the rest of the time while claiming to benefit society, so...it's not so bad ;)
 
I should leave physics and open a shop
 
user434058
12:21 PM
@ACuriousMind Then how do you manage to give so much time to PSE. If you'd have been old and retired, I would have understood, but it seems to me that you are employed and young, then how...?
 
passion to help others maybe ?
 
I think you overestimate the time I spend here and underestimate my ability to multi-task ;)
 
user434058
@ACuriousMind You're German, so I don't underestimate the latter, but I might be overestimating the former :)
 
user434058
5 hours ago, by FakeMod
Which is the best book for learning tensors and tensor calculus? I am looking for a book which starts the stuff from the basics and after reading it, you would know almost everything there is to know about tensors.
 
user434058
Suggestions please!
 
12:24 PM
if you understand tensors send some wisdom my way too
 
user434058
@dumbasarock not yet ;)
 
skipped it in undergraduate and still skipping
HK Dass has a bit about tensors and you find it's PDF in any CSIR NET exam preparation group
 
user434058
@dumbasarock I am finding a book dedicated entirely to tensors...
 
from Coordinate transformation to Three scalar invariants of second order tensors
okay
 
user434058
16
Q: Tensor Book Recommendation Request

Fork2Requirements Tensors Intuitive + Practical Reason for Tensor Introduction Current Knowledge Course Notes Abstract + Theoretical

 
user434058
12:28 PM
This page looks fine.
 
12:40 PM
I'm radio rebel
 
 
1 hour later…
1:44 PM
Nooooooooooooooooooooooooooooooooooooooo
 
So it's confirmed now?
 
user434058
Topology is nice...
 
user434058
I just don't seem to understand a few buzz words...
 
@Slereah Game-over of Life, I guess :'(
I distinctly remember coding and playing around with a GoL, probably the most fun thing we coded in school
 
any legends online?
@FakeMod Ray DeInverno
@dumbasarock I too think that...
@Slereah I heard morning... very sad... :'-(
Earthquake this morning, 3.5 RCKTT
 
 
2 hours later…
4:21 PM
I think I'll be buying a 3D printer because trying to cast melted plastic in a plaster mold would be a complete mess and the end result will look awful and no one's gonna buy that. I prefer to spend some money on a 3D printer if it means getting the product to look right
 
Nip
4:36 PM
Hello! Could any one suggest some links to questions related to Hamiltonian monte carlo.
 
user434058
4:49 PM
@AbhasKumarSinha Thanks, but I already found good one and I will stick with it :)
 
user434058
5:29 PM
Is giving partial answers to effortless blatant HW questions allowed?
 
If they're not "complete or near-complete", they're as "allowed" as answering any other off-topic question.
 
6:26 PM
I am radio rebel
 
user434058
@JingleBells what does that mean?
 
user434058
Or rather: wut dos taht mean!!?!!?!!
 
ma chaildhud
... just making shitty references :D
 
user434058
@JingleBells I was misled by the false notion that you were talking about something new and recent...
 
I'm Hannah Montana
that better?
 
user434058
6:31 PM
@JingleBells Please no!
 
I'm Justin Bieber.
ahh how I love talking trash
 
user434058
Because I don't know yet how bad "Radio Rebel" is, but I definitely know how bad "Hannah Montana" is ;P
 
user434058
@Loong I really need a haircut after being locked in home for ages...
 
user434058
I'll have to cut my hair at home I suppose.
 
6:34 PM
Yeah, we are not locked in; however, the barbershops are closed.
 
user434058
@JingleBells Nevermind, just be a radio rebel.
 
@FakeMod No, I'm tracer
But I'm already Tracer
 
user434058
Lena Oxton, better known as Tracer, is a fictional player character who appears in the 2016 video game Overwatch—a first-person shooter developed by Blizzard Entertainment—and related animations and literary media. Tracer was first seen in the 2014 Overwatch Cinematic Trailer short. She was later introduced as a playable character in an April 2016 update for Blizzard's crossover multiplayer online battle arena game Heroes of the Storm. The character, who is of British origin, has been noted by video game outlets to be peppy and energetic. In the game, Tracer has low health but is highly mobile...
 
user434058
Is this what you're talking about?
 
user434058
6:39 PM
@JingleBells Why do you suddenly wanna be a girl? Just asking.
 
@FakeMod I don't want to be a girl, I want to be Tracer
 
user434058
@JingleBells But isn't Tracer a girl?
 
user434058
Am I sounding dumb when I ask that? (You might not be hearing me but still...)
 
@FakeMod Yes, so?
 
user434058
So you want to be Tracer, Hannah Montana and Justin Bieber, all of which (except the last one, who was nothing less than girly) are girls, and that's why I am seeing a trend which I wasn't expecting...
 
6:45 PM
I wanna be Tracer, not a girl.
I will be gender neutral.
 
user434058
@JingleBells OK, I get it now! :)
 
I mean laser pistols and the ability to warp around and reverse time wouldn't be bad.
 
user434058
@JingleBells good!
 
