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12:03 AM
Hello, I have asked a question and get many downvotes: physics.stackexchange.com/questions/318140/…
What was wrong with my question could you explain as an experienced user?
So in the future maybe I do not make the same mistake if I understand the problem.
 
@mertyildiran I've left a comment just now - your question is somewhere between too broad and unclear what you're asking. While the name "quantum" originally comes from the dictionary definition you cite, quantum theory is not really about discreteness. It's an unfortunate terminology mishap that the modern technical usage of "quantization" has not all that much to do with the dictionary meaning that suggests it's synonymous to "discretization".
 
@ACuriousMind OK, thank you very much. I understand the problem.
 
he doesn't seem impressed
 
Yeah well he's a damn physicist. They're never impressed by the right things
 
He does appear at least a bit curious
 
12:38 AM
He's acting strange
Poor cat
@Slereah I have an unused copy of Weinberg GR at home. Amazon sent me two copies for reasons. What should I do with it? @BenNiehoff too
This was two years ago
I'm looking at it on the shelf here
 
I won't give you Steenrod for it
 
I didn't ask, but why not?
 
Neveeer
 
@ACuriousMind Do you want it?
 
I fear I would never look at it
 
12:51 AM
@ACuriousMind Why is there a swastika with indices in the transcript?
 
@0celo7 Since the topic was notation somewhen today, I guess it's related to that
 
So...are swastikas allowed?
 
OBE
sup
 
hello
 
@OBE inf
 
OBE
12:56 AM
lol
 
@0celo7 They are not forbidden as such but if you use them in any context where they could be remotely construed in their Nazi meaning you'd be on very thin ice.
 
OBE
speaking of thin ice
when I went to Iceland ppl were walking on a pond with super thin ice with half of the pond already liquid.
I guess it's normal there.
 
Good to know...
 
If it was super thin ice and only half of the pond liquid it must have been a very shallow pond ;)
 
Yeah sounds like a bad pond.
 
OBE
12:59 AM
it was because there was a small waterfall-like thing on one side since it was at least a few meters deep.
@0celo7 help
 
What
I don't care unless it involves a metric or an epsilon
 
OBE
lmao
 
Possibly a delta.
 
OBE
I was gonna ask
 
How do you feel about zetas?
 
OBE
1:01 AM
where do I go to learn geometry stuff for physics?
 
@ACuriousMind I'm a bit upset at Kato and he uses those, so not really a fan
I'm not a physicist, what kind of question is that?
 
OBE
where did you go for it?
you knew a lot of geometry/topology before nakahara
where'd you find it
 
you must go questing with your mathemagical staff (ahem, a pencil) and a whole lot of paper...
 
OBE
I found this 3 volume qft-math series by zeidler which is pretty good I think but I don't really get the way he orders the topics. kind of weird order for someone who's new to them.
 
The best way to learn about geometry is to learn it from not-physicists :P
Goes double for group/representation theory
 
OBE
1:05 AM
I know you guys say that a lot but physicists books are easier for me.
for now
I just want some exposure, learning the buzzwords and how to use them a bit etc
 
Physics books definitely make it sound easier, haha.
 
OBE
yeah exactly
idc about deep understanding for now
i have 3-4 years to do that
i've been reading baez's knots and gravity book and it's pretty good, close to what i want. should I just read that?
 
@ACuriousMind lol
 
@0celo7 I don't think I've ever seen Weinberg's GR book. I'm not sure I'd want to, after seeing his QFT books
 
1:31 AM
I am taking MIT's "Introduction to Computer Science and Programming Using Python" on edX
(mostly for physics)
but now Harvard's famous CS50 on edX -- "Introduction to Computer Science" looks more promising (but less focus on Python).
ppl taking that course said it teaches how to think "methodically"
while MIT's course teach quite in detail on Python (I like it)
not sure if I should switch to CS50?
(while CS 50 does not focus on Python)
 
OBE
just use codeacademy
 
*/ (I take the Python course mostly for doing physics)
 
@Shing I wouldn't recommend going too much into detail into python specifically, I guess
Python's a great language, but I wouldn't recommend it for a starting language
 
OBE
what?
everyone recommends it for a starting language.
 
@Giskard42 thanks for reply, but what's good for a starting language in your opinion?
 
1:38 AM
@Shing (This is entirely just my opinion)
I would recommend learning C, then immediately after grasping good practices, switch to python
Python's amazing, and it's easy, but it doesn't teach you comp-sci
(IMHO)
But of course your situation may well be different
 
@Giskard42 I see, thanks for the opinion, maybe I should try CS50 before making decision. (can't really afford the time to finish both )
 
@Giskard42 No programming language teaches you computer science at all
 
@Giskard42, I personally find Python an excellent language, especially to start with
 
Except maybe the more exotic ones like Haskell, but generally computer science is not that concerned with particulars of a programming language
 
OBE
@heather exactly
 
1:43 AM
new programmers don't need to learn about pointers and such matters when they don't even yet know the most basic concepts of programming, and they don't need to worry about arbitrary syntax when they could just indent.
 
pointers are the basic concepts of programming
 
so should we learn computer science , even if we learn it for doing physics?
 
i was thinking more of if statements, while statements, for statements, etc
@Shing, well, I mean, it depends on what you're doing
 
if you want to write efficient code for doing heavy numerics, you will have to learn C or Fortran
and you will have to learn some computer science
 
Mathematica is more common for simulations and such
 
1:48 AM
@heather Not if you wanna be efficient, and especially not if you have to run your code on a cluster
 
Mathematica for simulations? Only if you want them to be super slow :)
 
I know a few simulationists (are they called that?) and they all write in C since their cluster doesn't really allow them to run anything else even remotely as efficient to begin with
 
huh...well, my dad's always said Mathematica is best.
 
so computer science is almost a must?
(for simulation)
 
Mathematica is best for doing symbolic calculations, maybe for some numerics, but for simulations, not so much
 
1:49 AM
The only Fortran guy I've ever seen is @KyleKanos, before he defected to earn money
 
lol
 
I'm working with some numerical GR guys who use exclusively Fortran, I think
 
okay, I have a strange request:
 
@Shing I wish it were. I'm pretty sure most of the people writing academic code have never had formal training in computer science
 
could people try to break this? repl.it/GD0M/46
 
1:50 AM
fortunately I don't have to interact with their code, I hate Fortran :P
 
(i.e., find situations where it stops working?)
I've been testing it, and I think it works, but I'd like someone else to try to break it too =P
 
@heather I have no idea what to do with that
I mean, it's a python module alright, but what's the functions you want us to test and what do the inputs mean?
 
@ACuriousMind well its a simulation of an ideal quantum computer, and the user inputs the number of qubits they want to use, the state they want those qubits to be in, which gates they want applied to which qubits, and whether or not they are done applying gates to qubits, and then the program prints the results (end state of the qubits)
 
It immediately broke and crashed my browser, won't be clicking it again
 
i've been trying to run as many different combinations as possible, to try to find possible errors or scenarios where it gives the wrong solution.
@BenNiehoff what? like, the site did, or my code did?
 
1:54 AM
Uhhh...well, I can of course act as a pseudo-random number generator and input things at my whim, but I have no idea how to tell whether the result is correct
 
no idea, page would not load, and browser had to be restarted
 
@BenNiehoff i'm so sorry!
 
Also, what does a probability of "0j" mean?
 
python uses j instead of i (for imaginary numbers) - it's just a probability of 0
 
If j is the imaginary unit (ew), it shouldn't be in a probability - probabilities are real numbers, not complex numbers
 
1:57 AM
okay, yeah...let me see if there's a way to fix that.
okay, should be fixed now.
thank you!
 
@ACuriousMind I'm taking a class on it next semester
 
@0celo7 Fortran or making money? :P
 
aren't they the same?
 
it uses j for the imaginary unit apparently because that's used in engineering
 
correct
$j$ is the correct symbol
stands for jmagjnary
 
2:04 AM
I think you mean $\jmath$
 
@BernardoMeurer Did you see the new h3 vid? Brazil is crazy
 
what do engineers use for quaternion units $ijk$
 
why would they use quaternions?
 
rotations
 
yeah
 
2:05 AM
probably $j_i$, $i=1,2,3$
 
quaternions are used a lot in simulations
Since a rotation matrix is $3\times 3$
While a quaternion rotation is much simpler to do
6 values versus 4
 
@0celo7 Why not $j_j$ to make the perversion perfect?
 
@Slereah favoured method also for 3d visualization IIRC.
 
yes
it's slightly more efficient
 
@ACuriousMind we're not that savage
 
2:19 AM
@heather In fact this is because "i" often stands for the current (so I'm told).
 
@ZeroTheHero reading through the conversation between annoyed mathematician and python developer on a python forum, that seems to be one of the arguments =)
 
@heather you mean they are no longer annoyed at physicists for using spherical $\theta$ tombe from the North Pole?
 