@FakeMod Do you wanna be Tracer together?
@JMac Do you wanna be Tracer?
 
user434058
@JMac I would rather wanna be Ronan the Accuser (Marvel).(I know I am talking about a completely different territory, but I thought you would also find his powers interesting).
 
user434058
6:47 PM
Ronan the Accuser is a fictional character appearing in American comic books published by Marvel Comics. Ronan was created by writer Stan Lee and artist Jack Kirby and he first appeared in Fantastic Four #65 (August 1967). He is the Supreme Accuser of the Kree Empire, the militaristic government of the fictional alien race known as the Kree, and is commonly depicted as an adversary of superhero teams such as the Fantastic Four, the Avengers, and the Guardians of the Galaxy. He was also a member of various superhero groups such as the Starforce, United Front and Annihilators. He was married to the...
 
@JingleBells I'm good.
 
user434058
@JingleBells How do I be Tracer?
 
I wanna be The One Above All
@FakeMod You just...be...
@JMac Do you wanna be JMacDonalds?
or maybe JMacintosh?
i'm so smart...
My smartness is so high that I appear dumb to people
 
user434058
@JMac Is JMac your first name, or is it some sort of abbreviation/nickname?
 
JustMacintosh
@JMac You're the best, don't mind my bs
 
user434058
7:02 PM
MJac
 
Flap jack
 
user434058
OMG! If you rearrange the letters in jmac, you get jACM, which means "junior ACM". ILLUMINATI CONFIRMED! jk
 
omfg no
we're criminalisticists
dude, I think u just exposed the Zodiac
 
user434058
I don't know where did ACM get this skill from. He knows when someone is talking about him and he comes to the hbar to see them talking about him. Please @ACuriousMind , enlighten us.
 
I just finished cooking and returned to my PC :P
 
7:07 PM
He has bought a camera and a monitor and runs an AI algorithm to recognize text from the shots of the camera and whenever the word ACuriousMind or ACM is present, it rings a bell
 
@FakeMod It's an abbreviation. I explained it in detail somewhere but I'm too lazy to find that.
 
user434058
@ACuriousMind How good are you at cooking? :)
 
user434058
@JMac No problem! That much info is enough for me :)
 
I can survive on it
 
user434058
@ACuriousMind Everybody can survive on their own cooking, but what about others, what about your flatmate, do they like it?
 
7:11 PM
I haven't heard any complaints :P
Fortunately we both think of garlic as an ingredient, not a spice, otherwise I think there'd have been bad blood in addition to bad breath
 
Jog in natural glowing light else biggest enemy literally lies safely
oops
wrong chat
 
....you okay over there?
 
Jog in natural glowing light else biggest enemy literally lies safely
As currently unified riots increase, our unfriendly satan mindlessly initiates nothing dangerous
 
@JingleBells I don't know if some bot went rogue or you're just posting nonsense, but either way, please stop it
 
@ACuriousMind nonsense? look closely
 
7:22 PM
It's nonsense even if the initials spell my name :P
 
:(
it was my easter gift for u
@ACuriousMind how old were u?
 
when?
 
now, I forgot
u've said before
 
I just answered that question today (or maybe yesterday?), just search the transcript
 
@ACuriousMind u could have typed 2 digits instead of those 85 characters
That's a profit loss of 83...
opportunity cost too high buddy
I can guess ur age
 
7:31 PM
I'm on an unlimited characters plan to accommodate my bloviations
 
Are you above or below 25 and I can tell you with exact accuracy how old u are
@ACuriousMind Meh, I had to go with the Platinum plan cuz the unlimited was beyond my budget... gotta buy toilet paper during those times
@ACuriousMind If you just tell me whether you are above or below 25 I can guarantee to guess your exact age
c'moon let me do my joke :(
 
 
2 hours later…
9:11 PM
Am I right in saying that in SR the $(\hat t, \hat x, \hat y, \hat z)$ basis vectors are orthonormal in the rest frame and not in any other?
 
There is no "the rest frame", all rest frames are rest frames of a specific object/observer.
And orthonormality is a frame-independent property, two vectors that are orthonormal "in one frame" are so in all frames.
the inner product, after all, is invariant under Lorentz transformations pretty much by definition
 
In that case why in 2D $(\vec t,\vec x)$ spacetime diagrams do the axis of another observer appear non orthogonal?
 
@Charlie Note that "orthogonal" in Minkowski space-time does not mean that the two vectors have an angle of 90° degrees!
 
ahhhhh
 
Or, rather, that the notion of "angle" is really ill-defined there.
 
9:30 PM
ty that makes sense
 
 
2 hours later…
11:04 PM
Are the generators of a lie group a basis for its algebra?
 
The generators of a Lie group aren't even elements of its algebra, so of course they can''t be a basis.
 
@WillO Careful, "generator" has a double meaning - one in the sense of generic group theory (set of group elements that can generate all the rest by repeated multiplication) and one in the sense of Lie theory where the generators are indeed a basis for the Lie algebra
When a physicist says "generator", they almost always mean the latter
 
I guess that for a question of how physicists use words, I will defer to the physicist :)
 
11:37 PM
Wait so when we talk about the generators used in the exponential map which case is that?
 
@Charlie That's the basis of the algebra
 
tyvm
 

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