@ZeroTheHero ?
 
strange... ... meant to remove "tombe" but can't...
anyways... yes in math spherical coordinates are different from physics.
the polar angle is defined differently.
also I think their Fourier transforms are the reverse convention than in physics...
i.e. what we call the direct transform they call the inverse and vice versa.
take home message: never blindly trust the math textbook for conventional things, and do not assume physicists have the same conventions.
 
vzn
2:36 AM
!!! sig other just found this on her facebook feed, phenomenal! Sabrina Gonzalez Pasterski
 
2:49 AM
@0celo7 : does the theorem that states that $q \in I^+(p)$, resp. $J^+(p), E^+(p)$ is equivalent to $\vec{pq}$ being a future directed timelike/causal/null geodesic has as a corolary that the causal sets of the tangent space are mapped to those of the manifold?
That is, $\exp_p(I^+(0)) = I^+(p)$ and so on
Pretty sure it does but u never know
 
3:01 AM
@Slereah still awake?
 
I do not know
How can one be sure
Maybe you're the man of my dreams
 
@Slereah $E^+(p)$?
@Slereah Umm. That's probably not true.
 
$J^+(p) \setminus I^+(p)$
 
You'd have to restrict $I^+(0)$ significantly.
 
Well $I^+(0) \cap D_p$
We are talking convex neighbourhood here
 
3:05 AM
I think it's true then.
Let's see about a proof
 
Well I think it's just a direct consequence of that theorem?
 
So we're looking a convex set $\mathscr C\subset\mathscr M$.
Yeah it's a consequence. $\exp_p(I^+(0))\subset I^+(p,\mathscr C)$ is clear.
But that theorem gives $\supset$
Because $\vec{pq}$ corresponds to a timelike curve in $I^+(0)$ under $\exp_p^{-1}$
 
and vice versa
 
@Slereah where is that picture from with the shitty proof
what book
god, I can't into english
 
I do not know
The page has a header
 
3:09 AM
that's not from a book of yours?
 
It's probably not too hard to find
It is not
 
I should learn set theory
@Slereah I'm...not sure.
It might follow from the Gauss lemma, but I'd have to check.
Morally it should be true
What's definitely true is that a timelike line (straight line) in $T_p\mathscr M$ is mapped to a timelike geodesic in $\mathscr M$
 
Yeah
the famed theorem 5.33
well, part of it
 
I didn't bring O'Neill with me
gotta find my legal copy
 
My o'neill has a bunch of page markers
one of them is currently a candybar wrapper
 
3:13 AM
@Slereah No, you don't need 5.33.
Just note that a geodesic's tangent is has constant norm squared
So if it's timelike at $p$, then it is so everywhere
 
yeah I recall
 
How are you feeling?
 
Getting better
 
No sleep?
 
My glands are not as inflamed
 
3:18 AM
or did you wake up early
 
I woke up at 8 PM so no
 
@Slereah Ah, welcome among the vampires.
 
Been playing a lot of Rimworld
It's a good way to pass the time when sick
 
That's a funny game alright
 
> Provide a brief statement describing how you have financially contributed to your college education.
Does selling my soul to a bank count
 
3:20 AM
My best attempt was a colony made entirely of cannibal psychopaths
 
@ACuriousMind Lol you're up late too
 
::raises an eyebrow::
 
Cannibal psychopaths are hard to come by
They are the best colonists
 
I have to write some essays
 
cannibal psychopaths? i can already tell this is a weird game =P
 
3:21 AM
@ACuriousMind @Slereah Irish or American whiskey?
 
They don't complain when you feed them human flesh or sell prisoners to slavers
 
@0celo7 Irish.
 
I'm more of a vodka man
 
@heather You should never play Metal Gear :P
@ACuriousMind American it is.
 
@0celo7, never heard of that
 
3:21 AM
sad
 
Rimworld isn't very weird
But it's quite ruthless
It is best to have those guys to survive
 
It's dwarf fortress with less depth but a much better interface :P
 
@ACuriousMind I changed my avatar. Isn't it time for you too?
 
Man I wished dwarf fortress had a better UI and wouldn't get horribly slow in the later stages
 
@ACuriousMind pretty much
Although Dwarf Fortress isn't that ruthless
 
3:23 AM
@heather it's the weirdest game series of all time
I'd explain the plot but I'm afraid I can't
 
Well, at least not unless you chooses to
 
there's roughly 30 hours of cutscenes I'd have to summarize :P
 
in between invasions DF is mostly fine
It's pretty hard to starve to death in DF once you're used to it a bit
 
@Slereah Well, of course you play in a evil domain next to a necromancer tower
 
I'd rather not
I don't want my diner coming back to life
 
3:25 AM
It has everything from regular soldiers to super soldiers to parasitic super soldiers to vampires to wolves to parasitic super snipers to cyborg ninjas to regular super snipers to super alaskan tank raven dudes to a dude made out of lightning who is then later made out of lava
 
that's not very weird
 
wow @0celo7
 
It's no Antichamber
 
that's...a lot
 
@Slereah now, casting Raise Dead on the party's meal is of course an old adventurer's trick
Often hilarious, occasionally deadly
 
3:27 AM
quite rude
 
photosynthesis super sniper, many people with ESP, a crazy octopus person, a guy with a revolver who later has this clone's arm attached and gets possessed but wait it was all a ploy and the patriots got fooled
and more
oh and the main character has four clones
and there's a nuclear holocaust around the corner in each game
 
my head is spinning
 
have you seen pulp fiction?
 
It now occurs to me that I've never played a PnP game where there was easy access to resurrection or necromancy
 
eh...no? @0celo7
 
3:29 AM
it's a good movie, but told out of chronological order
these games are the same
 
@ACuriousMind There was an old Warhammer RPG plot like that
You go to a village and you have skeletons doing the dirty work
 
@0celo7 huh, okay
 
@heather vocal cord parasites, a DNA-targeting virus, nanomachines, private military companies rule the world, the war economy is crazy, there's a guy who has a really bad digestive system
 
that last one - how the heck does that play a role in the game?
 
also no one ever dies
 
3:31 AM
@Slereah Only know W40k, don't know anything about Warhammer Fantasy
 
@heather It's actually a pivotal point in the plot. Not necessarily that he has a bad digestive system, but it's why he has it
 
And what I know about 40k is from the strategy PC games
 
He doesn't have nanomachines, so he can't be controlled by SOP
 
SOP...?
wait, wait.
 
but that also means the water in the middle east makes him sick
 
3:32 AM
is this a video game?
or a board game?
 
@heather Sons of the Patriots. One of the AI systems that controls the world via nanomachines
 
huh, okay
so this guy's sick, doesn't have nanomachines, so isn't controlled by AI, okay...
 
@heather a series of video games
I think it's 9 of them or so
 
@0celo7 that makes a lot more sense
@0celo7 9!?
 
Yeah. Metal Gear, Metal Gear 2, Metal Gear Solid I - V, Metal Gear Portable Ops, Metal Gear Peace Walker
Nine
 
3:35 AM
wow.
 
My username comes from the best character in the series
@ACuriousMind My cat reacts to his name in his sleep by moving his tail
@ACuriousMind Are you gonna play MGSV? Otherwise I'll spoil it
 
Rimworld isn't bringing out the best in me
I'm doing medical experiments on prisoners to train my doctors
 
I got a demon horn in MGSV because I killed too many people
I've been burned too many times by guards waking up from being knocked out
 
@0celo7 Perhaps, so don't spoil it
 
@ACuriousMind Well...you didn't play No. III or the PSP game, did you?
You might want to do some google fu and figure out what those games were about
and at least I, II, and IV too
@ACuriousMind There's "assumed empathy" for the main characters
 
3:44 AM
@0celo7 nope
 
@ACuriousMind Imagine playing ME3 without the first two
but way worse, the story is confusing AF even if you know what's going on already :D
 
4:02 AM
My post here:

Book recommendation: [Book on condensed matter physics focusing on numerical method in quantum system \[duplicate\]][1]

How can I further improve my post so that it is not a duplicate?
i am in danger of getting blocked due to this question
 
0
Q: How can I improve my post here so that it is not a duplicate?

kyleMy post here: Book recommendation: Book on condensed matter physics focusing on numerical method in quantum system [duplicate] How can I further improve my post so that it is not a duplicate?

 
5:11 AM
GM :)
 
 
2 hours later…
7:23 AM
in Mathematics, 3 mins ago, by Daminark
My set is emptier than @Secret
NB Posting the actual message will screw up the chat, I will leave that for the next session of latex hacking festival later
 
7:48 AM
@Slereah I need to learn some differential geometry for my thesis.Have to become comfortable with parallel transport and the related concepts and do some calculations, but don't have much time.
Which book do you suggest? Spivak (calculus on manifolds) or Munkres (Analysis on manifolds) ? Any other book?
 
@Secret perhaps you make too many "vacuous" statements?
 
@skillpatrol Well, you just have to look at that yourself. It's a gigantic bracket that spans the whole screen
 
I saw.
 
Meanwhile, at least one DFT calculation have worked. Currently comparing the ground state energies with the x ray data
 
8:28 AM
Hello
If you had all the money and the power in the world to design the perfect lifestyle for yourself, what would your ideal life look like?
 
hey
@2017 They are afraid . lol
 
@Kenshin That would be pretty boring.
 
@2017 interesting remark. It may be boring, but surely with all the money and power in the world you can design an interesting and stimulating lifestyle for yourself?
@2017 but your comment does get to the heart of what I was thinking about. I feel that once I have my needs met, I don't feel happy, I feel bored. So what do we do then?
 
For me an interesting life would be a wholesome life that is filled with joy, sorrow, adventure, thrills, and struggles. One thing that I strongly believe in is that what keeps is alive is hope for the future. If you don't have any goals to achieve then probably you are living a very boring and unhappy life.
@Kenshin I doubt such a simulation is possible...
Money and power doesn't make one happy
(However lack of them can make you unhappy)
 
Yes you're on to something with the need to experience variety of emotions and suprises
 
8:41 AM
Money and power are like the fuel in a car
You don't drive your car only to collect fuel!
@Kenshin Yeah, sort of
 
I think before your needs are met this is your focus (e.g if you lack money for food or something) and fullfiling the need will lead to short term happiness.
but once the need has been confidently met, you won't have any further happiness from it
Then from here, one is happy when one sees the possibility of future rewards
e.g. a night out on the town with crazy friends where "anything can happen" may be exciting because there is so much potential for unexpected rewards
 
@Kenshin right! however, spending your life only partying would be boring too!
 
Correct, because after doing it too much, the element of "unpredictability" diminishes
the novelty goes away
then you need to seek out some other thing to do that has possibility of unexpected reward
and this gives rise to the exploratory nature of humans
 
human psychology is.....*complicated* ! :-)
 
yes
I wish it was simpler
I think one day humanity will understand it well
But we are kind of living in "pre-newtonian" psychology
Once the Newton of pschology/neuroscience comes along people will understand what activities truly bring lasting happiness to a person
But it is very suprising to me that people find it so hard to know what they really want
 
8:51 AM
I got to go for lunch :-)
Have a good day
bye!
It was a good talk :-)
 
9:31 AM
5
A: What is the differential-geometric formulation of field theories?

Urs SchreiberThe modern way to deal with this -- often referred to via the variational bicomplex -- is to consider primarily the jet bundle of the field bundle, instead of the infinite-dimensional space of sections of the field bundle. The infinite-jet bundle is itself mildly infinite-dimensional, but if your...

Sounds pretty cool but I don't think I've ever seen anyone use this bicomplex.
 
 
2 hours later…
11:41 AM
This is tricky---the OP thinks it's okay to close as duplicate because the answer happens to address his question as an aside, but the questions are not the same. What to do?
 
Not tricky at all. It's not a duplicate and I've voted to reopen.
 
Kind of tricky IMO, but I've voted to reopen too.
 
A method is a trick you've seen more than twice, right?
;-)
 
Just once is enough :P
 
Wouldn't that just be an isolated trick?
 
11:56 AM
Depends on how useful it is
 
True.
 
@Danu I agree with John
 
Did you change your clock? @DavidZ
 
@skullpetrol @skillpatrol is your alter ego. Right? :-D
 
You got it pal :-D
 
12:05 PM
But why?
 
12:19 PM
Wow! They are advertising The Feynman Lectures on Physics as the most popular physics book ever written?
 
12:55 PM
@skullpetrol what would be more popular?
 
@0celo7 nothing
 
Attempt to visualise metrics and inner products and bilinear maps in general
For reference, conjugate symmetry axiom: $\langle x,y\rangle=\overline{\langle y,x\rangle}$
 
hi @BenNiehoff
 
Therefore, in agreement with how inner products appeared in integrals $\int_a^b w(x)f(x)\overline{g(x)}dx$ the structure imposed by inner product is the weighting $w(x)$ for each basis component
For example in the standard inner product, $w(x)=1$
This weighting then controls the cancellations that can occur when computing the inner product hence the notion of orthogonality
and from orthogonality, angles, norms etc. then follows
Therefore, in short, if given a vector space and you need to put a grid on top of it so that you can compare between two vectors, then the inner product tells you what the grid will look like
There's a subtlety however in that while the inner product is independent of the choice of basis (since the result is a scalar), the grid is dependent on the choice of basis
3
Q: Is the standard scalar product in a coordinate space basis independent?

user36772Would you say that the standard scalar product in $K^n$, $\left< x,y \right>=\sum_i x_i y_i$, is basis-independent or not ? I would argue that it is, because we don't use the components of the vectors $x,y,$ to define this function, but the vectors themselves (although there is a basis, namely t...

 
hey
1:56 PM
Happy Holi to everyone
5
 
Thanks, same to you pal :-)
 

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